1. Chapter 5: Telescopes
When you think of astronomy you think of telescope, right? So it is fitting to discuss how astronomers use telescopes to gain information. They are one of the most important tools because they allow us to collect light from celestial objects. With the invention of the telescope, astronomy was able to separate from the pseudoscience of astrology because the telescope allowed astronomers a tool to test their hypothesis and, thus, implement all the components of the scientific method.
There are different kinds of telescopes; the telescopes that people might purchase for recreational purposes; telescopes that
are housed in observatories used by professional astronomers; telescopes that are launched in space. In this chapter, we will learn about all these different types of telescopes.
But most people have a misconception of astronomers. They think that they spend all their time looking through telescopes. Nowadays, most astronomers do not look through the telescopes, rather they look at the objects that the telescopes collect on their computer screen. This can be done because we attach a special kind of camera at the end of the eye piece to capture the images. Then we can look at them any time. Furthermore, most of the objects we look at are so faint that they do not show up when we try to view them through the eye piece. We have to take very long exposures of them in order to even detect them. Furthermore, we have to remove extraneous sources of noise so that we are only left with the signal from the object. In this chapter I will discuss the latest technology that have allowed astronomers to see celestial objects with more clarity and resolution than they have ever seen them in the past. I will also show you some of the major observatories from around the world.
This section has a lot of information, but some of the information is optional…just in case you are curious and have some time to read. I will let you know in the slides which parts are not required.
“Nature composes some of her loveliest poems for the telescope”
- Theodore Roszah

2. Invention of the Telescope
When we think of telescopes, we associate them with Galileo. However, as I mentioned in the previous chapter, Galileo did not invent the telescope. He gained fame by making his own after it was invented and using it to make astronomical discoveries.
The person who was credited with the invention of the telescope was the Dutch optician, Hans Lippershey, in 1608 more than 400 years ago. He put two eye pieces together and noticed that objects appeared closer. He built a tube for his new device, which he called “the looker”.
Actually, some people think that Lippershey wasn’t even the true inventor of the telescope, that it was the children who were playing in his shop who invented it. Supposedly, they were curious what the view would look like if they looked through two lenses at the same time instead of one and they noticed that the view was magnified. It is interesting to think that, children, because of their curiosity may have possessed the “imagination” that the adults did not have to invent the most important tool used by astronomers today! This tool has allowed us to learn so much about our universe and allows us to look at the universe billions of years in the past when it was in its infancy! In this case, Einstein’s phrase really comes into play that “Imagination is more important than knowledge.”
Galileo did not invent the telescope! The first idea was credited to the Dutch optician Hans Lippershey in 1608.

3. Early Telescopes
Although Galileo didn’t invent the telescope, he did construct his own version and was the first to make several discoveries with it. We talked about these discoveries in the last chapter, which proved that we do not live in a geocentric Universe. This telescope was constructed using two lenses. To the left is a lithograph of Galileo using his early telescope.
In 1670, Sir Isaac Newton invented a new type of telescope, this was one that used a mirror to collect the light and form an image. This invention was important because this is the type of telescope that professional astronomers prefer to use today. To the right is Newton’s first telescope. This telescope is currently housed in London, England at the Museum Victoria and owned by the Royal Society of London.
The first telescope to use a mirror to gather light invented by Newton
in 1670
Galileo with his early telescope 1609

4. Two Main Types Reflecting Telescope- Uses mirrors to bring light to
a focus and form an image
Refracting Telescope-
Uses lenses to bring light
to a focus and form an image
There are two main types of telescope in astronomy.
Refracting telescope:
The first one has two lenses connected by a tube. This is called a refracting telescope because as light is collected through one of the lenses, it gets bent through the lens to come to a focus. This bending of light through a transparent material such as glass or water is called refraction. Where all the light focuses, it forms an image.
The world’s largest refracting telescope, built in the 1800s is housed at Yerkes Observatory. This is owned by the University of Chicago but is located in a small town called Williams Bay in Wisconsin. When we talk about the size of the telescope, we do not mean the length of the tube but rather the diameter of the largest lens or mirror. In this case the lens is 40 inches in diameter.
A side story…I didn’t know where this telescope originally was located until I ran across it by accident. Several years ago, my colleague and I attended a conference held by NASA in Williams Bay, Wisconsin which is a very small, unassuming town. On the taxi ride to the hotel, my colleague and I noticed a beautiful observatory that looked very old, like it was built in the 1800s. We asked the taxi driver what that observatory was, and he told us that it was the Yerkes Observatory. My colleague and I looked at each other and said “really?!” We did not quite believe that such a famous observatory housing one of the oldest professional telescopes as well as the largest refracting telescope would be located in such a small quaint town. Wow, we said to each other. We both knew we needed a tour of it. So we called up the observatory, explained who we were and they were kind enough to agree to give us a private tour! It was truly amazing to be able to look through that historic telescope that night! Again, it was a pleasant surprise since we were not expecting it at all!
Reflecting telescope:
Uses a slightly curved mirror or reflecting surface to collect and focus the light to form an image. The light reflects off the surface in front of the mirror and comes to a focus and where it comes to a focus, the image is formed.
The largest of these telescopes is located in the Canary Islands and is called the Gran Telescopio Canarias. The diameter of the mirror is so large that there is not just one mirror, but rather many hexagonal pieces fused together to form one large mirror. The diameter of that mirror is 10.4 meters wide, or over 30 feet across! We will discuss this telescope a little more later and why I’m secretly really happy that it is known as the world’s largest reflecting telescope.

5. Refracting Telescopes
We are next going to discuss how each of these telescopes work. First, let’s talk about refracting telescopes. A refracting telescope is a very simple device. It just consists of two lenses placed at the appropriate distance from each other so that the image that you can obtain a focused and magnified image.
This slide shows you a schematic of a telescope. Light rays meet at a point called the focal point of the lens; the distance is called the focal length. This is where you see the image of the source producing the light. A refracting telescope is an arrangement of two lenses, with different focal lengths, used to gather light. The lens at the top of the telescope, called the objective lens has a large diameter and long focal length. Its purpose is to collect as much light as possible. The lens at the bottom of the telescope is the eyepiece lens; it is smaller and has a short focal length. It re-straightens the light rays making them parallel once again. Because the light is more concentrated, objects are brighter as seen through a telescope.
There are two focal lengths, the focal length of the objective lens and the focal length of the eyepiece lens. The distance between the two lenses (d) is just equal to the sum of the focal lenses (fobj + feye). So d= fobj+feye. This is also approximately the length of the telescope tube.
The ratio of these focal lengths give you the magnification of the telescope. M= fobj/feye
The curved surfaces of the lens cause light rays to emerge from the lens in different directions than they had before entering the lens. If the lens is shaped correctly, parallel light rays start converging once they enter the glass. Because the light that refracts through the lens is bent in the opposite direction, the image of the object that you would see through the eyepiece would be upside down and flipped. Astronomers don’t really care whether objects in space are upside down because in space there is no preferred up or down, also most objects in space are symmetric so it doesn’t really matter whether you see them upside down or not.
Interestingly, the reason why you are able to see is because everyone has lenses in their eyeballs. The lens in your eye is curved the same way that the lens is in the telescope and acts to collect light and bring it to a focus on your retina. My question is that if the image is suppose to be upside, why do we see everything right side up? Scroll down for the answer…
The answer is that we all also have brains. Our brain receives the image through the optic nerve and the image is upside down, but our brain is smart and tells us the world is not upside down so it flips the image right side up. Incredible, isn’t it?! They have actually verified this with experiments. They gave several people glasses that would turn the world upside down; this worked for a few days, but after that the brain again said, no the world is not upside down and even though they wore the glasses, the brain flipped the image right side up eventually. Of course when they took off their glasses, after the brain had adjusted, the image flipped back upside down!
The ideal distance between the two lenses is just the sum of the focal lenses!!

