Abstract: Since 1995 when the first exoplanet was discovered using the radial velocity method, the number has increased exponentially to a total 1969 confirmed planets by October, 2015. The Kepler space telescope is responsible for most of the confirmed discoveries with some 3666 planet candidates yet to be vetted and confirmed.
The first planets discovered were Jupiter-sized planets orbiting very close to their sun. It was easy to come to the conclusion that most exoplanets must be in that size range but we have enough data now to show planet sizes cluster around 2 times the size of Earth. They mostly have orbits much less than 1 AU from their host star and most have orbital periods measured in days, not years.
According to a recent analysis of Kepler data, 22% ± 8% of Sun-like stars have Earth-like planets in the habitable zone. This assumes planets between 1 to 2 Earth radii and a habitable zone where the stellar flux on the planet surface goes from 0.24 to 4 times the solar flux on Earth. This means that somewhere from 3% to 6% of the stars in our galaxy could harbor life. The exact boundaries of the habitable zone are a bit fuzzy and are based on climate models. According to the Planetary Habitability Laboratory, there are 61 planets determined to be in the Habitable Zone so far.
There are 4 main methods used to find planets, including the transit detection, the radial velocity method, gravitational lensing, and direct detection. The Kepler program (transit detection) is responsible for most of the confirmed planets and they only looked at 0.28% of the sky.
It is also possible for amateur astronomers to detect exoplanet transits using modest equipment. In fact, amateur observations can be used to estimate several orbital parameters, including the orbital period, orbital radius, planet size, and orbital inclination.
Ken Hose has been an active RCA member since 1999. Until about 2009 he did visual observing with 8” and 14” telescopes. He has completed several Astronomical League observing programs including the Herschel 400 list. In 2009 he started astro-imaging from his home observatory. He uses a portable setup for “pretty picture” imaging at star parties. As an engineer, Ken appreciates the science aspects of the hobby and his observatory is used mostly for exoplanet transit detection and photometry of variable stars. Ken is the Membership VP for the club and RCA’s the Astronomical League coordinator.