July 10
The Color Pair at the Crossroads
Sun Position
The Sun is in Cancer at about +21.4° declination. Northern Hemisphere summer days remain long and the sky does not fully darken until well after 9 p.m. at mid-latitudes; Southern Hemisphere winter nights are long and dark.
Sky Highlight
No major annual event peaks on July 10. Cygnus, home to Albireo, transits the meridian late in the evening for Northern Hemisphere observers this month, placing it high overhead for the best telescope views. From southern mid-latitudes, Cygnus is low in the northern sky and Albireo may be difficult to observe.
Deep Sky Object
NGC 6992, part of the Veil Nebula complex in Cygnus, a supernova remnant roughly 2,100 light-years away. The eastern filament (NGC 6992/6995) is the brightest section and shows delicate wispy structure in photographs; with a nebula filter it is detectable visually in a medium telescope under dark skies. Best from the Northern Hemisphere.
Featured Star
Albireo (β Cyg) sits about 430 light-years away in Cygnus, pairing an orange giant (K3II) with a blue main-sequence star (B8Ve). The contrast between their surface temperatures (roughly 4,400 K versus 11,000 K) translates directly into the amber-and-blue color split that has made this one of the most observed doubles in the northern sky.
Around This Date
- July 10, 1962Telstar 1, the first active communications satellite, was launched, and within hours relayed the first live transatlantic television pictures, a technological milestone that also required tracking of a known orbital path.
- July 11, 1979Skylab reentered the atmosphere after years of orbital decay, with NASA controllers making a final thruster burn to steer debris away from population centers before it broke up over the Indian Ocean and Australia.
The amber and blue of Albireo are not art. They are two different temperatures, separated by 430 light-years, coincidentally aligned in the same eyepiece.