6. Building Your Own Telescope is Easy!
Materials
two magnifying glasses: perhaps inches in diameter (it works best if one is larger than the other)
a cardboard tube: paper towel roll or gift wrapping paper roll (it helps if it is long)
duct tape
scissors
a ruler, yard stick, or tape measure
sheet of printed paper: e.g. newspaper or magazine
Anyways, getting back to the subject. A refracting telescope is very easy to make, easier than a reflecting telescope. So if you wanted to make your own telescope you could. In fact this is a very good science fair project. Just in case you were interested, this slide and the next tells you how to make your own very simple telescope. This simple telescope is good enough to look at objects on Earth during the day and the Moon at night.
To make more powerful ones, that would allow you to see fainter objects in space, you would need to purchase larger lenses. In the Astronomy lab, you will get a chance to make your own very simple telescopes.

7. Building Your Own Telescope is Easy!
Assembling
Hold one magnifying glass (the bigger one) between you and the paper. The image of the print will be blurry.
Get the two magnifying glasses and a sheet of printed paper.
Place the second magnifying glass between your eye and the first magnifying glass.
Move the second magnifying glass forward or backward until the print comes into sharp focus. You will notice that the print appears larger and upside down.
Have a friend measure the distance between the two magnifying glass and write the distance down.
Cut a slot in the tube the same distance from the first slot as your friend wrote down. This is where the second magnifying glass will go.
Place the two magnifying glasses in their slots (big one at front, little one at back and tape them in with duct tape)
Leave about inch (1-2 cm) of tube behind the small magnifying glass and cut off any excess tube remaining.
Check to see that it works by looking at the printed page; you may have to play slightly to get the exact distances between the two glasses right so that the image comes into focus.

8. Refracting Telescopes
Chromatic Aberration:
Different colors are focused at
different distances from the lens
Need to add extra lenses to correct
the problem, but the correction is NOT 100 %!
Refracting telescopes are easier to make at home than reflectors, but they have a major disadvantage. Whenever you have a lens, you will get an effect called chromatic aberration. This occurs when the light hits the lens, it gets bent through the lens. But any form of light for example sunlight or starlight contains all the colors of the rainbow in it. We will learn about this property of light a little later. So when the light hits the lens, the different colors of the lens bends by different amounts through the lens. For example on the left, the focal point for blue light is at a shorter distant than the focal point for red light. Thus, chromatic aberration is when all the colors of the light get focused at slightly different distances from the lens. Whenever this occurs, the image that is formed is slightly distorted by this effect, so you never have a perfectly clear crisp focused image.
Chromatic aberration can be mostly corrected by adding extra layers of coating on the lens that will change the focus for the colors so that they will be close to the same distance away. However, this correction is NOT 100%, that is there is always going to be a little chromatic aberration leftover and the colors will never be focused exactly at the same distance. In addition, adding the extra coatings on the lens is expensive so it makes the telescope more expensive to buy.
Since reflecting telescopes uses a mirror to collect the light, you do not have chromatic aberration to contend with.

9. Refracting telescopes have disadvantages
Chromatic aberration
More expensive!
Can’t be built too large
Sagging due to gravity distorting the lens
Refracting telescopes have several disadvantages over reflecting telescopes.
Among these are:
Chromatic aberration, which we talked about in the last slide
Because of the needed correction for chromatic aberration, you have to pay more for refractors to get the same quality image than for reflectors. That is you get less bang for your buck with refractors.
In addition, you cannot build a very large refractor. Reflectors can be built much larger in size. We will later learn that in order to see fainter objects in space, the telescope has to be larger in size (that means the size of the objective lens or mirror has to be built larger). When we discussed the largest telescopes in the world a few slides ago, we said that the largest refracting telescope was about 40 inches or 3 ½ feet across whereas the largest reflector is over 10 meters in size, which is almost 10 times larger than the largest refractor.
The reason why there is a size limitation on how large you can make the lens is because of how you support the lens. Since the lens is transparent, you have to support the lens on its side so that you won’t block out any of the incoming light. Whereas with a mirror, you can support the mirror on its back which is more stable. Thus, with a larger refractor, the side support is not as stable and when the telescope points upwards gravity causes the lens to sag since there is no support on the back of the lens. If the lens sags, its shape is distorted a little and the light that passes through cannot come to a focus. Because of this, the largest a lens can be without too much sagging by gravity is about 40 inches in diameter.
For a all these reasons, nowadays, when astronomers build professional telescopes for observing and doing research at professional observatories, they prefer to build reflectors over refractors.

10. Reflecting telescopes use mirrors to concentrate incoming starlight
Next we will discuss the different types of reflectors out there. Remember a reflecting telescope is one that uses a mirror or reflective surface in order to bring the light to a focus. A mirror collects light using reflection rather than refraction. If you shape the mirror into a curved shape; it will reflect light so that it converges to one point. The distance between the reflecting surface and the focal point where the image of the distant object is formed is called the focal length of the mirror.
Here are just some different types of reflecting telescopes. While there is only one kind of refractor, there are 4 main kinds of reflecting telescopes. These telescopes are different because of where the light gets focused and how many mirrors exist inside of the telescope.
The most popular styles of telescopes are the: 1) Newtonian focus which has two mirrors, the largest, objective mirror, and a smaller mirror in front of the objective that is tilted so that the light reflected off from the objective mirror gets focused to the side of the telescope. That would be where you put the eyepiece. 2) Cassegrain focus which also has two mirrors, but this time the secondary small mirror is placed parallel to the objective larger mirror so that the light reflecting off the objective mirror to the secondary mirror will bounce straight back through an opening on the objective mirror and the eyepiece would be placed in back of the objective mirror.
3) The Coude focus is kind of like the Newtonian focus; except that there is an extra mirror involved. Light comes through, reflects off the objective mirror, bounces to the secondary mirror and hits a third mirror which is tilted and brings light out to the side of the telescope.
4) The Prime focus was an old style telescope; it’s not really used too much now because it is so inconvenient (you’ll see why in the next slide). What happens is that light enters through and hits the objective mirror; then gets reflected to an eyepiece that is placed in front of the objective mirror. It has no secondary mirror.
Newtonian Focus
Prime Focus
coude’ focus
Cassegrain focus

