Types of Telescopes Dr. Charles Ophardt EDU 370

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.

Refractor II Diagram

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

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

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

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.

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

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

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

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

Optical / Visible Light Visible light views of Andromeda and Centaurs galaxies

Electromagnetic Spectrum

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

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

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

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

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.

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.

Chandra X-ray Images Crab Nebula and Milky Way

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.

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

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.

Crab nebula Optical, Radio, X-ray, UV

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