1. 25.1 Properties of Stars

2. Vocabulary

3. Constellation An apparent group of stars originally named for mythical characters. The sky is divided into 88 constellations.

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

5. Light-year The distance light travels in a year, about 9.5 trillion kilometers.

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

7. Absolute Magnitude The apparent brightness of a star if it were viewed from a distance of 32.6 light-years.

8. Main-sequence star A star that falls into the main sequence category on the H-R diagram.

9. Red Giant A large, cool star of high luminosity.

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

11. Cepheid Variable A star whose brightness varies periodically because it expands and contrasts.

12. Nova A star that explosively increases in brightness.

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

14. Key Concepts

15. Color is a clue to a star’s temperature.

16. Binary stars are used to determine the star property most difficult to calculate- its mass.

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

18. 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.

19. A Hertzsprung Russell diagram shows the relationship between the absolute magnitude and temperature of stars.