11. Inside the Cage!
Here is an example of a prime focus telescope. You can understand now why people don’t like to use this telescope anymore. Since the light gets focused in front of the main mirror because of this the astronomer would have to sit in a small cage located at the eyepiece. This is not very comfortable since these cages are small and it can get pretty cold at night!
If you are afraid of heights or are claustrophobic, sitting in the cage would not be a very pleasant experience. Also, there is no heating in the cage because that would interfere with the equipment so it can get pretty darn chilly in there. Nevertheless, some die hard astronomers feel proud to observe in such a telescope. Sometimes it can be seen as a rite of passage. As for me, I’d rather not!
In addition, observing time is precious so if you have a small bladder, it would be bad to observe with a prime focus because it takes time to move the telescope to the correct position. If you have to go down for a bathroom break, you will need to lower the telescope, use the bathroom, then move the telescope back to the proper position. All of that could take as much as minutes of your precious evening when you could be observing.
As a side story…there is a well known story of a man (this may be an urban legend) who brought up with him into the cage a full thermos of coffee. He observed through the night without ever coming down to take a break. By the end of the night when he finished the observing, his thermos was still full! (But not with coffee!)

12. Radio Telescopes Five Hundred Meter Aperture
Spherical Telescope (FAST)
Very Large Array
We mentioned that there are two main types of telescopes, refractors and reflectors. These two main types typically collect white light, which is the kind of light produced by stars and our Sun and many objects in space. But other objects in space can produce radio light. In order to collect this form of light, you need a third type of telescope and these are the radio telescopes. They do not have lenses or mirrors to collect light, but collect the radio signals by using large antennas and a dish. Unlike refractors and reflectors, radio telescopes can be used during the day since we do not get interference from the Sun (it doesn’t produce much radio signal).
On this slide are two famous examples of some of the largest radio telescopes in the world.
Arecibo Observatory, Puerto Rico: World’s largest single dish telescope. It can be built really large because it is built in the ground embedded in a large limestone sinkhole. The telescope is 305 meter in diameter (900 feet). It gets free energy as it uses the Earth’s rotation to move! This telescope was featured in one of the recent James Bond movie.
The Very Large Array, New Mexico : Laid out in a giant Y with a total diameter of 27 km. This large array of telescope consists of 27 radio telescopes, each 26 meters in diameter. These telescopes can be used individually or together to act as one giant telescope and gives images with very high resolution and light gathering power. This telescope was featured in the movie Contact.
Radio telescopes are useful for studying galaxies, gas clouds, dead stars, and radiation from the Big Bang. But in the movie “Contact” and in the past, the VLA were used to support the SETI (Search for Extraterrestrial Intelligence) project. It is assumed that if the aliens are like humans, radio may be one of their forms of communication, and if so, these signals will be broadcasted to the entire Universe…if there is intelligent life that uses radio communications, we can hear the signals with our radio telescope assuming we are pointed in the correct direction. In fact if the alien civilization had radio telescopes on their planet, they can also hear us if their telescopes are pointed in our direction!

13. Telescopes you might buy
Refracting Telescope
Newtonian
Reflecting Telescope
Cassegrain
Reflecting Telescope
If you are interested in purchasing a telescope read on…otherwise, you can skip this section….
This slide shows some of the different types of telescopes that you or I might want to buy. Usually when people draw telescopes or think of telescopes, they imagine a long slender tube. The types of telescopes that are long and slender are usually refracting telescopes like the one on the left. Remember refractors are made of two lenses, the big lens in the front and the eye piece lens on the back of the tube.
The other two telescopes represent reflecting telescopes with the two most popular types of focus, 1) the Cassegrain focus (in the middle). Here you have a main mirror on the back of the telescope tube and a secondary mirror in front that reflects light out to the eyepiece which is placed in back of the telescope tube. This type of telescope looks very different than a refractor. Instead of being long and narrow, it is short and squat. The other type of telescope is 2) the Newtonian reflecting telescope which has a longer tube than the Cassegrain, but shorter than a refractor. Here you have a main mirror on the back end of the tube and the secondary mirror which is tilted at an angle so that the light can reflect off to the side of the telescope tube where you would put the eyepiece.
On all the telescopes, you notice that there is a smaller telescope mounted on the main telescope. This smaller telescope is called a finder scope and helps you to locate the object because it has lower magnification and you can see a wider area of the sky through it than you can through the eyepiece. Usually you locate your object first, if it’s bright enough to see through the finder scope, center it there and if everything is calibrated and aligned, it should be close to centered on the eyepiece.
When you go out to buy a telescope, you should think about the aperture size of the telescope (how big the diameter of the lens or mirror is) NOT the magnification since magnification as I mentioned previously is not so important. Magnification = fobj/feye, so you can easily change it by replacing the eyepiece to one with a smaller focal length. The diameter of the telescope is what is going to allow you to see better, remember the bigger the diameter or aperture size, the higher resolution you can get and the fainter the object you can see.
We also mentioned that reflectors give you more bang for the buck. For example, the aperture size of the refractor on the left is about 3 inches whereas the aperture size of the telescope on the right is about 4.5 inches. However the refracting telescope with the smaller aperture size (3 inches) my cost you $ whereas the reflecting telescope with the bigger aperture size (4.5 inches) will cost you $
So if you want to see fainter objects with more detail and resolution, I would recommend purchasing a reflecting telescope over a refracting telescope. However some people still like refractors because with refractors you can see the colors of some objects a little bit better, whereas with reflectors, you will not be able to see color very well.
The middle reflecting telescope with an aperture size of about 8 inches in diameter might cost you $ That is the larger the aperture size, the more expensive the telescope is going to be.
Read the following for my recommendations if you may be interested in purchasing your own telescope…
The most notable and reliable brands of telescopes are the Orion and the Meade telescopes. In fact if you were thinking of purchasing your first telescope, I would recommend the one on the right, which is the 4.5 EQ (4.5 inches diameter) Orion Starblaster with easy finder telescope for $ This comes with an easy finder which has a little bulls eye on the finder telescope and allows you to find your object a lot faster. In addition, the aperture size is large enough to see the bright planets, the Moons, and some noteworthy fainter objects.
When you purchase telescopes you can also purchase them with eco-drive. This allows you to remotely make fine adjustments. You can also purchase telescopes that automatically track the object because without this feature, the object will appear to move outside of your field of view due to the Earth’s rotation. With tracking, the telescope moves to compensate for the motion of the Earth so that the object remains in your field of view.
For your first time observing, I would not recommend the more expensive, larger aperture middle telescope since it is heavy and cumbersome to transport and more expensive. This would be a good 2nd telescope.
Some telescopes are called GOTO telescopes because these come with remote controls that allows you to punch in the name of any object in its database and if it is up at night, the telescope can move automatically to that object once you have it calibrated on a known bright star. These telescopes are useful if you are teaching or have a large group. It is about $ But I think it takes the fun out of finding the objects. There is a thrill once you can find the object on your own. Don’t be frustrated if you can’t find the object on your first try. It does take some practice.
For my first try, it was difficult for me to even center the telescope on the Moon! I would recommend using the telescope first to find a very bright object such as the Moon, then practice using it on bright planets such as Venus, Jupiter, or Saturn. After that you can use it to find fainter objects such as nebulae and galaxies.
If you want to go to a store to purchase telescopes and live in the Salinas valley, I would recommend the Orion store in Watsonville or you can purchase them online.

