Eclipse
Article by: Jay M. Pasachoff, Hopkins Observatory, Williams College, Williamstown, Massachusetts.
Fred Espenak Goddard Space Flight Center, National Aeronautics and Space Administration, Greenbelt, Maryland.
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The occultation (obscuring) of one celestial body by another. Solar
and lunar eclipses take place at syzygies of the Sun, Earth, and Moon, when
the three bodies are in a line. At a solar eclipse, the Moon blocks the view of
the Sun as seen from the Earth (Fig. 1). At a lunar eclipse, the Earth's shadow
falls on the Moon, darkening it, and can be seen from wherever on Earth the
Moon is above the horizon.
Eclipses of the Sun could be seen from other planets as their moons are
interposed between the planets and the Sun, though their superposition is
not as coincidental in angular size as it is for the Earth-Moon system. Eclipses
of the moons of Jupiter are well known, occurring whenever the moons pass
into Jupiter's shadow. An eclipse of the Sun visible from Uranus that occurred
in 2006 was imaged by the Hubble Space Telescope. Certain binary stars are
known to eclipse each other, and the eclipses can be followed by measuring
the total light from the system.
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Content
• Solar Eclipses
• Phenomena
• Positions and timing
• Scientific value
• Annular eclipses
• Recent and future
eclipses
• Observing a solar
eclipse
• Lunar Eclipses
• Visibility
• Frequency
• Future lunar eclipses
Fig. 1: The August 21, 2017 total solar eclipse, as seen from Hopkins-
ville, Kentucky, USA at 2:25 p.m. EDT.
(Credit: NASA)
Key Concepts
• An eclipse is generally defined as the obscuring of one celestial body by another.
• Solar and lunar eclipses take place when the Sun, Earth, and Moon are aligned. This
type of event is also called a syzygy.
• During a solar eclipse, the Moon blocks the view of the Sun as seen from Earth. Solar
eclipses can be central or partial. Central eclipses can be total (when the Sun, Earth,
and Moon are in a direct line) or annular.
• Visible phenomena during a total solar eclipse include dots of light shining through
valleys on the edge of the Moon, known as Baily's beads; the diamond-ring effect,
which occurs when the last Baily's bead shines through; and prominence of the solar
corona with equatorial streamers.
• During a lunar eclipse, the Moon passes through some part of the Earth's two
shadows. Lunar eclipses can be penumbral, partial, or total.
• A lunar eclipse can only occur during the full moon phase, and the Moon must be
near one of the two nodes of its orbit.
