Lunar limb

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Two contrasting lightnesses of the lunar disc at crescent phase, overexposed to show earthshine Earth illuminates.jpg
Two contrasting lightnesses of the lunar disc at crescent phase, overexposed to show earthshine

The lunar limb is the edge of the visible surface (disc) of the Moon as viewed from Earth. [1] Libration of the Moon, with its irregular surface, leads to small changes in its profile; this complicates the task of precisely calculating eclipse times and durations. [2] However, data from the mapping of the lunar surface allows astronomers to predict the lunar profile for any given time with a high degree of certainty. [3] The irregularity of the lunar limb is the cause of Baily's beads, which are collimated rays of sunlight that shine through in some places while not in others during a solar eclipse.

Moon Earths natural satellite

The Moon is an astronomical body that orbits the Earth as its only permanent natural satellite. It is the fifth-largest satellite in the Solar System, and the largest among planetary satellites relative to the size of the planet that it orbits. The Moon is, after Jupiter's satellite Io, the second-densest satellite in the Solar System among those whose densities are known.

Earth Third planet from the Sun in the Solar System

Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space, especially the Sun and the Moon, which is Earth's only natural satellite. Earth orbits around the Sun in 365.26 days, a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times.

Libration perceived oscillating motion of orbiting bodies relative to each other

In astronomy, libration is the wagging of the Moon perceived by Earth-bound observers caused by changes in their perspective. It permits an observer to see slightly different halves of the surface at different times. It is similar in both cause and effect to the changes in the Moon's apparent size due to changes in distance. It is caused by three mechanisms detailed below, two of which are causing a relatively tiny physical libration via tidal forces exerted by the Earth. Such true librations are known as well for other moons with locked rotation.

The contrast of the lunar disc, brightly illuminated by direct sunlight, against a black night sky makes it a popular target when testing telescope (including binocular) optics.

Contrast (vision) difference in luminance and/or color that makes an object distinguishable

Contrast is the difference in luminance or colour that makes an object distinguishable. In visual perception of the real world, contrast is determined by the difference in the color and brightness of the object and other objects within the same field of view. The human visual system is more sensitive to contrast than absolute luminance; we can perceive the world similarly regardless of the huge changes in illumination over the day or from place to place. The maximum contrast of an image is the contrast ratio or dynamic range.

Night sky dark sky in the deep twilight or at night

The term night sky, usually associated with astronomy from Earth, refers to the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon.

Telescope Optical instrument that makes distant objects appear magnified

A telescope is an optical instrument that makes distant objects appear magnified by using an arrangement of lenses or curved mirrors and lenses, or various devices used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. The first known practical telescopes were refracting telescopes invented in the Netherlands at the beginning of the 17th century, by using glass lenses. They were used for both terrestrial applications and astronomy.

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Eclipse Astronomical event where one body is hidden by another

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. This alignment of three celestial objects is known as a syzygy. Apart from syzygy, the term eclipse is also used when a spacecraft reaches a position where it can observe two celestial bodies so aligned. An eclipse is the result of either an occultation or a transit.

Lunar eclipse when the Moon passes directly behind the Earth

A lunar eclipse occurs when the Moon passes directly behind Earth and into its shadow. This can occur only when the Sun, Earth, and Moon are exactly or very closely aligned, with Earth between the other two. A lunar eclipse can occur only on the night of a full moon. The type and length of a lunar eclipse depend on the Moon's proximity to either node of its orbit.

The saros is a period of exactly 223 synodic months, that can be used to predict eclipses of the Sun and Moon. One saros period after an eclipse, the Sun, Earth, and Moon return to approximately the same relative geometry, a near straight line, and a nearly identical eclipse will occur, in what is referred to as an eclipse cycle. A sar is one half of a saros.

A terminator or twilight zone is a moving line that divides the daylit side and the dark night side of a planetary body. A terminator is defined as the locus of points on a planet or moon where the line through its parent star is tangent. An observer on the terminator of such an orbiting body with an atmosphere would experience twilight due to light scattering by particles in the gaseous layer.

Bailys beads Feature of total and annular solar eclipses

The Baily's beads effect, or diamond ring effect, is a feature of total and annular solar eclipses. As the Moon covers the Sun during a solar eclipse, the rugged topography of the lunar limb allows beads of sunlight to shine through in some places while not in others. The effect is named after Francis Baily, who explained the phenomenon in 1836. The diamond ring effect is seen when only one bead is left, appearing as a shining "diamond" set in a bright ring around the lunar silhouette.

Selenographic coordinates coordinate system

Selenographic coordinates are used to refer to locations on the surface of Earth's moon. Any position on the lunar surface can be referenced by specifying two numerical values, which are comparable to the latitude and longitude of Earth. The longitude gives the position east or west of the Moon's prime meridian, which is the line passing from the lunar north pole through the point on the lunar surface directly facing Earth to the lunar south pole. This can be thought of as the midpoint of the visible Moon as seen from the Earth. The latitude gives the position north or south of the lunar equator. Both of these coordinates are given in degrees.

