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Geolens

Realm

Planet

Earth moves through space

Explore how Earth’s motion and its relationship with the Sun and Moon produce days, seasons, phases and eclipses.

Meteosat view of Earth's day–night boundary on the December solstice, with more of the Southern Hemisphere in daylight.
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Meteosat-9 SEVIRI, 21 December 2010. The tilted day–night boundary gives the Southern Hemisphere longer days. Axial tilt, rather than a change in Earth–Sun distance, controls this seasonal illumination.
Meteosat view of Earth's day–night boundary on the December solstice, with more of the Southern Hemisphere in daylight.
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Planet

Why seasons happen

Earth’s tilted axis changes the angle of sunlight and the length of the day as Earth travels around the Sun.

South African city lights beneath a curved glowing atmospheric horizon and stars, viewed from the ISS.
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Planet

Earth rotation and the terminator

Earth turns eastward, carrying each location into sunlight and then darkness.

A thin sunlit lunar crescent with crater shadows along the terminator against black space.
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Planet

Moon phases and Sun–Earth–Moon geometry

Sunlight illuminates half the Moon.

Saturn and its broad rings in a natural-colour mosaic photographed by the Cassini spacecraft.
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Planet

Solar system

Planets differ enormously in size, orbital distance and period.

Extreme-ultraviolet observation of the full Sun showing bright active regions, displayed in yellow.
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Planet

Sun and Earth

The same sunlight spreads across a larger area when it strikes a surface at a shallow angle.

A Hubble mosaic of Andromeda's bright central region, dark dust lanes and densely packed stars.
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Planet

Universe scale

Distances within the Solar System are commonly measured in astronomical units; distances between stars are more conveniently measured in light-years.

Younger gently dipping red sandstone overlies steep grey beds at Siccar Point, Scotland.
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Planet

Geologic time

Earth’s history spans about 4.54 billion years.

The dark lunar disc surrounded by the Sun's pale corona during the 2017 total solar eclipse.
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Planet

Eclipses

An eclipse requires the Sun, Earth and Moon to align closely enough for one body to enter another’s shadow.

A fishing boat rests on exposed mud beside a wharf at low tide in Nova Scotia.
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Planet

Tides

The Moon’s gravitational attraction varies across Earth, creating a tide-generating effect with two broad bulges.

A spherical sundial with hour markings and a movable gnomon at Green's Windmill, Nottingham.
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Planet

Solar altitude and sun path

Solar altitude is the Sun’s angle above the horizon.