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# Star Classification

## Stars are classified by color and temperature; main sequence stars are found on the Hertzspring-Russell diagram.

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Visiting Our Closest Neighbors

### Visiting Our Closest Neighbors

Source: http://commons.wikimedia.org/wiki/File:ESO_-_Alpha_Centauri_and_the_Southern_Cross_(by).jpg

Alpha Centauri is the closest star system to our solar system, only 4.4 light years away. Its three stars are Alpha Centauri A on left, B on right and Proxima Centauri in the red circle. If we were to go visit a star beyond our Sun, it would probably be Alpha Centauri.

#### Why It Matters

Source: http://en.wikipedia.org/wiki/File:Artist%E2%80%99s_impression_of_the_planet_around_Alpha_Centauri_B_(Annotated).jpg

The planet around star Alpha Centauri B (part of the triple star system that is closest to Earth) shown through an artist's impression. [Figure2]

• Alpha Centauri is a triple star system. All three are main sequence stars.
• Alpha Centauri A and Alpha Centauri B orbit each other has a binary star.
• They are orbited from a great distance by Proxima Centauri.
• Alpha Centauri A is a G-class star, the same as our Sun. Alpha Centauri B is a bright K-class star. Proxima Centauri is a red dwarf star.
• Alpha Centauri B may be orbited by an exoplanet, Alpha Centauri Bb. The planet orbits at one-tenth the distance between Mercury and the Sun.

#### Explore More

1. Why is Alpha Centauri so bright in the Southern Hemisphere sky?
2. What is the biggest problem with sending a space probe to Alpha Centauri?
3. Is Alpha Centauri Bb a place we might look for extrasolar life?
4. What technological developments do we need to wait for before it is practical to travel to Alpha Centauri? What is the problem with this?

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