In astronomy, declination (abbrev. dec or δ) is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Dec is comparable to latitude, projected onto the celestial sphere, and is measured in degrees north and south of the celestial equator. Therefore, points north of the celestial equator have positive declination, while those to the south have negative declination. It has an alternative name celestial latitude. Image File history File links Equatorial_coordinates. ... A giant Hubble mosaic of the Crab Nebula, a supernova remnant. ... The equatorial coordinate system is probably the most widely used celestial coordinate system, whose equatorial coordinates are: declination () right ascension () -also RA-, or hour angle () -also HA- It is the most closely related to the geographic coordinate system, because they use the same fundamental plane, and the same poles. ... Equatorial Coordinates Right ascension (abbrev. ... In astronomy, an objects hour angle (HA) is defined as the difference between the current local sidereal time (LST) and the right ascension () of the object: HAobject = LST - object Thus, the objects hour angle indicates how much sidereal time has passed since the object was on the local... Latitude, usually denoted symbolically by the Greek letter phi, , gives the location of a place on Earth north or south of the equator. ... The celestial sphere is divided by the celestial equator. ... World map showing the equator in red The Equator is an imaginary circle drawn around a planet (or other astronomical object) at a distance halfway between the poles. ...

• An object on the celestial equator has a dec of 0°.
• An object above the north pole has a dec of +90°.
• An object above the south pole has a dec of −90°.

Note that the sign must be included even if positive. The celestial equator is a great circle on the imaginary celestial sphere, which could be constructed by inflating the Earths equator until it intersects with said sphere. ... North Pole Scenery When not otherwise qualified, the term North Pole usually refers to the Geographic North Pole – the northernmost point on the surface of the Earth, where the Earths axis of rotation intersects the Earths surface. ... Amundsen-Scott South Pole Station. ...

A celestial object that passes over zenith, has a declination equal to the observer's latitude, with northern latitudes yielding positive declinations. A pole star therefore has the declination +90° or -90°. Conversely, celestial objects with a declination higher than 90° - φ, where φ is the latitude, are visible the whole sidereal day. Such stars are called circumpolar stars, while the phenomenon of a sun not setting is called midnight sun. In broad terms, the zenith is the direction pointing directly above a particular location (perpendicular, orthogonal). ... For other uses of the words Pole star and Polestar see Polestar (disambiguation). ... On a prograde planet like the Earth, the sidereal day is shorter than the solar day. ... Circumpolar stars are those stars which are located near the celestial poles of the celestial sphere, i. ... See the section Popular culture below for novels and other popular culture related to the Midnight Sun. ...

Varying declination

The declination of all celestial objects vary over time, in different periods. ...

Sun

The declination of the Sun (δ) is the angle between the rays of the sun and the plane of the earth equator. Since the angle between the earth axis and the plane of the earth orbit is nearly constant, δ varies with the seasons and its period is one year, that is the time needed by the earth to complete its revolution around the sun. The Sun is the star at the centre of the Solar System. ... This article is about divisions of a year. ... A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ...

When the projection of the earth axis on the plane of the earth orbit is on the same line linking the earth and the sun, the angle between the rays of the sun and the plane of the earth equator is maximum and its value is 23°27'. This happens at the solstices. Therefore δ = +23°27' at the northern hemisphere solstice and δ = -23°27' at the northern hemisphere winter solstice. A solstice is either of the two events of the year when the sun is at its greatest distance from the equatorial plane. ...

When the projection of the earth axis on the plane of the earth orbit is perpendicular to line linking the earth and the sun, the angle between the rays of the sun and the plane of the earth equator is null. This happens at the equinoxes. Therefore δ is 0° at the equinoxes. An equinox is one of two opposite points on the celestial sphere where the celestial equator and ecliptic intersect. ... An equinox is one of two opposite points on the celestial sphere where the celestial equator and ecliptic intersect. ...

Since the eccentricity of the earth orbit is quite low, it can be approximated to a circle, and δ is approximately given by the following expression:

where cos operates on degrees; if cos operates on radians, 360° in the equation needs to be replaced with 2π and will still output δ in degree; N is Day of the Year, that is the number of days spent since January 1. A degree (in full, a degree of arc, arc degree, or arcdegree), usually symbolized °, is a measurement of plane angle, representing 1／360 of a full rotation. ... The radian is a unit of plane angle. ... January 1 is the first day of the calendar year in both the Julian and Gregorian calendars. ...

An alternative form is given as:^[1]

A more precise formula is given by:^[2]

δ = 0.006918 − 0.399912cosγ + 0.070257sinγ − 0.006758cos2γ + 0.000907sin2γ − 0.002697cos3γ + 0.00148sin3γ

where

is the the fractional year in radians.

More accurate daily values from averaging the four years of a leap-year cycle are given in the Table of the Declination of the Sun. A leap year (or intercalary year) is a year containing an extra day, week or month in order to keep the calendar year synchronised with the astronomical or seasonal year. ...

A diagram demonstrating how the Sun's path over the celestial sphere changes with the varying declination during the year, marking the Azimuths in °N where the sun rises and sets at summer and winter solstice at a place of 56°N latitude.

A diagram demonstrating the varying declination of the Sun during the year, marking the Azimuths in °N where the sun rises and sets at summer and winter solstice at a place of 56°N latitude. ... The Sun is the star at the centre of the Solar System. ... Azimuth is the horizontal component of a direction (compass direction), measured around the horizon, usually from the north toward the east — i. ... A solstice is either of the two events of the year when the sun is at its greatest distance from the equatorial plane. ...

Moon

The Moon also has an annual cycle, with maximum declination at northern hemisphere midwinter and minimum at midsummer. There is also an approximately 19 year long cycle, varying the maximum declination from +28°35' to +18°18' and the minimum from -18°18' to -28°35'. Apparent magnitude: up to -12. ...

Stars

The stars have approximately the same declination from year to year, but they do have proper motion that can be measured in whole degrees after the passing of centuries. This article is about the astronomical object. ... The proper motion of a star is the motion of the position of the star in the sky (the change in direction in which we see it, as opposed to the radial velocity) after eliminating the improper motions of the stars, which affect their measured coordinates but are not real...

See also

• right ascension, celestial coordinate system
• geographic coordinates, ecliptic
• Setting circles

Declination is used in some contexts that rule out astronomical declination, to mean the same as magnetic declination. Equatorial Coordinates Right ascension (abbrev. ... In astronomy, a celestial coordinate system is a coordinate system for mapping positions in the sky. ... The plane of the ecliptic is well seen in this picture from the 1994 lunar prospecting Clementine spacecraft. ... Setting Circles are used on telescopes to find astronomical objects in the sky by their coordinates as listed in a star chart or ephemeris using the celestial coordinate system. ... The magnetic declination (or magnetic variation) at any point on the earth is a property of the geomagnetic field defined as the angle that must be added or subtracted in converting between two kinds of directional information: the direction of the needle on a magnetic compass located there, and the...

Declination is occasionally and erroneously used to refer to the linguistic term declension. In linguistics, declension is the inflection of nouns, pronouns and adjectives to indicate such features as number (typically singular vs. ...

External links

• Table of the Declination of the Sun: Mean Value for the Four Years of a Leap-Year Cycle
• Declination function for Excel, CAD or your other programs. The Sun API is free and extremely accurate. For Windows Computers.