Chapter 20 - Cosmology

Question 1

Define one Astronomical Unit (AU).

Answer 1

The mean distance from the Earth to the Sun.

Question 2

Define one light year.

Answer 2

The distance light travels in one year.

Question 3

What is an arcsecond?

Answer 3

1°/60²

Question 4

What is stellar parallax?

Answer 4

A technique to determine the distance to relatively close stars by comparing their motion to that of distant stars.

Question 5

How is stellar parallax measured?

Answer 5

Using the angle of parallax. The greater the angle, the closer the star.

Question 6

What is a parsec?

Answer 6

A star is one parsec away from Earth if the angle of parallax is one arcsecond.

Question 7

Describe the relationship between the angle of parallax and the distance to a star.

Answer 7

Inversely proportional.

Question 8

Explain the Doppler effect.

Answer 8

When a wave source moves, the waves ahead of it will be squished and the waves behind will be stretched.

Question 9

Describe the Doppler shift of a galaxy moving away from ours.

Answer 9

The EM radiation will be stretched, giving it a greater wavelength and shifting light to the red end of the spectrum.

Question 10

What is Hubble’s Law?

Answer 10

The recessional speed of a galaxy is almost directly proportional to its distance from Earth.

Question 11

What does Hubble’s Law prove?

Answer 11

The universe is expanding.

Question 12

Outline the big bang theory.

Answer 12

The universe started as a very hot and dense point and has been expanding ever since.

Question 13

How does the existence of Cosmic Microwave Background Radiation support the big bang theory?

Answer 13

Initially, the universe was saturated with gamma photons, whose wavelengths have been stretched by the expansion of the universe to microwave photons.

Question 14

How can we determine the age of the universe?

Answer 14

t = ⅟H₀

Question 15

Briefly outline the evolution of the universe.

Answer 15

-Rapid expansion from hot, dense point.
-Quarks, antiquarks & leptons are formed.
-Matter-antimatter symmetry is broken.
-Quarks join to make protons & neutrons.
-Fusion to helium nuclei.
-Electrons join nuclei to form atoms.

Question 16

Where does the idea of dark matter come from?

Answer 16

Galaxies are moving faster than they should given their mass, so extra mass that we can’t see has been suggested to allow Newton’s laws to hold.

Question 17

Where does the idea of dark energy come from?

Answer 17

The expansion of the universe is accelerating, despite the pull of gravity. Dark energy was suggested as a type of energy that fills the whole of space that pushes things apart.