September 30

September 30

Month's Last Light

Sun Position

The Sun is in Libra at about -5° to -6° declination, now solidly in the southern celestial hemisphere. In the Northern Hemisphere, nights are about an hour longer than days at 40° latitude; in the Southern Hemisphere, days are gaining with equal speed.

Sky Highlight

September ends with the autumn sky fully established for Northern Hemisphere observers: the Summer Triangle is declining in the west, Pegasus and Andromeda are dominant in the south, and Perseus and Cassiopeia are high in the north. From the Southern Hemisphere, Fomalhaut is high in the south, Achernar is well-placed, and the Large Magellanic Cloud is rising to prominence.

Deep Sky Object

NGC 7789, Caroline's Rose Cluster, Cassiopeia. An open cluster about 7,600 light-years away and discovered by Caroline Herschel in 1783, NGC 7789 contains roughly 1,000 stars and shows a distinctive pattern of arching star chains and dark lanes in a telescope. Circumpolar from much of the Northern Hemisphere; very low or invisible from southern mid-latitudes.

Featured Star

Schedar (α Cas), spectral type K0IIIa, about 228 light-years away, closes the month as the dominant light of Cassiopeia's W, a cool orange giant whose low surface temperature of roughly 4,530 K makes it one of the cooler first-magnitude stars in the northern sky. It is a mild variable and has been studied as a helium-shell burning star in the later stages of red giant evolution.

Around This Date

  • September 30, 1880Henry Draper made the first successful photograph of the Orion Nebula (M42), producing a 51-minute exposure that resolved nebular structure invisible to previous visual observers.
  • September 28, 1962NASA's first Director of the Manned Spacecraft Center, Robert Gilruth, formally activated Mission Control at Houston, Texas, the facility that would manage every crewed US spaceflight through the Space Shuttle era.

September ends not with a dramatic close but with a sky rotating slowly westward, each constellation handing off to the next, as the year continues its untroubled count.