Day and Night Across the Earth
Astronomical Applications Dept. Astronomical Applications Dept.
 
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This page provides a set of five synthetic images of the Earth's surface, each from a different perspective, that show the areas in sunlight (day) and darkness (night) at the specified date and time. Simply fill in the form below and click on the "Show Earth Views" button at the end of the form. The images can be produced for any date and time from year 1700 through year 2100. Specify Universal Time on the form.

Be sure to check Notes on the Images, located after the form.

Earth: Cylindrical Projection

             

    Universal Time (UT1)

Earth: Spherical Views

             

    Universal Time (UT1)

   

Notes on the Images:

These forms produce images of Earth from five different views. The first form produces a cylindrical projection, the second produces an orthographic view.

The whole-Earth map is constructed so that 0" longitude is always in the middle. The four orthographic projections (views of the Earth from infinity) are centered on the north pole, the south pole, the point where the Sun is at the zenith, and the point where the Moon is at the zenith. (To be strictly correct, straight lines from the center of the Earth to the Sun and Moon at the specified time would not pass exactly through the points used, but the difference is quite small and below the resolution of the images.) In the North and South images, a horizontal line would be parallel to the plane of the Earth's orbit around the Sun (the direction to the north ecliptic pole is up).

If you advance the requested time, you can see the continents shift to the right in the Sun and Moon views, due to the Earth's rotation. The north pole view would show the Earth rotating counterclockwise and the south pole view would show the Earth rotating clockwise.

The dividing line between day and night (which is fuzzy) is called the terminator. On the whole-Earth map, the Sun is rising at places along the terminator where the sunlit part of the Earth is to the right, and setting at places along the terminator where the sunlit part of the Earth is to the left. On this map, in the polar regions, the terminator is horizontal (along a line of constant latitude) or nearly so for part of its length; at such places, the Sun is "skimming" the northern or southern horizon. At any place along the terminator, the local direction of the Sun on the horizon is perpendicular to the terminator, toward the point on the Earth where the Sun is at the zenith.

The shape of the terminator curve on the whole-Earth map changes significantly over the course of a year, and it is instructive to compare the terminator at the equinoxes (on or about March 21 and September 21) with the same curve at the solstices (on or about June 21 and December 21). Because our atmosphere bends sunlight about a half-degree (60 km) into the area of the Earth that would otherwise be dark, the sunlit part of the Earth is slightly more than half of the entire surface (there is actually more than 12 hours of daylight at the equinoxes). The shape of the terminator shown on these images is adjusted for this effect. In particular, at the dates of the equinoxes, you can see that both the north and south poles are in sunlight. In fact, viewed from either pole at the exact time of the equinox, the entire disk of the Sun is clear of the horizon.

The Moon view shows the area of the Earth where the Moon is above the horizon. The Moon view also shows the phase of the Earth as seen from the Moon; it is opposite the phase of the Moon as seen from the Earth. For example, a gibbous Moon corresponds to a crescent Earth, a new Moon corresponds to a full Earth, etc. (See, for example, today's phase of the Moon for a comparison.)

In constructing these images, the geometry of the Earth, Sun, and Moon is computed from the data in the Jet Propulsion Laboratory DE405/LE405 planetary and lunar ephemeris. The cloudless Earth map that is used is a processed version of a mosaic produced at NASA's Earth Observatory.

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