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What Is a Partial Lunar Eclipse?

A partial lunar eclipse happens when the Earth moves between the Sun and the Full Moon, but they are not precisely aligned. Only part of the Moon's visible surface moves into the dark part of the Earth's shadow.

A partially eclipsed Moon in the night sky. A little over half of the Moon is covered by a reddish shade.

A partially eclipsed Moon.

During a partial lunar eclipse, part of the Moon can get a reddish hue.

©iStockphoto.com/cinoby

What Causes a Partial Lunar Eclipse?

A partial lunar eclipse occurs when the Earth moves between the Sun and Moon but the three celestial bodies do not form a straight line in space. When that happens, a small part of the Moon's surface is covered by the darkest, central part of the Earth's shadow, called the umbra. The rest of the Moon is covered by the outer part of the Earth's shadow called the penumbra.

Conditions for a Partial Lunar Eclipse

For a partial lunar eclipse to occur, two celestial events must happen at the same time:

  • A Full Moon.
  • The Sun, Earth, and Moon must be aligned in almost a straight line.
Illustration image
Lunar nodes are the locations where the Moon crosses the Earth's orbital plane.
A lunar eclipse only happens when the Moon passes a lunar node during the Full Moon phase, when the Earth is positioned between the Moon and the Sun.

Not Every Full Moon Night

Partial lunar eclipses do not happen every Full Moon night because of the inclination of the Moon's orbital plane. The Moon's orbital path around the Earth is inclined at an angle of 5° to the Earth's orbital plane (ecliptic) around the Sun. The points where the two orbital planes meet are called lunar nodes.

Lunar eclipses occur when the Moon is near a node at Full Moon and solar eclipses take place when it is near a node at New Moon.

Stages of a Partial Lunar Eclipse

  • Penumbral eclipse begins: The Earth's penumbra starts covering the Moon's surface.
  • Partial eclipse begins: The Earth's umbra starts moving over the Moon.
  • Maximum eclipse: The Earth's umbra covers the largest part of the Moon.
  • Partial eclipse ends: The Earth's umbra no longer covers the Moon.
  • Penumbral eclipse ends: The Earth no longer casts a shadow on the Moon. This marks the end of the eclipse.
Illustration image
Part of the Moon dips into the Earth's umbra during a partial lunar eclipse.
Part of the Moon dips into the Earth's umbra, the deepest part of the shadow, during a partial lunar eclipse.

How to See?

Partial lunar eclipses can be seen across the night-side of the Earth. No special equipment is needed to see a partial lunar eclipse. All you need is the exact date and time for the next eclipse to be seen from where you are, the weather forecast, some warm clothes, and a chair to keep you comfortable while you watch the eclipse unfold.

Upcoming 5 Partial Lunar Eclipses

More details about upcoming Eclipses

Topics: Eclipses, Moon, Sun, Astronomy

Next transit begins in

21Days 14Hrs 25Mins 47Secs

Mercury Transit

Nov 11, 2019 at 12:34 UTCSee more

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