Ch 5 Telescopes

Question 1

True/False - Modern telescopes typically use a lens to concentrate light.

Answer 1

False. mod telescopes use mirrors.

Question 2

what does a refracting telescope use to concentrate light?

Answer 2

lenses.

Question 3

If microscopes make things appear larger, what do telescopes do?

Answer 3

Makes things appear closer (and smaller) and brighter

Question 4

Do telescopes make objects look bigger?

Answer 4

No. makes objects brighter.

Question 5

What is chromatic aberration?

what makes this problem worse?

Answer 5

light bends different amounts. therefore, diff colours have different focal points.
Thicker lenses

Question 6

what do achromatic lenses do?

Answer 6

They match up the focal point for a pair of colours.

it helps, but doesn’t resolve the issue of chromatic abboration completely

Question 7

Why do lenses suck?

Answer 7

Chromatic abboration
two surfaces to make nice
large lenses are really hard to make
more dispersion, absorbs infrared light

Question 8

Why are mirrors better?

Answer 8

No chromatic abberation
only one surface to machine-> DOESN’T HAVE TO BE THICK
can reflect infrared

Question 9

what are the three types of telescopes?

Answer 9

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.

Question 10

How were images first recorded?

Answer 10

photographic plates

Question 11

What do modern cameras use?

Answer 11

CCD (charge coupled device)

small plates of pixels that meaure the amount of light energy coming in. (RGB).

Question 12

what do telescopes use to record iages?

Answer 12

Greyscale. then use filters to sperate out different colours of light.

Question 13

t?f

astronomers can assign any colour they want to grey scale photos

Answer 13

true bitch

Question 14

Could you see a nebula with your naked eye?

Answer 14

No. have a density 10-104 particles per cm^3

air has a density of 1019 particles per cm^3.

Question 15

Are visualimages the only way to get info about the heavens?

Answer 15

No. duh. can use spectroscopy to find the elemental composition, temperature, movement, ect.

Question 16

what is photometry?

Answer 16

A measurement of intensity of light

Question 17

what is a pattern in light intensity

Answer 17

Decreases with an inverse square law. If we know the distance, we can use this to calculate a normalize magnitude.

Question 18

What two measurements are used to classify stars?

Answer 18

Brightnes and temperature.

Question 19

What filters are required to make images?

Answer 19

literally any that you want.

Question 20

The twinkling of starlight is caused by what phenomenon?

Answer 20

Atmospheric turbulence

Question 21

What is an issue with telescopes?

how can we combat this?

Answer 21

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.

Question 22

What are the problems with long exposure?

Answer 22

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.

Question 23

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?

Answer 23

Total light collected = (exposure time)(radius of mirror^(squared))

2x expo= 2x more light
2x rad= 4x more light

Question 24

What is another issue with telescopes? (sim to microscopes)

Answer 24

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.

Question 25

what is the largest telescope ever propsed?

what is the largest one today?

Answer 25

overwhelmingly large telescope
European extremely large telescope planned for 2022.
thirty meter telescope (hawaii) planned for 2022

Question 26

Diffraction limited effects.

Answer 26

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.

Question 27

what is a limiting factor that cannot be corrected for by increasing the size of a mirror? (2)

how do we compensate?

Answer 27

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

Question 28

What characteristic of a telescope controls the amount of light
captured by the telescope?

Answer 28

diameter of apeture

Question 29

what does radio astronomy help us with?

Answer 29

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

Question 30

interferometry. what is it?

Answer 30

the combining of signals fro multiple radio telescopes to give us a better resolution.

Question 31

WHAT are three radio ast discoveries?

Answer 31

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

Question 32

Best wavelength to observe stars

Answer 32

infrared