Variable Star Measurements
Stars appear to shine with a constant light; however, thousands of stars vary in brightness. Broadly speaking, variable stars are of two types:
- stars that are intrinsically variable, that is, their luminosity actually changes, for example because the star periodically swells and shrinks
- eclipsing and rotating variables, where the apparent changes in brightness are a perspective effect
The behavior of stars that vary in magnitude (brightness) - known as variable stars - can be studied by measuring their changes in brightness over time and plotting the changes on a graph called a light curve. Amateur astronomers around the world observe variable stars and assist professional astronomers by sending their data to variable star organizations, such as the American Association of Variable Star Observers (AAVSO) in Cambridge, Massachusetts. One ASLC member has contributed well over 10,000 observations to the AAVSO!
Research on variable stars is important because it provides information about stellar properties such as mass, radius, luminosity, temperature, internal and external structure, composition, and evolution. This information can then be used to understand other stars. Professional astronomers work with only a handful of large telescopes, and so cannot gather data on the brightness changes of thousands of variable stars. Instead, it is amateur astronomers, utilizing small telescopes, who are making valuable contributions to stellar astronomy by observing variable stars and submitting their observations to the AAVSO International Database. The AAVSO coordinates, evaluates, compiles, processes, publishes, and disseminates variable star observations to the astronomical community throughout the world.
The Association of Lunar and Planetary Observers
Many of us can remember the thrill of our first view of the craters on the Moon, the four large satellites of Jupiter, the amazing rings of Saturn, and other celestial wonders. There can also be a thrill, or perhaps a feeling of satisfaction and achievment, in recording systematic observations having scientific value, surely including digital images, of our Solar Sustem neighbors. It is then of value to report such data to proper places for analysis and publication. Since 1947 the Association of Lunar and Planetary Observers has been encouraging and supervising such efforts. The email address of the hard-working Secretary is will008@attglobal.net.
The work of the ALPO is divided into sections: one for each bright planet, one for the Sun, several for lunar projects, one for Minor Planets (see Fred Pilcher's article here), one for planets beyond Saturn, and several others. Many of the sections furnish instructional materials and/or outline forms to make recording data easier.
The online location with many, many words is http://www.alpo-astronomy.org. ALPO members receive a quarterly Journal in either a digital or old-style print format. There is also an annual conference: last year at Calgary and this year at Des Moines. All interested persons are welcome as members.
- contributed by Walter Haas (ALPO's founder)
