Space

What is the star in our solar system?

The sun

What galaxy do we live in?

The milky way

How can we describe moons?

As a natural satellite which orbits around a planet

Where are stars formed?

• From a cloud of dust and gas (nebula)

  ↳ hydrogen gas

Describe the stages of a star forming

1. Gravity causes the nebula to collapse

2. As dust particles moves faster, the temperature increases

3. This produces a protostar

4. When the temperature of the protostar gets high enough, hydrogen nuclei join to form helium (Nuclear fusion)

5. This forms a main-sequence star

Which 2 forces act on a star?

• Gravity → causes the star to collapse

• The force from nuclear fusion → causes the star to expand

What happens when the hydrogen in a star runs out?

The force of fusion energy is less than gravity so the star starts to collapse

What happens when a star collapses?

The temperature of the star increases

How is a red giant formed?

When a star collapses and starts to fuse helium nuclei together

How is a white dwarf formed?

When the fusion of helium in a star no longer occurs

Why does the white dwarf cool down?

Because it no longer carries out fusion

How is a black dwarf formed?

When a white dwarf stops releasing any energy

What happens to stars which are much bigger than our sun?

When they run out of hydrogen, they leave the main sequence stage and expand to form red super giants

What happens in a red super giant?

Helium nuclei fuse together to produce heavier elements

What is the limit of nuclear fusion for a main sequence star?

Any element heavier than iron

What happens when red super giants stop carrying out nuclear fusion?

The star explodes → supernova

How are elements heavier than iron formed?

In a supernova since the temperature is high enough to produce elements heavier than iron

What happens when a supernova explodes?

The elements within it are distributed throughout the universe

What can the explosion of a supernova form?

• Neutron star → neutrons densely packed together

• Black hole → Large gravity → light cannot escape

How does a planet stay in orbit?

Due to the force of gravity acting between the sun and Earth

What happens in a circular orbit to the velocity of an object?

The force of gravity leads to a change in velocity but not a change in speed

What happens when you increase the speed of a satellite? Why?

The radius of the orbit decreases

↳ Higher speed → requires a greater force of gravity

↳ Prevents the object from flying off into space

What happens to the wavelength of light as the distance between galaxies increases?

Increases

What does the red shift prove?

That galaxies are moving away from eachother

↳ Light waves are stretched → observed wavelengths have increased

How do we know which galaxies are moving faster away?

galaxies which are further away have a bigger red shift

How do we know that the galaxy is expanding?

Since distant galaxies are moving away faster than nearby galaxies

What can happen if a satellite moves too slowly?

Fall towards the Earth

↳ the gravitational attraction will be too strong

How can artificial satellites orbit?

• Polar orbit (over the north and south pole)

• Geostationary orbits → takes 24hrs to orbit the Earth

What does the Big Bang theory suggest?

The universe began from a very small region that was extremely hot and dense