[ dek-luh-ney-shuhn ]
/ ˌdɛk ləˈneɪ ʃən /
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Origin of declination

1350–1400; Middle English declinacioun<Old French declinacion<Latin dēclīnātiōn- (stem of dēclīnātiō), equivalent to dēclīnāt(us), literally, turned aside (past participle of dēclīnāre;see decline, -ate1) + -iōn--ion

OTHER WORDS FROM declination

dec·li·na·tion·al, adjectivepre·dec·li·na·tion, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023


What does declination mean?

In astronomy, the declination of a celestial object (such as a star or planet) is its position in relation to the celestial equator—the imaginary flat surface that extends out from Earth’s equator in all directions.

In astronomy, heavenly bodies like planets and stars are considered in terms of their position in the celestial sphere—the imaginary sphere that extends out infinitely from Earth. (Picture an infinitely huge ball with Earth as its center.) The celestial equator cuts this sphere in half.

Declination involves the measurement of the position of such objects as being north or south of the celestial equator. Those north of the celestial equator are measured in positive degrees, and those south of it are measured in negative degrees. The declination of the north celestial pole is 90° and the declination of the south celestial pole is -90°. For example, during the summer solstice in the Northern Hemisphere, the Sun is at a declination of 23° north.

Declination also has several more general meanings, but none of them are commonly used. In most of these cases, there is another, more common word that can be used in its place.

Declination can mean a bending or sloping downward. Things that slope this way, such as the parts of a plant, can be described with the adjective declinate. Declination can also mean deterioration—the process or an instance of something getting worse. In both of these senses, it can often be replaced with the noun decline. Declination can also refer to deviation, such as from a standard.

A declination can also be a polite refusal, especially in a formal or official situation. In this sense, it is a noun form of the verb decline, meaning to refuse or to turn something down.

In most cases, it’s much more common for people to use words like deterioration, decline, deviation, and refusal than declination.

Where does declination come from?

The first records of the word declination come from the 1300s. It derives from the Latin dēclīnātus, meaning “turned aside.” Both decline and declination ultimately come from the Latin verb dēclīnāre, meaning “to slope” or “to bend away.”

Because space is three-dimensional, it’s often considered in terms of spheres, curves, and slopes, as opposed to straight lines. In astronomy, the declination of an object like a star is kind of like its latitude and longitude. But instead of being measured on the sphere of Earth, it’s measured on the celestial sphere—the imaginary sphere of space.

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What are some other forms related to declination?

  • declinational (adjective)
  • predeclination (noun)

What are some synonyms for declination?

What are some words that share a root or word element with declination

What are some words that often get used in discussing declination?

How is declination used in real life?

The term declination is mostly used in astronomy. Its more general senses are rarely used.



Try using declination!

Which of the following words is a synonym of declination?

A. decline
B. deterioration
C. deviation
D. all of the above

How to use declination in a sentence

British Dictionary definitions for declination

/ (ˌdɛklɪˈneɪʃən) /

astronomy the angular distance, esp in degrees, of a star, planet, etc, from the celestial equator measured north (positive) or south (negative) along the great circle passing through the celestial poles and the bodySymbol: δ Compare: right ascension
a refusal, esp a courteous or formal one

Derived forms of declination

declinational, adjective
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for declination

[ dĕk′lə-nāshən ]

On the celestial sphere, the position of a celestial object north or south of the celestial equator. Declination is measured in degrees along a great circle drawn through the object being measured and the north and south celestial poles, with positive values north of the celestial equator and negative values south of it, so that the equator itself is 0° and the north and south celestial poles are +90° and -90° declination respectively. See more at equatorial coordinate system.
See magnetic declination.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.