Astronomy Essentials 0

Astronomy Essentials

Stargazing has always inspired people to wonder what was out there in the night sky. Some thought the stars were past relatives or ghosts. Others thought they were Gods. One thing for sure was that no one knew for sure. From the beginning of time this has been the case. We have always wondered. Even in modern times where we know many things, we still wonder how modern astronomy evolved. As science and technology evolved, our understanding of astronomy has increased steadily though. Stargazing will forever be popular and rightly so. How modern astronomy evolved will forever be a journey to people.


Chapter 1 - How Modern Astronomy Evolved

Our understanding of the universe is faulty at best. It's not for lack of trying though. We are constantly refining our ideas and collecting knowledge.

This process started thousands of years ago and I hope it continues for another thousand years. The picture below shows the wondrous nature of this field.

Science Methods

The main reasons for our eventual increase of knowledge were better telescopes and improved scientific methods. Better telescopes allowed us to see stars better and make better judgements.

Galileo was the first who really made significant improvements to the telescope. He refined what it did and indeed made it better.  Refracting telescopes were what he used and improved.

They had their issues though which is why the reflecting telescope was then invented. Reflecting telescopes bypassed the limitations of the refracting telescope. It allowed even further refinement to celestial images of the day.

How modern astronomy evolved depended very much on establishing methods to test and review results.

  • Ask a question
  • Form an hypothesis
  • Make a prediction
  • Test the prediction
  • Analyze it

That is roughly the scientific method. It never really ends though. You keep making more hypotheses, more tests, and more analyses. This process helped early scientists sort through early ideas.


What good were these new devices if we did not use them well? This is where scientific method and the development of systematic observation made good use of the new telescopes we now had.  

With a defined set of procedures, science itself progressed more quickly. Why is the scientific method important? For one it formalizes the process. This means that everyone is testing and evaluating observations and results in the same way.

It was important because you could eliminate things that did not make sense and gain an interesting answer much quicker than just guessing your way through it. That is my analysis anyway.

With a system of observation now in place, everyone could make assertions based off equal conditions. If done correctly, there should be no outlandish results.

Everything that was then inferred had at least a chance of being correct until more testing and observation was done.

Better Telescopes

Telescopes have not been around for very long. There are many claims for earlier telescopes but even then the 1500's is the earliest it could have appeared. Galileo developed the first good one it seems.

It used concave lenses. He used it to start observing various planets and other objects in the night sky.

This happened around 1609 and was the turning point for Astronomy. He continued to improve his designs throughout his career.

Johannes Kepler again made another great improvement by using a convex lens. This greatly magnified objects in space. Switching to this style also gave him a much larger field of view.

This was very helpful. His telescopes suffered from light distortion which today is called chromatic aberration.

Johannus Hevelius wanted to construct longer telescopes because he theorized that the longer they were the sharper they would be. It was reported that he developed one that was 140 feet long! The telescope was impractical to use much because it kept moving.

Isaac Newton developed the first reflector telescope using a mirror and a combination of lenses. This was a huge discovery. There were still problems but viewing instruments were getting better.

Sir William Herschel was the great Astronomer who built a huge reflector telescope with a 4 foot mirror in it. The advantage of this is that it could gather much more light. This helped resolve pictures much more clearly.


This led to the heliocentric view of our galaxy.  This idea contrasted greatly with the predominant view of most people. Most, since anyone thought about it, thought that our own planet was the center of our galaxy and all there was.
While we know this is wrong today, you can not really blame those who first thought it. This earth was all that was understood and that was just on a basic level.
Because of that, it took a long time for people to accept that everything in our galaxy would revolve around the Sun. It was just too new of a concept and something that very few could understand.
How modern astronomy evolved , though , would have to lead us toward heliocentrism eventually anyway. Our little earth and many other heavenly bodies have some kind of orbit around the star that is our sun.
You would think that the life-giving light and radiation from the Sun would make it seem more important to our ancestors.
Indeed, not many made this connection. Nicolaus Copernicus was one of the very few. He was the most influential man in Astronomy. He read a lot of history books and anything on Astronomy.
After he proposed his heliocentric view of the solar system he became very unpopular. No one believed in this new system.
However, the math that he and many others had been working on suddenly worked out when you considered the Sun at the center of our solar system. He published his theories a year before his death.
He did this in case there was major backlash with the church. There would be of course. His heliocentric theory was revolutionary even after all the troubles it caused himself and others. We now know it to be accurate and was the key to finding more planets in our solar system.

Celestial Mechanics

This topic deals with how the many objects, stars for example, in our solar system and how they are affected by other celestial bodies. This really confused people for literally ages.

First, without the idea of heliocentrism mentioned above, these principles could not even begin to take off. If you think about the words, celestial mechanics, it really how it sounds. It is the mechanics that we know and love applied to celestial objects.

Celestial mechanics is ultimately the doing of Johannes Kepler. His laws of planetary motion were instrumental in explaining the motion of celestial bodies. This motion showed how everything interacted with each other. The key equation behind these laws of his was:

\(F = \frac{G*m1*m2}{r^2}\)

It described the gravitational force that any two particular objects exerted on each other. This equation therefore says that the masses of those objects are multiplied together along with the gravitational constant.

Then divide this figure by the square of the distance between the two bodies.

When we use this equation on all of the planets, moons, and other objects, we then see a better picture of what is going on in our solar system.

Now Newton had his theories about celestial mechanics but it was Kepler that solidified everything that they knew in that time.

This theory made it know that the Sun was the major force in the solar system. All other objects of any significant size acted upon everything else too. If the effect was too small then the effect would not be measurable.

When all of this was taken into account it made it easy to predict planets and their locations during orbits.



The laws of gravity were the next huge accomplishment. They spurred great innovations and knowledge about how bodies in space interact with each other. You see, everything in space has some effect on something else.
It can be a very minor effect like causing a slight wobble as something passes by. A more prominent example would be our Earth keeping the Moon close by which is due to gravity as well.
It can also be a huge effect like bringing the object into orbit because it got too close. Even objects that get taken into orbit of a larger mass slightly effect that larger mass.
I will say it again, everything in space affects something else to some degree. This is because of gravity. You might then ask what exactly is gravity?
Well we are still working on that. There are many ideas of course. Newton said it was a force and that every object in the universe has an attraction on everything else.
The masses of any 2 objects you select and their respective distances apart will tell you what force is applied on each.
Unless at least one of the objects are very large, however, the effects are so slight you will not notice. So telling the pretty girl sitting next to you that the closer we get the more attraction we will have for each other will probably not work.
I know, I tried it once during high school. She did not look convinced. Gravity has an effect on everything but it depends on mass and distance.
It is part of our daily lives. It always has been. Its effect at the Earth's surface is \(9.8 \frac{m}{s^2}\). The force is one of acceleration. This means that for every \(s^2\) our acceleration increases by \(9.8\) if we are in free fall.
The effect of gravity is also different on every other celestial object in space.

