September 7
Cornerstone Southwest
Sun Position
The Sun is in Virgo at about +4° declination, drawing steadily toward the equator. Day and night lengths are nearly equal at equatorial latitudes; the equinox is about two weeks away.
Sky Highlight
The Great Square of Pegasus is now prominent in the eastern sky by late evening, its four roughly equally bright corners making it a reliable signpost for autumn constellations. No major annual shower peaks today.
Deep Sky Object
NGC 7331, spiral Galaxy, Pegasus. Roughly 40 million light-years distant, NGC 7331 is often called a Milky Way look-alike and appears as a bright, tilted oval in modest telescopes. It is well-placed for Northern Hemisphere observers; from southern latitudes it is low but reachable.
Featured Star
Markab (α Peg), a blue-white giant of spectral type B9III about 140 light-years away, has exhausted its core hydrogen and is evolving toward a cooler, larger state, its current blue-white color is already a record of that transition. It stands at the southwest corner of the Great Square, the last corner to clear the horizon as the asterism rises.
Around This Date
- September 7, 2008Dawn spacecraft's xenon ion engine began its first extended thrust segment after launch, demonstrating sustained ion propulsion on a deep-space mission for the first time.
- September 7, 1995Space Shuttle Endeavour launched on STS-69, deploying and retrieving the Wake Shield Facility on its second flight to grow ultra-pure semiconductor films in the vacuum wake of the orbiting spacecraft.
The Great Square rises corner by corner, and Markab is always last up, a slow entrance that makes the asterism feel earned.