Topic 7 - Astronomy

Question 1

What does the gravitational strength of a body depend on?

Answer 1

The mass of the body. The larger the mass of the body, the stronger its gravitational field strength.

Question 2

How does the weight of the object depend on the mass of a body and its gravitational strength?

Answer 2

For example, the Earth is bigger than the moon, therefore it has a greater gravitational strength which means that the object would weigh more on the Earth than on the moon.

Question 3

What are the 6 things in our solar system?

Answer 3

• Planets
• Dwarf Planets
• Moons
• Artificial satellites
• Asteroids
• Comets

Question 4

What are Asteroids?

Answer 4

Lumps of rock and material that orbit the Sun. They are usually found in the asteroid belt.

Question 5

What are Comets?

Answer 5

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

Question 6

Name the eight planets, closest to the Sun to outwards.

Answer 6

1. Mercury
2. Venus
3. Earth
4. Mars
5. Jupiter
6. Saturn
7. Uranus
8. Neptune

Question 7

How did ideas of the structure of the universe change over time?

Answer 7

From a geocentric model to a heliocentric model

Question 8

What is the geocentric model?

Answer 8

This theory suggested that the Sun, Moon, planets and stars all orbited Earth in perfect circles. It arose because people on Earth saw the Sun and Moon travelling across the sky in the same way every day and night and they didn’t have telescopes. It was an accepted model of the universe from the Ancient Greeks until the 1500s

Question 9

What is the heliocentric model?

Answer 9

It said that the Earth and all of the planets orbited the Sun in perfect circles. Galileo found that the moons of Jupiter never moved away from Jupiter. This showed not everything orbited the Earth proving the geocentric model wrong. However, the orbits of planets around the Sun are actually elliptical than circular and the Sun is not the centre of the Universe.

Question 10

Which objects in space have slightly ellipticals orbits?

4

Answer 10

• Planets + Dwarf planets
• Moons
• Artificial satellites

Question 11

Which object in space has a very elliptical orbits?

Answer 11

Comets

Question 12

How can the force of gravity lead changing velocity of a planet but unchanged speed?

Answer 12

Objects in circular orbits is constantly changing direction due to the Earth’s gravity causing a centripetal force. This means that velocity is changing as it is a vector quantity which means that it is a magnitude in a given direction. Therefore the satellite is accelerating due to its changing velocity.

Question 13

How must the radius change if the orbital speed changes for objects in a stable orbit?

Answer 13

If the speed changes, the radius of its orbit must do so too. Faster moving objects will move in a stable orbit with a smaller radius than slower moving ones to stop the object from falling into the planet as the gravitational attraction is stronger therefore a faster speed is needed to stop it falling into it.

Question 14

Where are stars initially formed?

Answer 14

From a cloud of dust and gas called a Nebula

Question 15

How are Protostars formed from a nebula?

Answer 15

The force of gravity pulls the dust and gas together to form a protostar. The temperature rises as the star gets denser and more particles collide with each other. When the temperature gets high enough, hydrogen nuclei undergo nuclear fusion to form helium nuclei. This gives out huge amounts of energy, which keeps the core of the star hot. A star is born.

Question 16

Describe the life of a main sequence star

Answer 16

The star enters a long stable period. During this period, the outward pressure caused by thermal expansion (the energy produced by nuclear fusion tries to expand the star) balances the force of gravity pulling everything inwards. It typically lasts several billion years. The heavier the star, the shorter its time on the main sequence. (The Sun is in the middle of this stable period.)

Question 17

How does a main sequence star form a red giant or a red supergiant?

Answer 17

Eventually the hydrogen in the core begins to run out and the force due to gravity is larger than the pressure of thermal expansion. The star is compressed, until it is dense and hot enough that the energy (and so pressure) created makes the outer layers of the star expand. The star becomes a red giant (if it is a small star) or a red supergiant (if it is a larger star). It becomes red because the surface cools.

Question 18

How does a red giant become a white dwarf?

Answer 18

A small-to-medium-sized star like the Sun then becomes unstable and ejects its outer layer of dust and gas. This leaves behind a hot, dense solid core; a white dwarf.

Question 19

How does a red supergiant become a supernova?

