SP7: astronomy Flashcards
my very easy method just speeds up naming planets
mercury, venus, earth, mars, jupiter, saturn, uranus, neptune, pluto
for a planet, as the distance from the sun increases…
-the temperature decreases
-the time taken to orbit the sun increases
how does a planet form?
-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
what are moons?
natural satellites that orbit a planet
what is a dwarf planet?
-the gravitational field of a dwarf planet is not strong enough to clear the neighbourhood (eg: pluto, ceres)
what are asteroids?
-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
comets
-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
milky way galaxy
the galaxy containing the solar system
solar system
sun, planets, and all the other objects that revolve around the sun
weight equation
mass × gravitational field strength (w-mg)
weight units
-weight in newtons (N)
-mass in kilograms (kg)
-gravitational field strength in newtons per kilogram (N/kg)
gravity on the earth
9.8 m/s
why was it difficult to observe outer space in the past?
-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
geocentric theory
-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
heliocentric theory
-sun is the center of the universe
-copernicus
-detailed observations with telescopes have given us evidence that this is the correct idea
evidence for the heliocentric model
-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
when was pluto reclassified as a dwarf planet?
2006
how is a stable orbit around planets kept?
-gravity
-an object must be travelling at the right speed
at what speed do objects go into the earth’s orbit and why?
-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
at what speed do objects fall back in to the earth and why?
-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
at what speeds do objects leave the earth’s orbit and why?
-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
when an object moves in a circle at a constant speed, its _______ constantly changes
direction
a change in direction causes a change in _____
velocity
a change in velocity results in _____
acceleration, so an object moving in a circle is accelerating even though its speed may be constant
an object only accelerates if…
a resultant force is acting on it
what resultant force acts on objects moving in a circle?
-centripetal force
-gravitational attraction provides the centripetal force needed to keep planets and all types of satellite in orbit
how does distance affect the gravitational force affecting two objects?
gravitational attraction decreases with distance
why do objects in small orbits move faster than objects in large orbits?
-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
how to change orbital speed?
an object must change the radius of its orbit at the same time as velocity to maintain a stable orbit
artificial satellite
man-made equipment that orbits the earth or other planets
what two orbits do artificial satellites travel in?
-polar
-geostationary
polar orbits
-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)
geostationary orbits
-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)
emission spectrum
-a spectrum of the electromagnetic radiation emitted by a source
-dark lines show the absorbed light
red-shift
-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
the big bang
-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
what does red-shift tell us about the universe?
it is expanding
what does a larger red shift indicate?
the galaxy is moving away faster
CMB
-microwave radiation that is present throughout the universe
-thought to be the cooled remnants of the big bang
-temperature of -270 degrees
the steady state theory
-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
invisible observations
-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
space telescopes
(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
what are the advantages of putting telescopes on satellites?
-the telescopes aren’t affected by the weather, or by day and night light levels
when was the solar system formed?
4.6 billion years ago
how was the solar system formed?
-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
life cycle of stars
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)
nebula
-a large cloud of dust and gas
-mostly made of hydrogen
prostar
-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
main sequence star
-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
red giant star
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
white dwarf
-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)
supernova
-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
neutron star or black hole
depending on the mass at the start of its life, a supernova will leave behind either a neutron star or a black hole
optical telescopes
-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
radio telescopes
-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
