The star Deneb (Alpha (α) Cygni) is the faintest member of the asterism known as the Summer Triangle.
It’s also the northernmost star in the Northern Cross asterism, part of the constellation of Cygnus, the Swan.
Despite the fact that both Altair and Vega appear to outshine it in the Summer Triangle, in reality Deneb is the brighter star.
Its dimness is due to distance. While Vega is 25 lightyears away and Altair is 16.7 lightyears, Deneb is thought to be 2,600 lightyears.
Facts about star Deneb
A blue-white supergiant star, Deneb has a spectral classification of A2 Ia.
Despite ranking as the 19th brightest star, its great distance means that in reality it’s one of the most luminous stars, possibly 196,000 times more so than the Sun.
Deneb's size is estimated to be slightly greater than 200 solar diameters, with a mass in the range of 20 times greater than the Sun. Its magnitude varies from +1.21 to +1.29.
With a declination of 45˚ 17 minutes, Deneb appears circumpolar from the UK, just managing to pass above the northern horizon when it’s at its lowest point, due north.
Due to axial precession, the north celestial pole, which currently lies close to Polaris (Alpha (α) Ursae Minoris) will sit about 7˚ from Deneb in the period around 9800 AD.
Deneb rides high across the sky in summer, its prominence enhanced by being a key point in two prominent asterisms.
Deneb means 'tail' and this is the part of Cygnus the star is supposed to represent.
This guide originally appeared in the June 2019 issue of BBC Sky at Night Magazine.
