Sky Watch: Mira, the Wonderful

There's an extra star in the sky right now.

Hard to believe that anyone can tell but, actually, this one's not too hard to spot. Its name is Mira, and it's what astronomers know as a long-period variable star.

OK, so it's not really a "new" star, but it is one that we haven't seen for nearly a year. You see, Mira pulsates in brightness, becoming easily visible in the sky, and then fading well below naked-eye visibility.

The star was found little more than 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, when he looked for the star in the sky, it was nowhere to be found. Then, on Feb. 16, 1609, there it was again.

Not until 1660 did astronomers realize what was happening. The star had been there all the while, but varied in brightness over a period of eleven months. Mira, also known as Omicron Ceti, became the first star ever discovered to change its brightness.

Its name, "Mira," which contains the Latin root for such words as "miracle," means wonderful. And its discovery was rather wonderful as well, since it supported the intellectual revolution begun by 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 begins its cycle about as bright as the North Star, fades by more than 600 times, and then it brightens again -- all during a period of 332 days. Currently it shines near its brightest and outshines all but one star in its celestial region.

Perhaps even more interesting is that not only does Mira's brightness vary over time, but also 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 twenty percent. At its largest and brightest, the star is more than three hundred 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.

And, if that weren't enough, astronomers have discovered that Mira has a strange comet-like tail about thirteen light-years long, possibly formed out of material ejected by the star during the past three hundred centuries.

Before dawn between July 21 and 31, you can see this wonderful star at its brightest. In the 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 -- placed in the heavens to commemorate his heroic deed.

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