Huachuca Astronomy Club—Speakers

Dr. Jay Holberg, Senior Research Scientist, Lunar and Planetary Laboratory, University of Arizona

"Sirius: The Biography of a Star"


Synopsis: The story of Sirius throughout human history, from Ptolemy's Almagest to the January 31, 1862 discovery by Alvan Clark's son, Alvan Graham Clark, of the white dwarf companion Sirius B—"Father Sirius has a companion"—and onto today's accuracy of Sirius B's data from the Hubble Space Telescope.

Sirius—the brightest star in the night sky—has been a source of continual fascination to humans. Four thousand years ago, the ancient Egyptians regulated their calendars according to its first appearance each year in the morning sky. More recently, in the nineteenth century, astronomers were perplexed by the star's odd movement: they eventually deduced that this must be caused by a dark, dense companion, but the exact nature of it defied understanding for many decades, being much more bizarre than could have been guessed. The story of Sirius is therefore very wide ranging, from pre-history down through the ages, to many of the most intriguing mysteries and problems of modern stellar astronomy.

Jay Holberg is superbly qualified to tell this story, having studied the Sirius system for many years, and being a co-author of the definitive research paper on the white dwarf companion, Sirius B. Holberg and his colleagues obtained time with the Hubble Space Telescope to study the white dwarf, thus enabling them to determine its characteristics with unprecedented precision.

An artist's impression of Sirius A and Sirius B. Sirius A is the larger of the two stars. (Credit: NASA)



Biography: Jay Holberg is a senior research scientist at University of Arizona's Lunar and Planetary Laboratory in Tucson, Arizona, where he has been since 1983. He obtained his PhD in Physics from UC Berkeley in 1974. Dr. Holberg worked on the Voyager mission to the outer planets, which is where he developed his interest in Sirius and currently studies white dwarf stars, one of which orbits around Sirius. He has written a book on the topic of Sirius and it should be available very soon.

Dr. Holberg currently conducts research in several areas of ultraviolet and optical astronomy. Most of this work involves observations of white dwarf stars made using University of Arizona telescopes, together with various spacecraft, including the Voyager 1 and 2 ultraviolet spectrometers, the International Ultraviolet Explorer, the International Extreme Ultraviolet Explorer, and the Far Ultraviolet Spectroscopic Explorer. These studies focus on understanding the structure, composition, and evolution of white dwarf atmospheres, as well as binary systems containing white dwarfs.

Book: Sirius: Brightest Diamond in the Night Sky, by Jay Holberg

Of all the fixed stars in the night sky, Sirius is by far the brightest—almost twice as bright as its nearest rival, the star Canopus, which lies too far south to be viewed from most of the Northern Hemisphere. Only the Sun, Moon, and the planets Venus, Jupiter and, at times, Mars, appear brighter. Sirius, with its flashing brilliance, is a striking feature of the northern winter sky and has understandably drawn the attention of observers of the night sky for thousands of years.

Sirius has many names. Astronomers recognize over fifty designations for the star, but the most commonly used is Alpha Canis Majoris, the brightest star in the constellation Canis Major. This is Latin for the "Great Dog," which has led to its popular nickname the "Dog Star." Over the centuries many beliefs have come to be associated with Sirius. Some of these beliefs still echo in such phrases as the "dog days of summer," which the ancient Romans understood well. Other old beliefs long ago fell from public consciousness only to be revived and to grow into modern popular and scientific controversies. Although these beliefs may seem quite recent, many have their origins in the ancient lore surrounding Sirius; humans seem naturally drawn to its brilliance, and a surprising number of modern cults have nucleated around beliefs in which Sirius plays a prominent role.

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