eclipse

An eclipse is an astronomical event in which one celestial body is temporarily obscured by another as they align near a straight line with the Sun. The term most often refers to solar eclipses, when the Moon blocks the Sun, and to lunar eclipses, when the Earth’s shadow falls on the Moon. Eclipses occur when the Sun, Moon and Earth are near alignments at the orbital nodes.

Solar eclipses happen at new Moon when the Moon's apparent size covers part or all of the Sun. Types include total (Sun fully obscured), annular (Moon too small, Sun appears as a ring), and partial (only part of Sun obscured). A rare hybrid eclipse shifts between total and annular along its path. Totality lasts from a few seconds to about seven and a half minutes. Observers require eye protection to view solar eclipses.

Lunar eclipses occur at full Moon when the Earth lies between Sun and Moon. The Moon passes into Earth's umbra for total eclipses or through the penumbra for partial or penumbral eclipses. Total lunar eclipses often take on a reddish color due to sunlight refracted by Earth's atmosphere. Lunar eclipses are visible over large areas and can be observed with the naked eye; no special equipment is needed.

Two eclipse seasons occur each year, controlled by geometry of the Moon's orbit (inclination about 5 degrees). The Saros cycle, about 18 years 11 days, helps predict successive similar eclipses.

Safety note: Solar eclipses require eye protection; do not look at the Sun directly.