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 ...

Leap years account for the inaccurate measure of time on the 365-day calendar. Technically it takes 365.242190 days for the Earth to orbit the Sun, which is known as the "sidereal year," according ...