August 28
The Horse's Shoulder
Sun Position
The Sun is in Virgo at approximately +7° declination. The Northern Hemisphere's summer is in its final weeks; the Southern Hemisphere's winter is ending. Equinox is less than a month away for both.
Sky Highlight
The Great Square of Pegasus is rising usefully by 10 PM local time for northern mid-latitude observers, and the Andromeda Galaxy (M31) (just outside the Square's northeast corner) is accessible to the naked eye from dark sites. Autumn galaxy season is opening. Southern Hemisphere observers see the Square well-placed in the northern evening sky.
Deep Sky Object
NGC 7331, a large spiral galaxy in Pegasus roughly 40 million light-years away, is one of the finest galaxies in the autumn sky and a useful preview of the galaxy groups that become the focus of October and November observing. Its elongated disk is visible in a small telescope and it resembles our own Milky Way in structure. Best placed from northern mid-latitudes but accessible from both hemispheres.
Featured Star
Markab, the B9III blue-white giant at the southwest corner of the Great Square of Pegasus, lies about 140 light-years away. The name derives from the Arabic for 'the saddle' or 'the shoulder of the horse,' and the star's reliable placement makes it one of the easiest bright stars to identify as autumn approaches, the Square's southwest anchor.
Around This Date
- August 27, 1962Mariner 2 launched on the first successful planetary flyby mission in history, eventually confirming that Venus has a slow retrograde rotation and a scorching surface with no detectable magnetic field.
- August 28, 1993During its flyby of asteroid 243 Ida, the Galileo spacecraft discovered Dactyl, a small moon orbiting Ida, the first proven natural satellite of an asteroid.
Markab anchors the Great Square, and the Great Square announces autumn, one of those cases where the stars really do function as a calendar.