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Centennial Star of the Cleveland Astronomical Society

Consider the star Ruchbah to be the "Centennial Star" of the Cleveland Astronomical Society (CAS), which celebrates its 100th birthday in 2022. Ruchbah, in the constellation of Cassiopeia, is a variable star approximately 100 light years away. When the Ohio community of astronomers gathered in 1916, starlight left Ruchbah traveling at 186,000 miles per second, and that starlight is just now reaching our eyes.

Happy 100th Anniversary, CAS! Here’s a token gift that celebrates the Society's anniversary star Ruchbah. I appreciate the CAS programs I’ve been able to attend and CAS members I’ve met in previous years. Wishing you well in your next 100 orbits around the sun.

Activity: Star Finder With Ruchbah

For a family activity, make a simple planisphere of three north circumpolar constellations to find the star Ruchbah. Print out both pieces of paper, and cut out the star circle with months around the perimeter. Fasten the star circle over the whole piece of paper with the horizon and hours labeled.

Notice how Cassiopeia with its Centennial Star Ruchbah can be used to find Polaris when the Big Dipper is low near the horizon. Cassiopeia is like a mirror image of the Big Dipper that serves a comparable north-finding function.

Astronomer Dr. James Kaler describes the star Ruchbah (used with permission):

RUCHBAH (Delta Cassiopeiae). Among the most loved, most charming, and most visible of constellations is Cassiopeia, the celestial Queen. The five stars that make her familiar "W" (add one more to make her Chair) are circumpolar, always visible, from latitudes above 35 degrees north. Three of the W's stars carry classical proper names, Shedar (Alpha), Caph (Beta), and Ruchbah, the Delta star. (Gamma has no classical proper name, though "Navi" has been used in modern times.) And just over the line into third magnitude (2.68), Ruchbah is appropriately the fourth brightest star in the constellation, following right behind Gamma. The old Arabian astronomers commonly applied proper names to the stars according their positions within the classical figures, and "Ruchbah" is a fine example, the name a reduction of a longer phrase that refers to Cassiopeia's Knee. Just shy of Ruchbah, Delta Cas, lies both at the center of the picture and in the heart of Cassiopeia's delightful Milky Way. One hundred light years away, its light takes a century to come to Earth. A star with a temperature of 8400 Kelvin, a fair bit warmer than the Sun, it falls into mid-class A (A5). Stars produce radiation whose quality depends on temperature. Relative to what we see with our eyes, cool stars radiate vast amounts of invisible infrared, very hot stars a great deal of invisible ultraviolet, both of which must be factored in to estimate the star's true luminosity. White Ruchbah falls into a narrow temperature range where we simply do not have to worry much about either the ultraviolet or infrared, and little or no correction is needed, Ruchbah's luminosity 63 times solar. Marginally detected as a disk, the star is not quite four times the radius of the Sun and just barely classed as a giant, which means it has begun its death process, core hydrogen fusion shutting down. With a mass 2.5 times solar, this 600 million-year-old star will become a much larger orange giant in a mere 10 million years. Careful observations show that Ruchbah is slightly variable. Every 1.26 years it undergoes a partial eclipse when a small orbiting companion star, about which nothing is known, passes in front of it. Otherwise the star is quite normal, which makes it a good one against which to measure the properties of others. Ruchbah's greatest significance is that it provides a good background against which to study the local complex system of interstellar gas through which the Sun is now passing.


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