September 22
Equinox Eve
Sun Position
The Sun is in Virgo at roughly -4° to -5° declination, crossing the celestial equator at the autumnal equinox on or around this date. Day and night are nearly equal everywhere on Earth; the Sun rises almost due east and sets almost due west.
Sky Highlight
The September equinox falls on approximately September 22 or 23 each year (the precise date shifts slightly with the calendar). At the moment of equinox, the Sun crosses the celestial equator heading south; every latitude on Earth experiences a sunrise nearly due east and a sunset nearly due west. Aurora activity often increases around the equinoxes due to favorable geometry between Earth's magnetic field and the solar wind.
Deep Sky Object
M31, Andromeda Galaxy. The nearest large spiral galaxy at 2.5 million light-years is now well up in the northeast by 9 PM, its best evening position of the year. Under dark skies, its disk spans roughly three full moon-widths; even from light-polluted areas, the nucleus is a naked-eye smudge. Favors Northern Hemisphere; low but visible from southern mid-latitudes.
Featured Star
Alpheratz (α And) is a chemically peculiar blue subgiant of spectral type B8IVpMnHg, about 97 light-years away. On this equinox date, it occupies a symbolic position: it sits at the corner of the Great Square of Pegasus, which straddles the celestial equator itself, and its chemical peculiarities (driven by slow atmospheric settling of heavy elements in the absence of convection) make it a useful example of how stellar surface chemistry can diverge dramatically from cosmic averages.
Around This Date
- September 22, 1828Friedrich Bessel published an early rigorous determination of stellar proper motions, laying groundwork for the first successful measurements of stellar parallax that he would complete a decade later.
- September 23, 1846Neptune was discovered at the Berlin Observatory by Johann Galle, confirmed to within 1° of its mathematically predicted position, one of the great triumphs of Newtonian celestial mechanics.
At the equinox, the Sun stands on the celestial equator for one moment, no hemisphere tipped toward the light, no hemisphere shaded from it, a brief geometric fairness.