TOPIC 9 ASTROPHYSICS EXAM ACTUAL QUESTIONS
AND CORRECT ANSWERS ALREADY GRADED A+
GUARANTEED SUCCESS
where is focal point of concave mirror?
r/2 from mirror along principle axis
newtonian reflector diagram
Cassegrain reflector diagram
What is resolving power?
- measure of how much detail we can see
- smallest angle of separation at which two points can be distinguished
- is limited to diffraction pattern produced by circular aperture
What is spherical aberration?
- mirrors don't have chromatic aberration
- more compact as shorter barrel
- Newtonian reflector cheap as only one complex shape
- Cassegrain reflector doesn't produce significant aberration, produces very sharp
image
Differences between radio and optical telescopes?
- Radio cheaper as wire mesh used not mirror
- radio must move across area to build up image
- Radio experience large interference
How needs considering for IR telescope?
- Is heat radiation so need to be heat-resistant (cooled by liquid Nitrogen)
- IR strongly absorbed by water so must be in dry places
- used for imaging cool objects that don't emit much light
, what needs considering for UV telescope?
- Hot stars with temps above 10,000K emit mostly UV
- useful for studying spectral lines
- UV absorbed by atmosphere so must be in space/high altitude
What needs considering for X-ray telescopes?
- x-ray penetrate materials so need special components
- glancing incidence mirrors can be made from ceramic or metal foils to reflect at
shallow angles
- Are useful for observing extremely high energy emissions (black holes)
- must be in space as atmosphere absorbs x-rays
what needs considering for gamma telescopes
- Similar to x-ray telescopes
- observe GRBs
diagram for refracting telescopes
magnification in terms of angles
What is chromatic aberration?
- Different wavelengths refracted by different amounts
- causes different focal lengths for different colours
- Causes images to distort
- Most prevalent at edges of lenses as most refracted
- Focal point of blue closer to lens
What are the disadvantages of refracting telescopes?
- Blurs image
- bubbles/impurities in glass absorb/scatter light preventing very feint objects being
seen
- expensive to build large lenses
AND CORRECT ANSWERS ALREADY GRADED A+
GUARANTEED SUCCESS
where is focal point of concave mirror?
r/2 from mirror along principle axis
newtonian reflector diagram
Cassegrain reflector diagram
What is resolving power?
- measure of how much detail we can see
- smallest angle of separation at which two points can be distinguished
- is limited to diffraction pattern produced by circular aperture
What is spherical aberration?
- mirrors don't have chromatic aberration
- more compact as shorter barrel
- Newtonian reflector cheap as only one complex shape
- Cassegrain reflector doesn't produce significant aberration, produces very sharp
image
Differences between radio and optical telescopes?
- Radio cheaper as wire mesh used not mirror
- radio must move across area to build up image
- Radio experience large interference
How needs considering for IR telescope?
- Is heat radiation so need to be heat-resistant (cooled by liquid Nitrogen)
- IR strongly absorbed by water so must be in dry places
- used for imaging cool objects that don't emit much light
, what needs considering for UV telescope?
- Hot stars with temps above 10,000K emit mostly UV
- useful for studying spectral lines
- UV absorbed by atmosphere so must be in space/high altitude
What needs considering for X-ray telescopes?
- x-ray penetrate materials so need special components
- glancing incidence mirrors can be made from ceramic or metal foils to reflect at
shallow angles
- Are useful for observing extremely high energy emissions (black holes)
- must be in space as atmosphere absorbs x-rays
what needs considering for gamma telescopes
- Similar to x-ray telescopes
- observe GRBs
diagram for refracting telescopes
magnification in terms of angles
What is chromatic aberration?
- Different wavelengths refracted by different amounts
- causes different focal lengths for different colours
- Causes images to distort
- Most prevalent at edges of lenses as most refracted
- Focal point of blue closer to lens
What are the disadvantages of refracting telescopes?
- Blurs image
- bubbles/impurities in glass absorb/scatter light preventing very feint objects being
seen
- expensive to build large lenses
