31.3 & 31.4

Question 1

Galaxy.

Answer 1

A galaxy is a large group of stars, dust, and gas held together by gravity.

Question 2

Milky Way

Answer 2

The Milky Way is the galaxy that contains our Solar System, with the name describing the galaxy’s appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye.

Question 3

Local group

Answer 3

The Local Group is the galaxy group that includes the Milky Way. It has a total diameter of roughly 3 megaparsecs, and a total mass of the order of 2×10¹² solar masses. The Milky Way is part of a larger group called the Local Group, which includes some fifty galaxies spread over a distance of about 10 million light years across. Most of the galaxies in the Milky Way are elliptical dwarf galaxies and irregular dwarf galaxies.

Question 4

Cosmology

Answer 4

The study of how the Universe started, hot continues to change, and what it is made of is called cosmology. In 1929, the astronomer Edwin Hubble made an important discovery about the universe. Hubble discovered that almost all galaxies are moving away from Earth at speeds that depend on their distance from Earth.

Question 5

Big Bang Theory

Answer 5

According to the Big Bang theory, all matter and energy in the universe were compressed into a single point, which began to expand outward about 13.7 billion years ago. This was not an explosion, but an expansion of space itself. Telescopes pick up evidence of this expansion, such as the galaxies that formed approximately 3.7 billion years after the Big Bang.

Question 6

Cosmic Background Radiation

Answer 6

The cosmic microwave background, in Big Bang cosmology, is electromagnetic radiation which is a remnant from an early stage of the universe, also known as “relic radiation”. The CMB is faint cosmic background radiation filling all space.

Question 7

Dark Matter

Answer 7

Dark matter is a form of matter thought to account for approximately 85% of the matter in the universe and about 27% of its total mass–energy density or about 2.241×10⁻²⁷ kg/m³.

Question 8

Dark Energy

Answer 8

is a hypothetical form of energy that exerts a negative, repulsive pressure, behaving like the opposite of gravity. Dark Energy makes up 72% of the total mass-energy density of the universe. The other dominant contributor is Dark Matter, and a small amount is due to atoms or baryonic matter.

Question 9

Section 4:

How long ago did the big bang occur?

Answer 9

13.7 billion years ago

Question 10

What is name of the effect that shows us changes in light waves?

Answer 10

The Doppler effect

Question 11

What is the universe made of?

Answer 11

Regular matter and dark matter