August 27

August 27

The Pulsing Corner of the Square

Sun Position

The Sun is in Virgo at roughly +8° declination. Northern Hemisphere nights are noticeably longer than in July; the autumnal equinox is less than four weeks away.

Sky Highlight

The Great Square of Pegasus is now rising in the east by late evening from northern mid-latitudes, signaling the approach of autumn. Its four corners are visible in the east-northeast by 10 PM local time; Southern Hemisphere observers see it in the northern sky. The Square's interior is notably free of bright stars, a dark patch that mid-latitude observers can use to gauge sky darkness by counting faint stars within it.

Deep Sky Object

M15, the great globular cluster in Pegasus, rises in the east with the constellation and is well placed for late-night observing from both hemispheres in late August. One of the densest globular clusters in the Milky Way, at roughly 33,600 light-years, it contains a central black hole candidate and the planetary nebula Pease 1, the only confirmed planetary nebula within a globular cluster.

Featured Star

Scheat, the M2.5II-III red giant at the northwest corner of the Great Square of Pegasus, lies about 196 light-years away and is a semi-regular pulsating variable with a period of roughly 38 days, its diameter and brightness shift noticeably over weeks, though the variation is subtle to the naked eye without comparison stars. It is one of the first seasonal stars to indicate autumn is coming.

Around This Date

  • August 27, 1962NASA's Mariner 2 launched from Cape Canaveral, becoming the first spacecraft to successfully conduct a flyby of another planet when it passed Venus in December 1962.
  • August 28, 1993The Galileo spacecraft photographed Dactyl orbiting asteroid 243 Ida at a distance of about 1 kilometer from Ida's surface, resolving the question of whether small bodies in the asteroid belt could gravitationally retain companions.

Scheat pulses every five weeks and no one watching it casually would notice, the sky has rhythms that only patient observers pick up.