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The Large Globular Cluster in Hercules

Great Six-Tailed Comet of 1744
Sketch showing the six tails of the comet in the morning sky

There are comets, and then there are big comets. The fire that crossed the sky in 1743 and 1744 was definitely one of the later ones.

As it sped past Earth towards the Sun, the comet was reportedly bright enough to be seen in daylight and outshined Venus in the evening sky. It also developed a long and clearly visible double tail, which was already extremely unusual. Then, as it reached perihelion and orbited the Sun, the comet’s tail split into six clearly defined rays. In the morning, with the comet’s head still hidden below the horizon, these six tails were bright and visible, sticking out in a kind of “fan” in the sky that appeared to be coming from the sun.

Why the comet had this appearance is still a mystery. It may be that there were actually only one or two much broader tails, but they had areas obscured by heavy dust. In any case, it was recorded by astronomers around the world, including in China, where forensic astronomers claimed the comet actually made a crackling sound. That was a very strange comet.

A young Catherine the Young watched the comet as she traveled to Russia to get married. She seemed to take it as if it was all about heralding her future greatness, because… of course she did.

Back in France, the young Messier seems to have seen the comet as well, and it seems to have taken him a big step towards a future in astronomy rather than the surely fascinating career of leading people into a courtroom. Messier was able to secure a job as an assistant to Joseph-Nicolas Delisle, who was the French Navy’s official astronomer (setting courses, etc.) and, perhaps more importantly, was filthy rich.

Delisle had a newly built observatory and young Messier settled in quickly. Over the next decade he made a number of significant discoveries and earned a high-ranking position in government, as well as a number of honors and memberships in scientific societies. As might be expected, comets remained a particular interest of Messier, and he seemed good at spotting a distant comet before other astronomers managed to get their name on the approaching snowball. King Louis XV even gave Messier the adorable nickname “the Ferrets of the Comets’, which if you have a title carved on your tombstone, this should be it.

But it was Messier’s later work with deep sky objects that he is best remembered for today. Beginning in 1771, Messier began compiling a catalog of some of these fuzzy patches in the night sky—things we recognize today as nebulae, galaxies, and star clusters. The first list contained 45 such objects. The final list, which included some objects from Messier’s footnotes and marginalia, totaled 110. These became known as Messier objects.

Since then, finding these Messier objects has been something of a right-of-way for astronomers. Something like climbing the Seven Summits in mountaineering. Except with significantly less chance of dying in an avalanche.

And…okay, Messier 13 turns out to be what is variously known as the Hercules Star Cluster, Greater Globular Cluster in Hercules, or Hercules Globular Cluster. Messier wasn’t the first to spot M13. Credit goes to the other type of comet, Edmund Halley, who encountered it in 1714. But Messier included it in the catalogue,

M13 is a group of several hundred thousand stars, but not a galaxy. In fact, it’s one of many such blobs orbiting our good old Milky Way. It is located about 22,500 light years from Earth. If you want to find him, look where the name suggests – in the constellation of Hercules. But bring a telescope. Despite the number of stars in this cluster, it has a visual magnitude of over 11, too faint to see with the naked eye.

M13 is about 100 times denser with stars than the neighborhood around Earth. There are only about 135 stars within 50 light years of Earth. It is interesting to imagine what a sky with neighbors a few orders of magnitude closer might look like on a clear night. The stars in M13 are close enough together for the occasional pair to merge into an ephemeral blue-white giant.

Something about M13 has made the globular cluster Hercules a frequent subject of science fiction novels. That may be why the SETI people at the missing but not forgotten Arecibo telescope in 1974 looked for a target for a test message and settled on M13. Somewhere in between here and there is a message that contains basic information about mathematics, which then expands to describe the structure of atoms, then elements, then DNA, then some basic facts about human life.

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

As with most of the images I use in this feature, the top image was taken with my tiny but clever Vespera telescope. And as usual with this feature, I assume some of you have done a lot better. But probably no better than that…

Hubble Telescope image of M13.

Countdown for Webb: “NASA, in partnership with ESA and CSA, will release the first full-color images and spectroscopic data from the James Webb Space Telescope during a televised broadcast beginning Tuesday, July 12 at 10:30 a.m. ET.” And we will report about it live.