# An Introduction To Astronomy

This document is an introduction to astronomy and in it we will learn about the creation of astronomical objects and get a critical understanding of our galaxy.

First, who doesn’t just love Astronomy? Okay, I am sure there are some before people try to correct me. However, if you’re here, I am just going to assume that you have at least some passing interest if you are here and reading this.

I love Astronomy. It started by looking at those fascinating pictures of galaxies that get posted all the time on the internet when I was a kid. Those big composites with their color fixing did it for me.

Ever since then I have been interested. From there, I developed several other interests that were offshoots of Astronomy such as Mathematics, Physics, Programming, and yes even Writing.

We need to look at some of the history of Astronomy. Now, I’m not trying to write a book here so I will have to gloss over a few things. I want to get the highlights, though, so everything makes some sense for you.

We will assume the first interest in Astronomy came from the first primitive people in the world. I can’t even imagine what they thought when they looked up at the sky for the first time.

I am sure there was interest, curiosity, and maybe even dread at the unknown. This was the state of astronomy for many thousands of years. Not much they could do about it.

The first advancement was the creation of the telescope. It had been a long time coming. Glass and mirrors had been manufactured for quite a while before someone thought to apply it to look at the heavens.

Galileo is who we recognize today as the first to make good strides in using the telescope. He didn’t invent it, nor was he the first to use one. What he was good at, though, was in optimizing and improving what was already out there.

He had refracting telescopes and was very good at refining what they did. For the first time, people could see the heavens in better detail. Planets were visible now, and they were not just a dot in the night sky.

Galileo could see other objects, but at first he did not know what he was looking at. This was in the early 1600s.

Kepler made the next large advancements by using a convex lens. A convex lens magnified celestial objects. This led to many discoveries.

One of the most influential discoveries was explaining how objects in space moved. These were his laws of planetary motion and the basis of celestial mechanics that we use today.

These laws relied on the concept of heliocentrism, which was very advanced for the time. Heliocentrism basically meant that the Sun was the major force in the solar system.

The concept of gravity is the next advancement that spurred things along. Gravity was also independently worked on by multiple people.

This was a good indicator that they knew how important it was going to be. Gravity, if powerful enough, influences everything.

It won’t have a noticeable effect on small objects. However, large objects in space all affect each other. Of course, the Sun is the dominant force in the solar system.

The planets orbit around the Sun because of gravity. At some point, the different planets were each captured by the Sun and it would take some significant force to knock them out of the reach of its gravity.

Once we got an understanding of gravity, the light that we saw in space started getting attention. Astronomers started studying it. One of the first realizations was how fast it had to be.

Many experiments were done. At first these experiments were just confusing because our system of measurements and scientific equipment could not accurately portray light’s speed.

Eventually the early astronomers got a handle on it. One of the most important discoveries made was that speed is a constant. Its speed is always the same.

This is important because it allows us to measure distances to other things in space. By doing this, we can tell how far away something is and if that object in question is moving.

Astronomers got so excited about the study of light that a new field was created. This field is spectroscopy.

Light is radiation. Visible and non-visible light is all just radiation. This is interesting because most objects in space emit multiple forms of radiation.

Scientists study them as much as possible because they give us clues about what is going on.

Studying the light from stars, for example, can tell us relative distances and whether a star is moving. There are many other details light can tell us too, such as the temperature and what it is made of.

One of the first things Astronomers figured out a long time ago was that almost every star is different. They were of different ages, had different temperatures, and rotated at different speeds.

The next task was classifying all these different stars with similar characteristics. This has been a large and ongoing job, as you can imagine.

Eventually arbitrary classes were created so that we could better group stars. There are several groups and they all mean different things.

Stars come from molecular clouds. Molecular clouds are part of nebulae. These enormous clouds of dust can form into a star. This happens by gravity usually but there have been other ways occasionally.

The gravity of a close celestial object can grab and condense a molecular cloud. After it is condensed enough, processes begin the long journey to becoming a star.

## Important Stuff In The Galaxy

At this point we have a good idea what makes up our solar system. People have been constantly mapping it out since telescopes were invented. So this is a process that has been going on for hundreds of years.

It is called the solar system because that is the area that our Sun is dominant over.

