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In spherical astronomy
Spherical astronomy, or positional astronomy, is a branch of observational astronomy used to locate astronomical objects on the celestial sphere, as seen at a particular date, time, and location on Earth. It relies on the mathematical methods of ...
, quadrature is the configuration of a celestial object
An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''body'' are often u ...
in which its elongation is perpendicular
In elementary geometry, two geometric objects are perpendicular if they intersect at a right angle (90 degrees or π/2 radians). The condition of perpendicularity may be represented graphically using the '' perpendicular symbol'', ⟂. It c ...
to the direction of the Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
. It is applied especially to the position of a superior planet
In the Solar System, a planet is said to be inferior or interior with respect to another planet if its orbit lies inside the other planet's orbit around the Sun. In this situation, the latter planet is said to be superior to the former. In the ref ...
or the Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
at its first and last quarter phases. This is not to be confused with the Moon at dichotomy
A dichotomy is a partition of a whole (or a set) into two parts (subsets). In other words, this couple of parts must be
* jointly exhaustive: everything must belong to one part or the other, and
* mutually exclusive: nothing can belong simul ...
(exactly half-lit) as viewed from Earth, which occurs at 89.85 degrees and 270.15 degrees.
As shown in the diagram, a planet (or other object) can be at the western quadrature (when it is to the west of the Sun when viewed from the Earth) or at the eastern quadrature (when it is to the east of the Sun when viewed from the Earth). Note that an inferior planet
In the Solar System, a planet is said to be inferior or interior with respect to another planet if its orbit lies inside the other planet's orbit around the Sun. In this situation, the latter planet is said to be superior to the former. In the ...
can never be at quadrature to the reference planet.
At quadrature, the shadow that a planet casts on its planetary rings appears most offset from the planet (e.g., Saturn's rings); the dark side of a planet (e.g., Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
) is maximally visible.
See also
*Astrological aspect
In astrology, an aspect is an angle that planets make to each other in the Horoscope; as well as to the Ascendant, Midheaven, Descendant, Lower Midheaven, and other points of astrological interest. As viewed from Earth, aspects are measured ...
References
;Attribution *{{1911, author=Anonymous, wstitle=Quadrature Astrological aspects Celestial mechanics Observational astronomy Orbits Spherical astronomy First quarter moon