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1641 G. Walker Hist. Creation ix. 139 The space of the Sun, Moone, and Starres, compassing the earth, which is the space of 24. houres;..that day consists of an evening and a morning, and comprehends in it one night; and some call it a naturall, and some a civill, and some an astronomicall day.

1675 E. Sherburne in tr. M. Manilius Sphere 147 The beginning likewise of the Astronomical Day is computed from the Meridian Circle.

1738 Bayle's Hist. & Crit. Dict. (ed. 2) V. 777 The true Natural Day in its most proper signification, is the time betwixt the sun's quitting the Meridian to his returning to it. It is by this the Astronomical Day is measured.

1800 J. Gale Gale's Cabinet of Knowl. (ed. 3) 37 Our present political day begins at midnight, yet some compute the vernal equinox from the astronomical day, beginning 12 hours later.

1884 Nature 6 Nov. 10/2 The Astronomer-Royal proposes to adopt the recommendation of the Washington Conference by commencing on January 1 of next year to count the astronomical day from the midnight preceding the nominal civil date.

1925 Times 23 July 8/5 Some discussion took place on the use of the initials G.M.T., or Greenwich Mean Time, arising out of the change in the astronomical day, which formerly began at noon.

1970 Jrnl. Brit. Astron. Assoc. 80 210 The nautical day fell into disuse in the 19th century, but the astronomical day continued to be used until 1924.

2006 P. K. Seidelmann & G. A. Wilkins in P. K. Seidelmann Explanatory Suppl. Astron. Almanac (rev. ed.) i. 8 The integral values of the Julian date refer to the instants of Greenwich mean noon (since the system was introduced when the astronomical day began at noon rather than at midnight).