14. Three Main Functions of a Telescope
most important
brighten
(called light gathering power)
see fine detail
(called resolving power)
and least important,
magnify
One misconception that people usually have is the belief that astronomers use telescopes because it magnifies the object so that we can see it bigger and see more detail. In reality, the magnification power of the telescope is not as important as the other functions of a telescope. For example, even if you magnify an object and that object is blurry, you still can’t get much information from it right? Instead of a small faint blur, it would be a big faint blur. Like when we wear glasses; the glasses are not used to magnify objects, but to make objects more focused and less blurry, right?
The magnification of the telescope is one function of the telescope but it is perhaps the least important of the functions.
The more important functions of the telescope are 1) to brighten the image of objects so that it doesn’t look so faint (this is called the light gathering power because the more light that a telescope collects, the brighter the image will be) and 2) is its ability to allow us to see fine detail. Just like a microscope allows us to see fine details. This is called the resolving power, also known as resolution.

15. Bigger is Better!
the functions that depend upon the diameter of the telescope are:
Light gathering power
Resolving power (or resolution)
The function that depends upon the focal
length of the telescope is,
Magnification: M= fobj/feye
The two most important functions of the telescope, light gathering power and resolving power both depend upon the size of the telescope. When we talk about the size of the telescope, remember, we do not mean the length of the tube, what we mean is the diameter of the telescope. The bigger the diameter, the higher the light gathering and resolving power.
Magnification, which is the least important function of the telescope, however, does not depend upon the diameter of the telescope. The equation for magnification is M=fobj/feye. So the magnification of the telescope does not depend upon the diameters of the lenses but rather their focal lengths. The focal length of the lens or mirror just depends upon how curved the lens or mirror is. The more curved it is, the shorter the focal length. You cannot change the focal length of the objective lens or mirror since it is already built into the tube, but you can change the focal length of the eyepiece by replacing it with a different eyepiece. The magnification of the telescope can easily be changed. To increase the magnification, you would replace the eyepiece with one that has a smaller focal length.
Thus, when purchasing a telescope, buy it for the diameter of the lens or mirror (known as its aperture size) (since this is a property of the telescope that affects the two most important functions of the telescope and CANNOT be changed) and NOT fall for gimmicks that advertise high magnification.

16. Light Gathering Power A measure of how much light a telescope collects
Figure 4.1
Light Gathering Power:
A measure of how much light a telescope collects
You have two buckets; one that is small and one that is large; when it rains, which one will have more water in it? The bigger one, right?
This is the same with telescope, telescopes can be considered as light collecting buckets. The larger the telescope, the more light it will collect. And the more light it collects, the brighter the image will be in the eyepiece.
This is the reason why when it gets dark, the pupil in your eye dilates (grows larger). This allows you to see better in the dark because when your pupil is larger, your eyes can collect more and more light. Have you ever gotten your pupils dilated? When this happens, you become extra sensitive to the light, so they require you to wear sunglasses. This is because your pupils are larger and are collecting more light from the Sun.
The light gathering power of telescopes is a measure of how much light a telescope collects which depends upon the diameter of the telescope. The larger the diameter of the telescope is, the more light it will collect. That is why we constantly want to build big telescopes because it will allow you to collect more light and, thus, be able to see fainter objects.
The bigger the telescope, the more light it will collect,
and the brighter the image will be!

17. A larger diameter provides a brighter (not bigger) image
This slide shows two telescopes, one of them (the one on the right) has a larger diameter than the other. They are both pointed to the same galaxy in the sky. What can you say is different about the two images through the two different telescopes? Scroll down for the answer…
From first inspection, it looks like the image on the right has a higher magnification, but that isn’t true. Usually most galaxies are brightest in the center and get fainter outwards. The bigger telescope on the right allows us to see the galaxy’s faint outer parts. The smaller telescope on the left doesn’t collect enough light so we cannot see the faint outer parts. Since the larger telescope collects more light, all parts of the galaxy appear brighter including the faint outer parts. The two galaxies are the physically same size in both images; but it looks bigger on the right because we can see the faint outer parts better. And, if we were trying to determine the actual size of the galaxy using the image on the left, it would be an underestimate; that is the size we would measure from the image would be smaller than the actual size of the galaxy. Thus, a larger telescope would allow us to determine more accurately the properties of the object we are viewing, in this case the actual size of the galaxy.
Again, the size of the telescope determines the brightness of the image, not the magnification of the image. The magnification of the image depends on the ratio of the focal length of the objective mirror to the focal length of the eyepiece.
A larger diameter provides a brighter (not bigger) image

18. Resolving Power of a Telescope
Resolving Power: The ability to detect fine detail
Unresolved
Barely resolved
Fully resolved D
Telescope1
Telescope2
Telescope3
Everbody these days are aiming to obtain higher resolution…for example, a movie seen in high resolution HD is so much better than with normal resolution. With HD, you can actually see the individual strands of a person’s hair. Well, astronomers also want high res.
The resolving power of the telescope depends the size of the telescope. On this slide, we have three telescopes, each of them are observing the same objects, which in this case, we can say are two red stars. Telescope 1 has the smallest diameter, telescope 2 has twice the diameter of telescope 1, and telescope 3 has a diameter that is 4 times larger than telescope 1. You can see that with telescope 1, the resolution is so poor that the two stars seem to blend together as one, but as you increase the diameter of the telescope, you begin to see the two stars more in detail and determine their true separations from each other.
Thus, the bigger the telescope, the more resolved image, the better the resolution.
But there is a limit as to how high of a resolution you can get. We can only increase the resolution so much because we are limited by the resolution that our atmosphere allows through. Our atmosphere limits the resolution because it bends/scatters/blurs any light that passes through it. Even on the clearest day, there will still be air molecules that will scatter the light. That is why the Hubble Space telescope is so important because it gets above the Earth’s atmosphere so it can obtain much higher resolution than can be achieved by ground based telescopes. However, later in the chapter, we will discuss the latest technology that allows astronomers to counteract the affects of the Earth’s atmosphere and increase the resolution from ground based telescopes close to that which can be achieved from space.
2 X D
4 X D
D = Diameter of Telescope1
The bigger the telescope, the higher the resolving power, but
the maximum resolution is limited by the Earth’s atmosphere

19. Group Activity
What is the difference between a reflecting and a refracting telescope?
Which type of telescope do professional astronomers prefer to build and why?
What are the two most important functions of a telescope?
If the focal length of the objective is 20 cm and the focal length of the eyepiece is 5 cm, what is the magnification of the telescope?

