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Astronomy - Session 2

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Parandis Khavari

Astronomy - Session 2  apparent visual magnitude  describes how stars look to human eyes  apparent magnitude  the brightness of stars is measured using the magnitude scale  ancient astronomers divided the stars into six magnitudes  m =vapparent visual magnitude  a star may have negative or positive magnitude  Q. what is the name of the star that serves as the zero of the magnitude scale?  A. Vega  Q. what is brighter, a -1 star or a +3.5 star?  A. a -1 m vtar is brighter than a +3.5  12,000 BC  Vega was the northern star  distance is measured through ground-based parallax measurements  its spectrum was amongst the first to be measured  Q. the m ov a number of stars is given- sort them in order of descending brightness  a) Proxinma Centauri, +11.05  b) Betelgeuse, 0.42  c) Antares, +0.96  d) Dubje, +1.79  e) Sirius A, -1.46  f) Sirius B, +8.49  A. e), b), c), d), f), a)  distance and luminosity  two factors in determining m v  absolute magnitude  also known as "intrinsic brightness"  luminosity  total electromagnetic output of energy per unit of time  seconds  most convenient way to do measurement of time in astronomy  flux (F)  apparent magnitude is a function of flux  measurement of the received energy  defined as the energy (measured in Joules) per second per one square meter  by definition obeys the Inverse Square Law  directly proportional to luminosity  F ↔ ( d/s/m 2  watt= d /s  absolute magnitude  not a reliable measure for the true brightness of a star  true measurement for the intrinsic brightness of the stars is called absolute magnitude  definition as the apparent magnitude of all stars if they were moved to a distance 10 parsecs (33 light years) from the Earth  converting absolute magnitude to apparent m
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