Vega, Our Sometime North Star
Vega is the fifth-brightest star in the night sky and the second-brightest star in the northern celestial hemisphere (after Arcturus). Vega is also known as Alpha Lyrae (α Lyrae, Alpha Lyr, α Lyr), as it is the principle star in the constellation Lyra, the lyre. Vega has been one of the most important stars to humanity since ancient times because it is very bright and easily recognized by its blue color.
Vega, the North Star (Sometimes)
The Earth's axis of rotation precesses, like a wobbling toy top, which means "north" changes over a period of around 26,000 years. Right now, the North Star is Polaris, but Vega was the northern pole star around 12,000 BC and will the the pole star again about the 13,727. If you took a long exposure photograph of the northern sky today, the stars would appear as trails around Polaris. When Vega is the pole star, a long exposure photograph would show stars circling it.
How to Find Vega
Vega is seen in the summer sky in the Northern Hemisphere, where it is part of the constellation Lyra. The "Summer Triangle" consists of the bright stars Vega, Deneb, and Altair. Vega is at the top of the triangle, with Deneb below it and to the left and Altair below both stars and to the right. Vega forms a right angle between the two other stars. All three stars are extremely bright in a region with few other bright stars.
The best way to find Vega (or any star) is to use its right ascension and declination:
Right Ascension: 18h 36m 56.3s
Declination: 38 degrees 47 minutes 01 second
There are free phone apps that you can use to seek Vega by name or by its location. Many allow you to wave the phone across the sky until you see the name. You're looking for a bright blue-white star.
In northern Canada, Alaska, and most of Europe, Vega never sets. In the mid-northern latitudes, Vega is almost directly overhead at night in mid-summer. From a latitude including New York and Madrid, Vega is only below the horizon about seven hours a day, so it can be viewed any night of the year. Further south, Vega is below the horizon more of the time and may be trickier to find. In the Southern Hemisphere, Vega is visible low on the northern horizon during the Southern Hemisphere's winter. It is not visible south of 51° S, so it cannot be seen at all from the southern part of South America or Antarctica.
Comparing Vega and the Sun
Although Vega and the Sun are both stars, they are very different from one another. While the Sun appears round, Vega is noticeably flattened. This is because Vegas has over twice the mass of the Sun and is spinning so rapidly (236.2 km/s at its equator), that it experiences centrifugal effects. If it were spinning about 10% faster, it would break apart! The equator of Vega is 19% bigger than its polar radius. Because of the star's orientation with respect to Earth, the bulge appears unusually pronounced. If Vega was viewed from above one of its poles, it would appear round.
Another obvious difference between Vega and the Sun is its color. Vega has a spectral class of A0V, which means it is a blue-white main sequence star that fuses hydrogen to make helium. Because it is more massive, Vega burns up its hydrogen fuel more quickly than our Sun, so its lifetime as a main-sequence star is only about one billion years, or about a tenth as long as the Sun's life. Right now, Vega is about 455 million years old or half-way through its main-sequence life. In another 500 million years or so, Vega will become a class-M red giant, after which it will lose most of its mass and become a white dwarf.
While Vega fuses hydrogen, most of the energy at its core comes from the carbon-nitrogen-oxygen (CNO cycle) in which protons combine to form helium with intermediate nuclei of the elements carbon, nitrogen, and oxygen, This process is less efficient than the Sun's proton-proton chain reaction fusion and requires a high temperature of about 15 million Kelvin. While the Sun has a central radiation zone at its core covered by a convection zone, Vega has a convection zone at its core that distributes ash from its nuclear reaction. The convection zone is in equilibrium with the star's atmosphere.
Vega was one of the stars used to define the magnitude scale, so it has an apparent magnitude around 0 (+0.026). The star is about 40 times brighter than the Sun, but because it's 25 light years away, it seems dimmer. If the Sun was viewed from Vega, in contrast, its magnitude would only be a faint 4.3.
Vega appears to be surrounded by a disk of dust. Astronomers believe the dust may have resulted from collisions between objects in a debris disk.Other star that display excessive dust when viewed in the infrared spectrum are called Vega-like or Vega-excess stars. The dust is found mainly in a disk around the star rather than a sphere, with particle sizes estimated to be between 1 to 50 microns in diameter.
At this time, no planet has been definitively identified orbiting Vega, but it's possible terrestrial planets could orbit near the star, probably in its equatorial plane.
Similarities between the Sun and Vega are that they both have magnetic fields and sunspots.
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