Astronomical day

	See under Day.
	a period equal to the mean solar day, but beginning at noon instead of at midnight, its twenty-four hours being numbered from 1 to 24; also, the sidereal day, as that most used by astronomers.

astronomical day

[‚as·trə′näm·ə·kəl ′dā] (astronomy) A mean solar day beginning at mean noon, 12 hours later than the beginning of the civil day of the same date; astronomers now generally use the civil day.

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