Thursday September 15, 2011

1. ThursdaySeptember 15, 2011 (Telescopes)

2. The Launch Pad Thursday, 9/15/11 How do galaxies evolve, and what holds them together? Young galaxies are messy and random in shape. As they grow older, gravity forms them into more organized shapes, like spirals or ellipses. A strong gravity source holds them together, perhaps a massive black hole at their cores.

3. The Launch Pad Thursday, 9/15/11 Which of the following would probably be the farthest from Earth? the Moon the Sun the Andromeda galaxy a large galactic cluster

5. Optical (Visible Light) Telescopes Optical telescopes are made in two basic types: Refracting telescopes Reflecting telescopes

6. Refracting Optical Telescopes Refracting telescopes use a lens (called the objective) to bend (refract) the light to produce an image. Light converges at an area called the focus. The eyepiece is a second lens used to examine the image directly. Refracting telescopes have an optical defect called chromatic aberration (color distortion.)

7. Reflecting Optical Telescopes Reflecting telescopes use a concave mirror to gather the light, and there is no color distortion. Nearly all large telescopes are of this type.

8. Optical Resolution Appearance of a galaxy in the constellation Andromeda using telescopes of different resolution.The top picture is not “out of focus”, it’s a resolving issue, not a focus problem.

9. Deployment of the Hubble Space Telescope in Earth Orbit April 24, 1990 Figure 23.17

10. Other Types of Telescopes Detecting Invisible Radiation Photographic films are used to detect ultraviolet and infrared wavelengths. Most invisible wavelengths do not penetrate Earth’s atmosphere, so balloons, rockets, and satellites are used to put the cameras above the atmosphere.

11. Ultraviolet Telescopes

12. Infrared Telescopes

13. Radio Telescopes Radio wavelength radiation reaches Earth’s surface, so radio telescopes can be Earth-based.

14. Radio Telescopes Radio telescopes are “big dishes” used to gather radio wavelength electromagnetic radiation.

15. Radio Telescopes Radio telescopes have to be very large in order to gather radio waves, which are about 100,000 times longer than visible radiation waves. They are often made of a wire mesh, and have rather poor resolution. Radio telescopes can be wired together into a network called a “radio interferometer.”

16. A steerable radio telescope at Green Bank, West Virginia Figure 23.15 A

17. Radio Telescopes Radio telescopes have several advantages over optical telescopes: • they are less affected by weather • they are less expensive to build and maintain • they can be used 24 hours a day • they are able to detect material that does not emit visible radiation • and, they can “see” through interstellar dust clouds

18. Radio Telescope Images