Where did the names of the months of the year come from? Why are there seven days in a week? And how are seasons defined? Find out all the answers and more here. Plus, find out how calendars vary among different cultures around the world.

What and when is the autumnal equinox?
When is the autumnal equinox, what date does the autumnal equinox fall on and when does summer end?
Lunar new year dates and animals of the zodiac
Find out more about the new year festival celebrated by people across Asia
Summer and winter solstices explained – how the Sun determines the longest and shortest days of the year
Find out how the position of the Sun determines the longest and shortest days of the year in this special Royal Observatory Greenwich Illuminates extract
Full Moon calendar 2024
Check the dates for every full Moon throughout the year, and learn about lunar phases, 'supermoons' and more
When does spring start?
Did you know there are actually three main definitions for the start of spring?
How do people celebrate Chinese New Year?
What happens during Chinese New Year? The Newham Chinese Association explain some of the traditions, festivals and customs that take place when Chinese New Year is celebrated.
Summer solstice
When - and what - is the summer solstice?
Al Hijra, Ramadan and the Islamic calendar
Observations of the Moon determine the timing of the Islamic year Al Hijra and its months including the holy month of Ramadan. Find out the dates here
When is the winter solstice? The shortest day
When is the winter solstice this year? What does it mean? Is it the shortest or longest day?
When is Hanukkah?
The exact date of Hannukkah changes every year. Find out how the Hebrew calendar works and how it relates to the phases of the Moon.