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What Is a Total Solar Eclipse?

Total solar eclipses occur when the New Moon comes between the Sun and Earth and casts the darkest part of its shadow, the umbra, on Earth. The darkest part of the eclipse, the totality, is almost as dark as night.

Illustration of totality of a Total Solar Eclipse

Phenomena only visible near the totality.

The Sun's corona, Baily's beads, and the diamond ring effect are only visible near the totality (darkest point) of a total solar eclipse

©bigstockphoto.com/JohanSwanepoel

During a total eclipse of the Sun, the Moon covers the entire disk of the Sun. In partial and annular solar eclipses, the Moon blocks only part of the Sun.

Not Total Everywhere

Eclipses are named after their darkest phase. If a solar eclipse is total at any point on Earth, it is called a total solar eclipse, even though it's seen as a partial solar eclipse in most areas.

5 Phases

There are 5 stages in a total solar eclipse:

  1. Partial eclipse begins (1st contact:) The Moon starts becoming visible over the Sun's disk. The Sun looks as if a bite has been taken from it.
  2. Total eclipse begins (2nd contact:) The entire disk of the Sun is covered by the Moon. Observers in the path of the Moon's umbra may be able to see Baily's beads and the diamond ring effect, just before totality.
  3. Totality and maximum eclipse: The Moon completely covers the disk of the Sun. Only the Sun's corona is visible. This is the most dramatic stage of a total solar eclipse. At this time, the sky goes dark, temperatures can fall, and birds and animals often go quiet. The midpoint of time of totality is known as the maximum point of the eclipse. Observers in the path of the Moon's umbra may be able to see Baily's beads and the diamond ring effect, just after totality ends.
  4. Total eclipse ends (3rd contact:) The Moon starts moving away, and the Sun reappears.
  5. Partial eclipse ends (4th contact:) The Moon stops overlapping the Sun's disk. The eclipse ends at this stage in this location.

Protect Your Eyes!

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

To watch a solar eclipse safely, wear protective eclipse glasses or project an image of the eclipsed Sun using a pinhole projector.

Unique Sights at Totality

Certain phenomena can only be seen during a total solar eclipse:

  • Baily's beads: Seen about 10 to 15 seconds before and after totality, Baily's beads are little bead-like blobs of light at the edge of the Moon. These happen because the gaps in the mountains and valleys on the Moon's surface allow sunlight to pass through in some places but not others.
  • Diamond ring: As the Moon moves to cover the entire disk of the Sun, Baily's beads disappear, leaving 1 last bead a few seconds before totality. At this point in the eclipse, the Sun's corona forms a ring around the Moon. The ring around the Moon and the leftover Baily's bead give the appearance of a diamond ring.
  • The Sun's chromosphere: The Sun's atmosphere has 3 layers: the photosphere, the chromosphere, and the corona. The chromosphere, which gives out a reddish glow can only be seen for a few seconds right after the diamond ring disappears during a total eclipse of the Sun.
  • The Sun's corona: Like the chromosphere, the Sun's corona is only visible during a total solar eclipse. It can be seen as a faint ring of rays surrounding the silhouetted Moon during totality.
  • Shadow bands: About 1 minute before and after totality, moving wavy lines of alternating light and dark can be seen on plain-colored surfaces. These shadow bands are the result of the light emitted from a thin solar crescent being refracted by Earth's atmosphere.

The Science of Total Solar Eclipses

Illustration image
The Sun, Moon, and Earth are aligned
The Moon's umbra (full shadow) and penumbra (half shadow) determines where an eclipse will be total or just partial.

Only those located in the path of the Moon's full shadow, its umbra, can see a total solar eclipse. The Moon's umbra travels eastward at about 1,700 km/h (1,056 mph).

A total solar eclipse can last for several hours. Totality can range from a few seconds to 7.5 minutes. The longest total solar eclipse of the 21st century took place on July 22, 2009 when the totality lasted 6 minutes and 39 seconds.

Total solar eclipses typically happen a little less than once a year when:

  • There is a New Moon.
  • The Moon is near a lunar node.
  • Earth, the Moon, and the Sun are aligned in a straight line.
  • The Moon is near perigee.

Not Every New Moon Night

Illustration image

Total solar eclipse infographic. Click image for full version.

The Moon's orbital path around Earth is inclined at an angle of approximately 5° to 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.

Near Lunar Perigee

The Moon's path around Earth is elliptical, with one side of the orbit closer to Earth than the other. The side closest to Earth is called the perigee and the side farthest from Earth is known as the apogee.

Earth's orbit around the Sun is also elliptical, with the Sun closer to one end, the perihelion of the orbit than the other aphelion.

Earth's and the Moon's elliptical orbits mean that Earth’s distance from the Sun and the Moon's distance from Earth varies throughout the year. It also means that from Earth, the Sun's and Moon's apparent sizes change during the year.

When the Moon is about 400 times closer to Earth than the Sun, the Moon's and the Sun's apparent sizes roughly match. Because of this, total eclipses of the Sun can only occur when the Moon is near perigee – it is the only time when the disk of the Moon looks big enough to cover the entire disk of the Sun.

Topics: Astronomy, Eclipses, Moon, Sun

Next Total Solar Eclipse begins in

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Total Solar Eclipse

Aug 21, 2017 at 15:46 UTCSee more


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Eclipse Lookup

Solar Eclipses

  1. Different Types of 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. Magnitude of Eclipses

Eclipses


Protect Your Eyes

  1. Never Look Directly at the Sun
  2. Simple Pinhole Projector
  3. Eclipse Projector in a Box
  4. Binoculars / Telescope Projector

Eclipses & Transits


Eclipse Shadows

  1. Umbra
  2. Penumbra
  3. Antumbra

Why Are There 3 Shadows?


Lunar Eclipses

  1. Total Lunar Eclipse
  2. When is the Moon Red?
  3. Partial Lunar Eclipse
  4. Penumbral Lunar Eclipse
  5. Can I See a Lunar Eclipse?
  6. Blood Moon - Total Lunar Eclipse
  7. Magnitude of Eclipses

Eclipses

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