Earth's clock, live

Before anyone printed a calendar, the planet itself kept time. One turn on its axis gives the day; one lap around the Sun gives the year; the Moon's cycle in between gives the month. A calendar is a set of rules for counting those natural cycles in whole numbers — and the trouble is that none of them divide evenly into each other. A year is not a whole number of days, which is the entire reason leap years exist.

This page reads the "Earth clock" live: where the planet is in its orbit right now, how fast it is moving, how far it has gone since you arrived, and when the next season starts. Every number is worked out in your browser from published orbital elements — nothing is fetched from a server.

This map stitches together the satellite passes of the last day into one picture of the planet, then lays the live line between day and night over it. On the dark side you see city lights instead; the yellow dot is the spot where the Sun is directly overhead at this moment. It redraws every minute.

Earth is closest to the Sun in early January and farthest in early July — the opposite of what most people guess for the northern hemisphere. Distance is not what makes summer hot; the 23.44° tilt of Earth's axis is. But distance does change the length of the seasons. By Kepler's second law Earth moves faster near the Sun, so it hurries through the northern winter and dawdles through the northern summer.

The northern spring-plus-summer half of the year runs about a week longer than autumn-plus-winter. The gap is slowly shifting: perihelion creeps later by about a day every 58 years, so in roughly 10,000 years it will fall in July and the northern summers will be the short ones.

"How long is a year?" has more than one correct answer, depending on what you count Earth's return to.

The tropical year is about 20 minutes shorter than the sidereal year because Earth's axis wobbles like a slowing top, dragging the equinox points backwards around the sky once every 25,772 years. That is the precession of the equinoxes, and it's why Makar Sankranti (tied to the stars) now falls around 14 January while the solstice it once marked happens on 21 December.

The Gregorian calendar's 365.2425-day average beats the tropical year by about 27 seconds a year — one full day of drift every 3,000-odd years. Good enough that nobody alive needs to worry about it.

A solar day — noon to noon — averages 24 hours. A sidereal day, one spin relative to the stars, is 23 hours 56 minutes 4.09 seconds. The four-minute difference comes from the orbit: while Earth turns once, it also moves about 1° along its path, so it has to turn a little extra (about 361° in all) before the Sun is back overhead. That is why stars rise four minutes earlier each night and the night sky cycles through the year.

The day is also slowly getting longer. Tides raised by the Moon act like a brake, adding about 1.8 milliseconds per century on average, while melting ice, the liquid core and earthquakes nudge it by fractions of a millisecond either way. Clocks absorbed the mismatch with 27 leap seconds between 1972 and 2016; in 2022 the world's metrology body voted to stop adding them by 2035.

The edge between light and dark is called the terminator. It's only a straight north–south line at the two equinoxes. The rest of the year Earth's 23.44° tilt makes it lean: around the June solstice the whole Arctic sits inside the lit side and Antarctica stays dark round the clock; in December it's the other way round.

The yellow subsolar point races west at about 1,670 km/h at the equator — one lap of the planet per day. Over the year it also drifts between the Tropic of Cancer (around 21 June) and the Tropic of Capricorn (around 21 December). The two tropics are simply the farthest north and south the Sun is ever overhead, and the Arctic and Antarctic circles are the edges of the regions that get at least one 24-hour day or night a year.