astronomical day


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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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239]Pu [alpha]-decay over astronomical day (since 6 to 18 h by local, longitude, time) and, second, measured over astronomical night (since 18 to 6 h, in continuation of the first series) and inverted.
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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