Light and Distance


These developments led us to better understand the speed of light and distances in our galaxy. The speed of light is pretty fast. More accurately, it is the fastest thing we know of for sure.
There have been guesses that other things in space might be faster but right now that is all conjecture.
Knowing this speed allowed us to then measure distances to many objects in space. For example you can measure the distance to a comet and then a week later do it again.
By doing this you get an idea of how fast it is moving and its direction of movement. See how this is important?
Now that we can measure distances we begin to understand the vast distances to other planets and stars.  Maybe understand is too much credit but at least we are starting to get an idea.
Once astronomers started getting distances for everything and their movements, they realized how much more there was to learn. This opened up many avenues of study.  
How modern astronomy evolved led us toward discovering the vast distances in space as you can see below.



Once a reasonable level of understanding had been gained of the speed of light and distances, astronomers began focusing more on the light being emitted from stars and planets. Just about everything broadcasts some sort of light or radiation.

Looking at this light and analyzing it became huge for inferring a lot of characteristics about stars. Over time scientists of the day realized they could look at different wavelengths of light.

This development yielded a great deal of additional information. Using a spectroscope, astronomers studied the light captured and could tell how hot the star was and partly what it was even made of.

Once it was known how hot it was, you could then infer its age and size based other conditions.

Knowing what it was made of also helped. Stars with higher compositions of some elements had different characteristics than stars with other compositions. This became an important field of study called spectroscopy.

Basically that is where we are now in modern times. There are, of course better technology innovations and telescopes out in space to get more accurate readings.
Everything is progressing steadily like it always has. We are gaining insight continually and our understanding of the universe slowly evolves. Will we ever have a true understanding?

Probably not but it is seeing and discovering the wonders that is out there that has always kept us trying and hopefully forever will. How modern Astronomy evolved is a fascinating subject. Looking at past developments can also give us clues today.

 Chapter 2 - Star Classifications


Have you ever wondered about star classifications? Stars are classified based on their temperature, but started out being based on only their spectra. This classification process started in the 1890s by Edward Pickering at Harvard and was finished in 1901 by Annie Cannon, who worked for Pickering.

Cannon reorganized what Pickering started in the classification that we know today. The classification is as follows "O B A F G K M" that goes from the hottest stars to the coolest stars. These classifications are further subdivided in categories "0-9" where 0 refers to early in that star and 9 refers to a late type of star.

                                    Star Classifications

This classification is now called the Harvard Spectral Classification. Type O stars and Type B stars are both blue-white hot stars, but Type O stars are the hottest stars. Type A stars are white stars that give off Balmer absorption lines in early A stars.

Type F stars are yellow-white stars. Type G stars are yellow stars like our Sun. Type K stars are cool orange stars, whose spectra is dominated by metal absorption lines. Type M stars are cool red stars, whose spectra is full of molecular absorption lines.

The Sun is classified as a Type G2 star with a surface temperature of 5777 Kelvin. These spectral classes also relate to the surface temperatures of the stars.

The Hertzsprung-Russell Diagram

The Hertzsprung-Russell diagram, commonly called the H-R diagram, is a diagram that plots the stars luminosity (or brightness) versus their spectral classifications, which relate to their temperature. Another view of this diagram with a description is located at Enchanted Learning.
Stars have several luminosity classes: Ia, Ib, II, III, IV, V, VI, D. The chart below describes the different classes of luminosity, while the H-R diagram above shows where the different classes are located.

                        Chapter 3 - Guide To The Universe


When I was a kid growing up in Kentucky I always loved going out at night and seeing the sky. My home was very unpopulated and so had very little light pollution. The nearest town of 3 thousand people was about 15 miles away.

So it was an incredible place to dream about what may lie among the stars. That was the start of my love for science, astronomy, and physics.

I have carried this with me my whole life and always wanting to learn more because I loved it. I have always wanted to write about it as a result. This is a short guide to the universe and includes the beginning topics.

From here most of the advanced concepts come from these ideas and are developed more fully. 

Unlike the current thought in ancient times, we have learned that our planet is not the center of the universe. We are in a little isolated spot in a small galaxy. There are probably billions of galaxies.

That current number eludes us still. All of these galaxies, time, and the energy in it all make up the known universe. Astronomy is the study of the universe. Put another way, Astronomy is the study of all matter, space, and time since that is what the universe consists of.

  • universe= all of space, time, matter, and energy.
  • astronomy= study of the universe.

The Scientific Method

The scientific method is our way of testing and refining the results of a problem until we have the best answer we can. This starts by ideas. Once we have 1 or more that make sense to us and work a little bit, we then have a theory.

Testing this theory is the next step. In fact, we constantly test our theories even if we think they are right. This is the heart of the scientific method. If any particular theory lasts a long time and works for many people then it will be accepted.

Some may even call it fact. Watch out for that though, any theory or fact can eventually be proven wrong.

  • scientific method= methodical approach employed by scientists to explore the universe around us in an objective manner.
  • theory= framework of ideas and assumptions used to explain some set of observations.



Since humans could see the stars they have interpreted them as patterns in the sky. These patterns of course looked like familiar objects or scenes from their religion. These patterns pretty much stayed the same so they became very important to early people.

They were comforting. Predicting the seasons was made easier. Finding other objects in the sky was made easier when someone said to start at that section of the sky.

Navigating also became much easier when you could use the stars as a guide. That section or picture in the sky was an early constellation. Keep in mind, though, that the stars that made up a picture in the sky were never actually close together.

They aligned because they had similar brightness and were at least in the same section of the sky. Most often they were immense distances apart.

  • constellation= patterns of stars visible to the naked eye.

Movement of the Stars

For the longest time we thought the stars and the resulting constellations moved a great deal. Their movement across our sky had thoroughly confused early astronomers. It was not until later that a few attributed that motion to our own planet.

While everything moves some, even the far off stars, it was our planetary rotation that accounted for that degree of movement across our sky.

The Earth

We live on the Earth. Hopefully you have recognized that by now. This is a planet. It rotates and does so quickly, it also has an orbit around the Sun which is our nearest star,  and it is the 3rd rock from our star to be exact.

Tilt is what gives us our seasons. Revolving as quick as it does, it makes the stars above appear as if they are moving.

Orbital Motion

Our time is measured by the Sun and its progression across our sky. It works out pretty well. Our day is technically called a solar day and it is 24 hours long. It is 24 hours because that is how long it takes the Sun to arrive back at any one position the next day.

There is also a sidereal day which is a day measured by the stars. The time of a day is different than on a solar day. The reason is that our planet moves in 2 directions at once.


Eclipses are when the Sun and the Moon line up just right from our view here on Earth. This is a very nice and interesting event too. It can only happen at new or full moons too.

When the Sun and Moon are on opposite sides of the Earth, this is called lunar eclipse. Earth's shadow covers the moon. If they are close to being in alignment then it is called a partial lunar eclipse.

Now when the Sun and Moon are in the same directions it is called a solar eclipse. These are just plain awesome by the way. Day turns into night, almost. One of the unfortunate things about a solar eclipse is that only a small part our planet can see this great eclipse at a time.

There is not always an eclipse when the time is right either. The reason is that the moon's orbit is not perfectly circular. So sometimes it just does not line up right.


