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PHYSICS > SP7: astronomy > Flashcards

SP7: astronomy Flashcards

1
Q

my very easy method just speeds up naming planets

A

mercury, venus, earth, mars, jupiter, saturn, uranus, neptune, pluto

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2
Q

for a planet, as the distance from the sun increases…

A

-the temperature decreases
-the time taken to orbit the sun increases

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3
Q

how does a planet 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 pull smaller nearby objects into its orbit

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4
Q

what are moons?

A

natural satellites that orbit a planet

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5
Q

what is a dwarf planet?

A

-the gravitational field of a dwarf planet is not strong enough to clear the neighbourhood (eg: pluto, ceres)

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6
Q

what are asteroids?

A

-small objects made of metals and rocky material
-orbit the sun in highly elliptical orbits )oval or egg-shaped) and may take millions of years to complete
-there are many 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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7
Q

comets

A

-small objects made of rocky material, dust and ice
-as a comet approaches the sun, it begins to vaporise (turn into a gas), it then produces a distinctive tail

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8
Q

milky way galaxy

A

the galaxy containing the solar system

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9
Q

solar system

A

sun, planets, and all the other objects that revolve around the sun

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10
Q

weight equation

A

mass × gravitational field strength (w-mg)

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11
Q

weight units

A

-weight in newtons (N)
-mass in kilograms (kg)
-gravitational field strength in newtons per kilogram (N/kg)

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12
Q

gravity on the earth

A

9.8 m/s

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13
Q

why was it difficult to observe outer space in the past?

A

-before the development of the telescope, these ideas were based on what could be seen with the naked eye
-this restricted the details that could be gathered about the solar

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14
Q

geocentric theory

A

-an egyptian astronomer ptolemy described the geocentric model
-the solar system had the earth at the centre of it
-as observations of the motions of the planets became more detailed, the descriptions of the solar system had to get very complex in order to keep the earth at the centre

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15
Q

heliocentric theory

A

-sun is the center of the universe
-copernicus
-detailed observations with telescopes have given us evidence that this is the correct idea

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16
Q

evidence for the heliocentric model

A

-galileo’s observations of jupiter, using the telescope, provided evidence for the heliocentric model of the solar system
-it provided evidence that not everything revolved around the earth

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17
Q

when was pluto reclassified as a dwarf planet?

A

2006

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18
Q

how is a stable orbit around planets kept?

A

-gravity
-an object must be travelling at the right speed

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19
Q

at what speed do objects go into the earth’s orbit and why?

A

-7,600 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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20
Q

at what speed do objects fall back in to the earth and why?

A

-slower than 7,600 m/s
-the satellite will move too slow & then the gravitational attraction will be too strong
-the satellite will fall towards the earth

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21
Q

at what speeds do objects leave the earth’s orbit and why?

A

-11,200 m/s and above
-if the satellite is moving too quickly, the gravitational attraction between the earth & the satellite is too weak to keep it in orbit
-the satellite will move off into space

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22
Q

when an object moves in a circle at a constant speed, its _______ constantly changes

A

direction

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23
Q

a change in direction causes a change in _____

A

velocity

24
Q

a change in velocity results in _____

A

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

25
Q

an object only accelerates if…

A

a resultant force is acting on it

26
Q

what resultant force acts on objects moving in a circle?

A

-centripetal force
-gravitational attraction provides the centripetal force needed to keep planets and all types of satellite in orbit

27
Q

how does distance affect the gravitational force affecting two objects?

A

gravitational attraction decreases with distance

28
Q

why do objects in small orbits move faster than objects in large orbits?

A

-the closer the two objects are, the stronger the force of gravity between them
-greater force = greater acceleration

-the greater the acceleration, the greater the change in velocity
-this causes the object to move faster
-objects in small orbits travel faster than objects in large orbits

29
Q

how to change orbital speed?

A

an object must change the radius of its orbit at the same time as velocity to maintain a stable orbit

30
Q

artificial satellite

A

man-made equipment that orbits the earth or other planets

31
Q

what two orbits do artificial satellites travel in?

