We have a system... Earth-Moon system :))

An eclipse involving the Sun, Earth and Moon can occur only when they are nearly in a straight line, allowing one to be hidden behind another, viewed from the third. Because the orbital plane of the Moon is tilted with respect to the orbital plane of the Earth (the ecliptic), eclipses can occur only when the Moon is close to the intersection of these two planes (the nodes). The Sun, Earth and nodes are aligned twice a year, and eclipses can occur during a period of about two months around these times. There can be from four to seven eclipses in a calendar year, which repeat according to various eclipse cycles, such as the Saros cycle.

Between 1901 and 2100 there are the maximum of 7 eclipses in:^[8]

• 4 (penumbral) lunar and 3 solar eclipses: 1908, 2038.
• 4 solar and 3 lunar eclipses: 1917, 1973, 2094.
• 5 solar and 2 lunar eclipses: 1934

Excluding penumbral lunar eclipses, the maximum 7 eclipses have occurred in:^[9]

• 1591, 1656, 1787, 1805, 1917, 1935, 1982, and 2011

[edit]Solar eclipse

Main article: Solar eclipse

The progression of a solar eclipse on August 1, 2008, viewed from Novosibirsk, Russia. The time between shots is 3 minutes.

A solar eclipse occurs when the Moon passes in front of the Sun as seen from the Earth. The type of solar eclipse event depends on the distance of the Moon from the Earth during the event. A total solar eclipse occurs when the Earth intersects the umbra portion of the Moon's shadow. When the umbra does not reach the surface of the Earth, the Sun is only partially occluded, resulting in an annular eclipse. Partial solar eclipses occur when the viewer is inside the penumbra.^[10]

The eclipse magnitude is the fraction of the Sun's diameter that is covered by the Moon. For a total eclipse, this value is always greater than or equal to one. In both annular and total eclipses, the eclipse magnitude is the ratio of the angular sizes of the Moon to the Sun.^[11]

Solar eclipses are relatively brief events that can only be viewed in totality along a relatively narrow track. Under the most favorable circumstances, a total solar eclipse can last for 7 minutes, 31 seconds, and can be viewed along a track that is up to 250 km wide. However, the region where a partial eclipse can be observed is much larger. The Moon's umbra will advance eastward at a rate of 1,700 km/h, until it no longer intersects the Earth.

During a solar eclipse, the Moon can sometimes perfectly cover the Sun because its size is nearly the same as the Sun when viewed from the Earth. A total solar eclipse is in fact an occultation while an annular solar eclipse is a transit.

[edit]Lunar eclipse

Main article: Lunar eclipse

The progression of a lunar eclipse. Totality is shown with the last two images to lower right. These required a longer exposure time to make the details visible.

Lunar eclipses occur when the Moon passes through the Earth's shadow. Since this occurs only when the Moon is on the far side of the Earth from the Sun, lunar eclipses only occur when there is a full moon. Unlike a solar eclipse, an eclipse of the Moon can be observed from nearly an entire hemisphere. For this reason it is much more common to observe a lunar eclipse from a given location. A lunar eclipse also lasts longer, taking several hours to complete, with totality itself usually averaging anywhere from about 30 minutes to over an hour.^[12]

There are three types of lunar eclipses: penumbral, when the Moon crosses only the Earth's penumbra; partial, when the Moon crosses partially into the Earth's umbra; and total, when the Moon circles entirely within the Earth's umbra. Total lunar eclipses pass through all three phases. Even during a total lunar eclipse, however, the Moon is not completely dark. Sunlight refracted through the Earth's atmosphere intersects the umbra and provides a faint illumination. Much as in a sunset, the atmosphere tends to scatter light with shorter wavelengths, so the illumination of the Moon by refracted light has a red hue,^[13] thus the phrase 'Blood Moon' is often found in descriptions of such lunar events as far back as eclipses are recorded.^{[citation needed]}

[edit]Historical record

Records of solar eclipses have been kept since ancient times. Eclipse dates can be used for chronological dating of historical records. ASyrian clay tablet records a solar eclipse which occurred on March 5, 1223 B.C.,^[14] while Paul Griffin argues that a stone in Ireland records an eclipse on November 30, 3340 B.C.^[15] Chinese historical records of solar eclipses date back over 4,000 years and have been used to measure changes in the Earth's rate of spin.^[16]