Measuring the Stars Chapter 29.2
A. Groups of Stars 1. Constellations – used by ancients to group and organize stars for study. 2. Star Clusters – a group of stars that are gravitationally bound to each other. - may be open clusters or globular clusters. Wikipedia Wikipedia Wikipedia
3. Binaries – two stars that are gravitationally bound together and orbit a common center of mass. 4. Doppler Shifts – star motion can be determined by observing the direction of movement of its spectral lines. - red shift – movement toward red end of spectrum (star moving away). - blue shift – movement toward blue end of spectrum (star moving closer). Wikipedia
B. Stellar Distances 1. Units a. Light-year (ly) – distance light travels in one year. b. Parsec (pc) – equivalent to 3.26 light-years. 2. Parallax – method used to measure distance to nearby stars. Video – Light Years (3:48 min) Wikipedia
C. Properties of Stars 1. Apparent Magnitude – how bright a star appears from Earth. - depends on both brightness and distance from Earth. 2. Absolute Magnitude – how bright a star would appear if placed at a distance of 10 parsecs. - allows stars to be compared strictly on the basis of brightness alone. 3. Luminosity – a measure of the actual brightness of a star in terms of energy output.
D. Classification of Stars 1. Temperature – vary from 2800K (red) to 40,000K (blue) with orange and yellow in between. 2. Composition – all stars are basically the same with hydrogen and helium composing about 98% of their mass.
3. H-R Diagrams • used to classify stars based on their absolute magnitude and temperature (color). - about 90% of the stars lie along the main sequence. Wikipedia