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Studying the Stars
Magnitude
Magnitude (History)
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Magnitude is a measure of the
brightness of a star.
In 1856, British astronomer Norman
Pogson proposed a scale of stellar
magnitudes.
– He noted that we receive 100 times more
light from a first magnitude star as from a
sixth.
Magnitude
(Orders of Magnitude)
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Pogson assigned the brightest stars the first
order of magnitude (magnitude = 1), and
dimmer stars were 2nd, 3rd, 4th order, etc.
(magnitudes = 2, 3, 4, etc.)
Now that we can be more accurate in our
measurements, stars can have more specific
magnitudes like 1.5, 6.73, etc. and even
negative numbers for those stars that are
brighter than 1st order.
Magnitude (Brightness)
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Negative numbers are the brightest,
positive numbers are the dimmest.
– The naked eye can see down to around
the sixth magnitude (that is +6).
– Galileo saw about magnitude 9 with his
telescope.
– The Hubble Space Telescope? About
magnitude 29.
Magnitude
(Apparent vs. Absolute)
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Apparent Magnitude: How bright a
star appears from Earth
Absolute Magnitude: How bright a
star really is (if you could see them all
from the same distance)
Magnitude
(Apparent vs. Absolute)
Examples:
 The star Betelgeuse has an apparent
magnitude of 0.5 because it is so far away,
but if you could go closer to it, you would
see that it is VERY bright and has an
absolute magnitude of -7.2
 The sun is so close to us that it has an
apparent magnitude of -26.7, but if you
compare it to other stars, it isn’t really very
bright and has an absolute magnitude of
only 4.8