astrophysics

What is a universe?

A large collection of billions of galaxies

What is a galaxy?

A large collection of billions of stars

What is the name of our galaxy

Milky Way

What does our solar system consist of?

- Sun

- Planets

- Comets and asteroids

- Moons

What does the size of the gravitational force depend on?

Masses of objects

- Greater mass = greater gravitational force

Distance between the objects

- Close object = greater gravitational force

Why do larger planets exert larger gravitational forces?

Larger masses

Why does our weight vary on Earth and on the Moon?

gravitational field strength is weaker on the moon

weight = mass x gravitational field strength

mass is unchanged

Explain why gravitational force keeps objects in orbit

- Gravitational force attracts objects together

- Do not crash into each other as all objects are moving

- Gravitational force keeps objects moving in curved paths called orbits

- Moons orbit planets

- Planets orbit the Sun

- Artificial satellites orbit the Earth

- Comets orbit the Sun

What is a satellite?

An object which orbits a planet

What is a comet?

Ball of ice and dust that orbits the sun

Compare the orbits of comets, planets and moons

- Comets have very elliptical orbits, with a star at one focus

- Planets have circular/slightly elliptical orbits around a star

- Moons have circular orbits around a planet

State the differences between an artificial satellite's orbit and a planet's orbit

Satellite orbits a planet, planet orbits a star

Orbital radius of a planet is greater than satellite

Where is a comet's kinetic energy greatest?

When it is nearest the star

Gravitational force is strongest

Suggest why planets nearer to a star take less time to orbit the star

Smaller orbital path for close planets

Larger speed for close planets

State the similarities between an artificial satellite's orbit and a moon's orbit

Both orbit a plaent

Both have same shape of orbit

What is a day?

Time taken for Earth to rotate once on its axis

What is a month?

Time taken for the Moon to orbit the Earth once

What is a year?

Time taken for the Earth to complete one orbit of the Sun

What is the relationship between orbital speed, orbital radius and time period?

Orbital speed = 2 x pi x orbital radius / time period

Explain why the distance between planets is not constant

- Planets move at different speeds

- Planets have orbits with different radii

- Closest together = both on same side of the Sun

- Furthest away = on opposite sides of the Sun

What can the colour of a star tell you?

Its temperature

What do the following colours tell you about a star's temperature?

- Blue = very hot star

- Yellow = medium hot star

- Red = cooler star

What is a nebula?

- A cloud of dust and gas in outer space

- Gets pulled together by gravitational forces

Outline the life cycle of a small star

- Nebula → Protostar → Main sequence → Red giant → White dwarf → Black dwarf

Describe the life cycle of a small star

- Nebula - cloud of dust and gas in outer space pulled together by gravitational force

- Protostar - kinetic energy store of atoms increases, increases temperature

- Main sequence - forces are balanced and nuclear fusion of hydrogen occurs

- Huge amounts of thermal and light energy released

- Red giant - forms when hydrogen fuel runs out → heavier elements form by fusion

- White dwarf - nuclear reactions stop → gravity causes star to contract

- Black dwarf - star continues to cool and contract

Outline the life cycle of a large star

- Nebula → Protostar → Main sequence → Red supergiant → Supernova → Neutron star →

Black hole (if very large star)

Describe the life cycle of a large star

- Nebula - cloud of dust and gas in outer space pulled together by gravitational force

- Protostar - kinetic energy store of atoms increases, increases temperature

- Main sequence - forces are balanced and nuclear fusion of hydrogen occurs

- Huge amounts of thermal and light energy released

- Red supergiant - hydrogen fuel in core runs out → core contracts → layer around core heats up

and nuclear fusion restarts → star expands

- Supernova - nuclear reactions continue, getting hotter and expanding until star explodes

- Neutron star - left behind after supernova

- Black hole - formed from supernova of very large stars → light can't escape