A peak of eternal light (PEL) is a hypothetical point on the surface of an astronomical body that is always in sunlight. Such a peak must have high latitude, high elevation, and be on a body with very small axial tilt. The existence of such peaks was first postulated by Beer and Mädler in 1837. The pair said about the lunar polar mountains: "...many of these peaks have eternal sunshine". These polar peaks were later mentioned by Camille Flammarion in 1879, who speculated that there may exist pics de lumière éternelle at the poles of the Moon. PELs would be advantageous for space exploration and colonization due to the ability of an electrical device located there to receive solar power regardless of the time of day or day of the year, and the relatively stable temperature range.

Magnitude of eclipse fraction of the diameter of the eclipsed body which is in eclipse

The magnitude of eclipse is the fraction of the angular diameter of a celestial body being eclipsed. This applies to all celestial eclipses. The magnitude of a partial or annular solar eclipse is always between 0.0 and 1.0, while the magnitude of a total solar eclipse is always greater than or equal to 1.0.

Near side of the Moon Hemisphere of the Moon facing the Earth

The near side of the Moon is the lunar hemisphere that is permanently turned towards Earth, whereas the opposite side is the far side. Only one side of the Moon is visible from Earth because the Moon rotates on its axis at the same rate that the Moon orbits the Earth – a situation known as synchronous rotation, or tidal locking.

April 2014 lunar eclipse total lunar eclipse in April 2014

A total lunar eclipse took place on April 15, 2014. It was the first of two total lunar eclipses in 2014, and the first in a tetrad. Subsequent eclipses in the tetrad are those of October 8, 2014, April 4, 2015, and September 28, 2015.

October 2014 lunar eclipse lunar eclipse

A total lunar eclipse took place on October 8, 2014. It is the second of two total lunar eclipses in 2014, and the second in a tetrad. Other eclipses in the tetrad are those of April 15, 2014, April 4, 2015, and September 28, 2015.

April 2015 lunar eclipse lunar eclipse

A total lunar eclipse took place on 4 April 2015. It is the former of two total lunar eclipses in 2015, and the third in a tetrad. Other eclipses in the tetrad are those of 15 April 2014, 8 October 2014, and 28 September 2015.

September 2015 lunar eclipse

A total lunar eclipse took place between September 27 and 28, 2015. It was seen on Sunday evening, September 27, in the Americas; while in Europe, Africa, and the Middle East, it was seen in the early hours of Monday morning, September 28. It was the latter of two total lunar eclipses in 2015, and the final in a tetrad. Other eclipses in the tetrad are those of April 15, 2014, October 8, 2014, and April 4, 2015.

January 2019 lunar eclipse lunar eclipse

A total lunar eclipse occurred on January 21, 2019 UTC. For observers in the Americas, the eclipse took place between the evening of Sunday, January 20 and the early morning hours of Monday, January 21. For observers in Europe and Africa, the eclipse occurred during the morning of January 21. The Moon was near its perigee on January 21 and as such can be described as a "supermoon".

Solar eclipse of December 26, 2038

A total solar eclipse will occur on December 26, 2038. A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby totally or partly obscuring the image of the Sun for a viewer on Earth. A total solar eclipse occurs when the Moon's apparent diameter is larger than the Sun's, blocking all direct sunlight, turning day into darkness. Totality occurs in a narrow path across Earth's surface, with the partial solar eclipse visible over a surrounding region thousands of kilometres wide.

Solar eclipse of April 20, 2061 total solar eclipse

A total solar eclipse will occur on April 20, 2061. A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby totally or partly obscuring the image of the Sun for a viewer on Earth. A total solar eclipse occurs when the Moon's apparent diameter is larger than the Sun's, blocking all direct sunlight, turning day into darkness. Totality occurs in a narrow path across Earth's surface, with the partial solar eclipse visible over a surrounding region thousands of kilometres wide.

Solar eclipse of October 12, 1939

A total solar eclipse occurred on October 12, 1939. A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby totally or partly obscuring the image of the Sun for a viewer on Earth. A total solar eclipse occurs when the Moon's apparent diameter is larger than the Sun's, blocking all direct sunlight, turning day into darkness. Totality occurs in a narrow path across Earth's surface, with the partial solar eclipse visible over a surrounding region thousands of kilometres wide.

Solar eclipses on the Moon

Solar eclipses on the Moon are caused when the planet Earth passes in front of the Sun and blocks its light. Viewers on Earth experience a lunar eclipse during a solar eclipse on the moon.

References

  1. "List of basic lunar features". Archived from the original on 2006-02-03.
  2. O'Byrne, Chris. "Lunar Limb Corrections". Archived from the original on 2008-01-13.
  3. Watts, C. B. (1963). "The Marginal Zone of the Moon". Astron. Papers Amer. Ephem. 17 (1): 951.