July 30

July 30

The Split Constellation's Brightest Star

Sun Position

The Sun is in Leo at about +17.7° declination. Northern Hemisphere summer; Southern Hemisphere winter. Serpens Caput is setting in the western sky while Serpens Cauda is well-placed in the south, giving an unusual evening where both halves of the constellation are visible simultaneously.

Sky Highlight

The Southern Delta Aquariids are still near peak activity, maintaining elevated rates through July 30. The Perseid meteor shower begins its gradual build-up this week, adding very low background activity from the northeast in the predawn Northern Hemisphere sky, not yet worth staying up for, but measurable.

Deep Sky Object

M16 (NGC 6611), the Eagle Nebula, an emission nebula and open cluster in Serpens Cauda roughly 7,000 light-years away. The Hubble 'Pillars of Creation' image, taken in 1995, depicts dense gas columns within M16 where new stars are actively forming. A small telescope shows the cluster of young hot stars at the center; larger aperture begins to reveal the surrounding nebulosity. Visible from both hemispheres.

Featured Star

Unukalhai (α Ser) is an orange giant 73 light-years away in Serpens, classified K2IIIb. Serpens is the only IAU-recognized constellation divided into two separate regions; the split was formalized when the International Astronomical Union defined constellation boundaries in 1930, cleaving the snake in two around Ophiuchus. Unukalhai sits in Serpens Caput, the head section, and is the brightest star of either half.

Around This Date

  • July 30, 2020NASA's Perseverance rover launched from Cape Canaveral on the Mars 2020 mission, carrying the Ingenuity helicopter (the first powered aircraft designed to fly on another planet) and arriving at Jezero Crater in February 2021.
  • July 31, 1964Ranger 7 transmitted the first close-up photographs of the lunar surface before impact, returning 4,316 images and showing the Moon's surface in detail never previously seen.

Unukalhai marks the neck of a snake that the sky's mapmakers cut in two, the star does not seem to have noticed.