Types of Telescopes

1. Types of Telescopes Dr. Charles Ophardt EDU 370

2. Refractor • Refractor - Light gathered through objective lens on front of telescope • Advantages- • Rugged • Sealed so does not need cleaning • Sealed from air currents and temperature effects.

3. Refractor II • Diagram

4. Refractor III • Disadvantages • Chromatic aberration produces a rainbow of colors around image • Reduce with long focal length or multiple compensating lenses • UV does not pass through glass • Less light passes through thicker lens • Difficult to make lens perfect • Large lens sags under own weight

5. Reflector Telescope • Uses a parabolic mirror to gather and focus parallel light rays

6. Reflector Telescope II • Advantages • Do not have chromatic aberration • Objective mirror may be very large because back can be supported • Cheaper to make • Only one side of objective must be perfect • Example 200 inch Hale at Palomar Observatory. • 400 inch Keck with 36 hexagonal mirrors

7. Reflector Telescope III • Disadvantages: • Easy to get optics out of alignment • Open to outside - needs frequent cleaning • Secondary mirror to redirect light can produce diffraction effects • Primary mirror can have a defect if not curved enough. Hubble was too flat by 2 microns.

8. Powers of a Telescope • Light gathering power • Larger diameter objective lens gathers more light • Resolving Power • Is the ability to see small details • Again larger diameter objective • Can use several telescopes spaced apart and use interferometer to make sharper images

9. Atmospheric Refraction • Air molecules cause refraction of light • Turbulent motion of air molecules results in a twinkle effect and blurred images • Effect is called “seeing” • Correction is to put telescope as high up on a mountain as possible • Good seeing is when air is stable

10. Reddening • Air and dust absorbs and scatters electromagnetic radiation • Reddening happens when red light (longer wavelength) is scattered less by molecules and dust. • Reddening seen in the sun at low horizons - other colors scattered out of your line of vision • Blue light (shorter wavelength) scatters more - result is blue sky

11. Extinction • All wavelengths are scattered or absorbed by some amount. • Absorption of light is called extinction • Infrared absorbed by water and carbon dioxide • UV absorbed by O2, O3, N2 • Gamma / X-rays absorbed by O2 and N2 • Long Radio waves blocked by electrons

12. Optical / Visible Light • Visible light views of Andromeda and Centaurs galaxies

13. Electromagnetic Spectrum

14. Radio Telescope • Uses a large metal parabolic shaped dish or wire mesh • Signals are focused on an antenna • Amplified and computer processed • False colors are used to indicate the intensity of the image

15. Radio Telescope • Charged particles in magnetic field produce large amts. radio energy

16. Spitzer Space Telescope - Infrared • Infrared beyond red in the visible spectrum • All objects in space emit some IR or heat radiation - can even see through or detect dust around stars • Infrared radiation is largely absorbed by the atmospheric water vapor and carbon dioxide. • Space based telescope

17. Spitzer Space Telescope - Infrared • Kepler Supernova • False color views from • X-ray- blue/green • Visible - yellow • IR - red

18. Ultraviolet Image • A striking ultraviolet image of the spiral galaxy M81 from XMM-Newton's Optical Monitor camera - European X-ray Satellite • This ultraviolet image of M81 was obtained by the Optical Monitor (OM) on XMM-Newton in April 2001. The image is formed from three 1000 s exposures taken with different ultraviolet filters, centred on approximately 2000, 2300 and 2800 angstroms respectively.

19. Chandra X-ray • NASA's Chandra X-ray Observatory, • Launched and deployed by Space Shuttle Columbia on July 23, 1999. • Most sophisticated X-ray observatory built to date. • Observe X-rays from high-energy regions of the universe, such as the remnants of exploded stars.

20. Chandra X-ray Images • Crab Nebula and Milky Way

21. Compton Gamma Ray • The Compton Gamma Ray Observatory (GRO) is a sophisticated satellite observatory • Compton carries four instruments which can detect an unprecedented broad range of high-energy radiation called gamma rays. • Study energetic celestial phenomena: solar flares, gamma-ray bursts, pulsars, nova and supernova explosions, accreting black holes of stellar mass, quasar emission, and interactions of cosmic rays with the interstellar medium.

22. Compton Gamma Ray Images • Centaura galaxy - left gamma ray image; right visible

23. Crab nebula • The Crab Nebula's creation was witnessed in July of 1054 A.D. • Chinese astronomers and members of the Native American Anasazi tribe separately recorded the appearance of a new star. • Although it was visible for only a few months, it was bright enough to be seen even during the day! • Star which suffered a supernova explosion. Core of the star collapsed and formed a rapidly rotating, magnetic neutron star.

24. Crab nebula • Optical, Radio, X-ray, UV

25. References • http://www.astronomynotes.com/telescop/s1.htm • http://heasarc.gsfc.nasa.gov/docs/xte/learning_center/universe/crabneb.html