Answer to Question 1We have witnessed the effects of extrasolar planets on their parent stars, both in the periodic wobble of the parent star caused by the gravitational tug of the planet, and in the periodic dimming of light coming from the star as the planet passes in front of it. As of this writing, over 400 planets in 324 star systems have been discovered. For an up-to-date count, go to NASA's Planet Quest New Worlds Atlas Search, which can be found here:
http://planetquest1.jpl.nasa.gov/atlas/atlas_index.cfm.
Or, try the Extrasolar Planets Encyclopedia at:
http://exoplanet.eu/Answer to Question 2We can estimate Ng, the number of stars in a galaxy; fp, the fraction of stars that have planets; and ne, the number of Earthlike planets per planetary system. Currently, fl, the fraction of habitable planets on which life evolves; fi, the probability that life will evolve to a steady state; fc, the probability that intelligent life will develop the capacity to communicate over long distances; and fL, the fraction of a planet's lifetime during which it supports a technological civilization, are not well constrained.
Stars vary widely in size.
The Pleiades, an open cluster of stars in the constellation of Taurus. These stars share a common mo
Internal structures of main sequence stars, convection zones with arrowed cycles and radiative zones
Rising and Setting of Stars at the Equator
The same star field photographed with (a) a ground-based telescope, which is subject to poor seeing
Evaluate the following limits, if they exist - Pt 2