Good questions. I'd like to know approx how many stars within a radius of various distances from us. For example, you mentioned 12.5, 50, and 250 light years. How many stars within a radius of each of those?
Also what is the size distribution of our neighbor stars? What percentage are the size of our sun? Smaller? Larger?
Thanks for the link, which answers my last questions. There I find that 88% of all stars are smaller than our Sun. 3.5% of all stars are the size of our Sun, and only 8.5% of stars are larger than our Sun.
So Kepler should have complete data about Earth-sized planets, from 91.5% of stars in its' field of vision, that is from stars smaller or equal to our Sun, after about 5 years of operation. That is because even after 3 transits, it takes over a year for the investigators to catch up to all the data coming in. The last update in 2011 was for only 6 months of data gathering, and that is over 2 years after it was launched into space in April 2009. They are that far behind. Also Wiki reports noise levels higher than anticipated, which means a mission twice as long as expected:
"Since the signal from an Earth size planet is so close to the noise level (only 80 ppm), the increased noise means each individual transit is only a 2.7 σ event, instead of the intended 4 σ. This, in turn, means more transits must be observed to be sure of a detection. Recent estimates indicate a 7-8 year mission, as opposed to the 3.5 year planned, would be needed to find all transiting Earth-sized planets. The spacecraft has enough fuel for such a mission, but there is no funding for it so far."
http://en.wikipedia....ler_(spacecraft)
This post has been edited by Airbrush: 22 December 2011 - 12:32 AM
When in doubt, Wiki it out.
How do you dodge a bullet on your way to another star while traveling 12%C?