The sun sets due west this week, the equinox compass trick
Par Sam Arkwell · publié le 20 septembre 2026
The short answer: this week, and only this week plus its March twin, the sun rises exactly due east and sets exactly due west, everywhere on Earth. At the equinox the Sun travels along the celestial equator, and that path crosses every horizon at the true cardinal points: this week’s sunset is a free compass, accurate to about a degree around September 23. Use it to find true north without a phone, to settle once and for all which way your apartment actually faces, and to catch henge-style photos down any east-west street. Then it expires: the sunset point drifts south-west by about one sun-diameter per day, the fastest slide of the year.
Why the perfect alignment happens only twice a year, and three concrete ways to cash it in before Friday.
Two days a year: the geometry of a perfect line-up
Common wisdom says the sun sets “in the west”; a year of actual sunsets tells a different story. The sunset point drifts along the horizon with the seasons: north-west through spring to its June extreme, south-west through autumn to its December extreme, and the swing is bigger than most people guess, roughly 30 to 40 degrees either side of true west at the latitudes of New York, Chicago or London, nearly a tenth of the whole horizon between the two solstices. The June sun dies almost in the north-west, the December sun well into the south-west, and “the west” of everyday speech is strictly true on two days a year: the equinoxes.
The reason is clean geometry: at the equinox, whose exact moment falls on September 23 at 00:05 UTC, the Sun sits on the celestial equator, the sky’s projection of Earth’s own equator. That plane intersects every observer’s horizon, wherever they stand, precisely at the true east and west points. On that day, and for practical purposes all week, sunrise marks east and sunset marks west to within about a degree, in Boston as in Buenos Aires, the one appointment on the calendar when astronomy hands out a universal compass for free. Not to be confused with this same week’s other rendezvous, the equilux on the 26th, when day and night finally split even: late September stacks its curiosities.
Three ways to use it before the window closes
Find the cardinal points with nothing in your pockets. Face tonight’s sunset and you are looking at true west: north is on your right hand, south on your left, east at your back. The accuracy beats a phone compass, which magnets, cars and steel-framed buildings routinely fool, and the morning sunrise runs the same service for east. The trick that keeps on giving: line the setting sun up with a landmark, a steeple, an antenna, a distant rooftop, and you have marked true west in your personal landscape for the rest of the year.
Settle your home’s real orientation. “West-facing balcony,” says the listing; equinox week is the one time checking it is trivial. If the setting sun shines straight through the window these evenings, the exposure is true west; if it comes in at an angle, you are reading the offset directly. The same test orients gardeners and solar panels, due south sitting at a right angle from tonight’s sunset, and a dated photo of the living room in this week’s sunset light is worth a surveyor’s report to a house hunter.
Catch your street’s henge. Grid cities live their alignment moment this week: any street laid out true east-west gets the sun setting dead in its axis, an orange ball framed between the building lines. Manhattanhenge happens in May and July only because Manhattan’s grid is rotated 29 degrees off the cardinal directions; grids that run true, and many do, from Chicago’s to countless Main Streets, have their henge now. Pick an east-west street on a map, stand at its eastern end half an hour before sunset, and let the golden hour light do the rest. Move fast: the sunset point shifts by about one sun-width per day at this time of year, the fastest drift on the calendar, and this week’s perfect axis will miss the street by a lane in mid-October. Twice a year, no more, which is exactly what makes the shot worth having, and the online clock will give you the minute to be there.
Vos questions
Why does the sun set due west at the equinox?
Because at the equinox the Sun sits exactly on the celestial equator, and that plane crosses every observer's horizon precisely at the true east and west points. So for a few days around September 23, sunrise marks true east and sunset marks true west, everywhere on Earth from New York to Sydney: the only time of year the sun works as a perfect compass.
Where does the sun set the rest of the year?
It drifts along the horizon: after the September equinox the sunset point slides south-west each day until the December solstice, then back north-west until June. At mid-northern latitudes (New York, Chicago, London) the swing reaches roughly 30 to 40 degrees either side of true west, so 'the sun sets in the west' is only strictly true twice a year.
How do I find true north using the sunset this week?
Face the sunset: you are looking at true west, so north is on your right, south on your left, east behind you. Accuracy is within about a degree for two or three days around September 23 and stays very good all week, better than a phone compass near metal or magnets.
How long does the alignment last?
The sunset point moves by roughly one sun-diameter per day at this time of year, the fastest drift of the year. The alignment is perfect on equinox day (September 23), excellent from about the 20th to the 26th, and off by only a few degrees within a week either side.