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 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