Although the year is common to cultures around the world, ancient and modern, it is sometimes defined differently. For example, the lunar year is defined by the cycles of the moon, rather than by the earth’s orbit around the sun. Some lunar calendars make use of intercalation (the adding of days or months) to reorient the lunar year to the solar year. But the Islamic lunar calendar does not, meaning that every successive new year begins on a different day of the solar year.