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Final Exam Study Notes

Astronomy & Astrophysics
Course Code
Michael Reid
Study Guide

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Week 1
The solar system is huge and the vast majority of it is empty (not quite tiny, tiny
quantities of gas and dust fills the space)
Average distance between Sun and the Earth ~ 1 AU or 150 Billion metres
Light year is distance light travels in one year
1 AU ~ 8 light minutes, Black hole ~ 26,000 light years
Andromeda Galaxy is 2.5 million light years away (the closest galaxy to Earth)
Light travels at finite speed and therefore we cant see everything in the universe as
it is now. Thus, no matter where we look, we are looking back in time.
Stars are huge spheres of super-hot gas (plasma) that produces energy by nuclear
fusion (smashing atoms together). The Sun is a fairly typical star.
Planets are large bodies which orbits stars. Planets may be various mixtures of rock,
ice or gas.
3 main criteria for planets:
-Planets orbit stars directly (not other planets)
-Planets must be massive enough for their own gravity to compress them into
spherical shapes.
-Planets must have cleared their orbits. That is, there cant be a lot of other stuff
orbiting the parent star in orbits very similar to the planet
Pluto is now called a dwarf planet. 5 main dwarf planets at the moment: Pluto,
Ceres, Makemake, Haumea and Eris.
Moon is a large body which orbits a planet.
A nebula is a cloud of gas and dust. We see the light emitted by the gas (bright
parts) and the places where light is blocked by dust (dark parts). It is where stars
come from, they form when parts of nebulae are crushed by their own gravity.
A galaxy is a city of stars. Large galaxies, like the Milky Way, contain about 100
billion stars, all orbiting a common center of gravity. They are grouped into galaxy
clusters. The Milky Way is in a galaxy cluster called Local Group.
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The whole Solar System orbits the center of the Milky Way every 230 million years.
All of the galaxy clusters are moving apart from one another.
Enormous groups of galaxies all orbiting one another are called galaxy
superclusters. Our supercluster is called the Virgo. It is 110 million light years old.
Superclusters are located where huge long walls and filaments made of galaxies
Week 2
Science is the process of discovering the rules by which the natural world works,
using the method of testing falsifiable hypotheses.
Ideally, scientific hypotheses should be: falsifiable, simple, beautiful, universal and
A falsifiable statement is one which can be proven either true or false by
Newtons First Law: Objects at rest remain at rest and objects in motion remain in
motion in a straight line, unless acted upon by an external force.
The 4 Forces of Nature: Strong nuclear force, electromagnetism, weak nuclear force
and gravity.
Electromagnetism and Gravity have infinite range whereas the nuclear forces are
limited in range. Despite being the weakest force, gravity is able to hold the universe
together because of one single phenomenon. Gravity only pulls, and never pushes.
So, the more mass an object has, the more gravity it makes. Other forces do not work
that way as they push and pull and all that pushing and pulling tends to cancel each
other out. Thus, Gravity adds up but magnetism tends to cancel each other out.
Newtons Law of Gravity: The force of gravity between masses M and m is equal to
the product of their masses, times the gravitational constant G, divided by the
square of the distance between the masses.
An object moving under the exclusive influence of gravity is said to be in free-fall.
Orbits are just a kind of falling where you happen to miss the ground.
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