Space Physics Flashcards
Describe the planets in the solar system
Eight planets orbiting the sun. Rock planets: Mercury, Venus, Earth, Mars Gas Giants: Jupiter, Saturn, Uranus, Neptune
Beyond Neptune, there are dwarf planets such as Pluto.
What are moons?
Natural satellites which orbit planets.
Most planets in the solar system have at least one moon.
Some have a very large number of them.
What galaxy is the solar system a part of?
The Milky Way
What is meant by a galaxy?
A massive group of stars.
How do stars form?
They form clouds of dust and gas - a nebula.
The gas is mostly hydrogen.
Gravity causes the cloud of dust and gas to collapse.
As the dust particles move faster, the temperature rises to millions of degrees celcius.
This collapsing cloud of dust and gas is called a protostar.
If the temperature of the protostar gets high enough, then hydrogen nuclei join together to form helium- nuclear fusion.
Now it has turned into a star.
Nuclear fusion is releasing a huge amount of energy.
Two opposing forces acting within the star:
Gravity acts inwards and tends to make the star collapse.
The energy from nuclear fusion creates a force acting outwards, which causes the star to expand.
Gravity is balanced by the force due to fusion energy.
The star is in equilibrium.
What happens to stars that are about the same size as our sun?
In a main-sequence star, hydrogen nuclei fuse together to make larger nuclei such as helium. The hydrogen in the star begins to run out.
The outward force due to fusion energy is less than the inward force due to gravity.
This causes the star to collapse inwards, which then causes the temperature to increase.
Now helium nuclei fuse together to form heavier elements.
The star expands to form a red giant.
At some point, the red giant stops fusing helium.
The star shrinks and forms a white dwarf.
Because the white dwarf is no longer carrying out fusion, it gradually cools down.
Eventually it stops releasing energy and forms a black dwarf.
What happens to stars that are much larger than the sun?
Once they run out hydrogen, they leave the main-sequence stage and expand into red super giants.
Helium nuclei fuse together to form heavier elements.
Nuclear fusion cannot produce any element heavier than iron.
The red super giant stops carrying out nuclear fusion.
The star explodes- this is called a supernova.
The temperature of the supernova is high enough to produce elements heavier than iron.
When the supernova explodes, these elements are distributed throughout the universe.
After this, the remains of the star can form a neutron star or a blackhole.
What is a neutron star?
Consists of neutrons densely packed together.
What is a blackhole?
It has such a large gravity than not even light can escape.
How do orbits work?
The force of gravity acting between the Sun and the Earth holds the Earth in its orbit.
Planets orbit the sun, and it is gravity that holds them in their orbit.
This is the same with the moon’s orbit around the Earth.
What are geostationary satellites?
Orbit once every 24 hours.
This means they always point to the same part of the Earth.
But other artificial satellites orbit more frequently.
How do circular orbits work?
The force of gravity is leading to a change in velocity.
Not a change in speed, this is because the planet is constantly changing direction.
Velocity is the speed in a given direction.
The speed is constant.
What happens if the speed of a satellite orbiting the earth changes?
The radius of the orbit must change too.
If the speed increases, the radius decreases.
This is because at a higher speed, the satellite needs a greater force of gravity to prevent it from flying into space.
So by moving closer to the earth, the gravitational force is greater and the satellite remains in stable orbit.
What did astronomers in the 1900s notice about the light emitted from different galaxies?
The light from very distant galaxies has an increased wavelength compared to light from closer galaxies.
Why are there dark lines in the spectrum of light from the Sun?
Certain elements in the sun absorb light of specific wavelengths, so those wavelengths appear as dark lines.
