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SP7- astronomy Flashcards

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1
Q

What is the largest object in the Solar System?

A

The Sun, the Earth’s star

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2
Q

What is a star?

A

A large mass at the centre of the solar system (if there are other bodies present) that produces heat and light, eg, the star at the centre of out Solar system is called the Sun.

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3
Q

The different planets have different properties. What happens as the distance from the Sun increases?

A
  • The temperature decreases.

- The time taken to orbit the Sun increases

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4
Q

What must happen for a planet to form?

A

Its own gravity must be strong enough to make it round or spherical in shape. Its gravitational field must also be strong enough to ‘clear the neighbourhood’ pulling smaller nearby objects into its orbit.

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5
Q

What is a satellite?

A

A body that orbits a planet. For example, the Moon is a natural satellite of the Earth but communication satellites are artificial satellites of the Earth.

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6
Q

What are Moons?

A

Natural satellites that orbit a planet. Many planets have moons, and some planets have many - Saturn has over 50. The Earth has one - the Moon.

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7
Q

What is Pluto?

A

A dwarf planet.

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8
Q

Why is a dwarf planet a dwarf planet?

A

Because the gravitational field strength of a dwarf planet is not strong enough to clear the objects in its orbit around the sun.

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9
Q

What are asteroids?

A

Rocks in space.

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10
Q

What do asteroids do?

A

Orbit the Sun in highly elliptical (shaped like an oval/egg) and may take millions of years to complete. Asteroids are made of metals and rocky material. There are large numbers of asteroids orbiting the Sun in the asteroid belt between Mars and Jupiter. There are also many in a region beyond Neptune called the Kuiper belt.

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11
Q

What are comets?

A

Rocky material, dust and ice.

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12
Q

What happens to a comet when it approaches the Sun?

A

It begins to vaporise, which means that it turns into a gas. It then produces a distinctive tail.

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13
Q

What is the weight of an object?

A

The weight of an object is the force on it caused by the gravity due to the planet. The weight of an object and the gravitational field strength are directly proportional. For a given mass, the greater the gfs (or g), the greater its weight.

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14
Q

Weight= ?

A

Mass x gravitational field strength.

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15
Q 
What is the gravitational field strength on:
a) The Sun
b) Mercury
c) Venus
d) Earth
e) Moon (satellite)
f) Mars
g) Ceres
h) Jupiter
I) Saturn
J) Uranus 
K) Neptune
L) Pluto (dwarf planet)
A

a) 293.0 N/kg
b) 3.7 N/kg
c) 8.8 N/kg
d) 9.8 N/kg
e) 1.7 N/kg
f) 3.7 N/kg
g) 0.27 N/kg
h) 24.7 N/kg
i) 10.5 N/kg
j) 9.0 N/kg
k) 11.7 N/kg
l) 0.49 N/kg

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16
Q

What did Ptolemy’s model consist of?

A

That the Earth was at the centre of the Solar System and that all other bodies orbited it.

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17
Q

Who is credited with changing the structure of the Solar System with the Sun at the centre?

A

Nicolas Copernicus.

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18
Q

What is orbital motion?

A

Gravity provides the force needed to maintain stable orbit of planets around a star and also of moons and artificial satellites around a planet.

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19
Q

What must happen for an object to remain in a steady, circular orbit?

A

It must be travelling at the right speed.

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20
Q

What are the 3 possible outcomes should this criteria not be met?

A
  • If the satellite is moving too quickly then the gravitational attraction between the Earth and the satellite is too weak to keep it in orbit. If this is the case, the satellite will move into space. This occurs at speeds around or above 11,200 m/s.
  • If the satellite is moving too slowly then the gravitational attraction will be too strong, and the satellite will fall towards the Earth. This occurs at speeds around or below 7600 m/s.
  • A stable orbit is one in which the satellite’s speed is just right- it will not move off into space or spiral into the Earth, but will travel around a fixed path.
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21
Q

What happens when an object moves in a circle at a constant speed?

A

Its direction constantly changes.

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22
Q

What does a change in direction cause? Why?

