ASTR 207 Lecture Notes - Lecture 1: Small Solar System Body, Kuiper Belt, Asteroid Belt

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Milky Way Galaxy
a huge, disk-shaped collection of stars we are apart of. Contains over 100 billion stars.
Astronomical Unit (AU)
The earths average distance from the sun, which is about 150 million km (93 million meters).
One light-year (ly)
is the distance light can travel in 1 year, about 10 trillion km (6 trill miles)
Star
A large, glowing ball of gas that generates heat and light through nuclear fusion in its core. Our sun is a
star.
Planet
A moderately large object that obrits a star and shines primarily by reflecting light from its star. Criteria 1)
orbits star 2) Large enough for its own gravity to make it round 3) has cleared objects out of its orbital
path.
Dwarf planet
A planet that is rounded by gravity, orbits a star but hasn't cleared objects from its orbital path. IE Pluto
Moon (or satellite)
An object that orbits a planet. Satellite is generally used to refer to an object orbiting another object
Asteroid
A relatively rocky and small object orbiting a star
Asteroid
A relatively small and rocky object that orbits a star; asteroids are officially considered part of a category
known as "small solar system bodies"
Asteroids
Rocky bodies that orbit the Sun. (like small planets)Most found in asteroid belt between Mars and Jupiter
Comet
A relatively small and ice-rich object that orbits a star
Comet
A relatively small, icy object that orbits a star. Like asteroids, comets are officially considered part of a
category known as "smaller solar system bodies."
Comets
Small objects orbiting the sun, largely made of ice mixed with rocks.Are found mainly in two regions
outside away from the sun (see): Kuiper belt and Oort cloud
Comets
Ice-rich leftover planetesimals of the outer solar system. Initially populated entire outer planet region,
some grew into dwarf planets. Others created Kuiper belt.
Others got "kicked out" by planets orbits that see them way far out in random directions: created the Oort
cloud heavy
Small solar system body
An asteroid, comet, or other object that orbits a star but is too small to qualify as a planet or dwarf planet.
Solar System
The sun and all the material that orbit it
Star System
A star (or more than one star) and any planets and material that orbit it.
Galaxy
A great island of stars in space, containing from a few hundred million to a trillion or more stars, all held
together by gravity and orbiting a common center.
Cluster (or group) of galaxies
a collection of galaxies bound together by gravity. Small collections (up to a few dozen) are generally
called groups, while larger collections are called clusters
Supercluster
a gigantic region of space in which many groups and clusters of galaxies are packed more closely
together than elsewhere in the universe.
Universe (or cosmos)
THe sum total of all matter and energy- that is, all galaxies and everything between them.
Observable Universe
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