The distances in our galaxy and universe are astronomical! Ok that was kind of a joke. There is a lot of space between objects in, umm space. I seem to be on a roll here with my puns though not meaning to.

One of the main ways astronomers calculate distance is through the technique of triangulation. We used it centuries ago and still use it to this day. It is that useful.

Another part we use with triangulation is parallax. The two techniques together is how we get decent estimates of an object's distance in the sky.


Obviously this technique uses triangle. Then with some geometry we can do some pretty nifty calculations. After all, that is why we love topics like this. Figuring out the details and seeing where else we can apply them is so much fun isn't it!

So with triangulation, we want to be dealing with right triangles. This just makes things easier. To put it simple, we will know the length of the base of the triangle and then 2 of the angles. With those known we can then calculate the rest.

  • baseline=the distance of the base of a triangle


Astronomers use parallax a lot also when measuring cosmic distances. The amount of the visual displacement is what determines our angles. Then we just use a form of triangulation then to estimate our distances.

  • parallax=The apparent displacement of a foreground object relative to the background as the observers location changes.

Basically the closer an object is to the person looking at it, the larger the parallax will be. Meaning, it will appear to move more when looked at from another angle. The age old trick to this is look at an object like a house with both eyes open. Then cover one eye and see how its position changed. That is parallax. This is the technique astronomers use to measure distances on a cosmic scale. Technically, the amount of parallax is inversely proportional to the distance of the object you are looking at.

 Chapter 4 - Radiation

If you love Astronomy then looking at the sky is a regular task for you. You see all those stars and many other objects. What no one knew for a very long time is that we only see a small fraction of what the night sky is showing us.

The reason why is that the light we see with our eyes is just one form of radiation. We now know of many other kinds. If you want to know more then read on and I will explain.

 Radiation is the transmission of energy. At first we thought it through particles but now we know it is through waves. It can be between any 2 points or distance. The term electromagnetic is often applied to radiation and rightly so.

This is because radiation energy is carried by electric and magnetic fields. There are many types of radiation as denoted by the electro-magnetic spectrum.


Light is a form of radiation. We also call this visible light. It is the light we can see with our own eyes. The kinds of radiation or light that we can not see take special instruments to detect and measure. Some examples are radio, infrared, ultraviolet, x-rays, and gamma rays.

  • Radio - these waves are the largest. We use them to carry radio and tv signals.
  • Microwave - these waves have a length between a millimeter and a meter.
  • Infrared - wavelengths between 12 centimeters and 740 nanometers.
  • Visible Light - these wavelengths are between 740-400 nanometers.
  • Ultraviolet - these occupy the region of 400-10 nanometers.
  • X-rays - these range from 10 to .01 nanometers.
  • Gamma rays - These are the smallest waves at less than a picometer.

Waves of Light

All forms of light travel in a wave motion. A wave is a disturbance of the medium in which it travels. That is the simplest definition I can think of. The medium does not move. It is the energy that moves through the medium. That is a wave.

All waves have certain characteristics that can be measured. These are the period, frequency, wavelength, and amplitude.

  • Period= time needed for the wave to repeat itself
  • Wavelength= distance needed for the wave to repeat itself
  • Amplitude= height of the wave
  • Frequency= The number of waves that pass any given point in a certain amount of time

The Parts of Visible Light

All light is a combination of different colors. White light is, in fact, made up of red, orange, yellow, blue, green, and violet. These different hues and their resulting frequencies is how we see light.

Each of those colors has a different frequency with red having the lowest and violet the highest frequency. These colors are what we call the visible spectrum. Any light or radiation outside of these boundaries can not be seen by our eyes.

Electric Fields

The forces in an electric field can be either attract or repel each other. It depends on the charge of each individual component. Whether the particle is positive or negative it will put out an electrical force around it.

If two particles encounter each other they can either attract or repel away from each other. If the charges of the two particles are the same then they will repel each other and if they are different then they will attract each other.

This happens because the electric field of an object extends out in every direction at once. This means it extends out radially in every direction. The strength of this field also decreases with distance.

Electromagnetic Waves

James Maxwell was the first to figure out what these waves were. He developed a set of equations to deal with their effects. He combined the knowledge of electric fields and magnetic fields. You get a magnetic field every time an electric field changes.

They change all the time so you actually have a magnetic field all the time too. So to expand on our wave model of light, these waves are formed of electric and magnetic fields traveling together.

Interestingly enough, they travel perpendicular to each other. Together these two fields make up what we know as electromagnetism.

This is now an electromagnetic wave. These wave move at the speed of light which is roughly 300,000 km/s. That is very fast but it is not instant. Of course you could only tell that at long distances. Just something for you to ponder though.

Electromagnetic Spectrum

As you now know there are several kinds of electromagnetic radiation. Some of it is visible but most of it is not. They have their own characteristics too, meaning we can tell them apart with certain tests.

These differences are wavelength and frequency. So we have to measure these things with instruments and tests. Radio frequencies are on the low end of the spectrum and gamma rays are on the high end.

Spectrum of Radiation

This is all energy that moves as waves. Remember that each wave consists of electric and magnetic fields. These fields move together at the speed of light which is 300,00 km/s. It is collectively called an electromagnetic wave.

The wavelengths of radiation vary greatly by the way. Radio waves are quite long while gamma rays are atomic in scale. Another key point to know is that objects emit radiation in a variety of wavelengths.

Some of it might be in visible light but most will be some other form of electromagnetic radiation.

Opacity of Objects

The opacity of an object is how little light or radiation it lets through. This concept directly affects what we are able to perceive on this planet.

How this affects us is that even in the visible spectrum there will be more opacity and lower amounts of radiation that is let through. Then in other parts the opposite will be true and it will be less opaque.

Thermal Radiation

Thermal radiation is energy given off by heat. Every object gives off at least a little bit of heat too. This happens because electromagnetic radiation is given off at the particle level. This is also directly related to the object's temperature.

The hotter the temperature the more electromagnetic radiation is given off. Every object has a heat signature then. This is how you can detect what kind of object you are seeing when you look at its heat analysis.

Blackbody Analysis

No physical object emits all of its radiation at one frequency; it is actually scattered around a lot. This is the heat signature I referred to above. Every object will look a little bit different.

While signatures do have a lot in common usually, there are always differences. Just don't expect them to be radically different because they are not. When graphed this is called a blackbody curve.

Characteristics of Radiation

When graphing blackbody curves of objects you will notice that hotter items shift the curve upwards. Stars are a great example of this. Hotter temperatures are higher frequencies too. This is why we see objects when they are very hot.

Objects with less temperature or cooler emit radiation in the non-visible spectrum. It is all still radiation though. There is also a simple relationship between the temperature of the object and the wavelength the radiation is admitted at.


 $$ wavelength=\frac {1}{temperature} $$

As you might infer from this, the hotter the temperature the greater the amount of energy is involved. This is summarized by the equation:

$$ energy = temperature^4 $$

Uses In Space

Scientists use the blackbody curves to determine the temperature off far off objects in space. Since we can not observe it directly that is the best we can do. We can, however, infer a lot of information from an object's temperature.

