* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Absolute Magnitude - School
Survey
Document related concepts
Observational astronomy wikipedia , lookup
Timeline of astronomy wikipedia , lookup
Dyson sphere wikipedia , lookup
Corona Borealis wikipedia , lookup
Astronomical unit wikipedia , lookup
Astronomical spectroscopy wikipedia , lookup
Star of Bethlehem wikipedia , lookup
Star formation wikipedia , lookup
Canis Minor wikipedia , lookup
Canis Major wikipedia , lookup
Cassiopeia (constellation) wikipedia , lookup
Auriga (constellation) wikipedia , lookup
Aries (constellation) wikipedia , lookup
Corona Australis wikipedia , lookup
Cygnus (constellation) wikipedia , lookup
Perseus (constellation) wikipedia , lookup
Corvus (constellation) wikipedia , lookup
Transcript
Absolute Magnitude recall the definition of absolute magnitude demonstrate an understanding of the inverse square law nature of the intensity of light demonstrate an understanding of, and perform simple calculations involving, apparent magnitude (m), absolute magnitude (M) and distance (d in pc), using this formula:M = m + 5 – 5 log d involving powers of 10 only (students are not required to calculate d using this equation, only M and m) Apparent magnitude (m) is how bright a star appears to be but this obviously depends on how far away it is. The closer the star is to us the brighter it will appear to be. The Absolute Magnitude (M) of a star is a measure of how luminous it actually is, or rather how bright it would appear to be from a certain distance compared with every other star at the same distance. M is defined as how bright a star would appear to be if it were at a distance of 10 parsecs from Earth. (so if a star were actually 10 parsecs from Earth then M and m would be equal) If we know the apparent magnitude (m) and distance in parsecs (d) a star is away from us we can calculate its absolute magnitude (M) using this equation; M = m + 5 - 5 log d 10 I am not going to explain logarithms here. All you need to know is that there is a "log" button on your calculator which you can use to find log d. Examples: Star d (parsecs) m M Sirius 2.64 -1.47 1.41 Vega 7.67 0.04 0.5 Betelgeuse 73.6 0.41 Polaris 132 1.99 e.g. for Sirius M = -1.47 + 5 - (5 x log 2.64) = 3.53 - 2.11 = 1.42 (near enough!) In the exam it will be even simpler than this. Any distance involved will be a multiple of 10. If d = 100 then log10d = 2 If d = 1,000 then log10d = 3 if d = 10,000 then log10d = 4 So you shouldn't even need a calculator. Show that the absolute magnitude of Vega is the value shown in the table and calculate the absolute magnitudes of Betelgeuse and Polaris yourself. The Inverse Square Law Imagine an object, such as a star, which emits light. As the light spreads out it becomes less intense. One can see from the diagram below that if a certain amount of light travels twice as far then it spreads out over an area four times as big. This means that it will be 1/4 of the intensity it was. The intensity of the light is proportional to 1/r2 where r is the distance from the source. If there were two stars as luminous as each other but one was twice as far away as the other then it would appear 1/4 as bright as the other. If two stars appeared the same brightness but one was further away we know from the above that it is √ 2 x further than the closer star.