Space objects include:

1. comets
2. asteroids
3. planets
4. moons
5. stars
6. galaxies
7. nebulae
8. dust clouds
9. black holes

All of these are very different and have different origin stories.

One way we know their differences is because we compare everything once we measure everything. It is very insightful.

There is obviously a lot more to the solar system than I can mention here. Certainly each topic is a book itself. I will say that most people get really curious about planets at this point.

Are there planets that we have missed out there? Are there any planets that are exactly like Earth? That alone is an acceptable topic to explore.

If you study different objects, you quickly see that debris makes up a large part of our galaxy. They include asteroids and comets in this group. When celestial size objects collide, stuff flies everywhere.

This is where asteroids, comets, and large clumps of dust come from. How they all interact with each other is just fascinating!

Some asteroids are huge and every so often travel pretty close to Earth. This always makes for big news so watch for these events in your favorite publication.

Comets are fun too. When these get close I highly recommend grabbing your telescope or a good pair of binoculars. These are amazing to see and even better done with friends. These parties are great.

You may not think about it, but dust clouds play big roles in the galaxy. It is often the formational material for stars and planets. It’s the glue, so to speak.

Vast clouds can also blot out the sky in certain areas. A gigantic cloud can just absorb all the light and make portions of space look like nothing is there.

Stars are wonderful objects. Our own Sun is the closest star to Earth. Studies of it and others are very involved. They each have their own:

1. size
2. orbital velocity
3. rotation
4. temperature
5. brightness

Different temperatures usually imply a relative age. This is because stars usually have an evolution to follow. Different stages usually involve certain temperature ranges.

The size of stars is also very interesting. It is interesting because often that can tell us how it formed. Once we know how a star formed we can infer many other facts about it. Is it in a binary system?

Is it still growing through an accretion disk? Any question we can successfully answer leads to even more knowledge and questions to explore. It can be a deep rabbit hole indeed, but it is so very fun once you get started.

So now you may wonder how stars formed. That is an excellent question and is another area of study in Astronomy.

To put it as short as possible, stars form in the middle of huge gas and dust clouds when the cloud’s own gravity becomes very strong.

Much of the gas and dust is condensed and they generate so much heat that nuclear fusion happens. There is an immense amount of pressure in the middle of new construct and we can now call this a protostar. I have skipped a lot, but that should give you an idea.

Shockwaves are often the start of star formation. They often form right in the middle of the now compressed cloud. They then travel through the cloud in many directions at once.

This action will further compress and heat the material inside. This is so catastrophic to the cloud that it will separate into distinct parts. These distinct parts will now usually become stars themselves.

We have just mentioned how stars are formed. What happens when they die? This is another superb topic of study that astronomers have to choose from. When stars explode, we can see novas and the awesome supernovae.

These explosions often involve a binary system. The reason is that one star takes material from the other star. These have been called vampire stars for this reason.

While this vampire star is stealing energy, it gets super hot and dense. Anyway, after a while, one star gets too much material to handle. The pressure has also increased.

The star can’t take anymore. Its core has been squeezed by gravity until it is super tight and dense. Think of our planet squeezed so small it’s like the size of a golf ball.

I’m sure that analogy isn’t exactly right but just pretend with me. So, our golf ball can’t stay like that forever. The force compressing it will eventually give way.

What happens next? Well, an explosion happens next. It is an explosion so violent and large it makes anything that happens on Earth look like a balloon popping in comparison. That is what we know as a supernova!

Some supernovae turn into neutron stars. This is a misleading term. It’s not really a star anymore at this point. It is basically a ball of neutrons that defy the laws of physics as we know it.

So, after the explosion has finished, which can take a very long time, all the star’s material will get blasted away. The only thing left will be the core of the previous star.

We call this a supernovae remnant. It can take up the space of a small county here on Earth but have the mass of our Sun for example. This density is beyond comprehension.

Neutron stars can also spin. Some spin hundreds of times a second. Think about what has to be going on in the inside for something with the mass of our Sun to spin hundreds of times per second.

Truly incredible in my opinion. Neutron stars that exhibit this behavior are called pulsars. I’m sure you might have heard of them.

Astronomers are still trying to discover more about magnetars. There have been very few discovered. Astronomers have also had a hard time catching them in action.

