Charles Messier’s determination, accidental glory


By Tom Burns - Stargazing



This time of year, the constellation Taurus, the Bull, is hard to miss. Around 10 p.m., its v-shaped head sits beautifully just above the eastern horizon. It’s certainly hard to miss the bright star Aldebaran, which forms the red, bloodshot eye of the angry Bull.

Perched on the Bull’s shoulders is a tiny, dipper-shaped collection of six stars called, strangely, the Seven Sisters.

Over the millennia, humans have gazed upward at the Pleiades, as the Seven Sisters are more properly called, and marveled at their beauty.

What they did not know is that the Sisters are really a star cluster, a group of sibling stars formed out of the same giant cloud of hydrogen gas perhaps 100 million years ago.

Over the centuries, thousands of amateur stargazers have trained their small telescopes and binoculars on a tiny fuzzy patch, called M1, just off the star that forms the bottom horn of the Bull.

In 1054, Chinese astrologers in the emperor’s court saw a star where none had been seen before. They observed the sky to counsel their emperor in affairs of state. They did not know what to make of the blazingly brilliant “guest star.”

The new star shone so brightly that it was visible during the day for three weeks. They watched it slowly fade to black over the following three months.

Seven centuries later, in 1731, John Bevis discovered another curiosity, a misty patch of light, called a “nebula,” in the same location as the Chinese had observed the “guest star.”

We now know that M1 is a supernova remnant, the expanding debris of a mighty star that exploded in 1054. Little did they know it, but those astrologers had been the first humans in recorded history to see a star explode.

Today, we revel in M1’s telescopic beauty, but one of its first observers thought of it as a royal pain in the neck.

The “M” in M1 stands for Charles Messier, assistant to the head of the French naval observatory in 1758 when this ridiculous patch of fuzz passed into the field of his small telescope. Messier had a job to do, and M1 wasn’t helping any.

A bit earlier, in 1695, no one was quite sure what to make of another class of fuzzies called comets. Did they pass straight through our solar system, never to be seen again, or did they orbit the sun like planets?

Edmund Halley believed that they were in orbit. If they were, they should return to view periodically.

He predicted that a comet, which would later bear his name, returned to our earthly environs every 75 or 76 years. If so, the comet should return in late 1758 or early 1759.

The race was on to rediscover Halley’s comet. Charles Messier’s boss handed him the task of being the first to find the comet.

As Messier tells it, he finally found what he was looking for in late 1758 after a year of fruitless searching. He begged his boss for permission to proclaim his discovery to the world.

Inexplicably, the head of the naval observatory made him wait a month to make his announcement. By that time, others had seen the comet, and Messier’s claim became the subject of intense ridicule.

Messier spent the rest of his life trying to live down that ignominy. He became obsessed with comets, discovering more than any other astronomer. As he searched, he ran into stray fuzzy patches that weren’t comets.

M1 bears a striking resemblance to a tailless comet, and comets are often first sighted before they get close to the sun and develop a tail. In M1’s case, the only visual difference was that it doesn’t move against the starry background the way a comet does.

The only way Messier had to determine whether a given fuzzy thing was or was not a comet was to observe it over several nights to determine its motion. Such observations took valuable time away from the search for real comets.

So, Messier decided to catalog the non-cometary nuisances, draw them, and mark their locations so that he could avoid them.

The first published version of his catalog in 1774 included 45 objects. Many of them could be confused with comets, but others obviously were not. Most notably, the last on the initial list, was M45, the Seven Sisters.

M45 clearly resolved into six stars with the unaided eye, and that unalterable fact had been known since ancient times. Messier’s small telescope or any set of binoculars resolves it into dozens of stars. Clearly, nobody could confuse M45 for a comet.

The list had taken on a life of its own.

In the end, Messier identified and cataloged 103 non-stellar objects. Based on Messier’s detailed observational notes, subsequent stargazers expanded the list to 110.

As the centuries passed and telescopes got bigger, Messier’s nuisances began to explode into glittering star clusters, spinning whirlpools of light called galaxies, and beautiful clouds of glowing hydrogen gas. They are undoubtedly the most spectacular objects to see in a telescope.

As a result, amateur telescopists treat the list with almost cult-like fervor. Every March many amateurs, attempt to observe all 110 of the objects on Messier’s list in a single evening. They call the event a Messier Marathon.

More importantly, Messier objects began to take on incalculable scientific value.

M1 is decidedly a case in point. As telescopes finally got larger, astronomers began to discern details in the fuzzball. The 19th-century astronomer Lord Rosse described it as having “resolvable filaments” with a gap at its south end, all of which led to its nickname, the “Crab.”

In the first decades of the 20th century, astronomers began to make some sense of the Crab. By comparing photographs taken several years apart, they discovered that the nebula was rapidly expanding.

By studying its outward motion, they concluded that the expansion must have begun about 900 years earlier, and the connection with the Chinese guest star was finally established. It had all the earmarks of a stellar explosion of intense magnitude. The Crab thus had the distinction of being the first “supernova remnant” ever discovered.

Improved photographs of the object showed blue at its center with filaments of red gas at its edges. Why was the gas producing different colors? The answer came in the 1950s from Soviet experiments with a particle accelerator called a synchrotron. The Soviets discovered that electrons rotating in a powerful magnetic field produced a bluish glow of exactly the same kind as seen inside the Crab.

What then was causing the spinning magnetic field that in turn caused the electrons to whirl around? As astronomers pondered that question, they also began to use new-technology telescopes to study stars in parts of the energy spectrum that visual telescopes cannot see.

The Crab was emitting x-ray and radio energy, as they had come to expect from supernova remnants. However, unlike most supernova clouds, the Crab was rich in those energy bands deep inside the heart of the Crab.

In the end, astronomers discovered a tiny and extremely dense star rotating at the center of the Crab. By studying its radio waves, they determined that it was, like a celestial lighthouse beacon spinning out of control, rotating at an unbelievable 30 times every second.

Other, older supernova stars rotated much more slowly. This, then, was what happened when stars explode. Some of their material is ejected explosively into space. The rest collapses into a rapidly spinning ball. As the energy of its spin is converted over time into a massive magnetic field with spinning electrons, its rotation slows down.

The great Chinese mystery was at last solved. It only took 900 years — a long, long time in human history but the smallest trifle in the life and death of a star.

How must those long-dead Chinese astrologers have felt as they stared up at their discovery of a new star? What sense of glory must they have felt as it flared into view? What sense of wonder did they feel as the star faded slowly into darkness?

Do we chastise them for their astrological ignorance, or do we envy them for being among the chosen few in all of human history to see a supernova fill the night sky with ethereal light?

As for Charles Messier, the comets he discovered are now mostly historical curiosities. However, in a few days, thousands of Christmas telescopes will gather first light from dim M1. Thousands of holiday binoculars will be pointed at glorious Messier 45. Their owners will look in slack-jawed amazement as six stars are transformed into dozens of glittering jewels.

Not a night goes by that somewhere in the world, somebody observes from Messier’s list and speak Messier’s name — or at least his initial.

In March, perhaps I will join amateur astronomers around the world as they do a Messier Marathon. By doing so, I and others like me will share in some small measure Messier’s dogged determination and accidental glory.

We all feel isolated because of the pandemic, but I will be there under a dark sky with my brothers and sister stargazers. We will stand alone in the darkness, but we will be together as we share the light from distant stars.

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By Tom Burns

Stargazing

Tom Burns is the former director of the Perkins Observatory in Delaware.

Tom Burns is the former director of the Perkins Observatory in Delaware.