Solstices and equinoxes 2027

An equinox is the instant the sun crosses the celestial equator, and a solstice the instant it reaches its furthest point north or south. They are moments, not days: the 2027 March equinox happens at one second for everyone alive, and only the clock on the wall differs.

The popular idea that day and night are exactly equal at an equinox is nearly but not quite true. We measure sunrise from the moment the sun's upper edge appears rather than its centre, and the atmosphere bends its light so we see it before it has really risen. Both effects add daylight, so the day of equal length falls a few days before the March equinox and a few days after the September one.

The solstices are not the hottest or coldest days either. Land and sea take weeks to warm up and cool down, which is why the warmest part of the northern summer comes in late July and the coldest part of winter in late January — about a month after each solstice.