Cosmic Rulers
Planetary Planarity
Tools of the Trade


Galileo to Gamma Cephei

To the eye alone, the star system known as Gamma Cephei looks unremarkable: a faint, colorless pinprick in the dark dome of the night sky.

Diagram of a star and planet orbit a common center of mass.

To understand how radial velocities can find companions around other stars, and how astrometry can determine whether these companions are planets, let’s consider the teeter-totter or seesaw. [Tim Jones]

But with the aid of a technology that was pioneered four centuries ago — the telescope — astronomers have discovered that Gamma Cephei is quite remarkable. It consists of two stars that are locked in a mutual orbit around each other, and at least one planet orbiting one of the stars. What’s especially interesting is that the planet may move along in the same plane as the stars, as though they were all rolling along on a flat tabletop. If that alignment is confirmed, it will reveal important information about the process that gives birth to planetary systems, including our own.

Gamma Cephei is among a dozen or so stars that are receiving close attention from University of Texas astronomer Fritz Benedict and his colleagues in a project that involves Hubble Space Telescope and several telescopes on the ground.

One part of the project is studying Gamma Cephei and several other systems with known planets. The astronomers are not only looking for more planets in these systems, they are trying to determine whether the system’s stars and planets all revolve in the same plane, as is the case with the planets of our own solar system.

Hubble cluster

Another part of the project is watching several variable stars in the Milky Way galaxy. These stars pulse in and out like beating hearts, getting fainter and brighter as they do so. The pulse rate depends on the mass of the star, which in turn determines the star’s true brightness. By measuring the distances to these stars, astronomers “calibrate” the relationship between the pulse rate and brightness. With that information in hand, the pulse rate can reveal each star’s distance, making the stars important “rulers” in measuring the distance between galaxies, the rate at which the universe is expanding, and the effects of dark energy.

All of these studies are made possible by a technology that was pioneered by Galileo Galilei beginning in 1609: the telescope.

Although he didn’t invent the telescope, Galileo was the first to turn it toward the night sky. He discovered that the surface of the Moon is bumpy and uneven, that Jupiter has moons, and that Venus shows phases. These and other discoveries confirmed the notion that Earth is not the center of the universe, and that the universe is ever-changing.

The telescopes today are bigger and more sophisticated than Galileo’s, and astronomers have devised amazing tools and techniques for analyzing the light from objects as near as our own solar system and as far as the edge of the observable universe. Yet the concept remains the same. The telescope enhances our ability to see deep into the universe, helping us understand its workings and our place in it.