Ch 5 Telescopes Flashcards
True/False - Modern telescopes typically use a lens to concentrate light.
False. mod telescopes use mirrors.
what does a refracting telescope use to concentrate light?
lenses.
If microscopes make things appear larger, what do telescopes do?
Makes things appear closer (and smaller) and brighter
Do telescopes make objects look bigger?
No. makes objects brighter.
What is chromatic aberration?
what makes this problem worse?
light bends different amounts. therefore, diff colours have different focal points.
Thicker lenses
what do achromatic lenses do?
They match up the focal point for a pair of colours.
it helps, but doesn’t resolve the issue of chromatic abboration completely
Why do lenses suck?
Chromatic abboration
two surfaces to make nice
large lenses are really hard to make
more dispersion, absorbs infrared light
Why are mirrors better?
No chromatic abberation
only one surface to machine-> DOESN’T HAVE TO BE THICK
can reflect infrared
what are the three types of telescopes?
Newonian-. homegrown. common, cheap. eyepiece on side.
concave mirror, then flat mirror
Cassegrain- Eyepiece at the back. -> better for attaching equipment
concave, convex, eyepiece.
Nasmyth- the big boi. for proffessionals. Side eyepiece lined up with axel-> can attach big equipment.
3 mirrors.
How were images first recorded?
photographic plates
What do modern cameras use?
CCD (charge coupled device)
small plates of pixels that meaure the amount of light energy coming in. (RGB).
what do telescopes use to record iages?
Greyscale. then use filters to sperate out different colours of light.
t?f
astronomers can assign any colour they want to grey scale photos
true bitch
Could you see a nebula with your naked eye?
No. have a density 10-104 particles per cm^3
air has a density of 1019 particles per cm^3.
Are visualimages the only way to get info about the heavens?
No. duh. can use spectroscopy to find the elemental composition, temperature, movement, ect.
what is photometry?
A measurement of intensity of light
what is a pattern in light intensity
Decreases with an inverse square law. If we know the distance, we can use this to calculate a normalize magnitude.
What two measurements are used to classify stars?
Brightnes and temperature.
What filters are required to make images?
literally any that you want.
The twinkling of starlight is caused by what phenomenon?
Atmospheric turbulence
What is an issue with telescopes?
how can we combat this?
the light from far away bojects is super hard to capture bc brightness decreases with an inverse square law.
How to fight it? make the mirror bigger. or increase exposure time.
What are the problems with long exposure?
Need to use motor systems to track motion of the earth to focus on stars without creating lines.
limits the time we can use to study different parts of space.
by what proportion does exporsure time increase the total amunt of light gathered?
by what proportion does mirror size increase total amount of light garhered?
Total light collected = (exposure time)(radius of mirror^(squared))
2x expo= 2x more light
2x rad= 4x more light
What is another issue with telescopes? (sim to microscopes)
Resolving power-> angular resolution.
can sort of be fixed by increasng pixal count, but this reduces the amount of light gatherd by each pixal, bc overall, the light we’re collecting is still the same amount.
what is the largest telescope ever propsed?
what is the largest one today?
overwhelmingly large telescope
European extremely large telescope planned for 2022.
thirty meter telescope (hawaii) planned for 2022
Diffraction limited effects.
the mirrors radius acts like an apeture in a camera.
if two sources of lght are too close togetherr, then their light spread overlaps and they can’t be distinguished.
what is a limiting factor that cannot be corrected for by increasing the size of a mirror? (2)
how do we compensate?
Atmospheric Dispersion.
atmosphere is curved and acts like a lense-> dispersion
compensation-> taking images i seperate colours and manually aligning them
Also limitted by atmospheric blurring -> density fluctuations in the atmosphere
corrected by adaptive optics via sodium layer and a “guide” star
What characteristic of a telescope controls the amount of light
captured by the telescope?
diameter of apeture
what does radio astronomy help us with?
since it has a very high transimission through gases, it can tell us about large scale sructures. Radio Astronomy, we can see the effects of black holes hidden at the centre of very active regions of space
interferometry. what is it?
the combining of signals fro multiple radio telescopes to give us a better resolution.
WHAT are three radio ast discoveries?
planet formation in the HL tauri system (see red structure with clumping rings)
Gas jets from a supermassive black hole i HErcules A galaxy. (twin, giant purple jets)
bullet cluster showing location of gases post galaxy collision
Best wavelength to observe stars
infrared
