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Studying the Stars Magnitude Magnitude (History) 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) 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) 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) 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