declination

American  

[dek-luh-ney-shuhn] / ˌdɛk ləˈneɪ ʃən /

noun

1. a bending, sloping, or moving downward.

2. deterioration; decline.

3. a swerving or deviating, as from a standard.

4. a polite refusal.

5. Astronomy. the angular distance of a heavenly body from the celestial equator, measured on the great circle passing through the celestial pole and the body.

6. variation.

7. the formal refusal by a nominee of a nomination to public office.

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declination British  

/ ˌdɛklɪˈneɪʃən /

noun

1. Compare: right ascension.   δ.  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 body

2. See magnetic declination

3. a refusal, esp a courteous or formal one

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declination Scientific  

/ dĕk′lə-nā′shən /

1. 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.

2. See more at equatorial coordinate system

3. See magnetic declination

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Usage

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.

Other Word Forms

• declinational adjective
• predeclination noun

Etymology

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; decline, -ate ¹ ) + -iōn- -ion

Explanation

When you turn down an invitation, that's a declination. Another kind of declination is when something slopes down, like the declination of a playground slide. Look at the noun declination and you can see the verb decline, which means "to lessen," "to slope down," and "to refuse." Declination is the process of doing any of these things. In astronomy, it's also the distance between an object and the celestial equator, measured at an angle. The Latin root is declinatio, "a bending away."

Example Sentences

De La Cova was the detective who presented a case to the district attorney’s office, according to the declination memo.

From Los Angeles Times • Dec. 12, 2025

“We will say, and our declination letter does say, that the decision of the deputy to jump into the vehicle at that point was unusual,” he said.

From Seattle Times • Oct. 17, 2023

Rep. Kevin Kiley, California Republican, asked Heritage Foundation legal fellow Charles Stimson how the District’s prosecutors’ 66% declination rate in the past year compares with other jurisdictions around the country.

From Washington Times • Oct. 12, 2023

When the division does not provide the green light, they issue what is known as a declination memo.

From Slate • Jul. 26, 2023

“I don’t understand maps, Etienne. Minutes, seconds, declination adjustments? You know these things. All you have to do is find them, plot them, and broadcast the coordinates.”

From "All the Light We Cannot See" by Anthony Doerr