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Astronomy Research
Project
By Christina Ciganik
Star Brightness and Distance from Earth
Absolute Magnitude and Luminosity
Stars Distance from Earth
• The Sun is the star closest to the Earth at a distance of about 150 million kilometers
• This distance is one Astronomical Unit (AU)
• Astronomical units can be used to measure distances within our solar systems
Light Years
• A Light Year is the distance a single ray of light can travel in space in one year (9.5 trillion kilometers)
• A single ray of light travels at about 300,000 kilometers per second in space
Luminosity
• “A measure of the total amount of energy radiated by a star or other celestial object per second.”
- ATOE
• The actual brightness of a star which depends on its size and temperature
Apparent Magnitude• Apparent Magnitude – How bright a
star appears from Earth’s surface• Brightest star is the 1st magnitude • Stars with a weaker brightness have
lower magnitudes• A strong magnitude is 2.5 times
greater than the one after it• Does not show how bright a star
really is only how bright it appears
Absolute Magnitude
• Absolute Magnitude is the Apparent Magnitude of a star placed at 32.6 light years away from the sun
• Lets us compare the stars’ luminosities without the problem of distance
HR Diagram
Temperature Versus Absolute Magnitude
HR Diagram
Temperature
Luminosity
• HR stands for Hertzsprung-Russell
• Danish astronomer Ejnar Hertzsprung and American astronomer Henry Russell discovered the diagram originally
HR Diagram (cont.)
• “As stars live out their lives, changes in their structure are reflected in changes in their temperatures, sizes, and luminosities”
• These factors cause them to move on the H-R Diagram.
• The HR Diagram shows the basic characteristics of stars and the relationship between absolute magnitude, temperature, and luminosity of them
• You can use the diagram to find the temperature and brightness of a star
3 Major sections of the HR Diagram
• Main Sequence
• Giants and Supergiants
• White Dwarfs
Main Sequence• “A major grouping of stars that
forms a relatively narrow band from the upper left to the lower right when plotted according to luminosity and surface temperature on the Hertzsprung-Russell diagram.”
-dictionary
•The Main Sequence is a stable state where stars shine steadily for a long period of time•The greatest amount of stars are on the Main Sequence •Stars will spend almost 90% of their lifetime on the Sequence
Main Sequence (cont.)
Giants and Supergiants
• Very Luminous• Low surface temperatures• Stage in a star’s life after the Main
Sequence• Not as much time of the star’s life
is spent here• The two types are blue-white
giants and red giants
White Dwarfs
• Very Dense
• High surface temperature
• Last stage before death
• Very Faint
• About the size of earth
HR Diagram in Action
http://www.astro.ubc.ca/~scharein/a311/Sim/hr/HRdiagram.html
http://aspire.cosmic-ray.org/labs/star_life/hr_interactive.html
Bibliography--get full info• Gareth, James. "The Hertzsprung Russel Diagram." HR Diagram. 23 May
2006 <http://freespace.virgin.net/gareth.james/3__objects/HR_Diagram/hr_diagram.html>.
• "Hertzsprung-Russell Diagram." Wikipedia the Free Encyclopedia. 17 May 2006. Wikimedia Foundation, Inc.
• "Interpreting the HR Diagram." How Hot is That Star? 15 Dec. 1997. University of California. 18 May 2006 <http://www.smv.org/jims/l6a.htm>.
• "Main Sequence Stars." 18 May 2006 <http://www.astro.umd.edu/education/astro/stev/main_seq.html>.
• Smith, Gene. "The Hertzsprung-Russell Diagram." Gene Smith's Astronomy Tutorial. 21 Apr. 1999. University of California, San Diego. 19 May 2006 <http://cassfos02.ucsd.edu/public/tutorial/HR.html>.
• Soper, Davison E. "Hertzsprung-Russell Diagram." nstitute of Theoretical Science. 22 May 2006 <http://zebu.uoregon.edu/~soper/Stars/hrdiagram.html>.
• Spaulding, Nancy E., and Samuel N. Namowitz. Earth Science. Evanston Illinois: McDougal Littell, 1994. 379-382.
THE END