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9. A Year and A Day
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A year on Earth is 365 days
Vocabulary:
year
The time it takes Earth to orbit once around the sun
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The exact amount of time is 365 ¼ days
Because of the extra ¼ day1 day is added to the calendar
every 4 years
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That year is called leap year
February usually has 28 daysBut in a leap year it has 29
days
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So there are 366 days in a leap year
All other years have 365 days
2012 will be our next leap year
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A year is a different length of time on each planet
This is because it takes each planet a different amount of
time to orbit the sun
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Mercury is much closer to the sun than Earth
It takes Mercury only 88 days to travel around the sun
So a year on Mercury is 88 days long
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Pluto is very far from the sun
It takes Pluto a long time to travel once around the sun
A year on Pluto is equal to 248 year on Earth
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Day and Night
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An imaginary line goes through Earth from the North Pole to
the South Pole
This line is called Earth’s axis
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Vocabulary
axis
An imaginary line that goes through the Earth from the North Pole to the South Pole
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Earth spins on its axis
This spinning movement is called rotation
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Vocabulary
rotation
A spinning movement like when Earth rotates on its axis
once every 24 hours
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Each 24 hours is 1 day
Both daytime and nighttime are part of this day
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Only on side of Earth faces the sun at any time.
This side is having daytimeThe opposite side of
Earth is in darkness.
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When it is daytime in North America
it is nighttime in India
In a 24-hour dayeach part of Earth moves into
the sunlight and back into darkness again
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The spinning motion of Earth makes the sun look like it is
moving across the sky
Because Earth spins toward the east,
the sun appears to rise in the east and set in the west
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If Earth did not rotate,half of our planet would always
have day and half would always have night