20. Major Obstacles in Observing the Stars
Light Pollution from Cities
Scattering of light by Earth’s atmosphere
We said that astronomers want to build telescopes as large as possible because it will allow us to collect more light and see fainter objects with higher resolution. However, we also mentioned that there are limitations imposed by conditions on the Earth. Even if we have a super huge telescope, it would not be wise to keep it in an observatory in a town like Salinas.
Why not? The reason why Salinas would not be a good location for a research observatory with a large telescope is the conditions that occur in Salinas.
Salinas is a large city, and in most large cities, there is a lot of light pollution. So even if you have a large telescope that can collect a lot of light, it will collect more of the city light than the starlight. So you will get too much interference from the lights that human produce.
A lot of times Salinas gets cloudy or foggy. The molecules from the fog will scatter the light from objects in space and will reduce your resolution. So even if you have a large telescope that would increase your resolution, the best resolution you can get is what is allowed through the atmosphere. But if there are clouds or fog, the resolution allowed through will be very poor.
So it would not be financially sound for astronomers to put a huge telescope in Salinas. When they choose locations to build an observatory, they need to choose locations that have minimal obstacles to observing the stars.

21. Light pollution as viewed from space
Furthermore, since there are more people settling in cities and more technology; the amount of light pollution has increased with time. As you can see from these images taken from space of the night time side of the Earth, the US and Europe are the major producers of light pollution. If aliens visited the Earth, they would know there is intelligent life because they would be able to see our lights from space!
There is an Astronomical Organization which makes it a crusade to preserve dark skies for scientific observations; this organization is called the International Dark Sky Association. They suggest that if you have to use lights, you can do it more efficiently to minimize light pollution. For example, instead of using bright white light, cities can use sodium lights which still allow people to see, but are more dim. In addition, instead of pointing the lights upwards in the sky, you can point them downwards to the ground and have a cover to prevent the lights from shining upwards.
Some places located near major observatories such as San Jose or Hawaii have worked to minimize light pollution. It not only helps astronomers, but it allows the night sky to look more beautiful to you and me because more stars can been seen with minimal light pollution.

22. Earth’s Atmosphere Hinders Astronomical Research
Same picture taken with Hubble Space Telescope high above Earth’s blurring atmosphere
Image of stars taken with a telescope on the Earth’s surface
This slide shows you that no matter how big the telescope is, if it is located at the darkest and clearest location on Earth, the resolution will always be limited by the Earth’s atmosphere. No matter what the light from the stars will get scattered by the oxygen and nitrogen atoms in our atmosphere.
To the left is a view of stars taken with a telescope on Earth, and to the right is the same view taken with the Hubble Space Telescope. You can see much more detail and obtain much higher resolution with the telescope in space. So it is a huge advantage to get above the Earth’s atmosphere. It is more costly, but the benefit to science is huge.

23. Best places to build observatories
air has to be very dry!
little to no light pollution!
calm air currents!
- on mountain tops!
- on mountain tops in deserts!
- on mountain tops on islands!
- in space!
When astronomers decide to build observatories, it is important to choose good locations for the observatory or else it would just be a huge waste of money if you have a big telescope but it can’t function to full capabilities because of the limitations due to the locations.
This slide lists the conditions that are ideal for observatories and the best locations to build the observatories. Mountain tops are ideal places because they have drier conditions and many of them are at such high elevations that even if there was fog, the peak would be above the fog. Although mountain tops are great locations, you would not build an observatory on a mountain top in a rain forest (for obvious reasons). Mountain tops in deserts are the preferred locations because, of course, the air is extra dry; that means less water molecules to scatter light. Mountain tops on islands are also great because the air currents around islands are much calmer than other places, so you get less windy and turbulent conditions; wind also and air turbulence greatly reduce your resolution.
In the next several slides, I show some observatories from around the world starting with the ones that have the smallest telescopes to the ones that house the largest telescopes. There are more observatories that exist, but these were the ones that are notable to me because either I have done some observing at them or have association with them.

24. Fremont Peak Observatory, San Juan Bautista, CA
The closest observatory to Hartnell College is located in San Juan Bautista, called Fremont Peak Observatory. It is built on a mountaintop that is about 3000 feet in elevation. It was started in 1986 by a group of volunteers. In fact this observatory is staffed with volunteers, or amateur astronomers. Amateur astronomers are people who do not have careers in astronomy, but are passionate about the subject. This observatory is special to Hartnell because we send our students there to observe all the time. Every summer, we also select a few students to work there as summer interns. They learn how to use the telescope and help to run the Public night programs. In fact, one option for your astronomy project (this is a great one to do) is to attend one of these Public night observing programs. The largest telescope they have is called the Challenger. It is a 30 inch Newtonian reflecting telescope.
Since the elevation is not so high and it has some light pollution from San Jose, Fremont Peak Observatory is not the most ideal place to build an observatory. That is the reason why this observatory is not currently being used for research. It’s more of an educational facility for science outreach to the public. But the sky there is dark enough to see much more than you could in Salinas. And if you ever wanted to look through a large telescope, this would be the place for you to go.

25. Lick Observatory San Jose, CA
The closest research observatory to us is located on Mount Hamilton in San Jose, CA called Lick Observatory. It is located 4200 feet in elevation and has 9 telescopes. The largest is a 3 meter diameter reflecting telescope. Currently it is owned by UC Santa Cruz. Many of the new planets that have been discovered outside of our own solar system were discovered at Lick Observatory. The most famous telescope however is not the 3 meter reflector, but rather the 36 inch refracting telescope as it is one of the oldest, built in 1888.
This observatory was named after an eccentric millionaire, James Lick. If you visit the observatory, they can give you a tour and show you the 36 inch refractor. The observatory has a lot of history and character associated with it. In fact it is the only observatory in which the floor actually moves up with hydraulics. In addition, during the tour, they will give you the story of James Lick and how the observatory came to be built. It is a great observatory to tour if you are in the area. It takes about 2 hours to get there from Salinas, but warning, the way up is very windy and steep! However it is worth it to see the telescope, see the view at the top, and hear the interesting story! If you don’t think you will ever have the chance to visit the observatory or are curious about James Lick…scroll down and I will tell you…(this story will not be on the exam).
In short, James Lick was not always a millionaire. In fact he started off very poor. When he was a young man, he was in love with a young lady. When he asked her to marry him, her father did not approve since he was not rich enough or accomplished enough. Well James then decided to leave for New York (without explaining to the young girl the reason for his leaving). The reason why he left was because he wanted to make his way in the world and earn money so that he could come back and be good enough to wed his love. He did just that; he became a millionaire and returned back to California. Unfortunately this was years later; when he came back the lady already married another man. Wealthy, but heartbroken, James didn’t know what to do with all his money. Luckily for astronomy, he happened to be friends with an astronomer. His astronomer friend convinced him that he would be best remembered if he contributed to science by building an observatory. He listened to his friend and that was how Lick Observatory was constructed. It is also hard to forget James Lick because he decided to have his tomb there, right underneath the floor of the observatory housing the 36 inch telescope (I told you he was strange)! Some people even claim that the observatory is haunted by his ghost! If you believe that, it would make it very scary to observe there, I would think.

