July 21
The Rival of Mars
Sun Position
The Sun is in Cancer, approaching Leo, at about +20.3° declination. Northern midsummer; Southern Hemisphere winter. Scorpius is well-placed in the south for Northern Hemisphere observers and near the zenith for Southern Hemisphere mid-latitudes.
Sky Highlight
No named meteor shower peaks on July 21. Scorpius transits the meridian around midnight for mid-northern observers in July, sitting highest in the south, the best window of the year to observe the constellation's rich Milky Way field. Southern observers see Scorpius pass directly overhead, offering the finest views anywhere on Earth.
Deep Sky Object
M80 (NGC 6093), a globular cluster in Scorpius roughly 32,600 light-years away. It is one of the most densely packed globular clusters known; in 1860 a nova was observed within it, one of only a handful of novae ever seen inside a globular cluster. Best from Southern Hemisphere and southern northern latitudes. Binoculars show a small fuzzy star; a telescope reveals the dense core.
Featured Star
Antares (α Sco) is a red supergiant about 550 light-years away, classified M1.5Iab-b. Its name likely derives from 'anti-Ares' (rival to Mars) because its red color and position near the ecliptic make it easy to confuse with the planet when Mars passes through Scorpius every two years or so.
Around This Date
- July 20–21, 1969Neil Armstrong became the first human to walk on the Moon at 02:56 UTC on July 21, with Buzz Aldrin following 20 minutes later; the two spent about two and a half hours on the surface.
- July 21, 2011Space Shuttle Atlantis landed at Kennedy Space Center, completing STS-135 and ending the 30-year Space Shuttle program with the final mission.
Antares has been impersonating Mars since long before anyone named either of them, and it is better at the disguise than Mars suspects.