astronomical day

Since sometimes the earth travels a bit faster, sometimes a bit slower, this indicates that at times an astronomical day is about a quarter of an hour quicker or slower than a day as told by a watch.

Your correspondent DX. is mistaken in supposing that "foreigners ordinarily commence the astronomical day at midnight."

The civil day always commences at the midnight preceding this astronomical day.

A vigorous effort was made during the last fifteen years of the 19th century to bring the two uses into harmony by beginning the astronomical day at midnight.

Foreigners, however, ordinarily commence the astronomical day at midnight, at least those of France, Germany, Italy, and Spain do.