Topic 7 - Astronomy

Question 1

SP7a - What is the geocentric model?

Answer 1

The model of our solar system in which everything orbits the earth.

Question 2

SP7a - What is the heliocentric model?

Answer 2

The current model of our solar system where the sun is at the centre and other planes orbit it.

Question 3

SP7a - What shape is the earth’s orbit around the sun?

Answer 3

Elliptical

Question 4

SP7a - What developments in techonology have allowed us to make more detailed observations?

Answer 4

• Computers allow detailed analysis.
• Photography allows accurate and permanent storage of events.
• Telescopes can now be place outside of the earth’s atmosphere giving wider and more detailed detection.
• Space probes allow better analysis of the solar system.

Question 5

SP7a - Why are telescopes place outside the earth’s atmosphere more detailed than a regular telescope?

Answer 5

• The earth’s atmosphere absorbs many waves of the EM spectrum.
• Outside the atmosphere, these could be detected. (such as infrared radiation)

Question 6

SP7b - What is the difference between weight and mass?

Answer 6

Your weight is the force acting on you dependant on your mass and the gravitational field strength.

Question 7

SP7b - What is the gravitational field strength on earth?

Answer 7

9.81 N/Kg

(Can be rounded to 10N/Kg)

Question 8

SP7b - What are the four types of orbits for artificial satellites?

Answer 8

• Highly elliptical
• Circular geostationary
• Low earth orbits
• Polar orbits

Question 9

SP7b - What is a geostationary orbit and what are these satellites used for?

Answer 9

• Satellites that stay in the same place relative to the earth’s position.
• They move at 3070 m/s and are used for broadcasting.

Question 10

SP7b - A satellite in which type of orbit will eventually pass over all parts of the earth?

Answer 10

Polar orbits

Question 11

SP7b - A satellite in which type of orbit needs the least fuel for launching?

Answer 11

Low earth orbits

Question 12

SP7b - A satellite in which type of orbit is used for communication with parts of the earth near the poles?

Answer 12

Highly elliptical orbits

Question 13

SP7b - Why doesn’t a satellite continue moving in a straight line?

Answer 13

The gravitational force between the earth and the satellite causes it to continuously change direction and orbit the earth.

Question 14

SP7b - At what angle is the force between the earth and satellite?

Answer 14

90°

Question 15

SP7b - Explain the speeds that a satellite would have to be travelling at in relation to its orbit, and the changes in orbit it would experience if it changed speed.

Answer 15

• The gravitational force on an object in a lower orbit is a stronger than at a higher orbit so a satellite at a lower orbit would have to travel at a higher speed to stay in orbit.
• Once it eventually slows down, it will drop towards earth.
• However as it drops it gains speed and will eventually be able to be at a lower orbit at a faster speed.
• Once it drops enough that it passes through the earth’s atmosphere, the air resistance will slow it down and it will eventually fall to earth.

Question 16

SP7b - What reaction takes place inside a star?

Answer 16

Nuclear fusion

(typically H + H = He)

Question 17

SP7b - Describe the life cycle of a star the size of our sun. [6 Marks]

Answer 17

• It starts with a Nebula (A cloud of gas).
• The particles in this pull themselves together, becoming denser until their own gravity causes it to collapse in on itself forming a protostar.
• Eventually the pressure and temperature in the protostar become large enough that nuclear fusion starts to occur converting hydrogen to helium
• The energy released form the fusion reactions push the star outward causing it to expand.
• Once the force of the gravity pulling the star inwards matches the force of pressure from the fusion reactions, the star will be at a steady size and in its main sequence stage where it continues to convert hydrogen to helium
• Eventually, hydrogen runs out and heavier reactions take place.
• This creates more energy which expands the star more
• The outermost layers are no longer held in place by the force of gravity so they expand forming a red giant
• Once all the fuel has run out, all the layers disband forming a shell of gas.
• This leaves behind a highly dense white dwarf which doesn’t carry out any reactions.

Question 18

SP7b - Describe the life cycle of a star much larger than our sun. [6 Marks]

Answer 18

• It starts with a Nebula (A cloud of gas).
• The particles in this pull themselves together, becoming denser until their own gravity causes it to collapse in on itself forming a protostar.
• Eventually the pressure and temperature in the protostar become large enough that nuclear fusion starts to occur converting hydrogen to helium
• The energy released form the fusion reactions push the star outward causing it to expand.
• Once the force of the gravity pulling the star inwards matches the force of pressure from the fusion reactions, the star will be at a steady size and in its main sequence stage where it continues to convert hydrogen to helium
• Eventually, hydrogen runs out and heavier reactions take place.
• This creates more energy which expands the star more forming a red supergiant.
• These heavier fusions are carried out all the way to iron when it runs out of fuel.
• The star rapidly collapses causing a supernova
• This leaves behind a very dense neutron star
• If the mass of the star is even larger, then a black hole is formed in place of the neutron star.

Question 19

SP7d - What is the doppler effect?

Answer 19

When the pitch of a noise get lower as it travels aways from you. (and higher when it travels towards you)

Question 20

SP7d - Why does the doppler effect occur?

Answer 20

As a sound travels, the wavelengths are squashed or stretched meaning the sound’s pitch appears higher or lower.

Question 21

SP7d - What is red-shift?

Answer 21

When light form distant galaxies shift towards the red side of the spectrum due to wavelengths being stretched as the galaxy moves away from earth.

Question 22

SP7d - What do we use to check red-shift?

Answer 22

Absorption spectrums of the galaxy compared to the absorption spectrum of the sun.

Question 23

SP7e - What are the two main theories for the origin of the universe?

Answer 23

• The big bang theory
• Steady state theory

Question 24

SP7e - What is the Big Bang Theory?

Answer 24

• The whole universe started out from one point of concentrated energy.
• All matter started form this point and continued to expand outwards as the universe constantyl expands.

Question 25

SP7e - What is the Steady State Theory?

Answer 25

The universe always existed and as it expands matter is continuosly created.

Question 26

SP7e - Which theory of the universe is the currently accepted theory?

Answer 26

The Big Bang Theory

Question 27

SP7e - What provides evidence for both theories of the universe and why?

Answer 27

Red-shift; as galaxies are constantly moving away the universe is constantly expanding.

Question 28

SP7e - What provides evidence for the currently accepted theory.

Answer 28

CMBR (Cosmic Microwave Background Radiation) is found throughout all of the universe at the same rate suggesting that it all started form one point and expanded out from there.

Question 29

SP7e - What can we use as a model of why CMBR proves The Big Bang Theory?

Answer 29

* A Currant bun has currants close together. * As the dough rises, the number of currants stay the same but they are found at consistent rate throughout the bun.

Question 30

SP7d - What does it mean if one galaxy has a greater red-shift than another?

Answer 30

That galaxy is further away and moving faster than the other.