The Kepler Mission - kepler.nasa.gov
The Kepler Mission developed over several decades as a way of answering the question: How frequent are other Earths in our galaxy?
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| The figure shows what we believe to be the local structure of our Galaxy, the Milky Way. The stars sampled are similar to the immediate solar neighborhood. Young stellar clusters, ionized hydrogen (HII) regions and the neutral hydrogen (HI) distribution define the arms of the Galaxy. |
(see the post link for the Kepler website)