1. Homework #4
What is the maximum resolution of your eyes (assume the wavelength range that your eyes are sensitive to is 300 – 700 nm and that your iris is ½ cm in diameter.
What size eye would be required to see in the radio with the same maximum resolution of your eyes? (use 21 cm for the wavelength of typical radio waves)
What is the maximum resolution of the VLBA (longest baseline = 5000 km) at a wavelength of 21 cm?

2. Telescopes

3. Astronomical objects emit all of these different kinds of radiation in varying amounts

4. Mm/Submm

5. Maunakea’s height

6. Radio wavelength observations are possible from Earth’s surface

8. The Very Large Array (VLA) in New Mexico

9. Observations at wavelengths other than visible light are revealing previously invisible sights
Visible light image
radio wavelength image

10. Astronomers use different instruments to look at light of different wavelengths - sometimes, we even have to go above Earth’s atmosphere.

11. SOFIA - the Stratospheric Observatory for Infrared Astronomy

12. Observations at other wavelengths are revealing previously invisible sightsUV
infrared
Map of Orion region
Ordinary visible

13. Consider Orion as Seen in Different Wavelengths of Light!

14. http://www. cnn. com/2001/LAW/02/20/scotus. heatdetector. 01. ap/index

15. High above Earth’s atmosphere, the Hubble Space Telescope provides stunning details about the universe

16. Hubble Space Telescope Views of Orion Nebula showing stars hidden in clouds

17. The Sun as seen in visible light from Earth and from space in X-rays by satellites

18. High Energy Gamma Rays - Compton Gamma Ray Observatory (GRO) Satellite

19. The Sky’s emission of Gamma Rays

20. But, we receive GRBs from every direction !!
The fact that GRBs come from every direction imply that GRBs don’t come from our galaxy, but from other galaxies spread in every direction!

21. The typical refracting telescope:
magnification = (objective lens focal length / eyepiece lens focal length)

22. Three main functions of a telescope
brighten
(called light gathering power)
see fine detail
(called resolution)
and least important,
magnify
magnification = (objective lens focal length / eyepiece lens focal length)

23. A larger objective lens provides a brighter (not bigger) image

24. Two Fundamental Properties of a Telescope
Angular Resolution
smallest angle which can be seen
 = 1.22  / D
where  = wavelength; D = diameter of the aperture

25. Angular Resolution The ability to separate two objects.
The angle between two objects decreases as your distance to them increases.
The smallest angle at which you can distinguish two objects is your angular resolution.

26. Two Fundamental Properties of a Telescope
Angular Resolution
smallest angle which can be seen
 = 1.22  / D
Light-Collecting Area
The telescope is a “photon bucket” A =  (D/2)2 D A

27. Angular Resolution:

28. Parts of the Human Eye pupil – allows light to enter the eye
lens – focuses light to create an image
retina – detects the light and generates signals which are sent to the brain
A camera works in the same way where the shutter acts like the pupil and the film or CCD acts like the retina!

29. Lenses bend Light
Focus – to bend all light waves coming from the same direction to a single point
Light rays which come from different directions converge at different points to form an image.

30. Telescope Types Refractor Reflector focuses light using lenses
focuses light using mirrors
used exclusively in professional astronomy today

31. A refracting telescope uses a lens to concentrate incoming light
Similar to a magnifying glass

32. Refracting telescopes have drawbacks
Spherical aberration

33. Too spherical

35. Refracting telescopes have drawbacks
Spherical aberration
Chromatic aberration

36. Special achromatic compound lenses and lens coatings can often fix this aberration