1. Telescopes

2. Why Telescopes are Important
We spend a lot of time talking about light and images
But none of that does us any good if we don’t have a way of collecting that light in the first place
This is where telescopes come in

3. What is a Telescope? So just what is a telescope?
An object that uses lenses or reflecting surfaces to collect light from a distant object

4. The History of the Telescope
It is a common misconception that Galileo invented the first telescopes
In fact, Hans Lippershey, a Dutch spectacle make, was the first to designing the first telescope(a refractor)
Galileo is the first person known to have turned a telescope to the sky (he gets the credit)

5. Galileo’s Telescope He was astonished by what he saw
The rings of Saturn
Stars in the Milky Way
The moons of Jupiter
Spots on the sun
He also went blind-----

6. Can You Imagine?
Just imagine what he must have felt, being the first person to see these things
It was all completely unexpected-----
Galileo’s observations, and those of others, would literally change the course of human history

7. Telescopes Today Telescopes have come a long way since then
The biggest single telescopes have main mirrors that are over 12 meters in diameter!
Some telescopes are actually arrays that are made of dozens of smaller telescopes linked together

8. New telescopes
Isaac Newton developed the second generation of telescope.
He created the reflector telescope that fixed all the problems of the refractor

9. Largest GranTeCan or GTC 10.4m

10. Tied for 2nd at 10m The Hobby-Eberly Telescope or HET Ft. Davis, Texas

11. Keck 1 & 2 USA , Hi
10M

12. The Giant Magellan Telescope or GMT in 2020 will have 7-8
The Giant Magellan Telescope or GMT in 2020 will have 7-8.4m mirrors(24.5m)

14. Today, there are telescopes that are designed to see radio, microwave, infrared, visible, ultraviolet, x-ray and gamma-ray light?
True
False

15. How Telescopes Work There are two main types of telescopes
Refracting telescopes use lenses to focus light to a point
Reflecting telescopes use mirrors to focus the light
Catadioptric telescopes are a combination of the two

16. Refracting and Reflecting Telescopes

17. Anatomy of a Telescope
Although there are many types of telescopes, all have some basic key parts

18. Anatomy of a Telescope Aperture Primary Secondary Eyepiece
Optical Tube
Finder
Detector

19. Anatomy of a Telescope
The aperture is simply the part of the telescope that lets light in
The primary bends the light, bringing the rays to a point
The secondary aids in this process(changes the direction of the light)

20. Anatomy of a Telescope
The optical tube protects the rest of the telescope and blocks stray rays of light
The finder is a small telescope used for honing in on objects
The detector is the thing that actually records the light
Could be your eye

21. Focusing Light The idea of focusing light is important
Telescopes collect light from a large area
By focusing the light, we concentrate its power
The focal plane is the plane where the light rays meet
The focal length is the distance from the primary lens (or mirror) to the focal plane

22. Focusing Light

23. Focusing Light

24. The Focal Plane
If we put our eye at the focal plane, we would only see a bright point
The eye piece straightens out the rays of light so our eye can see the image
If we move the eyepiece out of the focal plane, the image will be distorted

25. Common Reflectors

26. Some Other Telescope Properties
There are some other properties of telescopes that astronomers are interested in
Some of these things are(in order)
Collecting Area
Resolution
Magnification
Cost

27. What is the most important property of a telescope for astronomers?
Magnification
Collecting Area
Focal Length

28. Collecting Area
Collecting area is the area of the surface that the telescope uses to collect light
This is usually the primary lens or mirror
Many people think that magnification is the most important property of a telescope, but it is actually collecting area

29. Collecting Area Why is collecting area important?
Suppose you are trying to see a very faint source
If it is faint, then it is not sending many photons to Earth
We need to collect as many photons as we can
Having a large collecting area does this – like casting a big net to catch more fish
Astronomers like to call telescopes “Light Buckets”

30. Collecting Area
Most astronomical objects are pretty faint, so we need to collect as much light as we can

31. Resolution
The resolution of a telescope defines how much detail we can see
All optical systems have some resolution limit
Eventually, the separation between objects becomes too small for us to see

32. Angular Size We measure the separation of objects in terms of angles
Remember that there are 360° in a full circle
There are 60 arc minutes in a degree, and 60 arc seconds in an arc minute
So there are 3600 arc seconds for every degree of sky.

34. Back To Resolution Consider looking at a distant mountain
Although the mountain is covered in trees, we cannot make out the trees themselves
Our eyes have too low of a resolution

35. Telescope Resolution
Telescopes have a much improved resolution, but there is a limit
The resolving power of a telescope (with a round primary) cannot be greater than
Copy this formula!
R will be in radians (1 radian = 57.3 degrees)
L = wavelength and D = Diameter of mirror
Both L and D must be the same unit!

