Stars and HR Diagrams

What is a star? Gases and radiant energy (heat and Light) Vary in color (red, blue, orange, yellow) Vary in size (12 km – 1,392,000,000 km) Vary in mass (1/50th – 50X the sun)

What is our Sun? A star Medium sized, or main sequence star 1,392,000 km 330,000 more massive than earth

How to tell elements Before Hubble telescope used: Spectrometer Device used to analyze light from stars Separates light wavelengths Like a prism

Star Composition Discover by dark-line spectra Different lines for every element in the star Stars are composed of elements found on earth Hydrogen and Helium are the most common in stars

Star temperature Indicated by color: Blue= hot (10,000 to 50,000 C) Yellow=middle (4,000 to 10,000 C) Red= coolest (2,800 to 4000 C) Steel melts at 1300 C

Star Motion Two types Apparent Actual Motion visible with unaided eye Move westward around polaris (N. Star) Earth Rotating See different stars in different seasons Earth Revolves around the sun Actual Rotate on axis Revolve around another star Move away or towards earth

Star Movement and Distance Circumpolar- star that are always overhead (North Star, Big Dipper, Little Dipper) Parallax- distance determined by star movement in the sky measure over 6 months Big Shift= close to earth Hardly Moves= far star Red Shift and Blue Shift Look at the spectrum of the stars Red Shift stars are moving away from earth (long wavelengths of light) Blue Shift stars are moving towards the earth Shorter wavelengths of light)

Star Distance Light Years: Distance light travels in a year Speed of light is 300,000 km/s or 670,616,629 miles per hour Sunlight takes about 8 minutes to get from the sun to here.

Star Brightness Two scales: Apparent Magnitude How bright a star APPEARS on earth Bright stars (low #’s), dim stars (high Numbers) Can have negative numbers (planets, sirius)

Star Brightness Cont. Absolute Magnitude Nearby Stars- Far Stars- How bright a star ACTUALLY is Measured from 32.6 light years away from earth Nearby Stars- Lower number apparent magnitude than absolute magnitude. Appear brighter because they are closer Far Stars- Higher number apparent magnitude than absolute magnitude Appear dimmer than they actually are

Star Classification Hertzsprung Russel Diagram (H-R Diagram) Surface temp vs. absolute mag. Brightness increases as Temp increases

Groups on H-R Main sequence stars Middle band, Visible Giants-cool, bright, because large Super Giants- very cool, bright, large White Dwarfs- hot, dim, because small http://sunshine.chpc.utah.edu/labs/star_life/hr_interactive.html