• 3340 BC – Earliest believed record of an eclipse.

• Eclipse

  This article is about astronomical eclipses.

  "Total eclipse" redirects here. 

  

  Totality during the 2000 solar eclipse. Solar prominences can be seen along the limb (in red) as well as extensive coronalfilaments.

  An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer. An eclipse is a type of syzygy.

  The term eclipse is most often used to describe either a solar eclipse, when the Moon's shadow crosses the Earth's surface, or a lunar eclipse, when the Moon moves into the Earth's shadow. However, it can also refer to such events beyond the Earth–Moon system: for example, a planet moving into the shadow cast by one of its moons, a moon passing into the shadow cast by its host planet, or a moon passing into the shadow of another moon. A binary star system can also produce eclipses if the plane of the orbit of its constituent stars intersects the observer's position.

  Umbra, penumbra and antumbra

  

  Umbra, penumbra and antumbra cast by an opaque object occulting a larger light source.

  Main article: Umbra, penumbra and antumbra

  The region of the Moon's shadow in a solar eclipse is divided into three parts:

  • The umbra, within which the Moon completely covers the Sun (more precisely, its photosphere).
  • The antumbra, extending beyond the tip of the umbra, within which the Moon is completely in front of the Sun but too small to completely cover it.
  • The penumbra, within which the Moon is only partially in front of the Sun.

  During a lunar eclipse only the umbra and penumbra are applicable. This is because Earth's apparent diameter from the viewpoint of the Moon is nearly four times that of the Sun.

  The first contact occurs when the Moon's disc first starts to impinge on the Sun's; second contact is when the Moon's disc moves completely within the Sun's; third contact when it starts to move out of the Sun's; and fourth or last contact when it finally leaves the Sun's disc entirely.

  The same terms may be used analogously in describing other eclipses, e.g., the antumbra of Deimos crossing Mars, or Phobos entering Mars's penumbra.

  A total eclipse occurs when the observer is within the umbra, an annular eclipse when the observer is within the antumbra, and a partial eclipse when the observer is within the penumbra.

  For spherical bodies, when the occulting object is smaller than the star, the length (L) of the umbra's cone-shaped shadow is given by:

  

  where R_s is the radius of the star, R_o is the occulting object's radius, and r is the distance from the star to the occulting object. For Earth, on average L is equal to 1.384×10⁶ km, which is much larger than the Moon's semimajor axis of 3.844×10⁵ km. Hence the umbral cone of the Earth can completely envelop the Moon during a lunar eclipse.^[6] If the occulting object has an atmosphere, however, some of the luminosity of the star can be refracted into the volume of the umbra. This occurs, for example, during an eclipse of the Moon by the Earth—producing a faint, ruddy illumination of the Moon even at totality.