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What is a Partial Solar Eclipse?

Next Partial Solar Eclipse: Sun, Sep 13, 2015 … See animation

Partial solar eclipses happen when the Moon comes between the Sun and the Earth, but they don't align in a perfectly straight line. Because of this, the Moon only partially covers the Sun's disc.

Illustration image
Partial solar eclipse, Novosibirsk, Russia.
A partial solar eclipse seen in Novosibirsk, Russia in 2006.
©bigstockphoto.com/underworld1

In a partial solar eclipse, the Sun looks like the Moon has taken a bite out of it. This is because the Moon casts the lighter, outer part of its shadow, the penumbra, on Earth.

Why "Total Eclipse", it's only partial?

Eclipses are named after their max point, so as long as an eclipse is total from any part on Earth, it will be called a total eclipse, even though it might be seen as a partial eclipse from most areas.

Both total and annular solar eclipses are seen as partial eclipses from the areas on Earth that are outside the Moon's umbra (inner shadow) but inside its penumbra (outer shadow).

Unlike total and annular solar eclipses, the Moon does not have to be at its perigee or apogee for a partial solar eclipse to take place.

Only at New Moon

However, a New Moon is necessary for a partial solar eclipse to occur, but partial solar eclipses do not happen during every new Moon night.

This is because the plane of 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 2 orbital planes meet are called lunar nodes. Solar eclipses occur only when a new Moon takes place near a lunar node.

Phases of a Partial Solar Eclipse

During a partial solar eclipse, the Moon's umbra completely misses the Earth. Everyone in the Moon's penumbra gets to see a partially eclipsed Sun. There are 3 distinct stages of a partial solar eclipse:

  • Partial solar eclipse begins: The Moon starts moving over the Sun's disc.
  • Maximum eclipse: The Moon partially covers the Sun. If you're somewhere in the eclipse's path, you'll see that the Moon appears to take a bite out of the Sun.
  • Partial solar eclipse ends: The Moon stops covering the Sun.

Where can I see One?

Partial solar eclipses occur more often and are usually seen more often than total or annular solar eclipses.

About 35% of all solar eclipses are partial solar eclipses. This is because the Moon's distance from Earth is irrelevant for partial solar eclipses. The larger size of the Moon's penumbra compared to its umbra also means that more places on Earth get to experience a partial solar eclipse.

How to View a Solar Eclipse?

Never look directly at the Sun, eclipsed or otherwise, without any protective eyewear. The Sun’s UV radiation can burn the retinas in the eyes leading to permanent damage or even blindness.

The only way to safely see a total solar eclipse is to wear protective eclipse glasses or to project an image of the eclipsed Sun using a pinhole projector.

Topics: Astronomy, Eclipses, Moon, Earth, Sun

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Partial Solar Eclipse

Sep 13, 2015 at 4:40 AM UTCSee more


In this Article

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All About Solar Eclipses

  1. Types of Solar and Lunar Eclipses
  2. What are solar eclipses?
  3. Total solar eclipses
  4. Partial Solar Eclipses
  5. Annular solar eclipses
  6. Solar Eclipses in History
  7. Solar Eclipse Myths and Superstitions
  8. Solar Eclipse Eye Safety
  9. Make a Pinhole Projector

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