Stars 1.ppt

Stars

By: Terri Downs, Mary Fuson, and Carrie Robison

What Are Stars? • Stars are balls of gas that release energy from inside themselves.

• In order to be recognized as a star, it has to have two characteristics: – be self-bound by gravity, – it has to radiate energy.

How are Stars Formed? • They are formed in space in large clouds of gas and dust called nebulae. • Atoms inside the nebula accelerate inward due to the force of gravity and they collide rapidly with each other, causing the center of the nebula to become very dense and hot, causing the temperature of the protostar to rise. • The object switches to become a “true star” and it is then able to make its own heat and light. • The life of the star then depends on its mass.

Colors of Stars • The color of a star measures its temperature. – Red=the coolest, – Yellow=an intermediate temperature, – Blue=the hottest temperature

• A star can appear bright just because it is really bright, or because of its closeness to the Earth.

Color and Temperature of selected stars Star

Color

Surface Temperature in Celcius

Proxima Centuari

Red

2,300

Epsilon Iridani

Orange

4,600

Sun

Yellow

5,700

Vega

White

9,900

Sirius

White

10,000

Alnilam

Blue

27,000

• The brightness of a star as seen from the Earth depends on two factors: 1. The distance 2. The actual brightness (or absolute brightness) of the star

• The star’s brightness as seen from the Earth is its apparent brightness. Apparent brightness- the star’s brightness as seen from Earth Absolute brightness- A star’s absolute brightness is the brightness the star would have if all stars were the same standard from the Earth.