September 23
The W Ascending
Sun Position
The Sun crosses the celestial equator at the autumnal equinox on or around this date (exact year varies). Declination is roughly 0°; the Sun rises very close to due east and sets very close to due west worldwide. In the Northern Hemisphere, nights now officially exceed days.
Sky Highlight
The autumnal equinox (one of the four cardinal points of Earth's orbit) marks the moment the Sun moves into the Southern Hemisphere celestially. For Northern Hemisphere observers, this is the official start of astronomical autumn; for Southern Hemisphere observers, astronomical spring begins. The day is not precisely 12 hours everywhere due to atmospheric refraction but is within a few minutes at all latitudes.
Deep Sky Object
NGC 869 / NGC 884, Double Cluster, Perseus. Two adjacent open clusters about 7,500 light-years away are well up in the northeast this evening, their combined glow visible to the naked eye and spectacular in binoculars. Best from the Northern Hemisphere; low but reachable from mid-southern latitudes.
Featured Star
Caph (β Cas) is a yellow-white subgiant of spectral type F2III-IV, 54.7 light-years away, marking the western tip of Cassiopeia's W as it climbs the northern sky. On the equinox, it is well-placed near the meridian in the north by late evening, one of the closest stars in the asterism and one of the few sky objects near enough that its light takes under 55 years to arrive.
Around This Date
- September 23, 1846Johann Galle and Heinrich d'Arrest discovered Neptune at the Berlin Observatory, confirming the independent predictions of Urbain Le Verrier and John Couch Adams within a degree.
- September 23, 1962The first episode of The Jetsons aired on ABC, presenting a mid-20th-century vision of space-age domestic life that would influence popular ideas about the future for decades.
The equinox is not a day but a moment, one instant when the Sun crosses a line we drew on the sky, and the seasons pivot.