H-R Diagram

Star Brightness Luminosity: the total amount of energy emitted by a star per unit time Measured in joules per second or watts Like a lightbulb!

Magnitude: logarithmic measure of brightness Apparent magnitude (m): brightness as it appears from earth Absolute magnitude (M): intrinsic brightness of an object as it would appear if all objects were the same distance from earth Smaller numbers = brighter! If you know the m (which we can measure directly), you can calculate the M if distance (d) is known:

An H-R Diagram is… A graph of stars’ BRIGHTNESS and TEMPERATURE It also shows color since color is related to temperature It was made by two astronomers who plotted the data for thousands of stars and noticed some trends. It stands for Hertzsprung-Russell Diagram

Which is hotter? main sequence white dwarf

Answer: white dwarf

Trends….. Temperature DECREASES as you move to the Right on the X-axis Absolute Magnitude INCREASES as you move up on the Y-axis. NEGATIVE absolute magnitude values are BRIGHTER than POSITIVE absolute magnitude values

Arrival on the Main Sequence The mass of the protostar determines: how long the protostar phase will last where the new-born star will show up on the Main Sequence i.e., what spectral type the star will have while on the main sequence