Vega
Category:Stars
- This article is about Vega, the star. For other uses: see Vega (disambiguation)
Vega (
Alpha Lyrae) is the lead
star in the
constellation Lyra, reaching near directly overhead in the mid-northern latitudes, during the
summer. It is a "nearby star" at only 25
light years distance, and together with
Arcturus and
Sirius, one of the brightest stars in the
Sun's neighbourhood. Vega is a
vertex of the
Summer Triangle. It is the fifth brightest start in the Northern night sky.
Its
spectral class is A0V (Sirius, an A1V, is slightly less powerful) and it is firmly in the
main sequence,
fusing hydrogen to
helium in its core. Since more powerful stars use their fusion fuel more quickly than smaller ones, Vega's life time is only one billion years, a tenth of our Sun's. Vega is two and a half times more massive than our Sun and burns at fifty times the power.
Vega has a disk of dust and gas around it, discovered by the
IRAS satellite in the mid
1980s. This either signifies
planets or that planets that may soon form. The
protoplanetary disk, as can be guessed from its name, is believed to be a precursor to the formation of planets but can persist long after planets have been formed if there are no
gas giant planets such as
Jupiter.
In about 14,000 AD, Vega will take over from
Polaris as the
North Star, owing to the
precession of the equinoxes. See Polaris for more information.
Professional astronomers have used Vega for the calibration of absolute
photometric brightness scales. When the magnitude scale was fixed, Vega happened to be close to zero magnitude. Therefore the
visual magnitude of Vega was decided to be, by definition, zero at all wavelengths. It has also a relatively flat
electromagnetic spectrum in the visual region (wavelength range 350-850 nanometers, most of which can be seen with the human eye), so the flux densities are roughly equal, 2000-4000
Jy. The flux density of Vega drops rapidly in the
infrared, and is near 100 Jy at 5
micrometers.
Fiction\n*
Carl Sagan's
Science Fiction novel and
movie Contact feature travel to a
planet near the
star Vega.
Mythology
\nSee Chinese Valentine's Day.
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