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The AAVSO turns 100

July 2011: An astronomical family stays strong after a century's worth of observations.
David Hl Levy
Last month’s Astronomy carried an article I wrote about the American Association of Variable Star Observers (AAVSO), which this fall celebrates the centenary of an idea. The plan, as it stood in 1911, was not to increase the number of scientists, but to organize an observing campaign that followed the changing brightness of variable stars. Ever since, amateur astronomers have contributed millions of such observations.

As the clock turns on the AAVSO’s 100th birthday this October, its role has expanded. The group has shown astronomers not just what these stars are doing, but also how to monitor them best, both from the ground and with the Hubble Space Telescope. Yet at its founding, there was no organized way of submitting observations. In fact, the AAVSO’s earliest years were devoid of meetings, concentrating instead on adding to the group’s series of observations of variable stars, now known as the AAVSO International Database.
 
In Montreal, Canada, I heard Isabel Williamson first mention the AAVSO in 1961 — I thought she was telling a joke. As we all chuckled, she went on to announce that the AAVSO would be holding their annual meeting in Kalamazoo, Michigan, and that several officers of the Royal Astronomical Society of Canada’s Montreal Centre would be representing our active astronomy club there. I soon learned that the AAVSO was a group well worth supporting.
AAVSO-7th-annual-meeting
The American Association of Variable Star Observers (seen here at its seventh annual meeting in 1918) will celebrate its centennial in October, but its work is still vital and it still feels more like a family than anything else. American Association of Variable Star Observers (AAVSO)
During the summer of 1966, I began observing three stars: the semiregular red supergiants g Herculis, X Herculis (see chart), and RR Coronae Borealis. These huge stars swell and contract, thus altering their brightness, on a not-quite-regular basis. I quickly followed up with other stars, like R Leonis, a long-period variable whose brightness slips from fainter than 10th magnitude up to 5.8 and back again, all in a period of just under a year. Soon, I began using the AAVSO’s classic blueprint charts, with white stars painted on a blue background. Nowadays, almost no one uses these charts, but their beautiful design and artwork (by D. F. Brocchi, R. A. Seeley, and R. Newton Mayall) are still a wonder to behold.

At its simplest level, a variable star is one whose light output changes. Mira-type stars, like R Leonis and its namesake Mira (Omicron [ο] Ceti) itself, are Sun-sized objects that have used up their cores’ hydrogen; this means our Sun will one day become a Mira-type star. Other stars vary cyclically; eclipsing binary variables, for example, decrease in light output when a fainter companion passes in front of the brighter of the pair. Other stars vary cataclysmically: When a binary system consists of two nearby stars, the less massive one can leak hydrogen to form an accretion disk around the more massive one, and after enough time, this extra hydrogen explodes, resulting in a dramatic rise in the system’s brightness.
blueprint-chart
The AAVSO's classic blueprint charts, this one depicting the two bright "semiregular variables" X and g Herculis, remain a testament to the group's devotion to the night sky. AAVSO/R. Newton Mayall
These are but some of the fantastic tales of variable stars. The science behind them might be interesting, but getting to meet the people who enjoy monitoring these stars can be even more fruitful. For my first meeting, in the fall of 1978, I drove down to Cambridge, Massachusetts, and checked in at the AAVSO’s then-headquarters at 187 Concord Avenue. Immediately after walking in the front door, I found myself embraced by director Janet Mattei. From then on, I knew the AAVSO was a family.
 
Over the next few days, I learned much about the history of this family. I even contributed my own story; during a 10-minute talk about teaching children astronomy, I discussed how stars are like people, with individual behaviors and even moods.

Variable star observing remains as vibrant today as it did a century ago. Its magic lies not just in the stars themselves; it also lies within the academic volumes written on the subject, and in stellar poetry written long ago and in modern times, by amateur astronomers motivated to add rhyme to their lists. And it rests within the senses of all those observers who, on the AAVSO’s centennial, relish the hours they spend gazing at these wonderful stars as they parade about the sky.
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