Their bursts are very sporadic. It has a magnetic field around a thousand times greater than a typical neutron star.

They are about the same size and mass as a neutron star but the difference is the magnetic field. Many stars have only a slight magnetic field.

So we do not know why some of these stars, namely magnetars, have magnetic fields thousand and millions of times stronger. It is surely an interesting area of research.

Magnetars are also a source of x-ray and gamma-ray bursts. These bursts are formed by starquakes on the surface which disturb the magnetic field. There are some theories about why the magnetic field is so strong but I will say that I don’t understand them yet.

They involve super dense fluids after a neutron star forms. I need to read up on them more but there is also very little literature to read, which is the problem.

We do not know a lot about black holes. For the longest, they were just theoretical. Now we have more evidence about them, but not much. They are really just a super dense neutron star with gravity so strong that it sucks everything into them, even light.

Objects would never disappear into a black hole. The gravity is too strong, it would disintegrate the object into atoms before it even got close.

There are many what-if scenarios that scientists have conjectured. Not much has really turned out to be true yet as getting any information from a black hole is incredibly difficult.

The only exception to that is Astronomers think a black hole can’t be larger than 3 solar masses, relative to our own Sun.

## Orbital Motion

The motion of planets and other space objects can seem strange. Hardly anything moves in a straight path. Planets and moons sometimes disappear. Even when you track something, its path is somewhere between circular and totally random. Everything is just counter-intuitive.

The reality is really not that bad. Once you know a bit about orbital motion and gravity, it will all make sense. I promise! So let’s get going and restore some order to our night skies.

The most important concept that we need to talk about is gravity. It is the reason for being. It is the key to it all.

Let me say right here that I am discussing the original interpretation of gravity and not Einstein’s curvature of spacetime.

### Planetary Motion

Let us start with Tycho Brahe. He was a Danish astronomer who observed the motion of celestial bodies for many years. He recorded all of his data. This data was essential to Johannes Kepler and his eventual laws of planetary motion. His laws of planetary motion catapulted modern science forward.

A planet such as our Earth, Mars, or Venus moves in an orbit. An orbit is the path it takes. Astronomers first thought the orbits of planets were big circles, but they soon discovered it was something else entirely. Planets just disappeared. They disappeared because scientists at the time were looking in a circular path. They did not know about elliptical motion.

### Ellipticals

This was the crux of the times. Kepler, however, soon found out that planets moved in an elliptical shape. He did not know why.

We can describe an elliptical as an irregular circle. There is not any definite shape to an elliptical because its lengths can vary. I can call any of the lengths an elliptical. The center of the elliptical to the longest side is called the semi-major axis. It is half the length of the diameter.

The eccentricity of the ellipse is also important. It is a measure of how circular or non-circular an ellipse is. We calculate it using a ratio of the distance between the foci to the length of the major axis. You can think of it as a triangle. You have the center of the ellipse, the foci in one direction, and then the major axis at the other end.

An eccentricity of 0 means the shape is perfectly circular. As eccentricity approaches 1, it is very elliptical. If eccentricity is over one the object is probably not orbiting the center of the ellipse at all.

### Newton’s Laws

This leads us to Newton’s laws. He was famous for his three laws, and they had a tremendous impact on the scientific world.

1. First Law = Every object continues to be in the same state of moving or non-moving and at a constant speed in a straight line unless another force changes this.

2. Second Law = The change of motion of an object is proportional to and in the force's direction acting upon it.

3. Third Law = For every action, there is an equal and opposite reaction.

These laws are pretty straightforward. However, let me explain to anyone that might not be familiar with them.

The first law says that objects will stay at rest or continue in the same line of motion unless some external force acts upon it. An example of a force that would change it could be friction or another object striking it. In either of these two cases, the original object would experience some change of motion or direction.

The second law is a little more vague. In a vacuum, this is what happens. However, hardly anything is in a vacuum, though space can sometimes be close. If you neglect friction, a pool ball can change its course to match perfectly the direction that another ball strikes it. The original pool ball will have the same direction and velocity as the one that hit it. Keep in mind, this is a vacuum instance we are talking about.

I think the third law of Newton was his most profound. If you think about it, it is true whether or not in a vacuum. The reason it is so important is that it implies their forces do not act alone. If there is an equal and opposite reaction, that means there are multiple forces at play.

