Dictionary Definition
declination
Noun
1 a condition inferior to an earlier condition; a
gradual falling off from a better state [syn: decline] [ant: improvement]
2 (astronomy) the angular distance to a point on
a celestial object measured north or south from the celestial
equator; expressed in degrees; used with right ascension to specify
positions on the celestial sphere [syn: celestial
latitude, DEC]
3 a downward slope or bend [syn: descent, declivity, fall, decline, declension, downslope] [ant: ascent]
4 a polite refusal of an invitation [syn:
regrets]
User Contributed Dictionary
English
Pronunciation

 Rhymes: eɪʃǝn
Noun
 At a given point, the angle between magnetic north and true north.
 At a given point, the angle between the line connecting this point with the geographical center of the earth and the equatorial plane.
 A refusal.
 Declension.
Translations
at a given point, the angle between magnetic
north and true north
 Finnish: eranto, deklinaatio
 French: déclinaison
 German: Deklination
 Italian: declinazione
 Russian: склонение (sklonénije)
at a given point, the angle between the line
connecting this point with the geographical center of the earth and
the equatorial plane
 Finnish: deklinaatio
 French: déclinaison
 German: Deklination
 Italian: declinazione
 Russian: склонение (sklonénije)
refusal
declension
 Finnish: taivutusluokka, deklinaatio
 German: Deklination
 Italian: declinazione
 Russian: склонение (sklonénije)
Related terms
Derived terms
Extensive Definition
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 declinations, while those to the south have negative
declinations.
 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°.
The sign is customarily included even if it is
positive. Any unit of angle can be used for declination, but it is
often expressed in degrees,
minutes, and seconds of arc.
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, at northern
latitudes φ > 0, celestial objects with a declination greater
than 90°  φ, are always visible. Such stars are called circumpolar
stars, while the phenomenon of a sun not setting is called
midnight
sun.
If instead of measuring from and along the
equator the angles are measured from and along the horizon, the
angles are called azimuth and altitude (elevation).
Stars
Because a star lies in a nearly constant direction as viewed from earth, its declination is approximately constant from year to year. However, both the right ascension and declination do change gradually due to the effects of precession of the equinoxes and proper motion.Varying declination
The declinations of all solar system objects change much more quickly than those of stars.Sun
The declination of the Sun (δ) is the angle between the rays of the sun and the plane of the earth's 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.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 summer solstice
and δ = 23°27' at the northern hemisphere winter solstice. Due to
the changes in the tilt of the Earth's axis, the angle between the
rays of the sun and the plane of the earth equator is slightly
decreasing.
When the projection of the earth axis on the
plane of the earth orbit is perpendicular to the 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.
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:
 \delta = 23.45^\circ \cdot \cos \left [ \frac \cdot \left ( N + 10 \right ) \right ]
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.
An alternative form is given as:
 \delta = 23.45^\circ \cdot \sin \left [ \frac \cdot \left ( N + 284 \right ) \right ]
A more precise formula is given by:
 \ \delta = \frac \cdot (0.006918  0.399912 \cos \gamma + 0.070257 \sin \gamma  0.006758 \cos 2\gamma + 0.000907 \sin 2\gamma  0.002697 \cos 3\gamma + 0.00148 \sin 3\gamma)
where
 \gamma = \frac ( N  1 )
is the fractional year in radians.
More accurate daily values from averaging the
four years of a leapyear cycle
are given in the Table
of the Declination of the Sun.
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'.See also
Declination is used in some contexts that rule out astronomical declination, to mean the same as magnetic declination.Declination is occasionally and erroneously used
to refer to the linguistic term declension.
