The average year is, in fact, 365.242 days long – just so long as you’re not talking about the sidereal year. So what’s that? Simply put, a sidereal year – it’s pronounced sy-dear-ee-al ...

The Romans added January and February to the calendar but ran into a problem — math and superstition. Here's why February became the odd month out.

Slightly less than the 24 hours of a solar day (23 hours, 56 minutes, 4.1 seconds). Used in astronomy, sidereal means "when a star crosses the meridian" (the meridian is an imaginary circle around ...

By adding a day to February every four years, approximately, the calendar years adjust to the "sidereal year," the actual time it takes for the Earth to orbit the Sun. If that's not confusing ...