Timekeeping

Evergreen

Leap Year Day, February 29, exists to reconcile the difference between calendar time and astronomical time. A tropical year, the time between successive vernal equinoxes, is abo...

Guides And Explainers

The Gregorian calendar, introduced by Pope Gregory XIII in 1582, defines the year numbering used by most of the world today. Years are counted from the traditionally recognized...

calendar-time

The Gregorian calendar year runs about 365.2422 days, yet our calendar year is fixed at 365 days. Without correction, the calendar would drift relative to seasons and astronomic...

astronomy

“When in the winter solstice” refers to how the date of the winter solstice is described and tracked each year. The winter solstice in the Northern Hemisphere is the moment...

time-measurement

A day is conventionally 24 hours, but Earth’s rotation can speed up or slow down, making days fractionally shorter or longer than 86,400 seconds of atomic time. When people as...