Stars have Unique Properties. Note the different colors of stars in this portion of a Hubble Space Telescope photo above. What do these colors mean? What about their brightness? Does their image size mean anything? How do astronomers known their distance? There’s more than meets the eye!.
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Note the different colors of stars in this portion of a Hubble Space Telescope photo above. What do these colors mean? What about their brightness? Does their image size mean anything? How do astronomers known their distance? There’s more than meets the eye!
Intensity is related to magnitude: definition of intensity is energy/second reaching a unit area at the observer
“Solar Constant” = 1500 Watts/sq. Meter--this is the amount of energy reaching the earth’s surface per second, per square meter…
Magnitude is a convenient measure of intensity!
A Magnitude difference of 5 = Intensity ratio of 100.
Intensity = IA
Magnitude = MA
Intensity = IB
apparent Magnitude is a measure of intensity, which is determined by both distance and intrinsic brightness.
Intensity can be the same for a flashlight close up, or a car headlight far away.
If all objects were at same distance,however, magnitude would measure Luminosity (intrinsic brightness)
Luminosity = Total energy output of object. The Sun’s luminosity is about 1025
watts (that is a lot of 100 watt light bulbs!)
m = apparent magnitude
M = absolute Magnitude
D = distance to Star, so the weird equation is…….
M-m = -5log(d) + 5
So what good is it?
If you know both M and m, you can find distance. If you know m and d, you can find M.
This chart is a plot of number of stars as a function of luminosity. Note that most stars are less luminous than our sun But a few are much more luminous….imagine a star Putting out 100 times the energy of our sun…but they are out there!
We find that there is a direct correlation between absolute magnitude and spectral type…in other words
Stars of the Spectral type have the same Absolute magnitude!
For more info: http://www.enchantedlearning.com/subjects/astronomy/stars/startypes.shtml
Astronomy picture of the Day