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Star color is an indication of temperature Very hot stars (30,000 K) emit high-energy, low wavelength radiation. What color do they appear?Blue Yellow Middle or average temp. stars (5000 – 6000 K) appear Yellow like our sun Cooler stars (< 5000 K) emit low-energy, large wavelength radiation. What color do they appear?Red
Difficult to calculate Unless the star is part of a pair Binary stars – two stars revolving around a common center of mass under their mutual gravitational attraction More than 50% of stars occur in pairs or multiples Stars of equal mass will be equidistant from the center of mass If stars’ mass is not equal, the center of mass will be closer to the more massive of the two If the sizes of their orbits are known mass can be calculated Binary Sunset Binary Sunset
Stellar parallax – slight shifting in the apparent position of a nearby star due to the orbital motion of Earth Thumb’s up demo Nearest stars have largest parallax effect Stellar Parallax Simulator Stellar Parallax Simulator This method only works with stars that are relatively close to Earth (within 100 light-years) Of the billions of stars in the Milky Way galaxy, only about 700 are within parallax range
1,000 m = 1 km 150,000,000 km = 1 AU = 93,000,000 miles Distances between stars are so large we need an even bigger standard of measure Light-year – the distance light travels in one year 1 light-year = 9,500,000,000,000 km (9.5 trillion) Proxima Centauri, our nearest stellar neighbor, is 4.3 light-years away How far is that in km? 40,850,000,000,000 km!!
The measure of a stars brightness is its magnitude Apparent magnitude – a star’s brightness as it appears from Earth; affected by three factors How big it is; larger = brighter How hot it is; hotter = brighter How far it is away; closer = brighter Absolute magnitude – brightness of a star if it were viewed from 32.6 light-years; compares true brightness Large negative numbers are bright, large positive numbers are dim For our sun; Apparent magnitude = Absolute magnitude = 5.0