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Mira, the Wonderful


Last updated 7/18/2023 at 12:04pm

Mira changes in both size and brightness over the course of a 332-day cycle.

Early morning sky watchers may notice a new star in their sky. OK, it's not really a "new" star, but it hasn't been easily visible for nearly a year.

Its name is Mira, and it's what astronomers know as a long-period variable star. It regularly pulsates in brightness, becoming easily visible in the sky, then fading well below naked-eye visibility.

The star was found over four centuries ago by German astronomer David Fabricius, who had been searching for the planet Mercury. Instead, he found this peculiar star that appeared nowhere in his catalogs, atlases or globes.

A few months later he looked again for the star, but couldn't find it. Then, on Feb. 16, 1609, there it was again.

Not until 1660 did astronomers realize what was happening. The star had been there all along but changed its brightness over 11 months. Mira, also known as Omicron Ceti, became the first star ever discovered to change its brightness.

They named it "Mira," which contains the Latin root for such words as "miracle," and means "wonderful." Its discovery was rather wonderful, too, since it supported the contention of Nicolaus Copernicus a few decades earlier that the heavens were not unchangeable. No wonder it soon became known as Mira, the Wonderful.

Today we know Mira as the most famous of all long-period variable stars. It can begin its cycle about as bright as the North Star, fade by more than 600 times and then brighten again – all over a period of 332 days. It is now near its maximum brightness and outshines all but one or two stars in this celestial region.

Perhaps even more interesting is that not only does Mira's brightness vary over time, but so does its size. Though we cannot see this with the naked eye or even a telescope, astronomers have calculated that its orb swells and contracts by about 20%. At its largest and brightest, the star is more than 300 times larger than the sun. This means that, if it replaced the sun in our Solar system, its glowing atmosphere would swallow the orbits of Mercury, Venus, Earth and Mars and would extend part of the way to Jupiter. (Coincidentally, Jupiter now lies to the upper left of this star.)

If that isn't amazing enough, astronomers have found that Mira has a strange comet-like tail about 13 light-years long. They suspect it may be formed from material ejected by the star during the past 300 centuries.

In a dark sky right now, you should be able to spot this wonderful star near its brightest just before dawn. In the east-southeastern sky lies the constellation Cetus, the sea monster or whale. Cetus is said to be the beast that Poseidon sent to plague Cepheus when Cassiopeia claimed to rival the Nereids in beauty. It was said to be placed in the heavens to commemorate his heroic deed.

With some imagination, one might almost be able to trace among the stars the whale's immense body, with its tail and fluke stretching toward the east. And there, in the middle of Cetus, shines the peculiar star known as Mira, the Wonderful.

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