Comparing how two objects are different also helps us classify too.

Electromagnetic radiation is the basis for a lot of interesting science. Understanding a little about it will tell us a lot about objects in space where we can not go.

Chapter 5 - Spectroscopy


Spectroscopy is one of the core techniques for understanding distant stars. We can not directly see these stars well enough to know much about them. Thanks to the fundamentals of light and how it behaves, we can collect the radiation from objects and infer many details from them.

How spectroscopy is used and its definition is the subject of this article.

The study of spectral lines emitted by objects is spectroscopy. Objects emit radiation and an instrument called a spectrascope can analyze it. Almost objects will give off radiation which is just another way of saying energy. 

Spectral Lines From Radiation


When you analyze spectral lines you are creating a spectrum. It is the division of the radiation's component wavelengths. The reason we want to analyze spectra is that it will give us a lot of information about the object that originally emitted the radiation.

The tool used to analyze radiation is the spectroscope. It is one of the core instruments of spectroscopy. Its main component is a prism that splits the light into its wavelengths. There are other smaller parts that help refine the process. You usually look through an eyepiece like on a telescope. 

Emission Line Spectra


Emission lines are what we see when we split the radiation into parts. Keep in mind when you do this, only the more prominent parts of the spectrum will show up. This is what characterizes each object, these different emission lines for every object.

When we repeat this process we get the same type of emission lines each time. If we analyze light from another source then the lines would be totally different.

Absorption Line Spectra


When looking at an object through a spectrascope you should see black lines throughout the spectrum. These black lines are actually gaps. They represent wavelengths that should be there but are not.

Something happened to them so they did not show up. These lines are officially called Fraunhofer lines or absorption lines and are a key ingredient to the study of spectroscopy.

Kirchhoff's Laws

A German physicist named Gustav Kirchhoff noticed there were similarities between types of spectra. He had a few famous laws.

  1. An object under high heat and pressure gives off a continuous spectrum.
  2. A gas with high heat and low pressure gives off an emission line spectrum.
  3. An object that emits a continuous spectrum and is behind a cool gas under pressure exhibits an absorption spectrum. 

Decomposing Starlight

In the last couple hundred years the field of spectroscopy has developed quickly and so scientists had several ideas on how to read starlight.

One of the most important things that was learned was that the lines on a spectrum corresponded to individual elements. So developing a spectrum for an object meant that we could discern its composition.

Atoms and Radiation

Before modern times we thought everything behaved as a wave. It made sense most of the time and was assumed to be true for a long time. Eventually, however, our technology improved as did our instruments and theory.

There was something missing, something not quite right. The answer we now know is that light does not behave purely as a wave but as a particle.

Understanding Atomic Properties

Atoms are the basic units from which everything is created. Even at their small size they are affected by radiation. Atoms absorb radiation which in turn changes the atom.

Historically the electrons in an associated atom were thought to be on precise orbits, kind of like planets. Scientists now think that it is a very loose orbit around the nucleus of an atom. Some may even be scattered about.

Radiation As Particles


Electrons are only found in atoms having a certain transfer. This goes whether they are absorbing or transmitting energy. So the radiation involved in these transactions must correlate to the difference in their separate states.

These defined transactions are known as photons. They are particles we now know. A photon is electromagnetic radiation. According to Einstein, the energy of a photon was about the same as the frequency of the radiation.

This concept was later worked on in depth by Max Planck and is known as Planck's constant.

Spectral Lines 


Every element has its own signature on its spectrum. They can be very simple and easy to organize or can be plain bewildering.



The spectrum of hydrogen covers most of the electromagnetic spectrum. When electrons absorb radiation they then have more energy. Electrons do not retain this radiation though. They will lose it. The question is how fast.

If it is lost fast then it will emit a single photon with the excess energy but if lost slowly it will emit two photons with the absorbed energy in both. Photons during this process can have differing amounts of energy obviously.

So each photon will be at a different wavelength. This is why the spectrum of an object has many lines at different frequencies and wavelengths, the photons that were releases after absorbing energy were each given a different amount of radiation or energy.

Carbon And Later Elements

An atom with more protons will have a much more complicated emission spectra. The reason why is that there are many more electrons that can get charged and developed into an active state.

Each one could get a differing amount of radiation and so give off emissions at a different frequency. Every different frequency will make the spectra taken from the atom look different.

So you can see how different and complicated this can be very quickly. Carbon and later atoms of course have larger and larger amounts of protons and electrons.

Molecular Spectra


What happens when different atoms join together and make a molecule? Well, things just get interesting. Those different atoms do not stop emitting radiation. They are all doing it at the same time or just a few at once.

It depends on what happens with their electrons and what particular atoms are involved in the first place. Since a molecule is just a bunch of different atoms held together by a chemical reaction between their respective electrons, we can expect their to be many more rules about how they interact.

The spectra that is emitted from various molecules is therefore a combination of those atoms that make up the molecule.

Analysis Of Spectra

Now that you have sort of an idea of how all of this works, what is exactly is the point you may be asking? The very interesting and valuable point is that you use the emission spectra to infer critical information from what you are observing.

This can be a star, galaxy, black hole, or planet. Almost everything we know from space is from these studies of radiation that reach us here on Earth.

Temperature Of Objects

Measuring the temperature is one of the important tasks for an astronomer. Knowing the temperature alone gives us a little information but put it together with known atoms and molecules and we get a much better picture of what is going on.

Speed Of Objects

The red-shifted lines of an object can tell us its velocity. This is done by the well known Doppler effect.  Looking at the source radiation and checking for either red-shifted or blue-shifted lines can tell us a lot.

If they are blue-shifted then the source is moving toward us. Red-shifted lines means the source is moving away from the observer.

Width Of Spectral Lines

Even the width of these spectral lines can tell us a lot about what is going on. The width is an indication of the environment of the source. Most often the velocity tells a lot. A higher velocity will usually mean a higher temperature too.

Magnetic fields can also broaden spectral lines. The stronger the magnetic field the more broad the line usually is.

Obviously I am only hitting the basics from each of these sub-topics. There is a lot more to each of them. Examples and more detail is certainly possible but not possible in my vision for this article.

 Chapter 6 - How Telescopes Are Used


How telescopes are used in modern Astronomy is changing every decade. We used to only use them to see objects with normal light. Now we can leverage our technology gains to see different wavelengths of light in the universe.

This has opened up our studies with a lot more data than we previously had. This article talks about the different fields and categories of astronomy and what they mean.

How Telescopes Are Used

There are many kinds of telescopes. With many different uses as well, there is a diverse market for every kind of telescope you could imagine. Narrowing down what your goal is can save you a lot of money in the end.

When looking for a telescope there are a few terms you should be aware of.

  • Aperture  -  This is the size of the mirror and is the most important factor.
  • Focal Length  -  This is the distance from the mirror to the focal point.
  • Magnification  - This depends on the focal length and is a good indicator of the telescope.
  • Focal Ratio  -  The focal ratio is the relationship between its focal length and the aperture of the telescope.

