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Calculating the stars5/21/2023 What Determines a Star's Luminosity?Īs we have seen in the section on spectroscopy, we can approximate the behaviour of stars as black body radiators. In astronomy, we generally give stars 3D spherical coordinates. So, finding the distance between them, becomes a simple matter of 3D trigonometry. This approach is convenient as the luminosity of stars varies over a huge range from less than 10 -4 to about 10 6 times that of the Sun so an order of magnitude ratio is often sufficient. Computing the Distance Between Two Stars or Planets In this case of computing the distance between two stars or planets, we are treating the bodies as simple points in 3D space. Thus if a star is twice is luminous as the Sun, L */ L sol = 2. Rather than always use this exact value it is often more convenient to compare another star's luminosity L * to the Sun's as a fraction or multiple. Our Sun has a luminosity of 3.84 × 10 26 W or J.s -1 which can be denoted by the symbol L sol (actually the subscript symbol is normally a dot inside a circle - the standard astrological symbol for the Sun but this cannot be shown in html). This is also used to measure a star's colour as described on the next page. Astronomers in practice also measure an object's luminosity in specific wavebands so that we can discuss an object's X-ray or visible luminosities for example. A star's power output across all wavelengths is called its bolometric luminosity. This is therefore the power output of a star. Luminosity, L, is a measure of the total amount of energy radiated by a star or other celestial object per second. The absolute magnitude of a star is simply a simple way of describing its luminosity. Using Luminosity to Compare Stars - Sample Problems. Deriving the Magnitude/Distance Equation.
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