Question

1. Cepheid variables are significant because a) their luminosity can be determined from knowledge of their period b) their luminosity can be determined from a single measurement of their flux c) their luminosity can be determined from knowledge of their surface temperature d) they are all the same distance away from 2. Equilibrium in a star is produced by a balance between ___ and ____. a) gravitational forces and radiation outward, gas pressure inwards b) gravitational forces and gas pressure inwards, radiation outward c) gravitational forces inwards, radiation and gas pressure outward 3. Galactic rotation curves in the vicinity of spiral arms are typically a) decreasing b) flat c) increasing 4. In the determination of the Hubble constant how are the most accurate distances to nearly galaxies determined a) using the average brightness of HII regions b) using the maximum brightness of novae and supernovae c) using the period- luminosity relation of cepheid variable stars d) using spectroscopic parallaxes 5. Suppose our universe has positive curvature. Which of the following statements would be FALSE? a) the universe has a center b) the universe will eventually begin to contract c) the universe has a finite volume d) the universe has no boundary

Answer 1

1.Cepheid variables are significant because their luminosity is proportional to their period of rotation.

Hence the answer is (a).

2.Equilibrium star is produced by a balance between gravitational forces inwards and radiation and gas pressure outwards.

This is from equilibrium of stars.

Hence the correct option is (c)

3.Galactic rotation curves in the vicinity of spiral arms are typically b) flat.

.Hopefully it is due to the presence of dark matter.

4.In the determination of hubbles constant the most accurate distances to nearby galaxies are determined by b) using the maximum brightness of novae and supernovae.

5.If universe has positive curvature, there is more than enough mass to stop the present expansion of the universe. The universe in this case is not infinite, but it has no end (just as the area on the surface of a sphere is not infinite but there is no point on the sphere that could be called the "end"). The expansion will eventually stop and turn into a contraction. Thus, at some point in the future the galaxies will stop receding from each other and begin approaching each other as the universe collapses on itself. This is called a closed universe.

Hence the correct option is (b).