Optical Telescopes

Optical telescopes collect light. That is why they are optical. Seems simple enough right? In a way it really is. The more light we then collect the more we can see.

When people think of telescopes these are the type that are thought of when first learning the basics of telescopes. It is how telescopes are used by the public. There are two kinds of optical telescopes:

  • Refracting-bends light that is then focused.
  • Reflecting-uses a mirror to reflect light.

Refracting scopes use a lens to gather and concentrate light. They do not do colors as accurately as they should either. A lens will also absorb some frequencies. This makes a refracting telescope a poor choice for infrared studies.

Reflecting telescopes use mirrors instead of lens to work with the light that is captured. Since a mirror is used there are no absorption issues to deal with. You can also use a much larger mirror than a lens.

So scopes that are large almost always use a mirror. Among reflecting telescopes there are different kinds as well;

  • Newtonian-reflected to an eyepiece at side of instrument
  • Cassegrain-light is reflected to the end of the instrument

The Keck Telescope and the Hubble Space Telescope are the two most famous. Keck is based in Hawaii while Hubble is orbiting in space.

Size Of Telescopes

The size of telescopes has steadily increased over time. Originally they were pretty small in Galileo's day. However, thanks to modern science, we are getting larger ones all the time. Indeed the space telescopes are also getting bigger.

What is the advantage to a larger telescope you may ask? Well the larger the telescope the more light it can collect. It is all about the amount of light it can gather. This is what helps us see far off objects.

The quality that we can see objects in space is directly related to the size of the telescope's mirror. This helps with another issue which is the telescope's resolving power. This is it's resolution which is also very important.

This lets us see details of the objects in space. For example, it lets us study far off objects and refine our theory of star classification.

A larger mirror also helps with diffraction. This is the tendency of light to bend. Basically the larger the mirror the less bending of light, or diffraction, that you will have.

Imaging With Telescopes

Imaging and the field of astrophotography are very popular these days because looking through a telescope is looking back in time and is a guide to the universe.

When individuals first want to know how telescopes are used, imaging the night sky is one of the first choices. More and more people all the time are doing this because of how useful and fun it is. The pictures created are just breathtaking.

Computers and associated software are being used to make this process even easier and more reliable. Done correctly, they can even reduce background noise in pictures. The background noise also has its own characteristics.

It can then be analyzed and useful information will be the result.

So what exactly is imaging then you may ask? It is the process of taking very long exposure photographs of cosmic objects. While your camera is doing this it goes onto its film.

There is a slight problem with this though. Can you guess? Yep, the Earth and everything moves. For astrophotographers to take those stunning pictures the telescope has to move.


If you are interested in the field of astrophotography then you will be buying a telescope that has a guidance system included in it that will track planets and stars.

This means there is a small computer that will adjust position in far greater detail than we could ever do by hand. The purpose is to keep our object that is being photographed squared in our view.

Most often this was done by hand and it could be quite difficult. It was easy to make errors doing it this way.

CCD Chips

Fairly recently technology has advanced and new CCD chips have come on to the market. This chips take digital images of objects.

Just like the previous method it takes time to gather enough light and information on to these chips but the results can be wonderful.

These chips also have the ability to autoguide, making the following of an object a much simpler process if you have the cash to pay for the hardware.

This leads to the next subject which can be very useful. It is the study of brightness of any object. This is called photometry. Astronomers combine photometry with the use of filters to analyze certain wavelengths.

As each range of wavelength can have different characteristics, this is very valuable.  To measure the light a telescope takes in we use an instrument called a photometer. It measures the amount of light received.

Spectroscopy , which is the study of the spectrum of light, goes right along with this. Without even looking at the source image much can be inferred from this and is one of the most important topics when dealing with the basics of telescopes.

Detailed Astronomy Pictures

It is hard to get great pictures on Earth. It is not really our fault though. The atmosphere affects our view so much. Not a lot we can do from here. This is why we launched telescopes into space.

Turbulence in the air is constantly messing with our telescopes and imaging. An interesting fact is that turbulence has less effect on longer wavelengths.

I do not know why this is but guessing it is because smaller wavelengths are much more sensitive. Because of turbulence, telescopes are usually placed at high altitudes.

Radio Astronomy

Since an abundance of radio waves reach us on the ground, radio astronomy is a growing field. Also since radio waves are a lot longer than, say gamma waves, the atmosphere does little to them.

Radio astronomy has only begun in the last few decades so we have a lot to learn about these techniques.

We can use radio waves to map out areas in space with much greater detail than using optical astronomy. This is very useful because we can not actually see these areas with our eyes.

Radio telescopes have a huge dish which is their collecting area for the radio waves it captures. It is so large because radio waves are quite rare compared to other kinds of radiation that hits the Earth.  

They also operate differently than optical telescopes in that they only see a few wavelengths at a time of radiation.

A huge advantage with radio astronomy is that poor conditions mean nothing. For example, if you want to go see a meteor shower and it is cloudy then you are out of luck.

It is the same situation with any optical telescope on Earth. If there is too much moisture or cloud cover then we just have to wait until conditions get better. Radio telescopes do not have this problem as radio waves are not affected.


One of the main issues with radio astronomy is the poor resolution. Those telescopes are not near as good as optical telescopes in showing details of an object. This is where interferometry comes in to play.

Interferometry is when two telescopes are used together to view an object. As each radio telescope takes in data, the data is then combined again using special software that makes a superior image than either took to begin with.

When used together like this an interferometer can make great images which get very close to optical images. An important fact to know is that the two radio telescopes that work together are separated by great distances.

By this I mean they can be on different continents or even further than that in some cases.

A very interesting thing happened as technology and computers got better in recent years. Instead of just detecting radio waves, we can now also detect smaller wavelengths. This opens up our universe even more.

Infrared Astronomy

Infrared telescopes are used to study long wavelength radiation and it is a good example of how telescopes are used to study light that we can not see. This is a very popular field. Longer wavelengths are easier to detect than much shorter wavelengths like gamma rays.

A good example of this type of astronomy is the Spitzer Space Telescope. It has given us some truly great images.

This is an important field because it lets us see the universe without the issues of light pollution. Interstellar dust is everywhere out there. There is so much of it that it makes some very large clouds.

All of this dust makes seeing difficult at times. The dust can completely block out a lot of faint objects.

This is why studies of the infrared spectrum are so valuable. They let us see without having to actually see. On the electromagnetic spectrum infrared lies between visible light and microwave radiation.

Its wavelengths are a little shorter than microwaves. Infrared radiation is given off by any object that produces heat. It can be a lot of heat like the sun or just a small amount like the snow.

Both still puts off some degree of heat and therefore radiates infrared radiation.

Ultraviolet Astronomy

At the opposite end of the spectrum we have ultraviolet astronomy. This is short wavelength astronomy. In this niche area of astronomy it is ultraviolet radiation that is studied. The wavelengths of this radiation are around 90 to 350 nanometers.