26. Kitt Peak National Observatory (KPNO) Tucson Arizona
Kitt Peak National Observatory is located 6,000 feet above the Arizona desert in Tucson, Arizona. It has over 19 telescopes (houses the most telescopes in the world), including a solar telescope. The largest telescope is the 4meter diameter reflecting telescope (at the top right). This is the observatory that I visited and observed at the most during my graduate school days. I did all my observations using the 4meter telescope. This has perhaps the best observational conditions in the continental U.S.

27. Cerro-Telolo Inter-American Observatory (CTIO) La Serena, Chile
Cerro Tololo Inter-American Observatory is located 50 miles from La Serena, Chile in the Andes mountain at 7,200 feet. The largest dome is the 4meter dome. I have also been lucky enough to observe here using the 4 meter a couple of times. Since some of the objects in my study were located in the Southern celestial hemisphere, I needed to come here to observe them (since KPNO is in the Northern Hemisphere, these objects would not have been visible there). I will later tell you about my observing experiences at this observatory.

28. Keck Observatory Mauna Kea Hawaii
Keck Observatory is located on Mauna Kea, on the big island of Hawaii. At an elevation of 14,000 feet, it represents the location with the best observing conditions in the world.
Mauna Kea is unique as an astronomical observing site. The atmosphere above the mountain is extremely dry and cloud-free, so that the proportion of clear nights is among the highest in the world. The exceptional stability of the atmosphere above Mauna Kea permits more detailed studies than are possible elsewhere, while its distance from city lights and a strong island-wide lighting ordinance ensure an extremely dark sky, allowing observation of the faintest galaxies that lie at the very edge of the observable Universe. A tropical inversion cloud layer about 600 meters (2,000 ft) thick, well below the summit, isolates the upper atmosphere from the lower moist air and ensures that the summit skies are pure, dry, and free from atmospheric pollutants. It houses 13 telescopes.
Since this location represents the world’s best observing conditions, some of the world’s largest telescopes are housed here. This includes the twin 10 meter diameter Keck Telescopes, 8 meter Gemini North telescope, and 8 meter Subaru telescope. These telescopes are owned by noteworthy academic institutions and several nations including the U.S., Japan, Canada, France, and the UK.
Since it is located at feet, observing here is quite a challenge because at high elevations, people often get light headed and nauseous due to lack of oxygen. So to acclimate, normally what people do is they first go to 10,000 feet and stay here for a night or two to get used to the high elevation. Then they continue up to 14,000 feet.

29. Keck Observatory
Since this observatory houses some of the world’s largest telescopes, it is very competitive to get observing time there. In fact only the top, most well known astronomers get to use this telescopes. During graduate school, I would have loved to use the telescopes here; however my advisor told me not to even apply for observing time because he know I would not get it (since I was not a hotshot famous astronomer). So unfortunately, I’ve only been to the Island for vacation and have never gotten the privilege to visit the observatory. This was the closest I could get to it  (this was a picture of the observatory taken from my plane leaving the island). But it was still very thrilling to be able to see it, even from the plane.

30. Gran Telescopia Canarias (GTC), Canary Islands
The Gran Telescopia Canarias (GTC) is located on the Canary Islands, off the coast of Spain at 7,000 feet in elevation. This observatory now houses the world’s largest telescope. The GTC is a high performance segmented 10.4 meter telescope. This telescope is co-owned by Mexico, Spain, and the University of Florida.
The reason why this telescope is so special to me is not just that it has the world’s largest reflecting telescope, but it is co-owned by the University of Florida (UF) which so happened to be where I attended school for my doctorate (PhD) degree. The reason why UF is able to co-own it is because many of the equipment that are used on the telescope was built at UF. Because UF co-owns the telescope, they are guaranteed many nights of observations. I’m currently envious of the graduate students who are lucky enough to be able to use this telescope for their research!
Make sure to watch the video clip that I posted this week of this observatory to get a taste of how large the telescope is.

31. What is it like to go observing?
Since I have been fortunate enough to observe at some of these places, I thought it would be interesting to give you a taste of what it is like. This will not be on your exam and you can skip this section if you don’t have the time…
One of the perks of being an astronomer is that you get to travel (for free!); you get to travel to conferences that are located all over the world and you get to travel to use telescopes which are also located all over the world. Many of my colleagues have traveled to Chile, Canary Islands, and Hawaii to use the telescopes. The first time I traveled outside of the country, in fact, was during graduate school. I had the opportunity to travel to Chile, Italy, and Mexico to attend conferences or observe at one of the observatories.
So how do would one get access to the observatories? Since you are talking about the world’s premiere telescopes and everyone wants to use them, you can’t just go and use a telescope whenever you want to. You need to apply for observing time. That is you would write up a telescope proposal explaining to the committee what you want to study; why it is important you get the data at their telescope; why your research is important to astronomy; what telescope and instruments you want to use; what time of the year you would like; how many nights. Once you are approved they grant you a certain number of nights.
Then you go there, you try to make sure you can get used to staying up all night by staying up the night before so that when you get to the observatory, you can sleep during the day. The upper left is an image of the dormitory I stayed in while observing at CTIO in Chile. Since it is located in the mountains, the view outside your window and balcony is very spectacular!
You have to be quite when you walk by the dorms during the day because there are people sleeping. Also usually there are tourists visiting the observatory and there are signs that are posted that say “Quiet Day sleepers”. Some places you are well provided for, like at CTIO. They cook for you and it’s all you can eat (so oftentimes I tend to overeat there)! You can even request a night lunch. It’s a well organized system. Some places you have to operate the telescopes yourself and other places they have telescope operators that take the data for you.
The typical schedule is that you wake up at around 5:30pm, have breakfast, stay up all night and then you go back down the mountain after sunrise. Every night, you hope, is a clear night because if it isn’t you won’t get your data and you have to reapply for observing time and wait another year to get it because your objects are only up in the sky during a certain time in the year. So that is why sometimes it takes a long time for grad students to graduate because they couldn’t get data due to whether. You have to have a back up plan. I had to use my back up plan because for several reasons, including bad weather, and also because I was using a new instrument which was in the process of being tested, I couldn’t get any data. My advisor tried to make me feel better by telling me that when he was a graduate student, he also had the hardest time getting data because the weather was always uncooperative, but after he graduated, all of a sudden the weather gods were more kind and he was able to easily get a lot of data.
Being there in the Andes Mountains and stepping out into the dome and looking at the 4 meter diameter telescope was one of the best experiences of my life! It was really an awesome feeling to think that I was just an inexperienced graduate student, but I was given the opportunity to use one of the world’s largest telescope! It made me feel pretty powerful!

