What is the brightest star in the night sky?
List of brightest stars
Stellar brightness is traditionally based on the apparent visual magnitude as perceived by the human eye, from the brightest stars of 1st magnitude to the faintest at 6th magnitude. Since the invention of the optical telescope and the documenting of binary stars and multiple star systems, stellar brightness could be expressed as either individual (separate) or total (combined) magnitude. The table is ordered by combined magnitude of all naked eye components appearing as if it they were single stars. Such multiple star systems are indicated by parentheses showing the individual magnitudes of component stars bright enough to make a detectable contribution. For example, the double star Alpha Centauri has the total or combined magnitude of −0.27, while its two component stars have magnitudes of +0.01 and +1.33.[2]
New or more accurate photometry, standard filters, or adopting differing methods using standard stars can measure stellar magnitudes slightly differently. This may change the apparent order of lists of bright stars. The table shows measured V magnitudes, which use a specific filter that closely approximates human vision. However, other kinds of magnitude systems do exist based on different wavelengths, some well away from the distribution of the visible wavelengths of light, and these apparent magnitudes vary dramatically in the different systems.[3] For example, Betelgeuse has the K-band (infra-red) apparent magnitude of −4.05.[4]
Some stars, like Betelgeuse and Antares, are variable stars, changing their magnitude over days, months or years. In the table, the range of variation is indicated with var. Single magnitude values quoted for variable stars come from a variety of sources. Magnitudes are expressed within the table are when the stars are either at maximum brightness, which is repeated for every cycle, e.g., the eclipsing binary Algol; or, if the variations are small, as a simple average magnitude. For all red variable stars, describing a single maximum brightness is often difficult because each cycle produces a different maximum brightness, which is thought to be caused by poorly understood pulsations in stellar evolution processes. Such quoted stellar brightness is sometimes based on the average maximum apparent magnitude [5] from estimated maximums over many observed light-curve cycles, sometimes spanning across centuries. Results often quoted in the literature are not necessarily straightforward and may differ in expressing an alternate value for a singular maximum brightness or as a range of values.
A select number of stars, thought to be uniformly fixed in brightness, are used as standard stars. These standard stars have carefully determined magnitudes that have been analysed over many years, and are often used to determine other star's magnitudes or their stellar parameters using comparatively consistent scales.[6]