From the September 2002 issue

You too can find a planet

This activity will walk you through the steps of discovering a planet with the "radial velocity" method.
By | Published: September 27, 2002 | Last updated on May 18, 2023
3-meter Shane Telescope
The 3-meter (120-inch) Shane Telescope made its first observations in 1959. The telescope’s name honors astronomer C. Donald Shane, who led the effort to acquire necessary funding from the California Legislature to build it, and who then oversaw the telescope’s construction.
Laurie Hatch
Over the past several years, astronomer Debra Fischer and her colleagues at the University of California, Berkeley, have discovered dozens of extrasolar planets. Because exoplanets can’t yet be seen directly, the group uses an indirect technique called the radial velocity method to look for “wobbles” in a star’s spectrum. If the star appears to be moving toward and away from us on a regular basis, it suggests that an unseen planet with that period is orbiting the star, using its gravity to tug on the star as it goes around.

This activity leads you through the process Fischer’s team uses to find a planet this way. First, stars within a field must be evaluated for their ability to support a planet. Some stars can be ruled out immediately by their known physical characteristics. Close binary stars, for example, aren’t good candidates for hosting a stable planetary system. Nor are stars that are too young or too old.

After some potential candidates stars are identified, you can go to your telescope and conduct your initial observations. Using a large research telescope — such as the 3-meter Shane Telescope at Lick Observatory, which Fischer’s group uses — you observe the spectra of your candidate stars to evaluate their potential for further observations. Some stars will not yield good enough spectral lines to determine whether a planet exists around it. But some stars will have good spectra, and you can continue to observe those over months or years to look for velocity changes (“wobbles”) in its spectra over time.

To begin your planet search, click on the link below.
Downloadable File(s)