Leap Day Earth Science Mr Doe Earth Motions

Earth Motions • The Earth goes through two (2) motions in space: – 1)

Earth’s Rotation • Rotation • = The Earth rotates (or spins) on it axis.

Earth’s Rotation • So the length of the day isn’t exactly 24 hours. •

Earth’s Revolution • Revolution • = The Earth revolves (or travels around) the Sun.

Earth’s Revolution • Page 15 of the ESRT

Earth’s Revolution • So the length of the year isn’t exactly 365 days. •

The Calendar • Since the calendar only shows whole days (the 24 -hour long

The Calendar • So after 1 year (or 365 days), we still have 6

The Calendar • And finally, after 4 years (or 365 more days), we have

That Extra Day • The extra day we add to bring the calendar current

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Leap Day Earth Science – Mr. Doe

Earth Motions • The Earth goes through two (2) motions in space: – 1) Rotation → This causes our DAY. – 2) Revolution → This causes our YEAR.

Earth’s Rotation • Rotation • = The Earth rotates (or spins) on it axis. • Speed of Rotation = once / every = 360° / 24 hrs day = 15°/hr • Direction of Rotation = West → East How do we know this? The Sun appears to move E→W.

Right? • Not Exactly!

Earth’s Rotation • Page 15 of the ESRT

Earth’s Rotation • So the length of the day isn’t exactly 24 hours. • It’s 23 hours 56 minutes and 4 seconds long. • So why do we say the day is 24 hours long? • We approximate the day to make it easier to measure time.

Earth’s Revolution • Revolution • = The Earth revolves (or travels around) the Sun. • Speed of Revolution = once / every = 360° / 365 days year ≈ 1°/day (a little less than 1° actually)

Right? • Not Exactly!

Earth’s Revolution • Page 15 of the ESRT

Earth’s Revolution • So the length of the year isn’t exactly 365 days. • It’s 365. 26 days (or about 365 and ¼ days) long. • How long is a quarter of a day? • Approximately 6 hours.

No big deal, Right? • Not Exactly!

The Calendar • Since the calendar only shows whole days (the 24 -hour long kind), we can’t easily fit those extra 6 hours into it. • We sort of just “forget” about those extra 6 hours. • For now. • (They’re still there but we just don’t know what to do with them yet. )

The Calendar • So after 1 year (or 365 days), we still have 6 extra hours not accounted for on the calendar. • After 2 years (or 365 more days), we have 12 extra hours not accounted for on the calendar. • After 3 years (or 365 more days), we have 18 extra hours not accounted for on the calendar. • Do you see where this is headed?

The Calendar • And finally, after 4 years (or 365 more days), we have 24 extra hours not accounted for on the calendar. • So what can we now do? • Right! We can ADD AN EXTRA DAY to get our calendar “back on track”.

That Extra Day • The extra day we add to bring the calendar current is called: LEAP DAY. • A year with a Leap Day is called: Everyone? A LEAP YEAR

Today is Leap Day! • Happy Leap Day!