Tilted Earth

One day drives everything. The slider picks a day in 2026. The year view, the close-up, the day bars and the chart all show that day. “Play a day” turns Earth once in about 9 seconds. “Play a year” takes Earth around the Sun in about 18 seconds. With Calm motion on, both show still pictures instead: every 3 hours, or the 21st of each month.

Sunrise and sunset use the US Naval Observatory’s approximate solar position (declination and equation of time) and the standard rule that the Sun’s centre is 0.833° below the horizon. That allows for air bending the light and for the Sun’s half-width, which is why the equator gets a little over 12 hours. Twilight on the bars is civil twilight (the Sun up to 6° below the horizon). Times are local clock times, with daylight saving time where the place uses it. Checked against USNO tables for Los Angeles, Anchorage, Sydney, Quito and Utqiaġvik to within a minute. Hills, buildings and weather are ignored. Reference: USNO approximate solar coordinates.

The pictures. Earth’s axis is tilted 23.4° and keeps the same direction in space all year. In the year view we look at the orbit from a little above, from the March side, so June is on the right and December on the left. Sizes and distances are squeezed to fit. The close-up keeps the Sun on the left and looks from a little above the half of Earth where the first place is. The coloured lines are each place’s circle of latitude: the path it travels in one day. The solid part is in sunlight and the dashed part is in night.

Seasons use the usual calendar months: in the Northern Hemisphere, winter is December to February and summer is June to August. The Southern Hemisphere is the reverse. Near the equator, wet and dry times often matter more than summer and winter.

ZIP codes are matched by their first three digits to an approximate latitude (the mean of GeoNames postal codes with that prefix). The first digit picks a rough region for the time zone and the dot’s east–west spot, so “Your town” times are approximate. Your ZIP code stays in this page’s memory only.

Keyboard. Use the arrow keys on the date slider (one day) or the month buttons. Tab to the clock on the close-up and use the arrow keys to change the time by an hour (Page Up and Page Down: 3 hours).