SP7 - Astronomy

Question 1

What is the geocentric model and who created it?

Answer 1

Ptolemy made the geocentric model. This is a model of the universe with the Earth at the centre and planets and the Sun orbiting it. In Ptolemy’s model, planets moved in small circles as they orbited the Earth.

Question 2

What is the heliocentric model and who created it?

Answer 2

Copernicus created the heliocentric model, in which the Sun is at the centre of the Solar system, and the planets orbit around it. This is the model we use today.

Question 3

What is in the solar system?

Answer 3

• 8 planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune)
• 5 dwarf planets (Pluto, Ceres, Makemake, Haumea, Eris)
• thousands of comets (small lump of dirty ice)
• millions of asteroids (small lump of rock)

Question 4

How have telescopes changed since their invention?

Answer 4

• they have got bigger
• they have got better magnification and resolution
• they can go into space
• they are often placed high on mountains
• can detect other waves not just light (e.g. IR telescopes)
• can take pictures
• can be attached to computers
• can be controlled robotically

Question 5

Why do we put telescopes into space?

Answer 5

• to observe the solar system
• to take pictures in space
• to stop interference from the atmosphere (dust, weather etc.)
• ‘see’ further
• detect wavelengths blocked out by the atmosphere
• can observe Earth
• better clarity as no distortion from atmosphere

Question 6

Describe the orbits of planets.

Answer 6

Planets orbit stars and have slightly elliptical orbits. The speed of the orbiting object therefore changes depending on the stage of the orbit it’s in. It has a closed loop orbit and it is a fixed plane. It is confined to a solar system.

Question 7

Describe the orbits of moons

Answer 7

Moons orbit planets. They have a circular orbit which doesn’t change speed. They have a closed loop and a fixed plane. Their orbits are confined to a solar system.

Question 8

Describe the orbits of comets.

Answer 8

Comets orbit stars with highly elliptical orbits. They therefore do change speed depending on what stage of the orbit they’re in (closer to the star = moves faster). They have a closed loop and a fixed plane but are not confined to a solar system.

Question 9

What is the lifecycle of an average star?

Answer 9

Nebula —> Protostar —> Main sequence star —> Red giant —> White dwarf —> Black dwarf

Question 10

What is the lifecycle of massive stars?

Answer 10

Nebula —> Protostar —> Massive main sequence star —> Red supergiant —> Supernova —> Neutron star OR Black hole

Question 11

What is a nebula?

Answer 11

A large cloud of dust and gas containing mainly hydrogen. When the mass of the hydrogen becomes large enough, the gravity will pull the hydrogen in on itself, which will make it contract and form a ball.

Question 12

What is a protostar?

Answer 12

A protostar is a ball of hydrogen. It continues to contract under its own gravity and as the hydrogen atoms accelerate, their kinetic energy increases. The extra kinetic energy raises the temperature of the hydrogen and the atoms collide with each other more frequently - fusion begins. Fusion turns hydrogen into helium and releases a huge amount of energy as heat and light. The protostar bursts into flame.

Question 13

What is a main sequence star?

Answer 13

A main sequence star is in a stable phase in which gravity pulling the star in balances pressure from hot gases pushing the star out. Therefore, the size of the star stays almost constant.

Question 14

What is a red giant?

Answer 14

Over time, the forces on a star become unbalanced. When the fusion reactions stop, the inward gravitational forces are stronger than the outward radiation pressure, causing the core of the star to collapse, the star swells and cools, turning red. This is a red giant.

Question 15

What is a white dwarf?

Answer 15

A red giant collapses to form a white dwarf that gradually cools over time. A white dwarf is a small, very dense star that is typically the size of a planet. When a white dwarf cools, it becomes a black dwarf.

Question 16

What is a red supergiant?

Answer 16

The forces become unbalanced when the hydrogen begins to run out. The star begins fusing helium and then increasingly heavy elements to maintain fusion. When iron is formed in the core, nuclear fusion stops and the star contracts under it’s gravity and a red supergiant is formed.

Question 17

What is a supernova?

Answer 17

Red supergiants quickly collapse, producing a giant explosion called a supernova. During the collapse and supernova explosion, element heavier than iron (such as uranium) are formed and ejected into space. The ejected material joins up with dust and hydrogen and begins the process of forming a new star.

Question 18

What is a neutron star?

Answer 18

High mass red supergiants form neutron stars. They are the cores of red supergiants that have collapsed. They are formed if the remaining core has a mass less than three or four times the mass of the sun.

Question 19

What is a black hole?

Answer 19

Black holes are the cores of red supergiants that have collapsed and they are formed if the remaining core has a mass of more than three or four times the mass of the sun. They are a point of mass with such high density that the force of gravity is so large that not even light can escape from its surface.

Question 20

What is red shift?

Answer 20

Waves emitted by something moving away from an observer have their wavelength increased and their frequency decreased compared to waves from a stationary object. The light emitted by objects moving away from the Earth is red-shifted (closer towards the red end of the spectrum). The further away an object is, the more its light is red shifted and the faster it moves.

Question 21

What is the Doppler effect?

Answer 21

The change in pitch of a sound heard when the source of sound is moving relative to the observer.

Question 22

What is the Big Bang theory?

Answer 22

The theory that the universe began from a tiny point with huge energy and has been expanding ever since. The Big Bang theory is the widely accepted theory today.

Question 23

What is the Steady State theory?

Answer 23

The theory that the universe is expanding but new matter is continually being created, so the universe will always appear the same.

Question 24

What is cosmic microwave background radiation (CMB)?

Answer 24

Microwave radiation received from all over the sky, originating at the Big Bang.

Question 25

What is the evidence for/against each theory?

Answer 25

Red-shift supports both theories as it shows an expanding universe, something both theories suggest.
CMB radiation only supports the Big Bang theory as the tiny point would have had a lot of energy and would have emitted lots of radiation which overtime had been stretched into microwave radiation. Steady State theory can’t explain the existence of CMB radiation.