3.9.1 Comparing Telescopes (Finish) Flashcards
What should discussion about telescopes involve?
Structure, positioning and use and collecting and resolving power
Compare the structure of optical and radio telescopes
Similarity; both use parabolic surfaces to reflect waves
Difference; Radio uses a single primary reflector, optical uses 2 mirrors.
Radio dish does not need to be as smooth as the optical mirrors
Compare the positioning of radio and optical telescopes
Similarity; Both can be ground based as the atmosphere is transparent to most radio and optical wavelengths
Difference; Radio must be located remotely (away from radio sources) and optical must be placed high up and away from cities (avoid light pollution)
Compare the uses of radio and optical telescopes
Similarity; both used to detect hydrogen emission lines
Difference; radio waves are not absorbed by dust whereas optical waves are, so radio telescopes can be used to map the Milky Way or galaxies
Compare the structure of IR and optical telescopes
Similarity; both constructed using a primary concave mirror and secondary convex mirror
Difference; mirrors in IR must be kept at low temperatures using liquid helium or refridgeration to prevent their own IR radiation masking the signal
Compare the positioning of IR and optical telescopes
Similarity; many ground based telescopes detect both IR and optical, so long as they are away from cities and high above the ground.
Difference; IR strongly absorbed by water vapour in the atmosphere, so telescopes must be in dry, high altitude locations or in space.
Compare the uses of IR and optical telescopes
Similarity; Most objects that emit visible light also emit IR radiation so valuable information can be obtained form both
Difference; IR telescopes can detect warm objects that do not emit visible light such as dust in nebulae and brown dwarfs
Compare the structure of UV and optical telescopes
Similarity; Both are constructed using a primary concave mirror and a secondary convex mirror
Difference; Mirrors in UV telescopes must be smoother than optical
Compare the positioning of UV and optical telescopes
Similarity; Many space-based telescopes are able to detect both UV and visible light
Difference; All UV wavelengths are strongly absorbed by the atmosphere so telescopes must be located in space
- space-based telescopes can be inconvenient to maintain
Compare the uses of UV and optical telescopes
Similarity; Both used to determine the chemical composition and temperature of objects. Objects who emit visible light also emit UV so valuable information can be obtained from both
Difference; UV telescopes can detect objects not visible at other wavelengths such as hot gas clouds near stars, supernovae and quasars
Compare the structure of X-ray and optical telescopes
Similarity; Both parabolic mirrors that reflect and focus waves
Difference; X-ray telescopes made from a series of nested mirrors as they tend to go through objects instead of being reflected. Mirrors must be extremely smooth, they are a combination of parabolic and hyperbolic mirrors which must be extremely smooth.
Compare the positioning of X-ray and optical telescopes
Similarity; All perform best in space, away from the restrictions of the Earth’s atmosphere
Difference; All X-ray/ gamma wavelengths are strongly absorbed by the atmosphere so telescopes must be in space. Space based telescopes are inconvenient to maintain
Compare the uses of X-ray and optical telescopes
Similarity; X-ray and gamma provide valuable information about visible objects like supernova remnants
Difference; X-ray and gamma can observe other wise non-visible objects like neutron stars, black holes, pulsars and gamma ray bursts