### Momentum

This brings us to the next concept that is important in understanding orbital motion, which is momentum. Specifically, I am talking about angular momentum. Let us use planets as example pieces. Angular momentum is its rotation as it revolves around the Sun. It is calculated by multiplying together its mass, velocity, and the square of its radius.

Another factor that Newton’s third law is talking about, is that momentum must be conserved. This is the equation for angular momentum.

$angular momentum \propto mass * rotation * radius^2$

You can see that mass is involved and that will become more important later on. This is because we must conserve linear and angular momentum at all times. So, with any change to the object, the properties just shift so that the momentum is conserved.

### Gravity’s Effect

Now we come to the culmination of our previous concepts. We talked about a force would have to affect any object in order for it to change its velocity. In space, this force is usually gravity. Gravity affects everything. It’s affect depends on the mass and distance of the objects in question.

Gravity is the reason the Earth and the other planets orbit around the Sun. The Sun is so massive that it influences everything in the solar system. All the celestial objects that include planets, moons, asteroids, comets, and gas clouds are all controlled by our Sun. This is what almost all stars do throughout the universe.

The equation that lets us calculate the force of gravity on certain objects is:

$F_gravity = G\frac{M_1*M_2}{R^2}$

This tells us the gravitational force between these two objects. R is the distance between these objects. G is the famous gravitational constant.

Gravitational attraction affects all forms of mass. Since nearly everything has mass, it is ubiquitous. The more mass an object has, the more gravitational force it applies.

Gravity gets weaker with distance, no matter the mass of the original object. However, if the distance is far enough away, the effect is minimal and not really noticeable. That is just the nature of mass and gravity.

### Asteroids And Comets

There is an abundance of asteroids and comets in our galaxy. Most were probably formed as our galaxy was birthed. Now, they don’t really have a purpose. They are just chunks of leftover material that got caught in the Sun’s orbit.

Their orbits are very eccentric. Most travel around the asteroid belt. The asteroid belt is a band of rocks(not a rock band) that orbits the Sun. Many have collisions and take trips through the galaxy, even though still fully under the influence of the Sun.

The asteroid belt is between Mars and Jupiter. Many astronomers study this area. They hope to find new and interesting objects, possibly another planet that is hiding there.

Comets usually have much larger orbits. Their paths are very eccentric through the solar system. There are several famous ones that come our way every once in a while. Take the chance to see them when you can. Many you will only see once in a lifetime.

## The Solar System And Beyond

The solar system is very interesting. There are countless objects wandering around out there. We have learned much from even the smallest things like dust in space. The Solar System is a very complicated and busy place. To learn, we measure everything we can and then compare constantly. That is the fun of it to me. I love looking at data and seeing how objects are different. Our resident star, the Sun, is the dominant force in the solar system.

The area that our sun has control over is collectively known as the Solar System. It includes:

• planets

• dwarf planets

• comets

• asteroids

• moons

• meteors

• dust

• one star

We have found planets that have ring systems. Saturn is the most famous example of this. Most planets have moons. Some 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

The way that we learn is by comparing. What is the mass of this planet versus the mass of this other one? 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 observe. But, how does it help us? When I first encountered this question in school, I really could not come up with an answer that satisfied me.

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 start somewhere.

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

### Size Of Our Solar System Objects

The size of our Solar System objects varies. The largest mass in the solar system is our Sun. It is also by far the largest thing out there besides other stars. The Sun is 99% of our galaxy, if you measure by mass.

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 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 Get Data On Solar System Objects

The previous section mentioned several properties that we try to figure out about any 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 1 AU. That stands for astronomical unit. It is an immense 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.

We often divide the planets in our solar system up between the rocky and gaseous planets.

The rocky planets are those closest to the Sun. Earth is one of those rocky planets. The other three are Mercury, Venus, and Mars. These four planets are much smaller 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 from the inner planets. They are the furthest away from the Sun and have huge orbits. The gas planets are mostly helium and hydrogen. These gases are compressed until they become liquids at their cores. The atmospheres are gaseous, however.

As far as we know, there are no solid surfaces on the outer planets. Gravity is immense as you get below the outer atmosphere. It is much stronger than here on Earth.

