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Oxford Reference. Publications Pages Publications Pages. Recently viewed 0 Save Search. Your current browser may not support copying via this button. Subscriber sign in You could not be signed in, please check and try again. Username Please enter your Username. For Sirius B, the location is 06h 45m Based on the star's spectral type of DA2 , Sirius B's colour and type is white white dwarf. The Sun's Mass is 1,,,,,,, billion kg. To give idea of size, the Sun is Sirius B apparent magnitude is 8.
Apparent Magnitude is also known as Visual Magnitude. Absolute Magnitude is the apparent magnitude of the star from a distance of 10 parsecs or This assumes that there is nothing in between the object and the viewer such as dust clouds.
A very bright object, such as the Sun or the Moon can have a negative apparent magnitude. With the recalibration of Hipparchus' original values the bright star Vega is now defined to have an apparent magnitude of 0. Following the telescopic discovery of faint stars in the early s the magnitude scale has also had to be extended to objects fainter than magnitude 6.
The table below shows the range of apparent magnitudes for celestial objects. If a star of magnitude 1 is 2. You need to be careful here. Two objects of different magnitudes therefore vary in brightness by 2. Example 1: Comparing two stars. Using equation 4. Example 2: How much brighter is the Sun than the full Moon? For this we recall from the table above that the Sun has an apparent magnitude of It is important to remember that magnitude is simply a number, it does not have any units.
The symbol for apparent magnitude is a lower case m ; you must make this clear in any problem. What does the fact that Sirius has an apparent magnitude of Another way of thinking about this is to ask why is Sirius the brightest star in the night sky? A star may appear bright for two main reasons:.
The apparent magnitude of a star therefore depends partly on its distance from us. In fact Sirius appears brighter than Betelgeuse precisely because Sirius is very close to us, only 2. The realisation that stars do not all have much the same luminosity meant that apparent magnitude alone was not sufficient to compare stars. A new system that would allow astronomers to directly compare stars was developed. This system is called the absolute magnitude, M. The absolute magnitude, M , of a star is the magnitude that star would have if it were at a distance of 10 parsecs from us.
A distance of 10 pc is purely arbitrary but now internationally agreed upon by astronomers. This logarithmic scale is also open-ended and unitless. Again, the lower or more negative the value of M, the brighter the star is. Absolute magnitude is a convenient way of expressing the luminosity of a star.
Once the absolute magnitude of a star is known you can also compare it to other stars. As you may recall from the section on astrometry, most stars are too distant to have their parallax measured directly.
Nonetheless if you know both the apparent and absolute magnitudes for a star you can determine its distance.
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