Most of the time, when looking at item imaged by a telescope, the reaction is to assume that the item being viewed looks pretty small to the naked eye. Except the image above is actually about eight times as wide as the full Moon — and it’s not even capturing the whole nebula. The entirety of the North American Nebula spans an apparent space greater than 10 full Moons, and that’s before brining in the closely connected Pelican Nebula. These are enormous features that span huge swathes of the night sky.
So why don’t they dominate the view every time we look up? Well, they’re large, but dim. The brightest points of the nebula actually hit a magnitude of 4, making them fairly easy to spot for someone with good eyesight in dark conditions. However, most of the nebula is several times dimmer, with a magnitude of 11 or higher (for astronomy, high numbers mean a dimmer object). The full span of the nebula is invisible, even in the best conditions.
The North American Nebula is named for an appearance that is said to resemble a map of the continent which … maybe. It would take a lot of squinting. Keep in mind that the image above is just a part of the whole nebula and that more detail could be revealed by a longer exposure. It’s an emission nebula, a cloud of ionized gas about 2,600 light years away that’s being lit by the energy of an enormously hot star that itself is almost hidden by the nebula.
But it’s big, and it’s up there, and it has an interesting history.
It was in 1783 that William Herschel first spotted what he called “a milky luminosity” at in the area of this nebula. Nebula were something of a specialty of Hershel. Considering that he cataloged over 2,000 nebula, but his son John only added this one to the catalog in 1829, that gives some sense of the faintness of this object.
Hershel was one of that generation of naturalists who seemed to have entered a field at just the right time when improved instruments made almost endless discoveries possible. He not only created some of the first serious catalogs of various types of objects in the sky, he was one of the first to work with spectrographs, winkling out the different bands of light coming from the stars. He observed the increase and decrease of the ice caps on Mars over the span of a Martian year. He named new moons around two planets.
He was actually born in Germany, and seemed destined for fame as a musician. Both his father and brother were oboists in the Hanover Military Band—which got up to a lot more at the time than oom-pahs—before his father decided to move the family to England as war with France loomed. This was at the time when both places were under the control of some guy you may have heard of … King George II. George may not have made a lot of great decisions, but moving William Hershel to England (and pardoning him from charges of dissertation for abandoning his critical war role of being an oboist) seems to be among his better acts.
In England, Hershel made the transition from musician to astronomer, first taking it on as a hobby, then having a larger scope constructed as he became more obsessed. It was the kind of transition only possible to folks who were wealthy. Which pretty much describes the vast majority of natural historians at the time.
For the next few decades, Hershel would be the astronomer. He made what seemed to be an unending string of discoveries that made him famous in astronomical circles. Then in 1781, he did something that made him famous in every circle.
Observing stars in the constellation of Gemini, Hershel spotted something that seemed to be shifting positions over the course of several observations. He made a lot of notes. He did more observations. He called on other astronomers to check what he was seeing. He made a spectacular announcement. Hershel had discovered the planet Uranus — the first planet to be discovered by telescope, and the first planet added to the Solar System since antiquity.
After that, George III made him Court Astronomer and money poured in for even bigger telescopes. Hershel was a science rock star.
But, in the best Jedi sense, there was another.
Every 155 years, the inner Solar System is visited by a comet named Herschel–Rigollet. It’s a fairly bright comet, but since it won’t be around again until 2092, don’t hold your breath. In any case, this comet is not named for William Hershel, or for his son. It’s named for his little sister, Caroline.
Afflicted by typhus as a child, Caroline’s growth was arrested and she never grew much more than 4’ tall. She also lost her vision in her left eye. Her disabilities meant that Caroline’s family assumed that she would never marry, and did what any moderately well off family would do for a young woman with a sharp mind and a frail body … they had her trained to be a house servant.
However, Caroline reputedly had an excellent voice, and when the senior Mr. Hershel died, William and his brother invited Caroline to move in with them, where she could join them in church performances where they still regularly showed off their oboe skills.
Noticing that William had to step outside to the telescope, wait for his eyes to adjust to the darkness before observing, then run inside to take notes by lamplight, then repeat, Caroline first joined in his astronomy work by offering to be his secretary. William would stay outside, calling in what he saw to Caroline, who wrote it down dutifully. She also took on the task of polishing the mirrors of the telescopes and maintaining the other equipment of William’s hobby-turned-occupation.
In 1783, as he was building a new 20’ telescope for himself, William commissioned a smaller scope for Caroline. With it, she soon made a number of discoveries on her own. Over the next five years, she discovered eight comets, including the periodic comet Herschel–Rigollet. William took the eyepiece and observed the comet a few minutes after Caroline. Considering the way things were at the time, the comet might easily have been named for him. It’s not. It is named for her.
Caroline Hershel would become the first woman to earn a salary as a scientist. She was also the first woman in England to hold an official position with the government. The first woman to publish in the official journal of the Royal Institute. She was a 4’3” giant.
William died in 1822 and a grief stricken Caroline moved back to Hanover. But she didn’t stop her work. She continued to observe the skies, and used her hard won knowledge of both astronomy and math to revise and expand on her brother’s work. In 1828, the Royal Astronomical Society presented Caroline with the Gold Medal for her lifetime of work. No other woman would receive the award until 1996. In 1835, she was one of the first two women inducted into the Royal Society. In 1847 the King of Prussia presented her with a Gold Medal for Science.
When she died in 1848, at the age of 97, Caroline Hershel was one of the most famous women in the world. She shone brighter than any comet she discovered.