The earth revolves round the sun because the sun attracts the earth. The sun also attracts the moon and this force is about twice as large as the attraction of the earth on the moon. Why does the moon not revolve round the sun ?
By Siv Schwink
September 3, 2013
Tonight, as the sun sinks below the horizon, the world’s most powerful digital camera will turn its gleaming eye skyward once again in its 5-year mission to map the southern sky in more detail than ever before. On August 31, the Dark Energy Survey (DES), with an international collaboration of more than 200 scientists, officially began the largest galaxy survey ever attempted.
Counting galaxy clusters. While gravity pulls mass together to form galaxies, dark energy pulls it apart. The Dark Energy Camera will see light from 100,000 galaxy clusters billions of light years away. Counting the number of galaxy clusters at different points in time sheds light on this cosmic competition between gravity and dark energy.
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