1. Pages 700 - 721

2.  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

3.  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

4.  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

5.  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!!

6.  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 = -26.7  Absolute magnitude = 5.0