The Gregorian calendar is the most widely used civil calendar in the world, with most countries adopting it as their official calendar.

The main difference between the Julian calendar and the Gregorian calendar is the way leap years are calculated. In the Julian calendar, a leap year occurs every four years, while in the Gregorian calendar, a leap year occurs every four years except for years divisible by 100 but not divisible by 400.

The Chinese calendar is a lunisolar calendar, which means that it is based on both the lunar cycle and the solar cycle. The calendar has a 12-month year, with each month being either 29 or 30 days long. Every three years, an extra month is added to the calendar to keep it in sync with the solar year.

The Islamic calendar is a lunar calendar, which means that it is based on the lunar cycle. The calendar has a 12-month year, with each month being either 29 or 30 days long. The months start with the new moon, and the year starts with the first day of Muharram, the first month of the calendar.

The Hebrew calendar is a lunisolar calendar, which means that it is based on both the lunar cycle and the solar cycle. The calendar has a 12-month year, with each month being either 29 or 30 days long. Every three years, an extra month is added to the calendar to keep it in sync with the solar year.

The Mayan calendar is a solar calendar, which means that it is based on the solar cycle. The calendar has a 365-day year, with each month being either 20 or 21 days long. The year starts with the vernal equinox, the day when the sun crosses the equator moving northward.

The Aztec calendar is a solar calendar, which means that it is based on the solar cycle. The calendar has a 365-day year, with each month being either 20 or 21 days long. The year starts with the vernal equinox, the day when the sun crosses the equator moving northward.

The Inca calendar is a solar calendar, which means that it is based on the solar cycle. The calendar has a 365-day year, with each month being either 30 or 31 days long. The year starts with the winter solstice, the day when the sun is at its lowest point in the sky.

The Ethiopian calendar is a solar calendar, which means that it is based on the solar cycle. The calendar has a 365-day year, with each month being either 30 or 31 days long. The year starts with the vernal equinox, the day when the sun crosses the equator moving northward.

The Bahá'í calendar is a solar calendar, which means that it is based on the solar cycle. The calendar has a 19-month year, with each month being either 19 or 20 days long. The year starts with the spring equinox, the day when the sun crosses the equator moving northward.

The Zoroastrian calendar is a solar calendar, which means that it is based on the solar cycle. The calendar has a 365-day year, with each month being either 30 or 31 days long. The year starts with the vernal equinox, the day when the sun crosses the equator moving northward.

The Hindu calendar is a lunisolar calendar, which means that it is based on both the lunar cycle and the solar cycle. The calendar has a 12-month year, with each month being either 29 or 30 days long. Every three years, an extra month is added to the calendar to keep it in sync with the solar year.

The Buddhist calendar is a lunisolar calendar, which means that it is based on both the lunar cycle and the solar cycle. The calendar has a 12-month year, with each month being either 29 or 30 days long. Every three years, an extra month is added to the calendar to keep it in sync with the solar year.

The Jain calendar is a lunisolar calendar, which means that it is based on both the lunar cycle and the solar cycle. The calendar has a 12-month year, with each month being either 29 or 30 days long. Every three years, an extra month is added to the calendar to keep it in sync with the solar year.

The Sikh calendar is a solar calendar, which means that it is based on the solar cycle. The calendar has a 12-month year, with each month being either 30 or 31 days long. The year starts with the vernal equinox, the day when the sun crosses the equator moving northward.