Lauren+and+Jane+-+Red+Class

=Milky Way/ Universe/ Light Years=

=Lauren S. and Jane U.= =Red Class=

Basics:

 * The Milky Way is the name of our galaxy
 * Spiral Galaxy
 * It has 100 billion stars in it
 * When we look at the sky, everything we can see (except the Andromeda Galaxy) is in the Milky Way
 * Our solar system lies in the spiral arm of the milky way
 * The Milky Way's spiral arms contain intersteller matter:
 * open star clusters
 * young stars

Dimensions of the Milky Way:

 * It takes our solar system 200-250 years to orbit around the Milky Way
 * The Milky Way is about 140,000 light years in diameter
 * The greatest thickness of the Milky Way is 20,000 light years

The Milky Way Contains...

 * 9 planets and at least 61 natural satellites (such as moons)
 * 1000s of asteroids, millions of meteroids, and many comets
 * A few hundred galatic clusters (such as the Pleiades). It is typical for spiral galaxies to have galactic clusters.
 * Our solar system, which is divided into two types of planets:
 * The terrestial planets are closest to our sun. These planets include Mercury, Venus, Earth, and Mars
 * The jovian planets are further from the sun than the terrestial planets. They are separated by an asteroid belt. These planets include Jupiter, Saturn, Uranus, Neptune and (Pluto)[[image:http://www.universetoday.com/wp-content/uploads/2006/08/2006-0816planets.jpg width="466" height="286"]]

Where is the Milky Way?

 * The Milky Way galaxy belongs to a small cluster of 17 galaxies called the Local Group
 * Magellanic clouds and Andromeda galaxies are our neighbors

The Milky Way is a spiral galaxy, with the sun in the spiral arm of the Milky Way.

Other Information about the Milky Way:

 * Constellations in the milky way, except for those near polaris, rise in the east
 * Ecliptic: name of the path followed by the Zodiac constellations
 * We haven't sent a spacecraft outside of the Milky Way

**References to Our Galaxy:**

 * Stars Test from 2/15
 * Questions 4-6, 8-10
 * Rotation and Revolution Test from 12/13
 * Questions 1-21, 11-14, 18,
 * Chapter 22: The Sun and it's Solar System
 * Section II Topic 7, 9

__Universe:__
From left to right: Spiral Galaxy, elliptical galaxy, irregular galaxy.
 * The Universe contains 100 billion galaxies
 * Formation of our universe. "Big Bang":
 * 15 billion years ago
 * The whole universe was packed into one dense sphere of hydrogen
 * Mass of hydrogen exploded and parts of this cloud moved outward and condensed into galaxies
 * Galaxies continued moving outward and the universe expanded
 * There are three types of galaxies in the universe:
 * Spiral galaxies: Milky Way
 * Elliptical galaxies
 * Irregular galaxies: magellanic clouds

**References to the Universe:**

 * Stars Test from 2/15
 * Questions 7
 * Chapter 21 Stars and their Galaxies
 * Section IV Topic 15, 16, 18

__Light Years:__

 * An Astronomical Unit (AU) is used to describe distances in our own Solar System. An **AU is 9,300,000 miles**
 * An AU is also the **average distance between Earth and the Sun**
 * The AU, however, is not big enough to measure vast distances in outer space. Light years are used to measure longer distances. A **light year** is **6 trillion miles**
 * A light year is also the distance a particle of light travels in one year
 * Light travels at the speed of 186,000 miles per second
 * Light years are used to describe distances in the **Milky Way**, the home of our solar system
 * To find the distance of a star when given the amount of light years, take the number of light years and multiply it by 6 trillion miles

**References** **to Light Years:**

 * Rotation and Revolution test from 12/13
 * Questions 25-35
 * Chapter 21 Stars and their Galaxies
 * Section I Topic 3

Practice Problems:

 * 1) Procyon, in Canis Minor, is relatively close to us. It is just 10 light years away. That means the twinkle of Procyon that we see on Earth left the star __(a)__ years ago. It also means that Procyon is about __(b)__ miles away from Earth.
 * 2) Sirius, in Canis Major, is just 8.5 light years away. That means it is about __(c)__ miles from our solar system.

Answers:

 * 1) (a) 10 years ago. (b) 60 trillion years old. (c) 51 trillion years old.