1. 25.1 Properties of Stars

2. Constellation An apparent group of stars originally named for mythical characters. There are 88 constellations dividing up the sky.

3. Binary Star One of two stars revolving around a common center of mass under their mutual gravitational attraction.

4. Light-year The distance light travel in a year, about 9.5 trillion kilometers.

5. Apparent Magnitude The brightness of a star when viewed from Earth.

6. Absolute Magnitude The apparent brightness of a star if it were viewed from a distance of 32.6 light-years; used to compare the true brightness of stars.

7. Main-Sequence Star A star that falls into the main sequence category on the H-R diagram; this category contains the majority of stars and runs diagonally from the upper left to the lower right on the H-R diagram.

8. Red Giant A large, cool star of high luminosity; a star occupying the upper-right portion of the H-R diagram.

9. Supergiant A very large, very bright red giant star.

10. Cepheid Variable A star whose brightness varies periodically because it expands and contracts; a type of pulsating star.

11. Nova A star that explosively increases in brightness.

12. Nebulae A cloud of gas and/or dust in space.

13. Key Concept Color is a clue to a star’s temperature.

14. Key Concept Binary stars are used to determined the star property most difficult to calculate its mass.

15. Key Concept The nearest stars have the largest parallax angles, while those of distant stars are too small to measure.

16. Key Concept Three factors control the apparent brightness of a star as seen from Earth: how big it is, how hot it is, and how far away it is.

17. Key Concept A Hertzsprung-Russell diagram shows the relationship between the absolute magnitude and temperature of stars.