As with all of the other areas of astronomy, you can tell a lot about the object when studying its radiation. Examples of what can be inferred are densities, composition, and temperatures.

The ultraviolet spectrum is divided up into the near, far, and extreme ultraviolet regions.

One of the cool things about ultraviolet radiation is that the objects with the highest temperatures in the universe give off a lot of ultraviolet radiation. This makes it a good source to study.

To study this type of radiation we usually have to analyze data taken by space telescopes.

I should point out that we use space telescopes to gather ultraviolet radiation because the Earth's atmosphere blocks most of the ultraviolet waves. Basically, to get to them we must be in space.

High Energy Astronomy

This is the part of the spectrum that is least known to us. High energy astronomy deals with gamma rays and x-rays. They are hard to detect and to capture. Gamma rays in particular have the most energy of any other type of radiation.

One of the really cool things about them is that they penetrate everything. This makes gamma rays hard to deal with.


An interesting fact is that the gamma rays and x-rays cover a large part of the electromagnetic spectrum. In contrast, visible light only covers a small fraction of the spectrum.

Just about every day we are discovering more sources for x-rays and gamma rays. The list is growing quickly. However, there are many more sources for x-rays than gamma rays. In our galaxy the Sun is the closest emitting source.

Throughout the galaxy there are sources that send forth much more radiation than our Sun. These are called the x-ray binaries which are systems of stars in which one is probably a neutron star.

These objects produce fantastic amounts of high energy radiation. Another super source of x-rays are supernovae which can send the detectors through the roof.

Gamma Rays

Right now there are only about 3000 known sources for gamma rays. That number should explain how rare they really are. As a result, it is more difficult to do a study using spectroscopy because other wavelengths are much more common.

We can sometimes wait a long time before we are able to detect one. Even more rarely we can observe gamma rays in lightning bolts or certain kinds of nuclear explosions. The typical gamma ray is highly energetic.

This means that it contains an abundance of energy.

Its energy is so great that it is used in the medical industry to kill certain cancers. I can't think of a better way to harness nature for a good cause!

I hope this has given you some inspiration for studying Astronomy. It is a wonderful science and there is much yet to learn. You even have several fields in which to specialize in.

Your first step is to get a telescope and start exploring and see where it takes you. 

Chapter 7 - The Solar System

The area that our sun has control over is collectively known as the Solar System that includes planets, comets, asteroids, moons, and many other objects. Objects are what the myriad of things in space are often called in order to group them together.

Planets that have ring systems have been found. Saturn is the most famous example of this. Most planets have moons. Some of the moons are like ours but some are very different like Titan and Enceladus.

Every year there are cool comets and meteor showers to see in the night sky. You do not even need a telescope to see these as binoculars work great for this.

Comparing Everything

One of the ways that we learn is by comparing. To do that we have to observe characteristics and take measurements in whatever way we can in order to build a profile about planets and everything else.

Some of these characteristics are brightness, density, mass, composition, distance from host star, orbits, and many other details. By doing this we can logically conclude that two objects with roughly the same attributes were made the same way.

This is the foundation of our experiments and theory and very important.

How Does Observing The Galaxy Help Us

This might seem like a strange question. I mean most people would say it is a good idea to constantly observe. But, how exactly does it help us? When I first encountered this question in school I really could not come up with an answer that I was satisfied with.

On homework I just put something generic. I am coming back to it now because I feel it is important and wanted to help others who might have had the same issue.

As we observe stars, planets, or comets in our night sky we measure everything that we can. Things like how bright does it appear or maybe how fast does it move across the sky. We start with basics just to be able to start somewhere.

After we do that a while we get an idea for how things work. It may not be  deep idea yet but its there and it takes hold. When we observe other Solar Systems we get to test those ideas and see of they hold true to these far away objects.

Size Of Our Solar System Objects

The size of our Solar System objects varies greatly. The largest mass in the solar system is our Sun. It is also by far the largest thing out there besides other stars. The largest planets are Jupiter and Saturn.

They are many times the size of our Earth. The smallest planets are Mercury and Venus. Venus is about 80% the size of Earth but Mercury is only around 40% of our radius.

Moons are generally much smaller than planets. Our moon approaches the size of some of the smaller planets but others are much smaller. Asteroids are much smaller still.

Types Of Measurements

As mentioned earlier, there are many attributes that we can measure about the objects in the solar system. Some of these measurements can be made directly but others must be indirectly made, or inferred.

  • Orbital Period   - This is the average time it takes for any object to completely orbit any other object.
  • Mass                    - The numerical measurement of the amount of matter in an object.
  • Radius                 - Distance from the center of an object to the outside edge.
  • Rotation period - Time for on object to complete a single rotation.
  • Density                - Calculated as mass per unit of volume.
  • Temperature      - Measurement of an objects temperature often in the unit kelvins.

How Do We Obtain Data On Solar System Objects

The previous section mentioned several properties that we try to figure out about any particular object. How do we go about this though? Geometry is key to this. Specifically the use of triangles and their properties.

We can learn much using these simple tools. If possible we even directly observe any moons, asteroids, or planets that we come across.

Distances In Our Solar System

Distances between the Sun, planets, and the Kuiper belt which is at the edge of our solar system are truly vast. The distance between the Earth and the Sun is called 1 AU. That stands for astronomical unit.

It is a huge distance and is defined as the distance between us and the Sun. There are around 50 AU to the edge of our solar system from the middle.

Our solar system is often talked about as flat. There is a relatively simple reason for this. It is because most everything that orbits around the Sun does so in the same geometric plane.

More About Our Planets

The planets in our solar system are often divided up between the rocky and gaseous planets.

The rocky planets are those closest to the Sun. The Earth is one of those rocky planets. The other three are Mercury, Venus, and Mars. These four planets are much smaller in size than the outer gaseous giants.

The rocky planets have some sort of atmosphere. Atmospheric conditions are all quite different among the four inner planets though. The Earth is the only planet with oxygen in its atmosphere.

There is a tangible surface on all of them too. Surfaces are all different as well.

The gaseous giants in the outer solar system are different than the inner planets. They are the furthest away from the Sun and have huge orbits. The gas planets are mostly helium and hydrogen.

As far as we know there are no solid surfaces on the outer planets. The magnetic fields on the gaseous planets are much stronger than here on Earth. They each have several moons in their immediate orbit. Ring systems are also a common factor among the gas giants.

Interstellar Medium

You might think space was totally empty except for all of those large objects floating around out there. It is not so. There are a multitude of rocks, dust, asteroids, and meteoroids in between everything.

Dust forms usually when objects grind together and debris ends up scattered everywhere. Larger objects are created through ancient explosions and collisions that have happened throughout time in our universe.

Meteoroids and asteroids are rocky objects flying around out there. Anything larger than 100 meters in diameter is an asteroid. Smaller objects are meteoroids. Comets are much larger objects. Their compositions are usually different as they contain a lot of ice.

How Is The Interstellar Medium Important

By doing detailed studies of the material between the planets we learn more about how the Solar System formed. This is the material that formed everything else in galaxies. Astronomers assume it is the stuff from early in the history of the universe.