36. Telescope Resolution
Notice that this depends on both wavelength and the diameter of a telescope
This is a natural limit…it is set by nature and we simply cannot do better

37. Telescope Resolution Other things affect the resolution of a telescope
Atmospheric distortions are notoriously bad
Think of the “waves” that come off of hot asphalt
But there are things we can do to compensate for these effects

38. Telescopes in Space
The most straightforward is to put our telescope above the atmosphere
There is another good reason for doing his, and it has to do with how light travels through the atmosphere

39. Atmospheric Transparency

40. Why Do We See What We See?
This provides a great explanation of why our eyes are sensitive to visible light
The Sun puts out most of its light in the visible part of the spectrum
Only visible light and radio make it through the atmosphere
Radio waves have very long wavelength, so we would need very big eyes to resolve anything

41. Magnification Astronomer’s do like magnification, too
But note that it does not matter how much you magnify something…if you cannot resolve it, magnification does you no good
Think of a pixelated image

42. Pixelation

43. Magnification fT is the focal length of the telescope
With that in mind, here is the jist on magnification
Magnification is defined as the increase in angular size
The formula to calculate magnification is
fT is the focal length of the telescope
fE is the focal length of the eyepiece

44. What will give you a larger magnification?
A short eyepiece focal length
A long eyepiece focal length

45. Magnification
A longer focal length for the telescope, or shorter focal length for the eyepiece, means a larger magnification

46. Cost
Cost is of course a practical concern, but it needs to be taken into account
Telescopes can cost as much as hundreds of millions of dollars, and guess who pays for most of it…
Space telescopes are especially expensive, so we need to make compromises

47. Nickels and Dimes…
Since it costs lots of money to put a telescope in space, space telescopes are usually smaller
No atmosphere, but less collecting area, =lower limiting resolution
There are also lots of practical concerns

48. Precision Instruments
If astronomers want the best possible data, their telescopes have to be very, very good
Consider that in order to get a clear image, your mirrors or lenses need to be perfect on scales of about the wavelength of light you are looking at
This can be nanometers

49. Some Famous Telescopes
Hubble Space telescope 2.4m primary

50. Some Famous Telescopes
Very Large Array is a radio astronomy observatory located on the Plains of San Agustin, between the towns of Magdalena and Datil, some 50 miles west of Socorro, New Mexico

51. Some Famous Telescopes
Mcdonald observatory Left to right meter Otto Struve Telescope, meter Harlan J. Smith Telescope and the 11-meter(9.4 (433-inch) mirror, the Hobby-Eberly Telescope (HET)

52. Some Famous Telescopes
Arecibo Observatory is a radio telescope in the municipality of Arecibo, Puerto Rico

53. Detectors So, we collected all our light…now what?
It doesn’t do us any good if we can’t see the light
Of course, we always have our eyes, but…

54. Do you think that you would ever see an image like this one if you looked through a telescope using only your eyes?
Yes No
0 of 5

55. Sorry I hate to tell you, but the answer is definitely no Why not?
Well, remember, most things we look at through a telescope are really faint
Even though we collect more photons with telescopes, we need to collect them for long periods of time to make images like those

56. More Reasons Your Eyes Aren’t Good
Our eyes are also only sensitive to visible light
They are subjective tools
They can not store images long term
They are horribly inefficient

57. STOP

58. CCDs CCDs revolutionized astronomy again
CCD stands for charged coupled device
This is the same technology at use in digital cameras

59. CCDs

60. CCDs CCDs are great because They are very efficient
They allow you to take digital data…analyze on computer
They have a linear response
They have a wide dynamic range

61. CCDs CCDs are by far the most common detector in astronomy
Although some others exist, it is not worth talking about them here

62. Spectrographs We don’t always want to make an image
Sometimes, we want to split the light into its spectrum
We use spectrographs for this

63. Spectrographs There are two basic types of spectrographs
Prisms
Gratings
Combining the two, we get Grisms

64. Prisms

65. Prisms
Prisms work because light of different wavelengths takes a slightly different path
Comes out at a different place, and is thus spread out

66. Gratings

67. Gratings Gratings are made up of hundreds or thousands of tiny grooves
They use a phenomenon of light known as diffraction to split the light

68. Grisms Grisms use both effects
Gratings and grisms are the most commonly used spectrographs in astronomy

69. Spectrographs
Once we split the light by wavelength, we usually use a specially designed CCD to actually measure the photons
Since we splitting the light up and smearing it, spectroscopy needs lots of photons, i.e. a bright source