Characteristics Of Stars Galaxy: A collection of stars, gases and dust. Universe: Contains billions of galaxies.

Types of Galaxies 1. Spiral 2. Elliptical 3. Irregular

Spiral Galaxies: Arms spiral outward like a pinwheel Our galaxy, The Milky Way, is a spiral galaxy

Elliptical Galaxies: Look like flattened balls or a football. Have billions of stars, but little gas and dust. Contain the oldest stars

Irregular Galaxies No definite shape Example: Large Magellanic Cloud

( Light will travel 9.5 million, million kilometers in one year!) Scientists use LIGHT YEARS to measure distances in space. A light year is the distance light travels in one year. Light travels at the speed of 300,000,000 meters/second.

Classifying Stars Stars are classified by 3 Main Characteristics: 1. Size 2. Temperature 3. Brightness

Hottest (20,000-50,000*C) : (10,000*C) (6,000*C) (4,000-5,000*C) Color reveals the temperature of a star. Hottest (20,000-50,000*C) : (10,000*C) (6,000*C) (4,000-5,000*C) (3000*C) Blue White Yellow Red-Orange Red

Brightness of Stars Apparent Magnitude: Brightness as seen from earth Absolute Magnitude: Brightness of a star from a standard distance

Hertzsprung-Russell Diagram A graph plotting brightness and temperature. 90% of stars are Main Sequence