Solar System

Sorting the Solar System



Approximate diameters(m)



Juno, Eros, Hygia


Often oblong-shaped has too small of a mass to be spherical


Sedna, Ceres, Pluto


It is not large enough to have moons orbiting it and has not cleared its orbit. It must have enough mass to be spherical.

Satellites/ moons

The moon, Phobos,  Europa


Orbits a planet

Rocky Planets

Earth, Mars, Venus


Orbits a star and has cleared its orbit of debris

Gas giant planet

Neptune, Saturn, Jupiter

15,000 - 200,000

A planet composed mainly of hydrogen and helium. No physical surface.


Sun, Sirius, Proxima Centauri

200,000- 1,000,000,000

a luminous spheroid of plasma held together by its own gravity. Very hot.




F = force

G = gravitational constant (6.67408 × 10-11 m3 kg-1 s-2)

M = Mass or objects

r  = Distance


With a negative mass, it would push things away.


Masses know the location of each other at all times and the force is instantaneously felt by both masses at all time.


Big bang theory


Quick stuff

Big bang evidence

  1. Universal expansion and Hubble's Law
    1. We know the universe is expanding because the light from nearby galaxies is redder than it should be. The Doppler Effect tells us that when the distance between the observer and the source of light is increasing, the wavelength of the light also increases. So the fact that the light is redder than it should mean the wavelength of light is increasing, meaning the nearby galaxies (sources of light) are moving away from us. 
  2. Background radiation
    1. Noise radiation is evenly spaced across space
    2. The amount of radiation matched predictions
    3. Law of conservation of energy says energy cannot be  created so it must have come from somewhere
  3. Quasars
    1. 10-15 billion light-years away.
    2. Nothing exists past them
  4. Radioactive decay
    1. Can date the formation of the earth and the moon using rates of radioactive decay.
  5. Stellar information and evolution
    1. The way solar systems form matches the way the universe is said to form
  6. Speed and light and stellar distances.
    1. The furthest stars are 10-156 billion years ago


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