Answers

2014-10-11T07:42:13+05:30
Revolution of Earth around sun.

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it is not only the revolution, it is the spinning, it is the variation in the distance between Earth and Sun.
2014-10-11T08:52:06+05:30
The earth's spin axis is tilted with respect to its orbital plane. This is whatcauses the seasons. When the earth's axis points towards the sun, it is summer for that hemisphere. When the earth's axis points away, winter can be expected.
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