32. Not all radiation can penetrate Earth’s atmosphere
Although we have some very powerful observatories located on the ground, we also need to have telescopes in space. One of the reasons for this is what we talked about earlier. Earlier we mentioned that anytime you observe from the ground, even in the best location such as Hawaii, you will always lose resolution since the Earth’s atmosphere scatters light.
But there is another reason why you would send up telescopes into space, and this slide illustrates the second reason. In addition to scattering light and degrading resolution, the Earth’s atmosphere only lets some forms of light through and blocks the other forms of light.
Here is a diagram which indicates the windows of transparency for the different forms of light. If the window is wide open, then the atmosphere allows all of that kind of light through, if the window is partially open, only some of that kind of light is allowed to get through, and if the window is entirely closed, the atmosphere will block out all of that form of radiation.
You can see that, for the most part, the only light that is allowed completely through to our surface is visible light and radio waves. The atmosphere lets in a little bit of ultraviolet radiation (that is why you need to wear sunblock) and infrared light. Luckily for us, our atmosphere blocks out most ultraviolet radiation and all of the high energy x-rays and gamma rays, which is harmful to us and will cause cancer.
But in terms of science and astronomy, our telescopes on Earth can be used to only study light in the visible, some infrared light, and radio light. So in order to study the other forms of light, we need to send spacecraft above the Earth’s atmosphere to collect the light.

33. Space Telescopes
Here are some examples of the telescopes that have been launched into space.

34. Hubble Space Telescope
The most famous of the space telescopes is the Hubble Space Telescope (HST), which was named after the famous astronomer Edwin P. Hubble who made many important discoveries such as verifying the existence of galaxies other than our own and discovering that the Universe is expanding.
Spacecraft Design: At the heart of Hubble are a 2.4 m primary mirror and a collection of five science instruments that work across the entire optical spectrum - from infrared, through the visible, to ultraviolet light.
Ideally, Hubble's orbit above the Earth's distorting atmosphere should have allowed astronomers to make the very high resolution observations that are essential to open new windows onto planets, stars and galaxies. However, when it was first launched, unfortunately, the images it took were not much better than those taken by the best ground based observatories. The reason for this was because an effect called spherical aberration was discovered in the Hubble primary mirror. In basic terms, the edge of the mirror was ground just a tiny fraction too flat, and because of this, light from the edge of the mirror could not come into focus with the light reflected from other parts of the mirror.
NASA received a lot of criticism for this from the public and from the news. In 1993, they, fortunately, sent up a servicing mission to fix the problem by installing corrective optics. (Essentially, you can think of it as Hubble is wearing glasses). With this pair of "glasses" HST’s golden age began. The images were as sharp as originally hoped for, and new, astonishing results started to emerge on a regular basis.
2.4 meter diameter reflector
Launched in 1990 and still
operational

35. Hubble Deep Field 1995

36. Hubble Ultra Deep Field 2004
Hubble Xtreme Deep Field 2012
HST has allowed us to see the Universe as we have never seen it before. One of the most important images it has been produced is that of the Hubble Ultra Deep Field taken in It represents the highest resolution and deepest view of the Universe we have today. In order to produce this image, the HST collected light for a total of 11 days exposure time (the more light it collects, the deeper in space you can see). All the objects in this image are not stars (except the ones with the spikes), but whole galaxies containing billions of stars. The most faint ones represent the most distant galaxies.
This powerful image allows us to peer back billions of years in time because we are able to see galaxies at such huge distances. With this image we can see galaxies as they appeared just 800 million years after the Big Bang, and thus allowed us to better understand what our Universe was like in its infancy and how it has evolved to be what it is today. This would not have been possible from the ground-based observations.
Because I never was able to get any of my own data due to bad weather, my back up plan was to use the data from the Hubble Deep Field (this was the image taken in 1995 before the Hubble Ultra Deep Field) to complete my dissertation. Even though that was the best available data at the time (with a total exposure time of about 30 hours), I wish I could have been able to work with the Hubble Ultra Deep Field, but sadly it was released way after I graduated.

37. The James Webb Space Telescope will replace HST in 2018
Hubble was launched in 1990 and has been operational for over 20 years now. 20 years is a long lifetime for a telescope. However, all good things have to come to an end. Even though it can still be serviced and can still work, like an old car, it will cost more to maintain than to replace.
Eventually in a few years, NASA will decommission Hubble, but not to worry, they will replace it with an even better telescope. The name of this telescope is the James Webb Space Telescope (JWST) scheduled to launch in The man whose name NASA has chosen to bestow upon the successor to the Hubble Space Telescope is most commonly linked to the Apollo moon program, not to science. Yet, many believe that James E. Webb, who ran the fledgling space agency from February 1961 to October 1968, did more for science than perhaps any other government official and that it is only fitting that the new space telescope be named after him.
JWST will have higher light gathering power than HST as it will have a larger mirror, 6.5 meters (20 feet) in diameter (HST was 2.4 meter) and a sunshield the size of a tennis court. Because this mirror is so large, it will be segmented (18 hexagonal segments).
The telescope is a large, infrared-optimized space telescope. JWST is designed to study the earliest galaxies and some of the first stars formed after the Big Bang. It will study the Universe at the important but previously unobserved epoch of galaxy formation. It will peer through dust to witness the birth of stars and planetary systems similar to our own. And using JWST, scientists hope to get a better understanding of the intriguing dark matter problem.
As HST was our generation space telescope, JWST will be your children’s generation space telescope and will allow us to see the Universe even better than we could with the Hubble Space Telescope.

38. Innovations and Advancements in Technology
In the last few decades, the rapid advancement in technology has allowed us to have a clearer view of the Universe than we have ever seen before.

39. A Charge-Coupled Device (CCD)
Ordinary Photographs vs. CCDs
One of these advancements was the CCD (Charge-coupled device). This was invented in 1969 by Bell Laboratories. Originally, the idea was for it to be a picture phone, but astronomers adapted it for telescope observations. Basically what it is, is a very high resolution digital camera.
At the heart of the camera is a single silicon wafer that is divided into an array with light sensitive photo-elements called pixels. Your digital camera has one of these silicon wafers in it, but of course the resolution is not as high as that of a CCD.
So instead of looking through the eyepiece of a telescope, you can attach a CCD to collect the light from the objects and form a picture of the objects. Before the invention of the CCD, astronomers, like you and I, took pictures the old fashion way, by using photographic plates. This is processed in a similar way to photographic film. But nowadays, no one uses photographic plates anymore because it simply has too many disadvantages compared to using a CCD. The disadvantages of using photographic plates instead of a CCD are the same as using photographic film instead of digital images.
The Advantages of CCD Imaging
Professional astronomers have been using CCDs for nearly two decades and have no thoughts about going back to film.  The advantages are impressive:
CCD cameras are up to 100 times more sensitive than film (e.g. the left most image was taken using photo-graphic plates, whereas the middle and right images of the same star field were taken using a CCD)
CCD images are digital, meaning no film-processing, scanning, scratching, or fading
CCD cameras have a much greater dynamic range than film, meaning they can more easily capture both faint and bright detail in a single exposure
CCDs are capable of resolving finer detail than film (this can, however, be limited by the telescope used and the atmospheric conditions)
For the amateur, several other advantages apply as well:
Taking images with a CCD is generally much easier than with film.
Learning goes faster due to the ease-of-use and shorter exposure times.
Light pollution is less obtrusive and more easily removed from CCD images, meaning imaging from a backyard site is more likely to be possible with CCD.