A

A change in velocity - this is because velocity is a vector quantity- it has an associated direction as well as a magnitude.

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23
Q

What does a change in velocity result in?

A

Acceleration, so an object moving in a circle is accelerating even though its speed may be constant.

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24
Q

What does an object need in order to accelerate?

A

A resultant force to act upon it.

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25
Q

What is the centripetal force?

A

A force, needed for circular motion, which acts towards the centre of the circle.

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26
Q

For an object moving in a circle, what is the resultant force?

A

The centripetal force that acts towards the centre of the circle. Gravitational attraction provides the centripetal force needed to keep planets and all types of satellite in orbit.

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27
Q

What happens to the gravitational attraction between 2 objects with a distance?

A

It decreases- this means that the closer the two objects are to each other, the stronger the force of gravity between them. If the force between them is greater, a greater acceleration will occur.

28
Q

What happens the greater the acceleration?

A

The greater the change in velocity- this causes the object to move faster. This means that objects in small orbits travel faster than objects in large orbits. In order to change orbital speed, an object mist change the radius of its orbit at the same time, to maintain a stable orbit.

29
Q

What are the 2 different types of orbit that an artificial satellites can travel in?

A

Polar orbit
Geostationary orbits - a satellite orbiting a planet at the same rate as the planet. A geostationary satellite orbiting Earth has a period of 24 hours.

30
Q

What does a light not contain all of?

A

The wavelengths of the electromagnetic spectrum.

31
Q

What do elements in the star do?

A

Absorb some of the emitted wavelengths, so dark lines are present when the spectrum are analysed.

32
Q

Different elements produce what?

A

Different patterns of dark lines.

33
Q

What can astronomers observe?

A

Light from different galaxies.

34
Q

What do the dark lines in the spectra from different galaxies show?

A

An increase in wavelength and a corresponding decrease in frequency.
This effect is called the red shift.

35
Q

Where do astronomers see red shift?

A

In virtually all galaxies.

36
Q

What is red shift the result of?

A

The space between Earth and all the galaxies expanding.
This expansion stretches out the light waves during their journey to us, shifting them towards the red end of the spectrum. The more red shifted the light from a galaxy is, the faster the galaxy is moving away from Earth.

37
Q

What happened according to the big bang theory?

A

About 13.8 billion years ago, the whole Universe was a very small, extremely hot and dense region. From this tiny point, the whole Universe expanded outwards to what exists today.

38
Q

How does evidence from the red shift support the big bang theory?

A

Astronomers have discovered that, in general, the further away a galaxy is, the more red shifted its light is. This means that the further away the galaxies are, the faster they are moving. This is similar to an explosion, where the bits moving fastest travel furthest from the explosion. Red shift data provides evidence that the Universe, space itself., is expanding.

39
Q

How does evidence from CMBR (cosmic microwave background radiation) support the big bang theory?

A

Astronomers have also discovered cosmic microwave background radiation (CMBR). This comes from all directions in space and has a temperature of about -270°C. The CMBR is the remains of the thermal energy from the Big Bang, spread thinly across the whole Universe.
The discovery of the CMBR, after it has been predicted by the theory, provided very string support for the Big Bang theory, and led to the Big Bang becoming the currently accepted model of the Universe.

40
Q

What is the Steady State theory of the Universe?

A

The Steady State theory says that the Universe has always existed, and that the universe is always expanding and constantly creating matter as the Universe expands. This idea is supported by the red shift evidence, but not by CMBR. After the discovery of the CMBR, the Steady State theory lost support and is no longer considered likely.

41
Q

What are invisible observations that can be used to observe the Universe?

A

Modern technology can be made sensitive to electromagnetic frequencies that human eyes cannot sense. This has opened up areas of astronomy that were not available previously. Observing the radio waves or infrared or X-ray emissions from stars and galaxies has allowed scientists to make a huge number of discoveries in a very short time.

42
Q

Why are Space telescopes used?

