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Keeping Time with the Skies

Calendars people use

Diwali is in October one year and November the next. The Gregorian date, the date on the usual calendar, keeps moving. Why?

A solar calendar matches the solar year.
Step 1 of 3
  1. A solar calendar matches the solar year.
  2. A lunar calendar falls short every year.
  3. A luni-solar calendar adds a month some years.

New word

  • Luni-solar — following the Moon, with a month added to fit the seasons.

The rule

Diwali follows Moon months. The Gregorian year follows the Sun. So Diwali's date moves.

A lunar calendar follows the Moon. A solar calendar follows the seasons. A luni-solar calendar follows the Moon. It adds an extra month every few years. That keeps it in step with the seasons.

Kinds of calendar
CalendarKind
GregorianSolar
Indian National CalendarSolar
Islamic (Hijri) calendarLunar
Hindu festival calendarsLuni-solar

Sort each fact by its kind of calendar.

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This track

  1. 0 Start here
  2. 1 Where a day came from
  3. 2 A shadow that tells the time
  4. 3 Where a month came from
  5. 4 Where a year came from
  6. 5 They do not divide
  7. 6 A spare day every few years
  8. 7 Calendars people use
  9. 8 Where to look for the Moon
  10. 9 Satellites above us
  11. 10 Checkpoint: the Moon in the sky and satellites
  12. 11 The big picture
  13. 12 Track quiz

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