The two primary techniques are transit photometry and the radial velocity method.
Transit photometry involves observing a distant star through a telescope (usually a very powerful one) and watching to see if its brightness dims.
As is the case for transit photometry, if this wobble occurs regularly, then we might reasonably conclude that the gravitational tug of an orbiting planet is responsible.
However, a major advantage of the radial velocity method over transit photometry is that a planet need not cross its star from the perspective of an astronomer on Earth.
And here's where multiple detection methods are helpful, because if transit photometry can measure a planet's size, and radial velocity measurements give us the planet's mass, then the density of the exoplanet can be calculated.
The most common method is called transit photometry
. Astronomers point a telescope at the star to continuously monitor the intensity of light coming from it.
Almost all of them have been found by one of three indirect methods: radial-velocity (Doppler) detections, transit photometry
, and microlensing.
The lightcurves of measured transit photometry
are presented in Figures 3 to 8.
Examples of research activities include variable star photometry; asteroid light-curve photometry; extrasolar planet transit photometry
; and search programs for near-Earth asteroids, supernovae, gamma ray bursts, and lunar flashes.
One of two new Discovery-class missions selected by NASA managers last year, Kepler is to search for Earth-like extrasolar planets using transit photometry
. Kepler's 0.95-meter-aperture Schmidt telescope will stare for four years at a single 12[degrees]-wide field in Cygnus, monitoring 100,000 stars brighter than 14th magnitude and measuring their brightness every 15 minutes to an accuracy of 0.0001 magnitude.