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Revolutions of Earth

Earth, and the other seven planets, revolve around the Sun in an orbit that is slightly elliptical.

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Leapin' Leap Years

Leapin' Leap Years

Credit: Anshad Ameenza
Source: http://www.flickr.com/photos/anshad/6628218005
License: CC BY-NC 3.0

Everyone knows that there are 365 days in a year; except during leap years, of course. Everyone knows leap years happen every four years; except once per century, of course. And even that’s not always true.

Why It Matters

If we had 365 days per year every year it wouldn’t take long before the seasons didn’t match the date. To keep us celebrating Thanksgiving in the late fall, we have a complex system. Between now and 2100, you can expect that there will be 29 days in February every four years. Leap years are also the years of the Summer Olympics and the U.S. Presidential Election. But what happens in 2100? What happened in 2000? Why do we need such a crazy system?

Show What You Know

With the link below, learn more about how we keep our calendars in sync with the season. Then answer the following questions.

  1. The number of hours in a year is 8765.81. If you divide that number by 365 (The number of days in most years), what have you calculated? What number do you get?
  2. Why isn’t the number of days in a year a whole number?
  3. Why doesn’t one extra day in February keep the calendar from getting off from the seasons?
  4. What is done to correct for that problem? Does this solve the problem or is there another correction that needs to be made?
  5. Why were there 29 days in February in 2000?
  6. The calendar will still be off one day in 8000 years. What should be done about that?

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Image Attributions

  1. [1]^ Credit: Anshad Ameenza; Source: http://www.flickr.com/photos/anshad/6628218005; License: CC BY-NC 3.0

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