Astronomy

Question 1

What is a planet?

Answer 1

A large object that orbits a star

Question 2

What are the planets in our Solar System, in order of distance from the Sun?

Answer 2

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

Question 3

What are dwarf planets?

Answer 3

Planet-like objects that aren’t big enough to be classified as planets

Question 4

What are moons?

Answer 4

Natural objects that orbit planets with almost circular orbits

Question 5

What is a satellite?

Answer 5

An object that orbits a second, more massive object

Question 6

What are asteroids?

Answer 6

Lumps of rock and metals that orbit the Sun, usually found in the asteroid belt

Question 7

What are comets?

Answer 7

Lumps of ice and dust that orbit the Sun. Their orbits are usually highly elliptical - some travel from near the Sun to the outskirts of the Solar System.

Question 8

What causes orbits?

Answer 8

Gravity causes a centripetal force, acting towards the centre of the orbit. This force would cause the object to fall towards what it was orbiting, but as it is already moving, it just causes it to change direction. It is accelerating towards what it’s orbiting but the instantaneous velocity, at a right angle to acceleration, keeps it travelling in a circle.

Question 9

What does gravity depend on?

Answer 9

The mass of the body creating the field - the larger the mass, the stronger the force
Distance - the closer you get, the stronger the force

Question 10

How and why does speed vary with orbit distance?

Answer 10

The closer the orbit, the faster the object moves. This is because the centripetal force from gravity is larger, so the instantaneous velocity also needs to be larger to balance it.

Question 11

How has the model for the Solar System changed over time?

Answer 11

Ancient Greeks - 1500s: Geocentric model
1500s - present: Heliocentric model
Later we realised planet orbits are elliptical rather than circular and the Sun is not at the centre of the universe

Question 12

What is the geocentric model?

Answer 12

The theory that said the Sun, Moon, planets and stars all orbited the Earth in perfect circles. People had no telescopes and saw everything travelling across the sky in the same way every day and night.

Question 13

What is the heliocentric model?

Answer 13

The theory that the Earth and planets all orbited the Sun in perfect circles

Question 14

What was Galileo’s evidence for the heliocentric model?

Answer 14

He looked at Jupiter with a telescope and noticed some ‘stars’ in a line near the planet (Jupiter’s moons). When he looked again, he found that they never moved away from Jupiter and seemed to be carried along with it. This showed that not everything orbited Earth, so that the geocentric model was wrong.

Question 15

What is the Steady State theory?

Answer 15

The theory that the Universe has always existed as it is now, and it always will do. The Universe appears pretty much the same everywhere. As it expands, new matter is constantly being created, so the Universe’s density is always roughly the same. There is no beginning or end to the Universe.

Question 16

What is the Big Bang theory?

Answer 16

The theory that initially all the matter in the Universe occupied a very small space, which was very hot and dense. This then ‘exploded’ - space started expanding, and this expansion is still going on. There is a finite age for the universe: ~13.7 billion years.

Question 17

What is the Doppler effect?

Answer 17

When an object is travelling towards you wavelengths of sound are bunched together, so the frequency of sound seems higher. When an object is travelling away from you wavelengths of sound are spread further apart, so the frequency of sound seems lower.

Question 18

What is red-shift and what does it suggest?

Answer 18

Absorption spectra from distant galaxies have the same patterns as ones from elements on Earth, but at slightly lower frequencies, with more light coming with increased wavelengths. The patterns are shifted towards the red end of the spectrum: red-shift. This shows that they are moving away from us, as with the Doppler effect. More distant galaxies have greater red-shifts, so are moving away faster. This suggests that the Universe is expanding.

Question 19

What is CMB radiation?

Answer 19

Cosmic microwave background radiation - low frequency electromagnetic radiation coming from all parts of the Universe, mostly in the microwave part of the EM spectrum.

Question 20

Why is the Big Bang theory the currently accepted model?

Answer 20

Red-shift supports both models, but CMB radiation shows the Universe had a beginning so only supports the Big Bang theory. In the theory it is the leftover energy of the initial explosion.

Question 21

What is the life cycle of a star about the size of the Sun?

Answer 21

Nebula
Protostar
Main sequence star
Red giant
White dwarf

Question 22

What is the life cycle of a star much larger than the Sun?

Answer 22

Nebula
Protostar
Main sequence star
Red supergiant
Supernova
Neutron star or black hole

Question 23

What is a nebula?

Answer 23

A cloud of dust and gas that will become a star

Question 24

What is a protostar?

Answer 24

A cloud of dust and gas pulled together by gravity. As it gets denser, the temperature rises until it is hot enough for hydrogen to perform fusion, creating a star.

Question 25

What is a main sequence star?

Answer 25

A long, stable period in a star’s lifespan where hydrogen undergoes fusion. It typically lasts several billion years; the heavier the star, the shorter this period.

Question 26

What is a red giant or supergiant?

Answer 26

When hydrogen in the core begins to run out, the star is compressed by gravity as thermal expansion decreases. When it is dense and hot enough that the energy created makes the outer layers of the star expand, it becomes a red giant or supergiant depending on the size. The surface cools so it turns red.

Question 27

What is a white dwarf?

Answer 27

A hot, dense solid core created when a small to medium sized star (e.g. the Sun) becomes unstable and ejects its outer layer of dust and gas.

Question 28

What is a supernova?

Answer 28

The explosion of a red supergiant. It occurs after it begins to undergo more fusion to make heavier elements. They expand and contract several times as the balance shifts between gravity and thermal expansion before the explosion.

Question 29

What is a neutron star?

Answer 29

A very dense core created after a smaller red supergiant’s supernova, when its outer layers of dust and gas have been ejected.

Question 30

What is a black hole?

Answer 30

An extremely dense point in space that not even light can escape from, created after a larger red supergiant’s supernova, when its outer layers of dust and gas have been ejected and it collapses.

Question 31

How can you improve the quality of an image produced by a telescope without moving it?

Answer 31

Increase its aperture, the diameter of the objective lens

Use a higher quality objective lens

Question 32

Why do telescopes on Earth, especially in urban areas, get worse images than those in space?

Answer 32

The atmosphere gets in the way, absorbing lots pf light coming from space
Light pollution (light from objects on Earth in the atmosphere) makes it hard to pick out dim objects
Air pollution can reflect and absorb light coming from space

Question 33

How have telescopes improved over time?

Answer 33

1500s: optical telescopes, using visible light to see close objects
1940s: telescopes for all parts of the EM spectrum e.g. X-ray telescopes for high-temperature events and radio telescopes, which discovered CMB radiation
Telescopes with greater resolution and magnification
Use of computers to analyse and store data