Formation And Explanation

Question 1

How many stars does a galaxy typically contain?

Answer 1

One billion stars

Question 2

How many galaxies is the Universe thought to contain?

Answer 2

Over one hundred billion

Question 3

What are stars mainly made of?

Answer 3

Hydrogen and helium

Question 4

What does hydrogen exist as in a star’s centre?

Answer 4

Nuclei (not atoms or molecules).

Question 5

How does nuclear fusion happen in stars?

Answer 5

Hydrogen nuclei are positive so normally repel each other.
The temperature of a star’s centre is more than 15 million degrees.
This means the nuclei move very fast.
They collide to form a heavier nucleus: helium.
Vast quantities of energy (electromagnetic radiation) are released.

Question 6

How are stars formed?

Answer 6

Clouds of hydrogen and dust are called stellar nebulae.
The particles coalesce due to gravity.
The clouds become more and more dense.
Hydrogen particles begin to spiral inwards and temperature rises to about 15 million degrees.
Nuclear fusion begins and the star is born.

Question 7

What main force forms stars, galaxies and planets?

Answer 7

Gravity.

Question 8

How are planets formed?

Answer 8

As a star burns, it pulls dust particles closer to it.
They are pulled more strongly as they have more mass.
They coalesce to form the inner rocky planets (Mercury, Venus, Earth and Mars).
This process is called accretion.
Gas particles have less mass so they are left further out.
They coalesce to form the gas giants (Jupiter, Saturn, Uranus and Neptune).

Question 9

What are Pluto and Ceres believed to actually be, as opposed to planets?

Answer 9

Captured asteroids.

Question 10

Why do planets orbit the Sun in the same plane and direction?

Answer 10

The gas and dust clouds originally spiralled in the same direction.

Question 11

What does a star do to planets formed around it?

Answer 11

Catch them in its orbit. This is due to gravity.

Question 12

Why does the Sun remain the same size?

Answer 12

The inward gravitational force equals the outward force of radiation pressure (which is due to thermonuclear explosions).

Question 13

What model is mostly accepted that explains the origin of the Universe?

Answer 13

The Big Bang Theory

Question 14

When did the Big Bang occur?

Answer 14

About 13.8 billion years ago.

Question 15

From what did the Big Bang occur?

Answer 15

A tiny point called a singularity.

Question 16

Explain the formation of the Universe.

Answer 16

An explosion occurred 13.8 billion years ago from a tiny point called a singularity.
The universe rapidly expanded and formed high-energy radiation like quarks.
As it got bigger, it cooled down and the quarks came together to form protons and neutrons.
As the universe cooled even more, electrons combined with nuclei to form atoms of hydrogen.

Question 17

What is the doppler effect?

Answer 17

Where as a source of waves moves, the wavelength in front of the source decreases and the wavelength behind the source increases.
This is why sirens have a lower pitch when they are moving away.

Question 18

Each colour in the spectrum has what associated with it?

Answer 18

A certain wavelength.

Question 19

What effect is red-shift associated with?

Answer 19

The doppler effect.

Question 20

What is red-shift?

Answer 20

Where the light we observe from a source is shifted towards the red end of the spectrum, as it is moving away from us and so has a longer wavelength.

Question 21

What does red-shift from distant galaxies suggest?

Answer 21

The galaxies are moving away from us. Therefore, it suggests the universe is expanding. It supports the Big Bang Theory.

Question 22

What is Cosmic Microwave Background Radiation (CMBR)?

Answer 22

Microwaves coming from various parts of the universe believed to be the remnant of the Big Bang.
It is further evidence of the Big Bang, as this is the only theory that can explain CMBR.

Question 23

What evidence approves the Big Bang? [2]

Answer 23

1. Red-shift

2. Cosmic Microwave Background Radiation.

Question 24

What three events may happen to the Universe in the future?

Answer 24

1. Big Freeze
2. Big Crunch
3. Big Bounce

Question 25

What is the Big Freeze?

Answer 25

If there is too little mass in the Universe, it will expand forever, becoming colder and colder and ending in a Big Freeze.

Question 26

What is the Big Crunch?

Answer 26

If there is enough mass in the Universe, gravity will cause expansion to stop and the galaxies will contract inwards and collide.

Question 27

What is the Big Bounce?

Answer 27

If gravity is big enough, the Universe may contract entirely back to a singularity. Then, another Big Bang would occur.

Question 28

How do we detect planets outside our Solar System?

Answer 28

We observe light coming from stars, watching for a transition. This is a small reduction in light reaching us when an orbiting planet passes between the star and us.

Question 29

How do we know that stars are mainly composed of hydrogen and helium?

Answer 29

We look at light we receive from the Sun.

Question 30

What evidence supports the idea that the Solar System was formed from a nebula?

Answer 30

Planets orbit the Sun in the same plane and direction.