They are most likely right. Since it is from early on it gives us clues about the early universe and its conditions. We can usually infer many properties then and know a little more what happened after everything first formed.

The Kuiper Belt

At the edge of the solar system is a huge asteroid field called the Kuiper belt. It is named from Gerard Kuiper who was a famous astronomer.  Located past Neptune, it is at the coldest part of our solar system. It is in the shape of a disc.  

It is filled with matter. Sizes of the matter range from dust particles to sub-planets like Pluto.  It is likely that the Kuiper belt is the source of most of the comets that we see.

They come our way because the comets get thrown out of orbit. While a few comets get vaporized by our Sun, many more make it to travel the solar system.

The One Orbital Plane

Almost every object in our solar system orbits or travels in the same plane. I mentioned this earlier but did not explain why. I am getting to that now.

With so many celestial bodies in space you might be tempted to think their orbits and paths would be all over the place. It would be easy to think this because their is just so much out there!

That is not the case though. Almost everything is on the same plane. Obviously there must be a common cause to this phenomenon. There sure is.

There is one object in our solar system that has the influence to accomplish the feat of aligning everything into a single plane. It is our massive Sun. The plane that everything travels about is the same as the Sun's equator.

The overwhelming and crushing gravity of our Sun is responsible for this. There are a few minor exceptions where objects were hit and knocked a bit off path but there are very few of these.

Formation of the Solar System

What probably happened, in a simple sense, is that a large disc formed that had a lot of matter in it. This disc was rotating rapidly and eventually matter began to stick together. Over time some matter broke apart and other matter got larger.

The larger pieces grew to be planets and moons. The largest piece of matter was our Sun that was much different then.


These primitive discs are called accretion discs. They grow by having matter collide and stick together. Small objects eventually become larger matter. The process just continues over and over.

Planetary systems and Black holes have this in common. Each can have accretion discs and grow in the same way. Of course different things can happen in Black holes but I will get to that another day.

Planet Characteristics

I mentioned earlier that the planets closer to the sun were more rocky and those further away were gas giants. There are reasons for this.

The main one is temperature. Temperature affects a lot of things  in the solar system. In this case it determines how matter behaves and what elements can form.

So what happens in the planets close to the Sun is that it is too hot for matter to stay together at times. In ways it is the same principle why we use hot water to clean things rather than cold water.

The higher the temperature the easier it is for the water to break chemical bonds of dirt and other matter that may be on your hands when you wash them.

It's the same principle next to the Sun. Matter exposed to those high temperatures breaks apart much easier. Therefore only the larger chunks of matter remain.

That is why there are only rocky planets close to the Sun and why there are gas giants in the cooler regions of the solar system.

In the outer solar system that matter did not break apart because it was much cooler out there. Clouds of dust formed and stayed together. Gases stayed together and compacted, forming dense clouds.

The early gas giants formed in this way after accreting enough material to form a core. Then gravity started affecting things like it always does.

In short, that is why the inner solar system planets are so much different than the outer planets.

Formation Of The Large Planets

There are different theories about how Jupiter, Saturn, Uranus, and Neptune formed.

One of which implies that the original bodies that would become these planets slowly leeched gas from its nebula. Growing like this would be possible due to strong gravity field.

The other main theory says that these large planets formed directly from the collapsed cloud. Strong gravity caused the cloud of gas to become unstable and break apart.

Formation Of The Gas Giants

The gas giants are mostly that, just gas. Hydrogen and helium constitute the majority of all matter in them. They obtained all this gas from the nebula in which they were first born. As long as there is gas then they will continue to grow.

Our Sun was already forming at this time too. You know every star goes through a series of phases in its development as a star. One of these phases is the [T Tauri] phase. During this time the Sun has incredible stellar winds.

Stellar winds that are very powerful and will blow away the nebula of gases around it.

So when the nebula disperses, planets that grow by leeching gas will stop their growth at this point. This bring up two important points.

  1. If the Sun grows slowly it will reach its [T Tauri] phase with high winds much slower. This lets the gas giants get a lot larger.
  2. When our Sun grows quickly it reaches the [T Tauri] phase quickly and disperses the gas. Therefore planets made of gas will be smaller.

Why Are There Definitions Of Inner And Outer Planets

They are so different, that's why. It just makes sense to divide them up like this. I am not sure who first proposed this idea but it made a lot of sense. Almost every property is vastly different.

Because of this, we can compare either inner or outer planets to similar groups that orbit around other stars. Usually we can infer they have similar properties in doing this too.

Movement Of The Planets

There is also an interesting theory that says our gas giants came from far away and not created where they are now orbiting at. This theory basically says that they were formed in the Kuiper Belt and moved towards the Sun slowly.

The reasoning is that the gases that are now on the Jovian planets could not have gone through the planet formation stages at high temperatures. So some think they formed way out in the Kuiper Belt.

Where The Water Came From

It has been long understood that the water in our solar system came mostly from comets. There are certainly reasons that make this plausible.

One of which is the frequency that comets occur in our solar system. They are constantly floating around out there. There are issues with this.

One main issue is that it takes a lot of comets to bring that much water. It is true that comets are frequent visitors in our solar system but that is still a lot of water. Once a comet gets close to a planet wouldn't the friction of the atmosphere burn up most of the water?

Even if they made it to the surface a fiery explosion generally creates a lot of heat too which would also burn up the water vapor. So there are a few holes and doubts in this theory too, at least to me.

Our magnificent Solar System is really quite interesting to study! For a very long time we have been told that Earth and its surrounding neighbors was very ordinary and not at all special in the universe.

I do not know about you but the more I study and read the more it seems we are truly special.

When I think about all of the processes that go on in order to make this Solar System the way it is, I think of many more questions than I ever get answered. That's the way it is though with everything probably.

Chapter 8 - The Moon

The Moon has been up there in the sky looking back at us for as long as there has been a sky. Where did it come from? Why do we see only one side continually? The Moon is mysterious and I think we can all agree on that.

There are many unanswered questions and the fact remains that many of them we just don't know. In this article I will try to answer some of these more common questions in ways that make sense.

Distance To The Moon

It is pretty close to us compared to anything else in our solar system. It's average distance is around 384,000 km but that will vary slightly depending on where it is in its orbit.

Radio telescopes and powerful lasers are often used to measure the distance from us to our only natural satellite. No matter how close it may seem though, it is really farther away than most people realize.

It is just the closest object to us by far and that makes it look closer. One interesting fact is that the Moon is getting further away from us by 1.5 inches per year on average. Someday that cosmic behavior will affect us here.

Getting There

It takes a decent amount of time to get there and that is on a fast flying rocket. Remember it is 384,000 km from the Earth at some times in the year. Originally  it was a 3 day trip but subsequent trips have decreased our rocket time to a matter of hours.

The New Horizons probe only took 8 hours. Newer ships will be even quicker. Everyone is hoping that the time it takes to get there will be quick enough for regular trips. We will have to see on that!

Characteristics Of The Moon

It's radius is about 1700 km which is a lot smaller than here on Earth and it means less gravitational influence as well. That means the Moon is only around 1/4 the size of the Earth.

