Astronomical day

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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.

See also: Astronomical, Day

References in periodicals archive ?
CARDIFF Family astronomical day at the National Museum.
As obtained in this experimental research, the sequence of the shapes of histograms (the spectra of the amplitudes of fluctuations), measured during an astronomical day from 6 h to 18 h of the local time, is very similar (with high precision of probability) to the sequence of the histogram shapes obtained during an astronomical night from 18 h to 6 h of the local time a half of year later in exact.
Thanks to the Earth's erratic rotation, the countdown to 2009 lasted a moment longer as British physicists and official timekeepers around the world inserted a leap second to bring the most accurate atomic clocks in line with the astronomical day.
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