The magnetic fields on the gaseous planets are much stronger than here on Earth as well. 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 universe's history. 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 about 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. We named it 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. The belt is filled with matter of all sizes. 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 there 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 handles 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 stuck 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.

### Accretion

These primitive discs are accretion discs. They grow by having matter collide and stick together. Gravity is the mechanism responsible for everything staying 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 on the planets close to the Sun is that it is too hot for matter to stay together. 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 from 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 because of a strong gravity field.

The other dominant 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.

### How Did The Sun Influence The Gas Giants

The gas giants are mostly that, just gas. Hydrogen and helium constitute most matter in them. They got 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 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 are 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.

3.

### Why Are There Definitions Of 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 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 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 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.

## How Do Telescopes Work

Telescopes are being used differently as time goes on. We used to only use them to see objects in 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.

### Essentials of Telescopes

There are many kinds of telescopes. With many 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 know.

• 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.

To do any meaningful research, you need a telescope, a wavelength filter or spectrometer, and a detector. The telescope needs to be as large as possible. A larger aperture gathers more light.

Bigger telescopes see fainter objects. Once they gather light, they can focus this light into an image. This is how they generally work, no matter the type of radiation.

The wavelength filter can be a variety of devices. Filters can be simple or complex. They can show you one color or a rainbow. It depends on what you are after. Different colors give different information.

After light has been collected, you must use a device to detect the wavelengths you are after. With a detector, you can get long exposures. This is key to observing faint objects far away.

### Optical Telescopes

Optical telescopes collect visible light. That is why they are optical. Seems simple enough, right? 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 we use telescopes. There are two main 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 through the atmosphere. This makes a refracting telescope a poor choice for infrared studies.

Using a lens in your telescope is also more expensive. This is because a lot more quality and effort goes into a lens.

Reflecting telescopes use mirrors instead of a lens to work with the light that is captured. Since they use a mirror, 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 ones as well:

• Newtonian-reflected to an eyepiece at side of instrument

• Cassegrain-light reflects light at the end of the instrument

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

### Size Of Telescopes

The size of telescopes has grown 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 helps us see far off objects.

The telescope’s mirror directly affects how much we can see. This helps with another issue, which is the telescope’s resolving power. Its resolution is also very important because it lets us see the details of 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.

Presently, telescopes can be huge. The largest ones are 10-11 meters in diameter. Larger ones are being built. I imagine, there will always be a larger one being built.

### Imaging With Telescopes

Imaging and the field of astrophotography are very popular these days because looking through a telescope is looking back in time. 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 astrophotography, then you will buy 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.

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. CCD stands for charged coupled devices. These chips take digital images of objects. On the CCD, a pixel stores the photonic information that it gathers.

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 CCD’s record starlight and allow much greater visibility into the heavens.

This process allows us to detect and analyze the faintest objects. Without doing this, we would not know they were there.

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

These chips are much more efficient than previous methods. Think cell phone camera versus Polaroid.

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

As each range of wavelength can have unique characteristics, this is precious. To measure the light, a telescope takes it in and then 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, we can infer much from this and is one of the most important topics when dealing with the basics of telescopes.

It is hard to get splendid pictures while on Earth. It is not really our fault though. The atmosphere affects our view so much. Not a lot we can do from here. Therefore, 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, we usually place telescopes at high altitudes.

### Telescope Resolution

Resolution is the detail in an image. We want as much as possible. With higher resolution, the smallest features become apparent. This is vital in the study of astronomy. Aperture size is the key ingredient of resolution.

The larger the aperture, the sharper the image becomes.

Our atmosphere contains many gas pockets. These pockets catch and distort the starlight. They distort it by making it reach Earth in weird ways. This is the big problem with optical telescopes.

The distortion of our atmosphere disrupts viewing a lot. Therefore, astronomers go to the highest and driest places available for viewing.

Radio astronomy, as we know it, was first started in the 1930s. We credit it to Karl Jansky. He was working on radio communications when he discovered radio waves from an unknown source away from Earth.

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.

In fact, radio waves are the longest form of radiation. 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. It’s like this because the atmosphere doesn’t affect a radio telescope. This is very useful because we can not actually see these areas with our eyes.

Radio telescopes have an enormous 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.

