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Astronomic Distances
Background
• Solar systemplanets and other
objects like comets
and asteroids that
travel around the
sun
Galaxy
• Galaxy- a large
grouping of stars in
the universe
– Made of multiple
solar systems
– There are billions
and billions of
galaxies.
• We live in the Milky
Way Galaxy
Universe
• Universeeverything in space
that we know
about
– There’s only one
universe
– Made up of billions
of galaxies
Putting it all together
Made of many
Universe
Made of many
Galaxy
Solar System
Distance
• AU- astronomical unit
– The distance from the
earth to the sun
– 1AU=93 million miles
• Psst… earth is 93 million
miles from the sun!
– Used to measure closer
objects in space (planets
in our solar system)
Distance
Light year—The amount of distance a
beam of light will travel in one year
– It’s a measure of distance, NOT time
• Can have light seconds, minutes, hours,
days weeks, and months!
– 186,282 miles per second/
5,878,625,373,183 miles per year
– Used to measure things really far
away
• Galaxies, stars
– When we see light from space, we’re
looking back in time
• Light has to travel to get to us, so we’re
seeing old light
Parsec
• Parsec: a unit of
length equal to
3.26 light years, or
30 trillion
kilometers
– Roughly 19 trillion
miles
A final note
• In astronomy, scientists
rarely use kilometers
– Just too small!
• Like measuring a person in
millimeters
– Scientists only use
kilometers to talk about
the diameter of a planet,
or how far away a moon is
from the planet