The great globular cluster in Hercules

Illustration showing the six tails of a comet in the pre-dawn sky

There are comets, and then there are great comets. It was certainly the fire that broke out in the sky in 1743 and 1744 One of the newest.

As the comet hurtled past Earth toward the sun, the comet was said to be bright enough to be seen in broad daylight and outsmart Venus in the evening sky. It also developed a long and clearly visible double tail, which is already unusual. Then, when it reached perihelion and swung around the sun, the comet’s tail split into six clearly defined rays. In the morning, when the comet’s head was still hidden below the horizon, these six tails were bright and visible, reaching the sky as a kind of “fan” that seemed to come from the sun.

Just why the comet gave this appearance remains a mystery. There might actually be one or two much wider tails, but there were areas that were darkened by the thick dust. In any case, it was recorded by astronomers all over the world, including in China, where court astronomers claimed that the comet made a crackling noise. This was a very strange sin.

The not-great young Catherine noticed the culprit while traveling to Russia for marriage. Apparently she considered it all about declaring her future greatness because… of course she did.

Back in France, the young Messier also appears to have seen the comet, and seems to have gone a long way toward propelding him into a future in astronomy, rather than the decidedly wonderful career path of taking people into the courtroom. Messier managed to get a position of assistant to Joseph Nicolas Deliel who was the official astronomer of the French Navy (drawing a course, etc.) and perhaps most importantly, the dirty rich.

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Delile had a newly built observatory, and the young Messier quickly settled in. Over the next decade, he made a number of important discoveries, receiving a senior position in government as well as a series of honors and membership in the scientific community. As expected, comets have remained a subject of special interest to Messier, and he seemed to be good at getting rid of a distant comet before other astronomers could get their names on the approaching snowball. Even King Louis XV gave Messier a very impressive nickname which is ” Mongoose Comets” which, if you’re going to have one title engraved on your tombstone, should be the title.

But Messier’s later work with deep sky objects is best remembered today. Beginning in 1771, Messier began compiling a catalog of some of those misty spots in the night sky—things we know today as nebulae, galaxies, and star clusters. The first list included 45 such items. The final list, which included some things pulled from Messier’s footnotes and marginals, totaled 110. These became known as miserable beings.

Since then, finding these Messier objects has been a right of passage for astronomers. Something like climbing the Seven Summits in mountaineering. Except for a much lower chance of dying in an avalanche.

And… well, it turns out that Messier 13 is something that’s known variously as the Hercules Star Cluster, the Great Globular Cluster of Hercules, or the Hercules Globular Cluster. Messier wasn’t actually the first to discover M13. This credit goes to another comet man, Edmund Halley, who encountered him in 1714. But Messier put it in the catalog,

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M13 is a group of hundreds of thousands of stars, but it is not a galaxy. In fact, it’s one of many such blobs orbiting our good old galaxy, the Milky Way. It is located about 22,500 light-years from Earth. If you want to find it, look for where the name suggests – in the constellation Hercules. But bring a telescope. Despite the number of stars in this group, their visible size is more than 11, and they are too faint to be seen with the naked eye.

M13 is about 100 times more densely packed with stars than neighboring regions around Earth. There are only about 135 stars within 50 light-years of Earth. It’s interesting to think of what a sky as big as a nearby neighbor might look like on a clear night. The stars in M13 are closer enough together than ever before and then a pair end up merging into a short-lived blue-white giant.

Something about the M13 has made the spherical Hercules cluster a recurring theme in science fiction novels. This may be why when SETI personnel were at the runaway but not forgotten Arecibo Telescope looking for a target for a test message in 1974, they chose M13. Somewhere in between here and there a letter with basic information about mathematics, and then expands on that to describe the structure of atoms, then elements, then DNA, and then some basic facts about human life.

If someone is out there, and they have a very good receiver, they will have mail in about 22,450 years.

As with most of the images I show in this feature, the top image was taken on the small but clever Vespera telescope. And as usual with this feature, I expect some of you will do much better. But maybe not better than this…

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Hubble Telescope M13 image.

Web countdown: “NASA, in partnership with the European Space Agency and the Canadian Space Agency, will release the first full-color images and spectroscopy data for the James Webb Space Telescope during a televised broadcast beginning at 10:30 a.m. ET on Tuesday, July 12.” And we’ll cover it live.

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