Download Chapter 7 Review Answers

Chapter 7 Review Answers
1. Astronomy is the study of the universe and the objects in it.
2. (a) The moon is the celestial object that orbits our planet.
(b) The sun is the celestial object that our planet orbits.
3. Astronomers use astronomical units (AU) and light-years (ly) to measure
distances between celestial objects.
AU – distances in our solar system
ly – distances outside our solar system
4. (a) A galaxy is a collection of hundreds of billions of stars held together
by gravity.
(b) We live in the Milky Way galaxy.
5. The four types of galaxies are:
(i) spiral
(ii) barred spiral
(iii) elliptical
(iv) irregular
6. (a) This is an irregular galaxy.
(b) This is a spiral galaxy.
7. (a) Hubble discovered that the 46 galaxies he first studied were moving
away from each other.
(b) Lemaître had said that the universe was expanding; since Hubble saw
that galaxies where moving away from each other, this providing
evidence for the universe’s expansion.
8. This universe is thought to be about 13.7 billion years old, or about 15
billion years old.
9. Red light has a longer wavelength than the blue light.
10.(a) Sketch the spectral lines.
(b) A large red shift means that the light source (star) and observer (us)
are moving away from each other at very high speeds.
11.When the universe cooled and the wavelengths lengthened, scientists
wondered where that extra energy created by the hot, short wavelengths
at the beginning of the universe (BBT) went. That extra radiation should
be present throughout the universe if the BBT was to be true. We believe
now that the cosmic background radiation is that extra energy/radiation.
The CBR found fits with the predictions consistent with the BBT,
supporting the BBT.
13. It is unlikely that we will travel across even our own galaxy because it is
100,000 ly across, meaning that it would take 100,000 years travelling at
the speed of light to get across the galaxy.
14.All galaxies with a high rate of production of stars have lots of dust and
gas, which are the birth place of stars.
15.The night sky would be different in one of two ways (make sure you can
justify either or):
(i) There are more stars near the centre of a barred spiral galaxy such as
the Milky Way, therefore our night sky would be much brighter.
(ii) Since there is theoretically a black hole in the centre of every galaxy,
there should be one at the centre of the Milky Way. Black hole do not
allow anything (not even light) to escape, therefore our night sky would
be much darker.
16.Various reasons and justifications.
17.Various reasons, answers, and justifications.