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.
In the solar system, planets can make shadows, one falling on another, according to their position in respect of the Sun.
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.
An eclipse involving the Sun, Earth, and Moon can occur only when they are nearly in a straight line, allowing one to hide behind another, viewed from the third. Because the orbital plane of the Moon is tilted with respect to the orbital plane of the Earth, eclipses can occur only when the Moon is close to the intersection of these two planes i:e the nodes.
The Sun, Earth and nodes are aligned twice a year (during an eclipse season), 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.
A solar eclipse happens when the Moon comes between the Earth and the Sun and projects a shadow on the Earth which can hide the whole or a part of sun. During a total eclipse the sky darkens and only the corona of the Sun is visible, which we can see with special filters.
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 occulted, resulting in an annular eclipse. Partial solar eclipses occur when the viewer is inside the penumbra.
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.
During a solar eclipse, the Moon can sometimes perfectly cover the Sun because its size is nearly the same as the Sun's when viewed from the Earth.
A lunar eclipse takes place when the Earth comes between the Moon and the Sun and the Moon passes through the shadow of the Earth. The Moon is not completely obscured, but is a red colour. This is because some rays of Sun still reach it, through the atmosphere of the Earth.
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.
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 crosses entirely into the Earth's umbra. Total lunar eclipses pass through all three phases.
The phrase 'Blood Moon' is often found in descriptions of Total lunar events as far back as eclipses are recorded.