SOLAR SYTEMS: WEEK 1
Scale of the universe:
Planet Size: Largest to Smallest
4. Uranus • The sun is 100x larger than
5. Earth • The sun’s radius is roughly
6. Mars 10x larger than Jupiter.
7. Mercury / Venus
Unit of measurement: 1 Astronomical Unit = 1 AU= 150 million km.
(Distance from Earth to Sun = 1 AU)
• Closest Star = Alpha Centauri (271,000 AU)
• Light Year = 10 km
• Light travels to Earth in 8 minutes
• Alpha Centauri is 4 ly away.
• Avg. distance to the moon is 30x farther away than Earth’s diameter.
Chapter one: From the text
Solar System: Consists of the sun, the planets and their moons and countless smaller
objects that include rocky asteroids and icy comets.
Our Sun is a star
Our solar system belongs to the huge, disk shaped collection of stars called the Milky
Galaxy: A great island of stars in space, containing between a few hundred million and a
trillion or more stars.
• The Milky Way is a relatively large galaxy, containing more than 100 billion stars.
Our solar system is located a little over half way from the galactic center to the
edge of the galactic disk.
• Billions of galaxies are scattered throughout space. Some are fairly isolated, but
many others are found in groups.
• Our milky way is one of the 2 largest among about 40 in the local group. SOLAR SYTEMS: WEEK 1
Galaxy Cluster: Groups of galaxies with more than a few dozen members are often called
Super Clusters: Clusters of galaxy clusters
Universe: Sum total of all matter and energy encompassing the super clusters and
asteroids and everything within them.
Sirius Brightest star in the night sky
▯ Page 4: BASIC ASTRONOMICA DEFINITONS
If we look at something 8 light years away we see it as it looked 8 years ago.
Observable Universe: The portion of the entire universe that we can potentially observe.
Big Bang: Beginning when galaxies must have been closer together. ( The universe has
expanded yet gravity still keeps the galaxies close)
Nuclear Fusion: Process in which lightweight atomic nuclei smash together and stick to
make heavier nuclei.
Supernovae: When massive stars explode and blow their content back into space—that
content later forms new stars and the cycle continues.
The most basic motions of Earth are its daily rotation (spin) and its yearly orbit
(revolution) around the sun.
• Earth rotates once each day around its axis at the same time Earth orbits the sun.
(Takes roughly one year.)
• Earth’s orbital path defines a flat plane that we call the ecliptic plane.
• Axis tilt points almost directly to Polaris/ North Star.
• Earth orbits the sun and