space

Question 1

What conclusions can you draw from redshift?

Answer 1

• the galaxy is receding (moving away) so the universe is expanding
• an increase in the distance from earth means there is a greater velocity

Question 2

why can’t parallax lines be used beyond a certain uncertainty?

Answer 2

parallax angle becomes very small giving a large % uncertainty

Question 3

describe how a spectral line is produced by a hot gas

Answer 3

1)electron absorbs photon and moves to higher energy levels
2) electrons move to lower energy levels
3)energy is given out in the form of a photon
4)energy levels are discrete
5)energy of photon is equal to the difference between the energy levels E=hf1=hf2
6)there is a limited number of energy levels corresponding to the frequencies

Question 4

what is meant by redshift?

Answer 4

the increase in wavelength of a wave as the source moves away from the observer

Question 5

how did astronomers propose the existence of dark matter?

Answer 5

-observations of galaxies indicated they contained more mass than can be seen
-dark matter has mass but does not emit electromagnetic radiation
-existence of dark matter increases the average density of the universe

Question 6

why does the observable universe have a finite size?

Answer 6

-the universe started from a small point when the Big Bang occurred
-light reaching us could only travel a finite distance since the Big Bang 14bn years ago

Question 7

how did astronomers determine the velocity of a galaxy?

Answer 7

-measure wavelength of light
-compare with wavelength of source on earth
-use a line spectrum to determine redshift due to dopplers effect
-redshift formula

Question 8

why are scientists uncertain about the fate of the universe?

Answer 8

-critical density is unknown
-because of the existence of dark matter
-uncertainty in the value of Hubble’s constant

Question 9

How does critical density affect ultimate fate?

Answer 9

-if average density> critical density then universe is closed
-if av density> critical density universe keeps expanding
if av density =critical density the expansion rate decreases to zero

Question 10

how does a line spectrum determine the motion of stars?

Answer 10

-look for the corresponding pattern of lines at different places in the spectrum