Physics - 6.4 Stars and Planets

• Planets

• Moons

• Dwarf planets

• Asteroids

• Comets

1. Mercury

2. Venus

3. Earth

4. Mars

5. Jupiter

6. Saturn

7. Uranus

8. Neptune

Between the orbits of Mars and Jupiter.

The closest four planets to the sun are rocky planets.

The four outer planets are gaseous.

Similar to a planet, but not big enough to be classified as one.

A moon is a body that orbits a planet. The amount varies from planet to planet, with some having no moons at all.

A small rocky object that orbits the sun. Most are found in the asteroid belt, between the orbits of Mars and Jupiter.

A lump of frozen gas, rock and dust that orbits the sun. They have a tail that always points away from the Sun due to the Sun’s radiation pressure.

Elliptical orbit.

A star and all the objects that orbit it e.g. our solar system.

A huge collection of billions of stars and their solar systems e.g. our solar system is a small part of the Milky Way galaxy.

Astronomical units and light years are used because distances in space are so large.

The mean distance from the Sun to Earth.

The distance that light will travel in a year.

3 × 10⁸ m/s

speed = distance/time

1. Stars are formed from clouds of gas, hydrogen, helium and dust.

2. Protostars form when gravity collects this cloud together and as it is compressed it heats up.

3. In main sequence stars, hydrogen fuses to form helium. This creates enough radiation and gas pressure to balance the gravitational forces.

1. The hydrogen fuel begins to run out and the star will begin to fuel helium into larger elements (e.g. carbon). This increases the gas radiation and pressure. The star will expand and become a Red Giant.

2. The helium fuel begins to run out and the reaction will slow. The gas and radiation pressure will decrease. This star will shrink and become a white dwarf.

1. The hydrogen fuel begins to run out and the star will begin to fuel helium into larger elements (e.g. iron). This increases the gas radiation and pressure. The star will expand and become a Supergiant.

2. The helium fuel begins to run out and the reaction will slow. the star becomes very unstable and will explode in a supernova throwing gases and dust out into space. The high pressure and temperature in a supernova will cause the fusion of the heaviest elements.

Will collapse, due to gravitational force as gas and radiation pressure will be small and shirk to form a neutron star or a black hole.

Failed stairs that never have enough mass in order to get hot enough to achieve nuclear fusion.

These are low mass stars that achieve nuclear fusion. They are not very bright and have long lifetimes. They are main sequence stars.

Where smaller nuclei fuse to form heavier nuclei. Apart from hydrogen (and some helium), all elements have been produced through fusion in stars.

In main sequence, hydrogen nuclei fuse to form helium nuclei. The forces acting on a star are balanced. Gravitational inward forces match outward gas and radiation pressure forces.

In supernova explosions. These elements, together with the elements produced through fusion inside the star, are expelled out to space. Stars and planets are formed from these elements.

Formed around 4.6 billion years ago from the collapse of a cloud of gas and dust, including elements ejected in supernovae.

Gravitational forces caused the matter to get closer together creating the Sun and the planets.

During formation, rocks gathered close to the Sun and formed the rocky planets, whilst gaseous substances gathered together at distances further away and formed the gas planets.

Gas giants.

The sun would shrink if the gravitational forces are larger than the forces released from nuclear fusions/ rate decreases (gas and radiation pressure from nuclear fusion). It would grow if there is a higher rate of nuclear fusion forces compared to gravitational forces.

It’s in its main sequence because gas pressure and radiation pressure (from nuclear fusion) are balanced with gravity. This means that it is stable.

The fusing together of two Hydrogen atoms to release helium; it is how our sun makes energy.