Physics - 6.4 Stars and Planets

The solar system consists of the sun and the objects orbiting it. What does this include? (5)

• Planets

• Moons

• Dwarf planets

• Asteroids

• Comets

What is the order of the 8 planets?

1. Mercury

2. Venus

3. Earth

4. Mars

5. Jupiter

6. Saturn

7. Uranus

8. Neptune

Where does the asteroid belt lie?

Between the orbits of Mars and Jupiter.

How do you describe the closest four planets, and the four outer planets?

The closest four planets to the sun are rocky planets.

The four outer planets are gaseous.

What is a dwarf planet?

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

What is a moon?

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

What is an asteroid?

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

What is a comet?

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.

What kind of orbit does a comet have?

Elliptical orbit.

What is a planetary system?

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

What is a galaxy?

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.

What distances are used in space and why?

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

What is one astronomical unit (A.U)?

The mean distance from the Sun to Earth.

What is a light year?

The distance that light will travel in a year.

What is the speed of light?

3 × 10⁸ m/s

What’s the equation for speed?

speed = distance/time

3 Steps of how all stars begin.

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.

2 extra steps of low mass stars?

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.

What are the 2 next steps of large mass stars?

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.

What happens to the remaining matter after a supernova?

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.

What is a brown dwarf?

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

What is a red dwarf star?

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

What is nuclear fusion?

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

What happens in main sequence?

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.

Where are elements heavier than iron produced?

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.

When was the solar system formed and how?

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

How are the sun and planets made?

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

What happened during the formation of 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.

What are the four outer planets?

Gas giants.

In what case would the sun shrink and grow?

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.

How is there sun stable?

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.

Define ‘nuclear fusion’.

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