References
External links
 Table of the Declination of the Sun: Mean Value for the Four Years of a LeapYear Cycle
 Declination function for Excel, CAD or your other programs. The Sun API is free and extremely accurate. For Windows computers.
declination in Arabic: میل
declination in Asturian: Declinación
(astronomía)
declination in Bulgarian: Деклинация
declination in Czech: Deklinace
declination in Danish: Deklination
(astronomi)
declination in German: Deklination
(Astronomie)
declination in Estonian: Kääne
(astronoomia)
declination in Modern Greek (1453): Απόκλιση
αστέρος
declination in Spanish: Declinación
(astronomía)
declination in Esperanto: Deklinacio
(astronomio)
declination in Persian: میل
declination in French: Déclinaison
(astronomie)
declination in Irish: Diallas
declination in Korean: 적위
declination in Croatian: Deklinacija
(astronomija)
declination in Indonesian: Deklinasi
declination in Italian: Declinazione
(astronomia)
declination in Latin: Declinatio
(astronomia)
declination in Luxembourgish: Deklinatioun
(Astronomie)
declination in Lithuanian: Deklinacija
declination in Latvian: Deklinācija
(astronomijā)
declination in Malayalam: ഡെക്ലിനേഷന്
declination in Dutch: Declinatie
(astronomie)
declination in Japanese: 赤緯
declination in Norwegian: Deklinasjon
declination in Norwegian Nynorsk:
Deklinasjon
declination in Polish: Deklinacja
(astronomia)
declination in Portuguese: Declinação
declination in Slovak: Deklinácia
declination in SerboCroatian: Deklinacija
(astronomija)
declination in Finnish: Deklinaatio
declination in Swedish: Deklination
(astronomi)
declination in Thai: เดคลิเนชัน
declination in Vietnamese: Xích vĩ
declination in Chinese: 赤纬
Synonyms, Antonyms and Related Words
Cartesian coordinates, aberrancy, aberration, abjuration, abjurement, abnegation, abscissa, altitude, azimuth, bend, bias, branching off, cascade, cataract, chucking, chucking out,
chute, circuitousness, collapse, comedown, contempt, contradiction, coordinates, corner, crash, crook, crosswiseness, curve, cylindrical coordinates,
debacle, debasement, decadence, decadency, declension, declinature, decline, declining, deflection, deflexure, defluxion, deformation, degeneracy, degenerateness, degeneration, degradation, demotion, denial, departure, depravation, depravedness, depreciation, deprivation, derogation, descending, descension, descent, despisal, despising, deterioration, detour, deviance, deviancy, deviation, deviousness, devolution, diagonality, digression, disagreement, disallowance, disapproval, discard, disclaimer, disclamation, discounting, discursion, dismissal, disobedience, disownment, disregard, dissent, divagation, divarication, divergence, diversion, dogleg, double, down, downbend, downcome, downcurve, downfall, downflow, downgrade, downpour, downrush, downtrend, downturn, downward mobility,
downward trend, drift,
drifting, drop, dropping, dying, ebb, ebbing, effeteness, equator
coordinates, errantry,
exception, exclusion, excursion, excursus, exorbitation, fading, failing, failure, failure of nerve,
fall, falling, fallingoff, gravitation, hairpin, holding back, ignoring, inclination, indirection, indirectness, involution, lapse, latitude, longitude, loss of tone,
nay, negation, negative, negative answer,
nix, no, nonacceptance, nonapproval, noncompliance, nonconformity, nonconsent, nonconsideration,
nonobservance,
obliqueness,
obliquity, ordinate, passing by, pererration, plummeting, polar
coordinates, pounce,
putting away, putting out, rambling, rapids, rebuff, recantation, refusal, regression, rejection, renouncement, repudiation, repulse, retention, retrocession, retrogradation, retrogression, right
ascension, scouting,
sheer, shift, shifting, shifting course,
shifting path, skew,
skewness, slant, slippage, slump, spurning, squint, stoop, straying, sweep, swerve, swerving, swinging, swoop, tack, throwing out, thumbsdown,
transverseness,
turn, turndown, turning, turning out, twist, unwillingness, vagary, variation, veer, wandering, wane, waning, warp, waterfall, withholding, yaw, zigzag