Observing Project 12E Mira and the Pulsating Giants

No object in the heavens outside of the solar system exhibits such a radical brightness change as Mira (Omicron Ceti) does. The star normally shines at tenth magnitude, but each 332 days the star builds to a peak at magnitude +3.4. Mira should always be carefully monitored when it reaches maximum because the cycle is not always perfectly precise nor it the intensity of the peak brightness level. As recently as 1997, Mira peaked at magnitude +2.5 and remained there for nearly a month. In other years, the star has failed to reach fifth magnitude. In the middle part of this decade Mira reaches peak brightness about the same time or within a few weeks of reaching solar conjunction so we will not get to monitor Mira's peak again until later in the decade.

Mira is by far the brightest of the long-period red giant variables and by far exhibits the greatest range of magnitude change. Most naked-eye variables exhibit very little range of magnitude change, which in turn may explain how Mira became known as the "Wonder Star." It also has a reasonably short and stable period, which not all of these stars do. Betelgeuse is a massive example of this same type of star that can shine as bright as neighboring Rigel (Beta Orionis) and fade as dim as Bellatrix (Gamma Orionis). That would range between magnitude +0.3 and +0.9. Betelgeuse's cycle is poorly defined but photometric observations over a period of more than a decade suggest a cycle of about six years. Because Betelgeuse is a star that may or may not be fusing silicon and sulfur into iron in its core, its end is very near. When that end comes, it will be one of the most spectacular events viewed in our sky in many hundreds of years. Because layers of gas being blown off from its interior surround Betelgeuse, it defies attempts to measure its exact size and internal makeup. It may not erupt as a supernova for another fifty million years. But it might do so tomorrow, therefore any change in the behavior of this star would be of great interest to the astronomical community. Can you measure the changing brightness of Betelgeuse? Since good comparison stars are in close proximity in Orion, all you need to do is make regular wide field photographs of Orion and see how that red star at the top left compares to the blue one at the top right and bottom right.

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