- by Johannes Hlynialuk
In Act III of Julius Caesar, William Shakespeare has the title character speak these words (it was boast that no doubt enflamed those around him):
But I am constant as the Northern Star,
Of whose true fixed and resting quality
There is no fellow in the firmament.
None can argue that Shakespeare was a remarkable story-teller and an equally remarkable judge of human character. But I have always appreciated his astronomical knowledge as well. There are references to stars, comets, the Moon and Sun in his many plays, but this particular line about Polaris has always stuck with me. The rest of Caesar's speech continues the astronomical theme and he says:
The skies are painted with unnumbered sparks;
They are all fire, and every one doth shine;
But there's but one in all doth hold his place.
No spoiler alert is required here as to Caesar's fate. I think we all know the story (and that, gentle readers, is a tribute to your English teachers.) It is only a few moments after this speech that the conspirators put an end to Caesar's life.
Alas, Shakespeare did not have the acquaintance of an astronomer named David Fabricius, who lived at the same time (1564 to 1617) but in the Netherlands, quite a distance from Stratford-on-Avon. Shakespeare might have then learned of a star that was not so constant after all. Fabricius was studying Omicron-Ceti, a star in the constellation Cetus the Whale which had been behaving strangely for centuries. Sometimes it was visible and others times not, -a behaviour very different from the rest of the sky which, except for comets, consisted of unchanging stars arranged in familiar constellations.
By 1638, 22 years after Shakespeare died, another astronomer, Johannes Holwards, also in the Netherlands, had amassed enough observations of Omicron-Ceti to reveal that it was a variable star, changing brightness quite dramatically over time. Mercifully, in 1642, Omicron-Ceti was re-christened, "Mira", (the Wonderful) by another Johannes, Hevelius, and by now Mira's status as the first variable star discovered was assured. Mira's variations were quite "miraculous" ranging from being totally invisible to the naked eye, to a star as bright as any in the Big Dipper and then back again to obscurity over a period of 11 months (the modern value is 331.96 days). Of the several thousand Mira variables now known, none varies so extremely across the visual range.
Astronomers now know that Mira (like Caesar when he spoke about Polaris) is a star on the verge of death. It is a red giant that varies from 300 times the Sun's size to 400 times the Sun and its size pulsations are in step with its brightness changes. If Mira were our star instead of the Sun, Earth would be orbiting as a burnt-out cinder beneath its surface and so would Venus, Mercury and Mars, as well. Furthermore, our Sun when
it nears the end of its life will eventually become like Mira, pulsating as a variable star and shedding shells of material into space. This is the ultimate fate of all Sun-like stars. Shakespeare's constant stars are not so constant after all.
This year, totally by coincidence, the peak of brightness for Mira falls during the holiday season, -in a sense Mira is taking up the role of a modern Christmas Star. It does this every time that its 11 month peak in brightness comes in late December, -the last time this happened was in 2008.
As of this writing, Mira is still magnitude 8.3, (visible in binoculars) and it is brightening slowly. When it reaches maximum (Dec 29) it will likely be about magnitude 3. Some years it even reaches magnitude 2, the same brightness as Caesar's 'Northern Star' and 6 of the 7 stars in the Big Dipper. Regardless of how bright it gets, it will be an "extra" star in Cetus for the winter months.
To locate Mira, stretch an imaginary line between the Pleiades, (the Seven Sisters) and a lone rather bright star, Fomalhaut just above the southern horizon. Halfway along the line is where Mira should appear in mid-December. The star chart shows the location of the "Miracle Star".
May all your stars shine bright this holiday season!
PS: Sharp-eyed readers may have noticed that the name Johannes comes up several times in this column, including in the byline. This "preponderance of Johannes" is totally coincidental and what's more, even Shakespeare's father's first name was Johannes. It is after all, a good name, and my parents thought so too.