Therefore, we need to maximize our chance at capturing these them. They also operate differently than optical telescopes in that they only see a few wavelengths at a time of radiation.

A tremendous 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.

### Interferometry

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.

They are linked together to form an array of telescopes. This makes it possible for them to be very geographically separated.

As each radio telescope takes in data, we then combined the data again using special software that makes a superior image than either took to begin with.

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

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

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 longer 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, it makes some gigantic clouds. All of this dust makes seeing difficult. The dust can completely block out a lot of faint objects.

Therefore, studies of the infrared spectrum are valuable. They let us see without our eyes. In the electromagnetic spectrum, infrared lies between visible light and microwave radiation. Its wavelengths are a little shorter than microwaves.

Any object that produces heat gives infrared radiation off. It can be a lot of heat like the sun or just a small amount like the snow. Both still puts off some heat and therefore radiate infrared radiation.

### Ultraviolet Astronomy

In the shorter wavelengths, 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 the other areas of astronomy, you can tell a lot about the object when studying its radiation. Examples of what we can infer are densities, composition, and temperatures.

We divided the ultraviolet spectrum 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 an excellent 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.

### X-Rays

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 skyrocketing. 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. We call these 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 is 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 can 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 we use it in the medical industry to kill certain cancers. I can’t think of a better way to harness nature for a good cause!

### The Astronomer’s Life

Astronomers rarely peer into an eyepiece like they used to. There are a couple reasons for this. One reason is that technology has advanced, and it allows us to do so much more with the data gathered by a telescope.

The other reason is that the atmosphere is degrading which makes seeing objects a lot harder. This is mostly due to all the satellites launched in the last few years. A lot less star light gets to us now.

The light that we can see is often distorted because of our atmosphere.

Most Astronomers spend their time in front of a computer. They are using software to analyze data. They want to use the good telescopes but these have limited time. So they might get a few days a year and spend the rest of the time analyzing their data.

## Why Does The Earth Support Life

The Earth is an averaged sized planet in our Solar System. Since it is one of the inner planets, it comprises heavier elements. The Earth’s orbit is nearly circular. It is also the right temperature to keep water on its surface. This temperature means it is not too hot or cold.

### Interior

We not know a lot about the interior of our planet, but we can make some good guesses. Our planet comprises metal and rock, mostly. The majority is solid, but there is a portion on the inside that is a liquid. This liquid is molten rock near the center.

The rock layer closest to us at the surface is called the crust. Crust comprises basalt rocks and covers over half of the Earth’s surface. A majority of this is under the oceans and is very hard for anyone to study in those areas.

The layer beneath the crust is called the mantle. It is much thicker than the crust and is denser as well. It is mostly solid but does contain pockets that are molten.

Finally, we have the core at the center of the planet. It is even more dense and hot there. It is mostly solid and is the size of smaller planets. The core is made up of metals and dense rock.

Since the Earth is divided into sections, most think the core was entirely molten. If it was molten, this would allow the heavier elements to sink toward the center core.

### Magnetic Field

Our planet has a decently strong magnetic field. It affects a lot throughout the interior. Just like in stars, it formed the magnetic field from hot and dense metal moving in the center. Our magnetic field extends away from the Earth’s surface into space. It traps a lot of dangerous radiation there that would otherwise hit the surface.

The region where the magnetic field keeps out these particles is the magnetosphere. It protects us and is vital to our survival on Earth. These dangerous particles usually come from the Sun with the solar wind.

### The Crust

There is a lot going on in our crust. Volcanic eruptions created a lot. Erosion by wind and water constantly reforms it. The Earth is the most geologically active planet that we know of. The crust is made of basalt, with the remaining portion being granite.

### Tectonics

Plate tectonics describe the movement of rock in the mantle. These large sections of rock creep along. They have been doing so since the formation of this planet. This movement forms mountains and other large planetary features.

While plate tectonics is often the domain of Geology, it plays a role in Astronomy as well. This is because formation of other planets in the Solar System and beyond must go through many of these same processes. By learning about our own planet, we can surmise details about other planetary spheres.

Tectonics cool the planet. If there is any purpose to it, then it is this. Heat originates around the core and must go somewhere. The shifting of mantle sections brings this heat to the surface.