40. Adaptive Optics uses a deformable mirror to correct for the loss of resolution due to Earth’s atmosphere
I mentioned previously that you can increase your resolution by using a telescope with a larger diameter, the maximum resolution you can get is always limited by the Earth’s atmosphere, and that was one of the reasons why we needed to send telescopes up into space. I also briefly hinted that astronomers now have a new technology to actually fix this problem. This technology that corrects for the loss of resolution due to the Earth’s atmosphere is called adaptive optics.
From the image on the left, you can see that due to the turbulence (motions of the molecules) in the Earth’s atmosphere, the starlight will get scattered so that instead of seeing the star as a point, you would see it as a fuzzy blob. The image on the top right shows you what happens to the light of the star as it passes through the Earth’s atmosphere in comparison to what it actually looks like. You can see, that there is a loss in resolution of the starlight as it passes through the Earth’s atmosphere.
The image on the lower right shows you how the adaptive optics system works. The light that passes through the Earth’s atmosphere gets reflected off a deformable mirror. This mirror is made really thin so that it’s shape can be easily bent or deformed. Well some of the light is sent to a sensor which calculates how much bending and in which direction the light is being bent by the atmosphere. This sensor then sends the corrections to the control system (the computer) which then bends and distorts the deformable mirror so that it bends the light in the opposite direction as the atmosphere (thus compensating for the scattering of light by the atmosphere). This light is reflected off and sent to the CCD camera as the final, higher resolution image.
In order to keep up with the changes caused by the motion of the molecules in the Earth’s atmosphere, the mirror has to bend about a thousand times per second. With this revolutionary and relatively new technique, the resolution we can obtain from the ground is now almost as good as what we can obtain from space, but in this case you would not have to spend the money to send a telescope into space. I include a little animation on the website about how the adaptive optic system works on one of the major telescopes.

41. Adaptive Optics: Laser guide star
In order for the corrections to be made or determined by the computer, you usually need to perform adaptive optics on a bright star. Sometimes, the faint object you are looking at has a bright star nearby it; in this case, you can determine the corrections using the light of this nearby bright star and apply it to your faint object assuming that its light is distorted in the same way since it is passing through the same area of the atmosphere.
However, many times, your faint object will not have a nearby bright star. It used to be that in this case, you were out of luck, that you could not perform adaptive optics on the faint object. However, nowadays, they have fixed this problem. A lot of telescopes with adaptive optics also has a laser guide star (an example of one in use is shown in this slide at the Keck observatory). You can shoot this high powered laser in any direction in the sky and ignite the molecules in the Earth’s atmosphere. When it does this, it creates an artificial star. So even if your faint object does not have a nearby star whose light passes close to the same area in the Earth’s atmosphere, you can aim this laser so that it appears in the same area of the sky as your faint object and do adaptive optics on the laser guide star. This tells the computer how the molecules in the Earth’s atmosphere near to your object are behaving and how much and in which direction they are scattering the light.
This laser guide star is so powerful that you have to get clearance from the airports and from the Internationals Space Station before you can use it!

42. Adaptive Optics
Here is a close up of the 10 meter mirror of one of the Keck telescopes.
It’s hard to see, but it is actually consisting of 36 hexagonal segments fused together to make one 10 meter mirror. The Keck mirror uses adaptive optics, In back of the segments are little pistons which adjust the mirrors so that it counteracts the effects if the Earth’s atmosphere.
So the Keck telescope is huge; it is not only one of largest telescopes on Earth with a diameter in excess of 30 feet, it has adaptive optics to help counteract the blurring of light due to the Earth’s atmosphere, but even with these advantages, the HST is still a much more powerful instrument.
20 times less expensive than sending telescope into space. Potential to have 5 times better resolution, and 20 times more light gathering power.
Have to make distort mirror several hundred times per second.

43. Era of Extremely Large Telescopes with Adaptive Optics
Normally, without the revolutionary adaptive optics technology, there would be no use in building really large telescopes as you couldn’t increase the resolution pass that what the atmosphere allows. You would be able to increase the light gathering power, but your maximum resolution would only be matched by conditions in the Earth’s atmosphere.
However, with adaptive optics, there is more of a rational for building really large telescopes as now you can increase both the light gathering power and the resolution by making the telescope as large as possible. The resolution, remember, increases with the size of the telescope. Since adaptive optics would remove the limitations in resolution due to the Earth’s atmosphere, if you have a very large telescope, you can achieve higher resolution that what is possible from space, in theory.
Remember, how I said that the largest telescope is the 10.4 meter diameter telescope that was built in the Canary Islands? Well the reason why it was 10.4m was that that was probably the largest telescope that can obtain the maximum resolution allowable by the Earth’s atmosphere. Now with adaptive optics, astronomers have plans to build a 30 meter (close to 1000 feet!) diameter telescope to gain even higher resolution since it will not be limited by Earth’s atmosphere. The slide shows you a schematic of what this telescope would look like.
They plan to build this telescope in Hawaii probably by the end of this decade. Think of the amzing images you can gain with this large telescope!

44. Interferometry
The last piece of technology is called interferometry. The idea behind interferometry is that it is easier to link several telescopes together to act as one large unit rather than to build one large telescope. This type of technology is based upon adding the light from one telescope with the light from other telescopes to get a brighter and more resolved image. This will increase the light gathering power and the resolution.
This slide shows you some of the interferometers that currently exist. The top image is the Very Large Array (VLA) which I talked about previously.
The bottom left image is the Very Large telescope (VLT) which consists of four 8 meter reflecting telescopes, plus several smaller telescopes. They can be used individually or together to give more finely detailed images. Used together, it would have the light gathering power and resolution of a 16 meter telescope meaning it could distinguish the gap between the headlights of a car located on the Moon.
The largest interferometer, however is the Very Long Baseline Array. This interferometer consists of 10 radio telescopes, each 25 meters in diameter. The are mostly spread over the continental U.S; there is one in Hawaii, and one as far out as to the US Virgin Islands. If used together,
this telescope would essentially have an effective diameter of 8611km or 5351 miles! In the radio, the resolution you can get would be equivalent to being able to stand in New York and reading the words on a newspaper located in L.A!
Very soon though we will also send out telescopes using interferometry technology out into space, which will make it even more powerful; powerful enough to get images of planets around other stars which are too faint to be seen with our current technology. Indeed we live in exciting times for astronomy as the technology is increasing so rapidly!

45. Building Your Own Observatory
What kind of telescope (reflecting or refracting) and why?
What is the difference between a reflecting and refracting telescope?
Diameter of objective (express in meters)?
Where would you build it and why?
What would you observe with it?
Draw and name your telescope or observatory.
Think about cost versus scientific gains.