SP7 Astronomy

Question 1

What objects does the Solar System include?

Answer 1

1. One star - the sun
2. Planets
3. Dwarf planets
4. Moons
5. Artificial satellites
6. Asteroids
7. Comets

Question 2

What are planets?

Answer 2

Large objects that orbit a star (in this case, the sun)

Question 3

What are the 8 planets in our Solar System, in order?

Answer 3

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

Question 4

What are dwarf planets?

Answer 4

Planet-like objects that aren’t big enough to be planets e.g. Pluto

Question 5

What are moons?

Answer 5

Natural satellites that orbit planets with usually almost circular orbits.

Question 6

What are artificial satellites?

Answer 6

Satellites that are man-made that usually orbit the Earth in fairly circular orbits

Question 7

What are asteroids?

Answer 7

Lumps of rock and metals that orbit the Sun. They’re usually found in asteroid belts.

Question 8

What are comets?

Answer 8

Lumps of ice and dust that orbit the Sun. Their orbits are usually highly elliptical (a very stretched out circle). Some travel from near to the Sun to the outskirts of the Solar System.

Question 9

What model of the Solar System did Ptolemy suggest and what did it state?

Answer 9

The Geocentric Model:
The Earth was the centre of the Solar System.
Planets orbited around the Earth and moved in their own small circles.

Question 10

What model of the Solar System did Copernicus suggest and what did it state?
How did Galileo’s discovery support this idea?

What have new developments proved about this model?

Answer 10

The Heliocentric Model:
The Sun at the centre of the Solar System.
Planets orbit the Sun in perfect circles.
Galileo:
Jupiter’s moons never moved away from Jupiter.
This showed that not everything was in orbit around the Earth - proving the geocentric model was wrong.
Current model:
Planets in our Solar System orbit the Sun, but these orbits are elliptical rather than circular.

Question 11

What are orbits?

Answer 11

The paths objects take as they move around each other in space

Question 12

How does gravity provide the force that creates orbits?

Answer 12

1. Planets move around the Sun in almost circular orbits
2. Objects in circular orbits moving at a constant speed constantly accelerate because their velocity is changing
3. The force causing the acceleration is centripetal force
4. The object keeps accelerating towards what it’s orbiting but the instantaneous velocity keeps it travelling in a circle
5. This is because of the gravitational pull between the planet and Sun / planet and satellite.

Question 13

What does gravitational field strength depend on?

Answer 13

1. Mass of the body creating the field:
   Larger mass = Stronger gravitational field
2. Distance
   Closer to star/planet = Stronger gravitational force
   In circular motion, stronger force = larger instantaneous velocity needed to balance it. So the closer you get to the star/planet, the faster you need to go to remain in orbit.
   For an object in a stable orbit: if change speed = radius of orbit must change to. Faster moving objects wll move in a stable orbit with a smaller radius than slower moving ones.

Question 14

What are the steps of the life cycle of a star like our sun?

Answer 14

1. Nebula
2. Protostar
3. Main sequence star
4. Red giant
5. White dwarf

Question 15

Explain the steps of the life cycle of a star like our sun.

Answer 15

1. Nebula:
   Stars intially form from a cloud of dust and gas, called a nebula.
2. Protostar:
   The force of gravity pulls the dust and gas together to form a protostar. The temperature rises as the star gets denser. 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 hot.
3. Main sequence star:
   This is the star’s 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.
4. Red giant:
   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 core of the star is compressed, until it is dense and hot enough that the energy released (and so pressure created) makes the outer layers of that star expand. It becomes red because the surface cools.
5. White dwarf:
   The star then becomes unstable and ejects its outer layers. This leaves behind a hot, dense solid core - a white dwarf.

Question 16

What are the steps of the life cycle of a star much bigger than our sun?

Answer 16

1. Nebula
2. Protostar
3. Main sequence star
4. Red supergiant
5. Supernova
6. Neutron star 6. Black hole

Question 17

Explain the steps of the life cycle of a star much bigger than our sun.

Answer 17

1. Nebula:
   Stars intially form from a cloud of dust and gas, called a nebula.
2. Protostar:
   The force of gravity pulls the dust and gas together to form a protostar. The temperature rises as the star gets denser. 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 hot.
3. Main sequence star:
   This is the star’s 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.
4. Red giant:
   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 core of the star is compressed, until it is dense and hot enough that the energy released (and so pressure created) makes the outer layers of that star expand. It becomes red because the surface cools.
5. Supernova:
   The star starts to glow brightly again as it undergoes more fusion to make heavier elements. The star expands and contracts many times, as the balance shifts between gravity and thermal expansion. Eventually, the star explodes into a supernova.
6. Neutron star:
   The exploding supernova throws out several layers of dust and gas into space, leaving behind a very dense core called a neutron star.
7. Black hole:
   If the star is massive enought, it will collapse and become a black hole, a super dense region of space that not even light can escape from.

Question 18

What is the Doppler Effect?

Answer 18

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

Question 19

What is red shift?

Answer 19

A measure of how far along the spectrum the lines have moved.

Question 20

What does red shift suggest and how?

Answer 20

The galaxies are moving away from us and the Universe is expanding.

The visible spectrum of light from stars contain patterns of dark lines. If these are red shifted (moved towards the red end of the spectrum) the star is moving away from us. The further the lines are shifted, the faster the star is moving relative to us. We can use this to suggest that the Universe is expanding.

Question 21

What is the Steady State Theory?

Answer 21

A theory for the Origin of the Universe.
It says that:
The Universe has always existed as it is now, and always will exist.
As the Universe expands, new matter is constantly being created.

Question 22

What is the Big Bang Theory?

Answer 22

A theory for the Origin of the Universe.
It says that:
Initially, all the mater in the Universe occupied a very small space, that was very dense and therefore very hot.
Then, it exloded. Space started expanding and the expansion is still going on.
This theory gives a finite age for the Universe - 13.8 billion years.

Question 23

What evidence do we have for the Big Bang Theory?

Answer 23

CMB radiation - Cosmic Microwave Background radiation.
Scientists have detected low frequency electromagnetic radiation coming from all parts of the Universe, that is mainly in the microwave part of the EM spectrum, known as CMB.
The presence of CMB radiation shows that the Universe was once much hotter and denser, suggesting the universe had a beginning, thus supporting the Big Bang Theory.