Solar and lunar eclipses are fascinating astronomical events that occur when the Earth, the Moon, and the Sun align in space. The duration of an eclipse, whether solar or lunar, varies depending on a number of factors including the type of eclipse, the relative distances of the Earth, Moon, and Sun, and their relative velocities.

A solar eclipse can be total, partial, or annular. During a total solar eclipse, the Moon completely covers the Sun, as viewed from Earth. This event can last as little as a few seconds to over 7.5 minutes in totality, but the entire process from the start of the partial eclipse to the end can take several hours. The longest total solar eclipse of the 21st century occurred on July 22, 2009, and lasted for 6 minutes and 39 seconds in totality, but from beginning to end, it lasted about 3 hours.

An annular eclipse, where the Moon covers the Sun's center, leaving a ring-like appearance, also varies in duration. The annularity can range from a fraction of a second to over 12 minutes, but like total eclipses, the full event from start to end lasts several hours. An example is the annular eclipse on December 26, 2019, which had a maximum annularity of 3 minutes and 40 seconds.

Lunar eclipses occur when the Earth lies between the Sun and the Moon, casting its shadow on the Moon. These can also be total or partial. Total lunar eclipses can last up to nearly 2 hours in totality. The entire event, from the beginning of the partial eclipse through the total phase and then back to the end of the partial phase, can last up to 5 or 6 hours.

The duration of an eclipse is determined by the speeds at which the Moon orbits the Earth and the Earth orbits the Sun, as well as the distances between these bodies. The Earth's atmosphere can also extend the duration of a lunar eclipse by refracting sunlight into the shadow.

In addition to the celestial mechanics, the observer's location on Earth also affects the perceived duration of an eclipse. For solar eclipses, totality can only be observed along a narrow path on Earth's surface, and the duration will be shorter towards the edges of this path.

The timings and durations of eclipses can be precisely calculated by astronomers using the laws of celestial mechanics. These calculations take into account the orbital inclinations, eccentricities, and other perturbations that affect the orbits of the Earth and Moon.

In summary, the length of an eclipse from beginning to end can vary widely, but typically lasts several hours, with the total or annular phases lasting from a few seconds to several minutes. The specific duration of an eclipse can be predicted using complex astronomical models that account for the various factors influencing the motions of the Earth, Moon, and Sun.
November 30, 2023 — Roger Sarkis

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