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