A

-polar
-geostationary

32
Q

polar orbits

A

-take the satellites over the earth’s poles
-the satellites travel very close to the earth (as low as 200 km above sea level)
-they must travel at very high speeds (nearly 8,000 m/s)

33
Q

geostationary orbits

A

-take 24 hours to orbit the earth
-satellite appears to remain in the same part of the sky when viewed from the ground
-higher than polar orbits (typically 36,000 km) -satellites travel more slowly (around
3 km/s)

34
Q

emission spectrum

A

-a spectrum of the electromagnetic radiation emitted by a source
-dark lines show the absorbed light

35
Q

red-shift

A

-a shift in the spectra of distant galaxies toward longer wavelengths & lesser frequencies (red side
-the more red shifted the light from a galaxy is, the faster the galaxy is moving away from earth

36
Q

the big bang

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

37
Q

what does red-shift tell us about the universe?

A

it is expanding

38
Q

what does a larger red shift indicate?

A

the galaxy is moving away faster

39
Q

CMB

A

-microwave radiation that is present throughout the universe
-thought to be the cooled remnants of the big bang
-temperature of -270 degrees

40
Q

the steady state theory

A

-the universe has always existed
-the universe is expanding and constantly creating matter as the universe expands
-supported by the red shift evidence, but not by the CMB

41
Q

invisible observations

A

-modern tech 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

space telescopes

A

(a telescope that is located in outer space)
-objects in the universe emit other EM radiation eg: infrared, x-rays & gamma rays
-these are all blocked by the earth’s atmosphere, but can be detected by telescopes placed in orbit round the earth

-telescopes in space can observe the whole sky
-they can operate both night and day.
However, athey are difficult & expensive to launch and maintain
-if anything goes wrong, sometimes only astronauts can repair them

43
Q

what are the advantages of putting telescopes on satellites?

A

-the telescopes aren’t affected by the weather, or by day and night light levels

44
Q

when was the solar system formed?

A

4.6 billion years ago

45
Q

how was the solar system formed?

A

-a large cloud of dust and gas, called a nebula
-this collapsed under its own gravity & transferred gravitational potential energy to kinetic energy in its particles
-as the nebula collapsed 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 form a hot, dense protostar

46
Q

life cycle of stars

A

nebula > protostar > main sequence star > then it splits, it goes:
1. red giant > white dwarf > black dwarf (around same mass as sun)
or 2. red super giant > supernova occurs > black hole or neutron star (greater in mass than sun)

47
Q

nebula

A

-a large cloud of dust and gas
-mostly made of hydrogen

48
Q

prostar

A

-gravity begins to pull the dust and gas together, it gets hot
-a prostar forms when it’s hot enough for the hydrogen nuclei to fuse & make helium
-the fusion releases energy, which keeps the core hot

49
Q

main sequence star

A

-stable phase in the life of a star force of gravity
-gravity tends to pull the star inwards & 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
-stage lasts 4-5 billion years
-the sun is at this stable phase in its life

50
Q

red giant star

A

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

51
Q

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
-the star becomes a white dwarf which fades and changes colour as it cools (becomes black dwarf)

52
Q

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

53
Q

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

54
Q

optical telescopes

A

-observe visible light from space
-small ones let amateurs view the night sky cheaply
-large optical telescopes sited around the world for professional astronomers to use

disadvantages:
-only used at night
-cannot be used if the weather is poor or cloudy

55
Q

radio telescopes

A

-detect radio waves coming from space
-Usually very large and expensive
-these telescopes have an advantage over optical telescopes
-can be used in bad weather because the radio waves are not blocked by clouds as they pass through the atmosphere
-can be used in daytime & night

-x-rays are partly blocked by the earth’s atmosphere
-x-ray telescopes need to be at high altitude, flown in balloons or carried in satellites above the earth’s atmosphere

PHYSICS (15 decks)

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