Answer 19

Big stars, however, start to glow brightly again as they undergo more fusion to make heavier elements. They expand and contract several times, as the balance shifts between gravity and thermal expansion. Eventually, they explode in a supernova.

Question 20

How does a supernova become a neutron star?

Answer 20

The exploding supernova throws the outer layers of dust and gas into space, leaving a very dense core called a neutron star.

Question 21

How does a supernova become a black hole?

Answer 21

If the star is massive enough, it will collapse and become a black hole - a super dense point in space that not even light can escape from.

Question 22

Describe the use of telescopes

Answer 22

Telescopes help you to see distant objects clearly. There are loads of different kinds and they all work in different ways. The one you’re most likely to have seen is an optical telescope ones that detect visible light. Telescopes use refraction and reflection to allow you to see distant objects.

Question 23

How do you achieve a higher quality image when using a telescope?

Answer 23

1) Increase the aperture of the telescope. This is the diameter of the objective lens - the big lens at the end of the telescope where light from the distant object enters the telescope.
2) Use a higher quality objective lens.

Question 24

Why is it hard to look in to space using a telescope from Earth?

Answer 24

If you’re trying to detect light, Earth’s atmosphere gets in the way - it absorbs a lot of the light coming from space before it can reach us. To observe the frequencies absorbed, you have to go above the atmosphere. Then there’s pollution. Light pollution (light thrown up into the sky from street lamps, etc.) makes it hard to pick out dim objects. And air pollution can reflect and absorb light coming from space.

Question 25

How can you achieve the best possible image through a telescope from Earth?

Answer 25

So to get the best view possible from Earth, a telescope should be on top of a mountain (where there’s less atmosphere above it), and in a dark place away from cities (e.g. on Hawaii). dark place To avoid the problem of the atmosphere completely, you can put telescope in space.

Question 26

How does the life cycle of stars depend in size?

Answer 26

Stars that are far greater in mass than the Sun follow this path: red super giant star → supernova → neutron star, or a black hole (depending on size). Stars that are about the same mass as the Sun follow this path: red giant star → white dwarf star → black dwarf star.

Question 27

Describe the Steady State Theory

Answer 27

The ‘Steady State’ theory says that the Universe has always existed as it is now, and it always will do. It’s based on the idea that the Universe appears pretty much the same everywhere. As the Universe expands, new matter is constantly being created. This means that the density of the Universe is always roughly the same. In this theory there is no beginning or end to the Universe.

Question 28

Describe the Big Bang theory

Answer 28

Initially, all the matter in the Universe occupied a very small space. This tiny space was very dense and so was very hot. Then it ‘exploded’ - space started expanding and the expansion is still going on. This theory gives a finite age for the Universe (around 13.8 billion years). Currently, the Big Bang is the accepted theory of how the universe began as there is more evidence for the Big Bang theory.

Question 29

What happens when a wave source moves past an observer?

Answer 29

There will be a change in the observed frequency and wavelength. The frequency and wavelength increases as the wave source travels towards the observer and a decrease as it travels away.

Question 30

What is red-shift? (4)

Answer 30

Astronomers can observe light from distant galaxies. When they do this, they see it is different to the light from the Sun. The dark lines in the spectra from distant galaxies show an increase in wavelength and a corresponding decrease in frequency. The lines are moved or shifted towards the red end of the spectrum. This effect is called red shift.

Question 31

How does red-shift suggest that the Universe is expanding?

Answer 31

More distant galaxies are more red-shifted so they are moving away faster than closer galaxies. This shows us that the galaxies are moving away from each other as they are moving away at different rates therefore it proves that the Universe is expanding.

Question 32

What is CMB radiation?

Answer 32

Cosmic Microwave Background Radiation. Scientists have detected low frequency electromagnetic radiation coming from all parts of the Universe.

Question 33

How does CMB radiation prove the Big Bang Theory only?

Answer 33

As it shows that the Universe had a beginning. According to the Big Bang Theory, the CMB radiation is the leftover energy of the initial explosion. This is why the Big Bang Theory is currently our accepted model for the start of the Universe.

Question 34

How does red-shift prove both models?

Answer 34

In both models, objects are moving away from the observer as the Universe expands, so red-shift would be observed for either model.