Measuring Distances in Space
Astronomical Unit: unit describing the
average distance from the Sun to the
Earth.
-used most frequently when measuring
distances within the Solar System.
Earth
SUN
This distance is 1 A.U.
Light-Year!
-is a unit equal to the
distance that light
covers in a year.
-How fast is light?
Extremely fast!
299,792,458 m/s or
300,000 km/s!
-A light-year is about
63,240 astronomical
units.
Which unit should one use to
describe the distance between
these pairs of objects in the
Universe, AU or LY?
1. Earth and Moon
2. Sun and nearest Star
3. Width of the Milky Way
4. Saturn and Pluto
5. Sun and the nearest Galaxy
Galaxies…
• Galaxies are large
systems of stars and
interstellar matter,
typically containing
several million to some
trillion stars.
• Galaxies are classified
according to their
shapes.
Three Classifications of Galaxies
Spiral Galaxy
Irregular Galaxy
Elliptical Galaxy
Asteroids vs. Comets
Made up of rocks and metals.
“potato heads”
Made up of ice and dust:
“dirty snowballs”
Do not form tails
Form tails when they pass through
the inner solar system
Usually orbit the Sun in the
asteroid belt, a region between
Mars and Jupiter
Usually orbit the Sun in two
regions: the Kuiper belt (about 30
to 100 AU from the Sun) and the
Oort Cloud (extending out to about
50,000 AU from the Sun).
Orbit the Sun in the same direction
as the planets.
May or may not orbit the Sun in the
same direction
as the planets.
of the Solar System
Inner Planets:
M, V, E, M
Rocky, Terrestrial
Outer Planets
J, S, U, N
Gas Giants
Remember: My Very
Educated Mother Just Sent Us
Nine Pizzas!
Also, the Asteroid
Belt is between Mars
and Jupiter!