SEASONS GREETINGS
Question: As the winter cold greets us in the Northern Hemisphere here on Earth,
it's time to ponder: Do comets have seasons?
Here are your clues:
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Think about Earth during different seasons.
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Think about its orientation in space, its geometry.
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Would a comet in orbit around the sun have seasons too?
View MPEG Animation (5.61 MB)
View Large Animated GIF (4.68 MB)
Answer: Yes, consider what makes the seasons on Earth. The planet Earth rotates on its axis once a day. That
same axis is tilted with respect to the plane formed by the Sun and the planets, called the ecliptic. The angle formed between
the Earth's axis and the ecliptic plane, results in the seasons. When the Northern Hemisphere is tilted toward the Sun, the days are
longer and there is more sunlight hitting the Earth, this is summer. When it is tilted away from the Sun, there is less sunlight on the
Northern Hemisphere and it is winter.
Comets have their own geometric orientation in space and hence they too have seasons. We currently do not know the
orientation of Tempel 1's axis but we will learn that when we approach and flyby the comet observing it over time as it rotates in
space. Note that Tempel 1 rotates on its axis very slowly, once every 42 hours. Our animation does not show this rotation, but its
there.
Season's Greetings from the
Deep Impact team.
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