NATS 1585 Lecture Notes - Lecture 6: Globular Cluster, Open Cluster, Main Sequence
21 Sep 2017
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Document Summary
The brightness of a star depends on both distance and luminosity. Luminosity: amount of power a star radiates (energy per second = watts) Apparent brightness: amount of starlight that reaches earth (energy per second per square meter) Relationship between apparent brightness and luminosity depends on distance: We can determine a stars luminosity if we can measure its distance and apparent brightness. The effect whereby the position or direction of an object appears to differ when viewed from different positions, e. g. , through the viewfinder and the lens of a camera. P = parallax angle d (in parsecs) = 1/p (in arcseconds) d (in light-years) = 3. 26 x 1/p (in arseconds) Level of ionization also reveals a star"s temperature. Remembering spectral types (hottest) o b a f g k m (coolest) We the light from both a and b. We can directly observe the orbital motions of these stars. We determine the orbit by measuring doppler shifts.
