Where it is light on Earth right now, where it is dark, and the twilight in between. Drag the slider to move through the next seven days, or press play and watch the line sweep round. The same picture as the world clock's map, with time attached.
Play runs at about six hours a second: one full turn of the Earth takes four seconds, and the whole week about half a minute. Nothing on the map slides sideways while it runs — the shaded shape is re-solved for each moment, meridian by meridian — so the picture never runs off the edge and jumps back. The one thing that does cross the edge is the sun marker, and that is honest: this map is a cylinder cut open at the date line, so the point the sun stands over leaves at one side and arrives at the other.
Half of the Earth is in sunlight at every moment, and half is not. This map draws that division for one instant: the bright half is where the sun is above the horizon, the dark half is where it is below, and the soft band between them is twilight — the places where the sun has set but the sky has not finished going dark.
The yellow dot is the one place on Earth where the sun is directly overhead at that moment — straight up, no shadow at noon. It is the middle of the lit side, and everything else follows from it: the further you are from that dot, the lower the sun sits in your sky, until at ninety degrees away it is exactly on your horizon and you are standing on the line.
The line is called the terminator, and it moves west at about 1,670 kilometres an hour at the equator — the speed of the Earth's own turn. Watch it with Play and you are watching sunrise sweeping across one edge of the world while sunset sweeps across the other. Every place on the map crosses it twice a day, which is the definition of a day.
If the Earth spun upright, the day/night line would be a straight vertical line — every place on the planet would get twelve hours of daylight, every day, forever, and this map would be very dull. The Earth does not spin upright. Its axis is tilted by 23.4°, and that single fact is what puts a lean on the line, gives us seasons, and makes the length of your day depend on where you live and what month it is.
Press June solstice above and look at the top of the map: the whole Arctic is inside the lit half, all the way round. Press December solstice and it is inside the dark half instead. That is the midnight sun and the polar night, and you are looking straight at the reason for both.
Two motions are on show at once and they run at wildly different speeds. The turn — the line sweeping west — takes a day. The lean — the whole pattern tipping north and south — takes a year, so it barely changes across the seven days the slider covers. That is why the jump buttons exist: they are the only way to see the slow one.
The Earth is a sphere, and no flat picture of a sphere can be honest about everything at once. Every world map ever drawn has chosen what to get right and what to sacrifice. This one is an equirectangular map, and its choice is simple: longitude is drawn evenly across, latitude evenly down. Every vertical line is a meridian, every horizontal line a parallel, and the grid is a plain rectangle.
That is exactly the right choice for this picture and the wrong one for most others. Because longitude runs evenly across it, an hour of the Earth's turn is the same distance everywhere on the map — 15° of longitude, one twenty-fourth of the width, at the top of the map and at the bottom alike. The terminator can therefore sweep across at a constant rate, and time zones are straight vertical strips. On a Mercator map, or a globe drawn in perspective, none of that holds.
What it sacrifices is size. On the real Earth the meridians converge — they meet at the poles — so a degree of longitude is a shorter distance the further you get from the equator, by exactly the cosine of the latitude. This map draws them all the same width anyway. So everything is stretched sideways, by 1 ÷ cos(latitude), and the further from the equator you look, the worse it gets:
Greenland is the famous victim. It sits between about 60° and 83° north, so this map stretches it by a factor of two to eight, and it ends up looking like a continent. It is not. Greenland covers about 2.17 million square kilometres; Africa covers about 30.4 million — roughly 14 Greenlands. On the map above they look comparable. Africa straddles the equator, where this projection is honest, so Africa is the one drawn nearly right and Greenland is the one blown up.
The same distortion is why this map is cropped at 82.0°N and 62.0°S rather than drawn to the poles. At the poles the stretch is infinite: a single point becomes the entire width of the map. Those two bands are where the projection stops meaning anything, so they are not drawn.
The honest way to see all of this is a globe. The Sun, Earth and Moon simulator draws the Earth as a ball with the same day/night line on it, from the same maths — the terminator you see leaning here is the one you see curving round the globe there. Compare the two and the projection stops being an abstraction.
What is the line between day and night called? The terminator — or the day/night line, or the grey line. It is the circle around the Earth where the sun is exactly on the horizon, so everywhere along it is either rising or setting at that moment. It sweeps west at the speed of the Earth's rotation, about 1,670 km/h at the equator and slower the further from the equator you go.
Why isn't the day/night line straight up and down? Because the Earth's axis is tilted by 23.4° relative to its orbit. The line is only vertical at the two equinoxes, when the sun stands over the equator. At every other time of year the sun is north or south of the equator, one pole leans into the light and the other away from it, and the line leans by the same amount — up to 23.4° at the solstices.
What is the yellow dot? The subsolar point: the single place on Earth where the sun is directly overhead at that instant. It circles the planet once a day and drifts slowly between the two tropics over the year. It is always at the centre of the lit half, so the sun's height in your sky is set by how far you are from it.
Why is there a soft band instead of a sharp edge? Because sunset is not the end of daylight. The band is twilight — the sun is below the horizon but still lighting the sky from underneath. The band's outer edge is 18° below the horizon, the point where the sky is fully dark. It is wider near the poles, which is why a summer night in Scotland or Scandinavia never gets truly dark.
Why does the map look stretched near the top and bottom? Because it is an equirectangular projection: it draws every degree of longitude the same width, when on a sphere they get narrower toward the poles. Everything is stretched sideways by 1 ÷ cos(latitude) — 1.4× at 45°, 2× at 60°, 4.8× at 78°. It is why Greenland looks like Africa here when Africa is really about 14 times bigger.
Is the map showing real time? Yes. It opens at the current moment and repaints every minute while it is left alone. The slider moves it forward through the next seven days, and Now brings it back. Everything is computed in your browser from the sun's position — nothing is fetched from a server, and there is nothing to sign up for.
Where can I see the exact sunrise and sunset time for my town? On the sun pages: they give sunrise, sunset, day length, twilight and a seven-day outlook for more than a thousand cities, or for any location you name. This map is the shape of the thing; those pages are the numbers.
This map answers "where", to the nearest few hundred kilometres. For "when", to the minute, in your own town:
Sunrise & sunset for your city Tonight's moon phase What time is it there? The same line, on a globe How sunrise is worked out Using these in a lesson