2020 p2

Question 1

what is the mirror called at the bottom of a cassegrain reflector

Answer 1

objectuve mirror

Question 2

what is the mirror called at the top of a cassegrain reflector

Answer 2

secondary mirror

Question 3

(observe transit of venus)

explain why ppl at south and north pole had more accurate results than people at +30 N and -40 S
(2 marks)

Answer 3

-ppl at poles are further apart
-so there was a larger difference in their measurements (of angle/time/position f transit)

Question 4

why were astronomers using earlier telescopes unable to discover red shift from other galaxies

Answer 4

-earlier telescopes had smaller apertures
-insufficient light grasp so galaxies too faint
-only really distant galaxies show red shift (outside of local group)

Question 5

why is light from andromeda galaxy and tringulum galaxy blue shifted?

Answer 5

-they’re in local group
-so they are moving towards us

Question 6

state 2 ways in which observing images with optical telescope will change near large city
(4 possible)

Answer 6

1. objects appear fainter
2. objects appear with distorted shape
3. objects appear in different position
4. colour of object is changed

Question 7

state the reason why the dish on radio telescope is made from metal

Answer 7

as metal reflects radiowaves

Question 8

state 2 ways resolution of telescope using aperture synthesis could be increased (4 possible)

Answer 8

-larger dishes
-more dishes in same area
-shorter operating wavelength
-increase baseline

Question 9

how to calculate distance to star using heliocentric parallax if parallax angle is 0.2
(ly)

Answer 9

1/0.2=5
so it is 4 parsecs away as 1 parsec has angle of 1 arc second and angle is 5x smaller so it is 5x further away
times this by conversion from parsec to ly
to get 16.3 ly

Question 10

why is it theorised that stars further from galaxies core should move slower

Answer 10

because as distance increases, gravitational attraction decreases (gravity is weaker near edge)
-so stars must move slower to stay in a stable orbit

Question 11

why are 21cm radio waves used to observe stars from different distances from core of galaxy

Answer 11

-light cannot penetrate areas towards core of galaxy
-due to dust/scattering

Question 12

when describing theme of graph shown by curve what do u say

Answer 12

-what is incr/decre relevant to what
whether gradient is increasing / decreasing

Question 13

why have we said stars move faster than predicted as distance from core increases

Answer 13

due to dark matter
-whose gravity attracts stars further from core
-provide s a£itional force to allow outer stars to rotate quickly enough to explain this

Question 14

define nebula

Answer 14

cloud of hydrogen gas in space

Question 15

explain why stars have difference in absolute and apparent magnitude

Answer 15

-apparent magnitude is measured from star’s actual distance
-absolute magnitude is measured from 10 parsecs from all stars