An asterism, formed by the bright stars
Vega in Lyra, Deneb
in Cygnus, and Altair in Aquila, which lies
high overhead on summer and early autumn evenings at mid-northern latitudes.
All three of these white stars have similar surface temperatures, Vega,
at 9,500 K, the warmest. Though Vega and Altair are really quite luminous,
they are first magnitude primarily because they are close to us, averaging
only 25 light-years away, while Deneb is an extraordinarily luminous star
at a distance of some 2,500 light-years.