A

Many of the extra wavelengths of EM waves that astronomers would like to observe do not penetrate the atmosphere. This means that any telescope which is to use these parts of the EM spectrum, such as most ultraviolet light, needs to be based on a satellite above the atmosphere. The Hubble Space Telescope has detectors for visible light and also for infrared and ultraviolet.

43
Q

What are the advantages of putting telescopes on satellites?

A

They aren’t affected by the weather, or by day and night light levels.

44
Q

When was the Solar System formed and what was it formed from?

A

4.6 billion years ago from a large cloud of dust and gas, called a nebula.

45
Q

What happened to nebula?

A

It collapsed under its own gravity, transferring gravitational potential energy to kinetic energy in its particles.

46
Q

What happened to the nebula as it collapsed?

A

It became denser, and rotated more rapidly. Collisions between particles caused kinetic energy to be transferred as internal energy and thermal energy. The core of the nebula began to fomr a hot dense protostar?

47
Q

What is a protostar?

A

The early stage in the formation of a star, before nuclear fusion occurs.

48
Q

What happens when the Sun’s core become hot enough and dense enough?

A

Nuclear fusion reactions began, giving out energy and radiation.

49
Q

What is nuclear fusion?

A

The joining of two smaller atomic nuclei to produce a larger nucleus. Electromagnetic radiation is released when this happens.

50
Q

What is the main element in nuclear fusion?

A

Hydrogen.

51
Q

What is a star like the sun at?

A

An equilibrium - gravity tends to pull it inwards, and radiation pressure from the nuclear reactions tends to expand it outwards. In other words, the gravitational collapse is balanced by the expansion due to fusion energy.

52
Q

What is the Sun currently?

A

A main sequence star and will remain so for another 4- 5 billion years.

53
Q

What does main sequence mean?

A

A stable stage in the life cycle of a star. Nuclear fusion occurs, fusing hydrogen nuclei into helium nuclei. There is a balance between the outwards radiation and the force of gravity pulling inwards.

54
Q

What will then happen to the Sun?

A

It will expand and cool down to become a red giant, after which it will shrink and heat up again to become a white dwarf. The white dwarf will run out of nuclear fuel and slowly cool down over many billion years.

55
Q

What does the life cycle of a star depend on?

A

Its size.

56
Q

What is the life cycle of a star that all stars begin with?

A

A cloud of dust and gas (nebula), becomes a protostar, which goes on to become a main sequence star?

57
Q

What then happens to stars which a similar mass to the Sun?

A

They follow on with a red giant star to white dwarf star to a black dwarf star.

58
Q

What then happens to the stars which have a much greater mass than a sun.

A

The star becomes a red super giant star to a supernova to a neutron star or a black hole (depending on its size)

59
Q

What is a supernova?

A

The large explosion at the ends of a large star’s life, which distributes much of the elements formed in the star across space.

60
Q

Describe nebula

A

A star forms from massive clouds of dust and gas in space, also know as nebula. Nebulae are mostly composed of hydrogen. Gravity begins to pull the dust and gas together.

61
Q

Describe the protostar

A

As the mass falls together it gets hot. A star is formed when it is hot enough for the hydrogen nuclei to fuse together to make helium. The fusion process releases energy, which keeps the core of the star hot.

62
Q

Describe the main sequence.

A

During the stable phase in the life of a star, the force of gravity holding the star together is balanced by higher pressure due to the high temperatures. The Sun is at this stable phase in its life.

63
Q

Describe a red giant star.

A

When all the hydrogen has been used up in the fusion process, larger nuclei begin to form and the star may expand to become a red giant.

64
Q

Describe a white dwarf?

A

When all the nuclear reactions are over, a small star like the Sun may begin to contract under the pull of gravity.
In this instance, the star becomes a white dwarf which fades and changes colour as it cools.

65
Q

Describe a supernova.

A

A larger star with more mass will go on making nuclear reactions, getting hotter and expanding until it explodes as a supernova.
An exploding supernova throws hot gas into space.

66
Q

Describe a neutron star or black hole.

A

Depending on the mass at the start of its life, a supernova will leave behind either a neutron star or a black hole.

Physics (7 decks)

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