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
Luminosity
Temperature
• HR stands for HertzsprungRussell
• 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
Main Sequence (cont.)
•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
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.cosmicray.org/labs/star_life/hr_interactive.html
Bibliography--get full info
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Gareth, James. "The Hertzsprung Russel Diagram." HR Diagram. 23 May
2006
<http://freespace.virgin.net/gareth.james/3__objects/HR_Diagram/hr_diagra
m.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.
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