Solar and Lunar Eclipse

An **eclipse** is an astronomical event. It occurs when an astronomical object (Sun, Moon) is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer.

From the Earth we can observe an eclipse involving the Sun, Earth and Moon. It can occur only when all this three objects are nearly in a straight line, allowing one to be hidden behind another, viewed from the third. The orbital plane of the Moon is tilted with respect to the orbital plane of the Earth. Therefore eclipses can occur only when the Moon is close to the intersection of these two planes. We call them 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.

A lunar eclipse occurs when the Earth passes between the Moon and the Sun, and the Earth's shadow obscures the Moon or a portion of it. A solar eclipse occurs when the Moon passes between the Earth and the Sun, blocking all or a portion of the Sun. An eclipse can be total, partial, or annular.

On May 29, 1919, a total solar eclipse occurred between South America and Africa. This event would provide the first successful test of Albert Einstein’s general Theory of relativity. One prediction of general relativity was that light should not travel in a straight line. While traveling through spacetime and nearing the warp induced by an object’s gravitational field, light should curve. A total solar eclipse occurred just as the Sun was crossing the bright Hyades star cluster. The light from the stars would have to pass through the Sun’s gravitational field on its way to Earth, yet would be visible due to the darkness of the eclipse. This would allow accurate measurements of the stars’ gravity-shifted positions in the sky. The measurement was successful and the findings made Einstein a celebrity overnight, and precipitated the eventual triumph of general relativity over classical Newtonian physics.