Wednesday, June 4, 2025

The Summer Triangle Arrives (all night)

After dusk in June, Vega, Deneb, and Altair are the first stars to appear in the darkening eastern sky. Those three bright, white stars form the Summer Triangle asterism - an annual feature of the summer sky that remains visible until the end of December! The highest and most easterly of the trio is Vega, in Lyra. At magnitude 0.03, Vega is the brightest star in the summer sky, mainly due to its relative proximity to the sun - it's only 25 light-years distant. Magnitude 0.75 Altair, in Aquila, occupies the southern corner of the triangle. Altair is 17 light-years from the sun. By contrast, Deneb, which shines somewhat less brightly at magnitude 1.25, is a staggering 2,600 light- years away from us; but it ranks so high in visible brightness because of its greater intrinsic luminosity. The Milky Way passes between Vega and Altair and through Deneb, which sits high overhead in Cygnus as dawn begins to break.

(Data courtesy of Starry Night)
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