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

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Preparing the 3D view

Preparing lighting and the first complete frame…

Model scale

Earth–Moon radii and separation share one scale.

At day 11.8 of the model month, the Moon is 90.3% illuminated as seen from Earth (waxing gibbous). Moon misses Earth’s shadow. Open Shadow close-up for a closer view.

How to read these results

The orbit model illustrates phase and eclipse geometry without predicting a calendar date. Lunar terrain data come from NASA SVS, LROC and LOLA, with colours adapted for this view.

Eclipses

Explain how the Sun, Earth and Moon must align for an eclipse, and identify the regions of total and partial shadow.

Drag to rotate. Hold Ctrl and scroll to zoom, or pinch on a touch screen.

Why it happens

An eclipse requires the Sun, Earth and Moon to align closely enough for one body to enter another’s shadow. The Moon’s orbital tilt usually carries it above or below the necessary alignment.

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NASA's airborne view of the 21 August 2017 total solar eclipse. The Moon blocks the bright photosphere, revealing the corona.

Try a comparison

Select Shadow close-up, Lunar and Node direction 0°. Scrub through the umbra and penumbra. Choose Solar and compare near and far Moon distances.

Reading the result

The shadow experiment isolates alignment and angular size; it is not a calendar of future eclipses.

A common misunderstanding

Every full Moon produces a lunar eclipse.

A lunar eclipse requires the full Moon to pass through Earth’s shadow. The Moon’s orbital plane is tilted by about five degrees relative to Earth’s orbital plane, so it usually passes above or below that shadow. An eclipse occurs only when the alignment is sufficiently close to an orbital node.

Cases

Exam language

Umbra

The central part of a shadow where the light source is completely obscured. During a total lunar eclipse the Moon lies within Earth’s umbra. The surrounding penumbra receives light from part of the source and produces a less complete darkening.

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NASA's airborne view of the 21 August 2017 total solar eclipse. The Moon blocks the bright photosphere, revealing the corona.

Penumbra

The part of a shadow where the light source is only partly obscured. On the Moon it produces subtler dimming than the umbra.

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NASA Kennedy Space Center photograph, 20 January 2000. Earth's shadow falls on the Moon; sunlight filtered through Earth's atmosphere gives the eclipsed surface a reddish colour.

Node

One of the two places where the Moon’s orbital plane crosses Earth’s orbital plane. Eclipses require a new or full Moon close enough to a node for the Sun, Earth and Moon to align within the relevant shadow.

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SDO's time sequence of the 2012 Venus transit. Such alignments require the planet to be near an orbital node. Historical transit timing helped determine the Earth–Sun distance, now represented by the precisely defined astronomical unit.

Ecliptic

The plane of Earth’s orbit around the Sun, projected onto the sky as the Sun’s apparent annual path. The Moon’s orbital plane is inclined by about five degrees to it, so most new and full Moons do not produce eclipses.

Orbital inclination

The angle between an orbital plane and a chosen reference plane. The Moon’s orbit is inclined by about five degrees to Earth’s orbital plane. This usually carries the Moon above or below the alignment required for an eclipse.

Solar eclipse

An eclipse near new Moon when the Moon passes between Earth and the Sun close to an orbital node. The apparent sizes determine whether it is total, annular or partial.

Lunar eclipse

An eclipse occurring when the Moon passes through Earth's shadow near full Moon and an orbital node. It can be penumbral, partial or total.

Synodic month

The time from one lunar phase to the next occurrence of the same phase, averaging about 29.5 days. It is longer than the Moon’s orbital period relative to the stars because Earth also moves around the Sun.

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The Moon's sunlit crescent photographed from Artemis II. A synodic month is the interval between matching lunar phases, about 29.5 days; one photograph records only one moment in that cycle.

Month0.40Node direction0°Moon distance384400kmEclipse close-up