The average density is 3300 km/m^3 and is also quite a bit less than Earth's density. Why is the Moon so much less dense? Being less dense suggests that there are a lot fewer heavy metals under its surface.

Metals such as Iron and Nickel are extremely dense. Gravity is also a lot less on the Moon because it is not near as massive as the Earth. For example, Earth's gravitational field is 6 times stronger than the Moon's field.

There is no atmosphere on there either which is due to its low gravity. Wildly changing temperatures, because of the Sun's intense electromagnetic radiation, are a fact of life since it does not have any real atmosphere.

Temperatures range from 100k to 400k and that is below freezing to hotter than boiling.

Surface Properties Of The Moon

The surface of the Moon has been battered by meteors non stop since its existence. The meteors have caused huge craters and cracks in the surface as some of the impacts have been enormous.

The Moon has large cliffs and mountains because of this and its surface is changing still. Ancient volcanoes have also helped form its surface appearance. The volcanoes are no longer active but their effects are still easy to view in the large flat plains.

These flat plains look quite eerie with their smooth surfaces. They contrast with the rest of the beaten surface in a magnificent way.

Always The Same Side

We always see the same side and you probably wonder why that is. There is a simple reason for this. It rotates on its axis in the same time as it takes t complete one orbit around the Earth.

That reason is why we only see one side and there is the dark side of the moon that you hear about occasionally. While that is cool it also means studying the other side is difficult unless your in space.

Rotation Of The Moon

The Moon rotates just like we do even though it does not look like it from Earth. I mentioned above one section that we always see the same side of the Moon and that is because our orbits are synchronized.

An orbit that is synchronized means that it's rotation period is the same as its rotation around Earth. It rotates around the Earth every 27.3 days.

Your next question is probably how could this happen to where the orbits are synchronized so closely together. It is due to two things and they are time and gravity. Time and gravity are probably the two most influential factors in the universe.

Earth's gravity has been pulling at the Moon for a very ling time. At first the orbits were not nearly so close. Over time with the Earth constantly nagging and pulling at the Moon it eventually just conformed pretty closely.

Now that I think about it, the Earth sounds just like a woman I know...I'll probably get in trouble for that comment.

The Moon's Atmosphere

Does the Moon have an atmosphere? No, not really, it doesn't have one to speak of at all. The reason why is that there is very little gravity exerted by the Moon. Earth's gravity, for example, holds our atmosphere in place which lets us breathe air.

Without it, we would would not survive and its as simple as that.

It does contain a few gases that have not escaped but they are in quite small amounts. What we can detect is mainly Helium and Argon but there are trace amounts of other gases too. 

Gases that are there come from the solar wind for the most part but there are just not many gases on our Moon.


Our Moon's composition is basically one big rock, or more accurately, many tiny rocks just stuck together. These tiny rocks have been mashed together by gravity and other impacts for a very long time.

Remember that it is not very dense and there is a major lack of heavy metals. It also does not have wind and water erosion like we do on Earth.

So with all the meteor impacts it has we just see hole after hole on its surface. Some are very small and some are massive.

There is some debate whether it has a solid iron core  or not one at all. The consensus is that if it does then it would be pretty small. We already know the density is a lot less than here on Earth so whatever iron it has is going to be tiny.

Moon Dust

The Moon is covered with dust. It is not only covered but it is very thick too. The amount can vary between 20 meters and 100 meters. That is a lot of dust and it shows no sign of going anywhere.

The reason there is so much dust is because of all the meteor impacts. After meteors hit the Moon's surface they just destroy everything remotely close to it. Other rocks nearby are ground into dust and this is where all of the moon dust comes from.


There are volcanoes on the Moon! They are the reason for many of the craters however they may all be dead volcanoes now. Early in the Moon's history there were probably lots of surface volcanoes but for some reason geological activity stopped at some point.

The volcanoes were very active at one point as we can see from the significant plains and smooth surfaces.

The Interior

The inside of our Moon is not very dense and in fact it is just about the same density as regular rock. This means that it most likely does not have very many heavy metals like I mentioned above. The composition is likely very much the same throughout.

No Magnetic Field

There is no heavy metal core and therefore no substantial magnetic field. Magnetic fields probably require an iron-nickel core under high pressure and heat. There is none of that and most likely never has been one.

There is a tiny magnetic field but it is so small that it basically has no effects.

Origin of the Moon

I hate to say this but we don't really know where our Moon came from. There are many theories and a few really do make sense. They can't all be right though so what we have left are best guesses.

  • Moon and Earth formed separately but close together
  • The Earth captured its Moon when it got too close
  • Our Moon formed from the Earth itself
  • The Moon formed from an impact

Based on the little evidence we have I will have to say I don't know where it came from either. The above points all make a little sense but there is no theory that is just right.

Moon and Earth Formed Separately but Close Together

This used to be a popular theory until we had a better understanding of planetary formation. This theory says that the Earth and Moon both formed around the same time in the same region.

This is plausible because the Moon is in our orbit which is a hard thing to do. It does not make sense when you remember how different the makeup is for each object. The Earth has an iron core and many other metals scattered throughout.

The Moon has virtually none and its entire makeup is closer to a big rock.

The Earth Captured its Moon

This was another popular theory at first and made a lot of sense because many planets capture their own moons. However, the one thing that stands out here is that our Moon is much too large for this to happen the usual way.

Our Moon is around the largest non planet in our solar system and Earth is far from the largest. The gravity of Earth is just not strong enough to capture something the size of our Moon.

Our Moon Formed From The Earth Itself

There is a huge hole in the Earth's surface and it is the pacific basin. This theory says that a young Earth could have been spinning so fast that part of it spun off into space and then became our Moon.

The density is similar between the rock in the pacific basin and our Moon. The main problem here is that there is no reason for the Earth to be spinning that rapidly nor is there any evidence of this ever happening.

The Moon Formed From An Impact

This is the most popular theory currently. Remember theories can change in a heartbeat when we find new evidence so it is important to keep that in mind. This one does make a lot of sense though as we have pointed out the flaws of the other theories above.

Did this really happen? I don't know. It could have though and that is about as much as we have to go on. This theory says that a large impact by something similar to another planet did a glancing blow that knocked loose a large portion of the Earth's surface.

It does at least make sense since the material would be the same and that would make the orbit problem resolve in a nice way.

The Moons's Distance 

The distance to our Moon was originally measured by using geometry and measuring the length of shadows. This was done pretty accurately because they knew the Earth was round by this point.

We use lasers and bounce them off a reflector that is currently on it that was put there by astronauts.

Primary Source Of Erosion

Erosion on the Moon is different than on Earth. Really small meteors that constantly bombard the Moon are what erodes it. Since there is no atmosphere they do not burn up but instead constantly hit the surface.

However, this process is much slower than erosion on the Earth. On this planet the wind and water erode objects much faster.


The Moon has been up there in our sight for all of our short human history but it is amazing how much we still do not know. We are finding out more details steadily and hopefully we will advance our knowledge at a quicker rate than before.