We divided the crust up into several plates. These plates are below the oceans and landmasses on the surface. They all fit together, but are constantly moving. In fact, the continental structure of our planet is continually evolving. Some plates are moving away from the ones closest to them, while other plates are moving toward their respective partner plates.

The plates move through the convection system. Convection is the transfer of heat which causes cooler material to sink and warmer material to rise.

When the plates run into each other, mountains form and other large changes occur. We can describe these interactions of plates in a couple ways. They are rifts and rises.

A rift is where plates are getting farther apart and causing continents to move away from each other. A rise is the opposite effect. This is where plates are getting closer and their respective continents are being pushed together.

### Earth’s Atmosphere

Most of our atmosphere, by mass, is concentrated near the surface. We live at the bottom of the atmosphere. The troposphere is here and is another example of convection. Warm air rises and while cooler air is forced downwards.

In the troposphere, the warmest air is near the bottom, while the coolest air is at the top. Above the troposphere is the stratosphere, which is freezing and moisture free.

At the edge of the stratosphere layer is the famous ozone layer. This is another form of oxygen and it has a different chemical formula. Since it is denser oxygen, it is very effective at stopping radiation from outer space, harming us here on Earth.

The atmosphere consists mostly of nitrogen and oxygen. There are a few other trace amounts of gases. These gases form a fine balance for our living conditions. If there were less or more of them, life would not be possible in the way we know it currently.

We do not know how our atmosphere originally formed. There are guesses involving impacts from outer space, volcanic activity, and formation along with the surface. There is evidence of them all, so deciding on one is not feasible right now. So, most think it is a combination of these events.

### Earth’s Weather

Every celestial object with an atmosphere has weather. Weather is the circulation of our atmosphere and its effects on the surface. The Sun plays a significant role in our weather patterns. Its radiation heats the surface, which gives the atmosphere energy.

Rotation of the Earth plays a role as well. As our planet spins, different areas get direct sunlight. This will create weather patterns unique to those particular areas. Weather has the same effects year after year in regions. This gives rise to a climate that does not change much when looked at for long periods of time.

Climates change, though. Change often takes thousands of years for permanent effects to take place. However, change has happened continually on Earth for its multi billion year history.

Therefore, we should not be surprised that climates change and different regions shift its weather patterns. For example, oceans became deserts and vice versa. This has happened many times in our history and will happen many times more.

### Life On Earth

Since the Earth is the only place we have identified life, scientists have been trying to figure out why this is. Life has been here since our planet’s very beginning stages. We do not know how long life has been here, but it’s estimated to be around 4 billion years.

Why did life form here but in no other place in our Solar System? There is not an answer for that yet. Many planets have similar formations. We can assume close to the same conditions in countless other planets in other Solar Systems too.

Our atmosphere and surface were much different 3-4 billion years ago. There was very little to no oxygen early in our history. Despite this, life has consistently grown and and become more sophisticated.

### Why Is The Sky Blue

The sky is blue because of the scattering throughout our atmosphere. Specifically, light is scattered through air and dust molecules. Scattering is where radiation is absorbed and redirected. When radiation is redirected, blue light is scattered easier.

Blue light is scattered easier because its wavelength is on the smaller side. Since it is smaller, it gets distributed through the air more. This makes our sky blue.

This effect is also why the Sun appears yellow or orange, depending on time of day. In the early morning or late evening the Sun will appear orange. This is because radiation of the Sun has a lot more atmosphere to travel through to reach our eyes than midday.

Since there is more atmosphere to travel through, the blue wavelengths are almost totally gone or scattered through the atmosphere by the time that radiation reaches our eyes. Being gone, all that is left are the other wavelengths. This makes the Sun appear orange to us.

## Why Is There Debris In The Galaxy

When people think of our solar system, they often just think of the planets and larger objects. However, most of our galaxy is made of smaller debris. Debris that forms from collisions and other such processes is very common.

### Asteroids

Asteroids are small rocky objects that travel through space and orbit around larger objects. They are smaller than planets. Astronomers sometimes call them planetoids. Their orbits are pretty crazy and eccentric.

Most are pretty small. In fact, most moons that we know of are much larger than asteroids. We refer to asteroids as debris for this reason. Since they are so small on average, their combined mass is not much.

