Herschel discovers Uranus, changes world


Every time I show somebody Uranus in a telescope, I think about the power of technology. Technically, the planet is visible to the unaided eye, but humans looked at the entire sky for thousands of years and didn’t see it.

It took a significant technological advance for one of those humans to figure out what everybody else had been seeing all those years.

You can find Uranus easily enough in an inexpensive pair of binoculars. It’s visible in the constellation Aries right now. You’ll also need a finder chart, which you can find at www.nakedeyeplanets.com/uranus.htm.

In a small amateur telescope, Uranus will resolve into only a tiny disc. After all, the planet is only 31,518 miles in diameter and about 1.75 billion miles away. That you can see that disc at all is a practical example of telescope technology at work.

Occasionally, I have my doubts about technology. The same impulse that put humans on the moon and gave us powerful hand-held computers masquerading as cell phones also gave us air pollution, climate change, and ultra-violent video games.

Technology may or may not have improved our lives, but it has produced at least one significant benefit. With every technological leap forward, we have also learned more about the universe.

Uranus is an astronomical case in point. In 1781, humans knew about six planets, the same fixed number known for all of recorded history. Then along came the reflecting telescope, which uses a mirror to gather light from stars and planets.

Unfortunately, a decent telescope cost a king’s ransom to build. Unless you were a professional astronomer supported by a government or had a wealthy private patron, you were out of luck.

William Herschel was an amateur astronomer who decided to make a telescope himself. His life epitomizes a critical moment in the growth of technology when a single human being could change our view of the cosmos if that person is gifted and dedicated enough to do so.

He was born Friedrich Wilhelm Herschel on Nov. 15, 1738, in the Electorate of Hanover in Germany, which was then part of the Holy Roman Empire.

His father played the oboe in the Hanover Military Band. As was the practice in those days, Wilhelm and his brother, Jakob, learned to be oboists early in their lives. By 1855, they had also joined the Military Band.

At that time, a single monarch, George II of England, ruled over England and Hanover. The Hanover Guards Regiment was in 1855 called to service in England, where the Herschel family got a brief taste of English life.

As tensions heightened between England and France, the regiment returned to Hanover. After France’s victory at the Battle of Hastenbeck in 1757, Herschel’s father sent his sons back to relative safety in England.

Friedrich Wilhelm Herschel quickly adapted to his new life as a war refugee. He adopted the British version of his name, Frederick William Herschel. He made a good living traveling from one musical job to another across England, performing concerts on the oboe, harpsichord, violin and church organ.

Herschel obtained positions in orchestras, chapels, and churches. Throughout his life, he composed 24 symphonies, many concertos, and some church pieces.

Life was good, but his musical talent and natural intellectual curiosity led him to want to see the harmonies of the universe for himself.

Back in those days, astronomy enthusiasts used lens-based refractors to study the sky. However, refractors were expensive and difficult to make. They also produced objectionable color fringes that we call chromatic aberration today.

The reflecting telescope, invented in 1668 by Isaac Newton, was slowly coming into fashion. Herschel decided to build one himself.

In those days, mirrors were painfully cast and polished from disks of speculum metal, a mixture of copper and tin. A telescope maker had to slowly and painstakingly grind and polish the mirror to an exact spherical, concave surface. Because the metal tarnished quickly, the mirror had to be taken out of the telescope and repolished every few months.

Herschel had no formal education in mirror making, so he took a course from a local optician. With the help of family members, he cast the discs himself and ground and polished them for up to 16 hours a day, mixing his telescope obsession with his other duties as organist and composer.

He produced an instrument with a six-inch-diameter mirror as his second telescope, a beginner’s ‘scope by today’s standards.

With it, he decided to scan the entire sky and record everything he saw. His initial work was to observe and catalog as many multiple star systems as he could find as he systematically scanned England’s entire sky.

And so it was on March 13, 1781, just after 10 p.m., that Herschel pointed his small telescope in the direction of the constellation Taurus and saw a bluish dot.

Here then was the great leap forward in technology. Working primarily alone, Herschel had learned to create a telescope good enough to see Uranus (for that’s what it was). However, he first concluded that the mysterious blue dot must be a comet or a star resolved into a tiny disc.

Two hundred years later, telescopes far better than Herschel’s painstakingly fabricated creations are available to anyone for about $300. It’s worth the price to point yours in the general direction of Ares and observe Uranus for yourself.

Four nights after his discovery, Herschel returned to his telescope and observed the strange object again. Now he was sure it was a comet because it had moved slightly against the fixed background of stars.

Herschel had made the most spectacular discovery in astronomical history, but he didn’t know it.

He observed the object over several months, carefully recording its changing position. His positional data, combined with those of other astronomers, allowed Swedish mathematician Anders Lexell to compute the object’s orbit, a nearly circular orbit around the sun.

The object was 19 times farther from the sun than Earth and with a startling orbital period of 82 years. At that distance, it must be 35,000 miles wide, over four times the diameter of our planet.

Herschel had not spotted a mere comet. He had become the first person since the dawn of human history to discover a new planet.

Fame and fortune soon followed. Fortune came because of his skills as a telescope creator. He sold over 60 telescopes to enthusiasts in Europe and England.

He also created telescopes for his own and his sister Caroline’s use. In all, he ground and polished over 300 mirrors, large and small.

His most powerful telescope remained the largest in the world until 1845. It had a speculum mirror 48 inches wide with a cast-iron tube 40 feet long. The mirror alone weighed just over half a ton.

Herschel was appointed “The King’s Astronomer” and elected to the Royal Society, England’s most prestigious scientific organization, and received its Copley Medal.

He later concluded that the elements of each of the multiple star systems he had carefully cataloged were gravitationally bound and orbiting each other.

His discovery of Uranus pales to his most significant contribution. He used a prism to spread out the light from the sun into the rainbow band called the spectrum, a well-known technology at the time.

But he went further. Using a simple hand thermometer, he measured the temperature of the red light at the low-frequency end of the spectrum. Then, brilliantly, he measured the temperature of a spot next to the red light where no light seemed to be shining.

The temperature of the supposedly blank area beside the red was one degree warmer than the red area.

He had discovered that the spectrum of light is not limited to the colors we see in the visible spectrum. His discovery of infrared light, the invisible light below red light in the spectrum, led inexorably to the science of infrared astronomy and the discovery of other forms of light.

As I write these lines, the world awaits to launch of the James Webb Space Telescope. It will study distant galaxies in the process of their formation billions of years ago. The best way to do that is in infrared light, the primary light in which the Webb Telescope operates.

The great irony is that Uranus is often visible, albeit barely, to the unaided eye. Astronomers back to ancient times had probably seen the seventh planet, shrugged it off as a faint star, and moved on. Herschel’s telescope was good enough to see it as a blue-green dot, and he was curious enough to observe it night after night. That made all the difference.

The moral: Technology is only as good as the hearts and minds of the human beings who use it. Keep that in mind the next time you pull out your cell phone.


By Tom Burns


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

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