Asteroids are usually discovered by Astronomers searching for larger objects. They are usually searching for planets and things like that. When scanning the sky or watching for transits, asteroids will show up in the most unexpected of places.

Astronomers reportedly first discovered an asteroid a little over 200 years ago. Of course, I am sure we saw them, but observers did not know what they were. I am sure they were mistaken for other things in the sky.

Most asteroids that were discovered are in the famous asteroid belt. Almost all the known asteroids are in this region. It is a belt that orbits the Sun and there are many thousands of asteroids there.

Why are there so many in one region? Most astronomers think they are remnants of an explosion that never formed into a planet. This is because there is far too little mass for them to be a broken up planet. They then escape into the solar system. This happens when they collide with each other and they are responsible for most of the cratering seen around the solar system.

Asteroids are a major source of debris in the galaxy. While not very large, there are a multitude of them. They are also easy to find when you want to look for them.

They are usually denser than comets because of their composition. Asteroids are made of more rocky material.

### Comets

Comets are another form of space debris. However, they differ greatly from asteroids. Telescopes from far away can pick them up. Comets are almost always brighter than asteroids. This is because they reflect sunlight. Sunlight is reflected because comets are mostly ice chunks and this makes them highly reflective. This also makes them less dense than asteroids because they contain a lot of water ice.

Comets have highly eccentric orbits. Most of us will only see a particular comet once because of their very long travel period. Orbits can be a hundred years to millions of years.

They have a nucleus, coma, hydrogen envelope, and tail. These attributes can all vary in size. Their characteristics all change, depending on how close to the Sun they are. The nucleus makes up most of their mass. When they get close to the Sun, the envelope and tail form.

Most comets come from the Kuiper Belt and the Oort cloud. These are regions left over from the formation of the galaxy and contain millions, if not billions, of comets. Despite their distance from the Sun and our local galaxy, they are still gravitationally bound by the Sun.

### Meteors

Meteors are very common and also known as “shooting stars”. They often appear in our night sky as streaks of light. Friction and the Earth’s atmosphere cause these streaks of light. Friction heats the meteor, and this process emits light.

The smaller meteors are probably pieces of comets that broke apart. As comets get near the Sun, parts break away and these become meteors. Their density is very similar to a comet.

However, the larger meteors that make it to the ground are more similar to asteroids. Their density is much greater. So that tells us something else happened. It could be a stray object from the asteroid belt or a fragment from some collision. It is hard to say for sure.

### Origins Of Debris

I mentioned the Kuiper Belt and Asteroid Belt earlier. These regions are where most of our galaxy debris come from. Their objects constantly collide with each other and then shoot off in different directions. This is how everything gets scattered around.

### The Asteroid Belt

The Asteroid Belt is the boundary between the inner and outer planets in our galaxy. The asteroids contained within are classified into wet and dry objects. We do not know how this asteroid belt formed exactly. There are a few different theories, of course.

One of the leading theories is that the asteroid belt was leftover from the formation of the Sun. This is certainly plausible. Astronomers think some of our large planets came from this left over material too.

Another theory is that this region just filled up with these planetesimals. This is because it was a region devoid of material and rocky objects slowly got trapped by the Sun as they wandered by.

Both theories are equally plausible. It will take more time and data before a leading theory can emerge.

### The Kuiper Belt

The other primary source of debris in the galaxy is the Kuiper belt. This is an extensive region of rocks, asteroids, and comets. It starts around 30 AU from the Sun and it is around 50 AU thick. This means it encircles our solar system, and it is quite large. Like the Asteroid Belt, when collisions occur, objects get sent directly into the solar system.

Also similar to the Asteroid belt, the Kuiper Belt is leftover remnants of the formation of the Solar System. Astronomers think it could have come together to form a planet if Neptune had not interfered with its gravity. Its gravity disrupted the Kuiper Belt so often, so the pieces could never come together.

Astronomers think the Kuiper Belt used to be much larger. Our large gas giants have captured much of the material there. Constant collisions have ejected objects toward the Solar System and the surrounding Oort Cloud. The ejected objects are both asteroids and comets, depending on their makeup.

Many of the objects in the Kuiper Belt are large and have their own moons. We do not know exact numbers, but there are probably thousands of such objects.