Category: Astronomy

The period known as the Scientific Revolution (ca. 16th to the 18th century) was a time of major scientific upheaval. In addition to advances made in mathematics, chemistry, and the natural sciences, several major discoveries were made in the field of astronomy. Because of this, our understanding of the size and structure of the Solar System was forever revolutionized.

Consider the discovery of Uranus. While this planet had been viewed on many occasions by astronomers in the past, it was only with the birth of modern astronomy that its true nature came to be understood. And with William Herschel‘s discovery in the 18th century, the planet would come to be officially named and added to the list of known Solar Planets.

Past Observations:

The first recorded instance of Uranus being spotted in the night sky is believed to date back to the 2nd century BCE. At this time, Hipparchos – the Greek astronomer, mathematician and founder of trigonometry – apparently recorded the planet as a star in his star catalogue (completed in 129 BCE).

This catalog was later incorporated into Ptolemy’s Almagest, which became the definitive source for Islamic astronomers and for scholars in Medieval Europe for over one-thousand years. During the 17th and 18th centuries, multiple recorded sightings were made by astronomers who catalogued it as being a star.

This included English astronomer John Flamsteed, who in 1690 observed the star on six occasions and catalogued it as a star in the Taurus constellation (34 Tauri). During the mid-18th century, French astronomer Pierre Lemonnier made twelve recorded sightings, and also recorded it as being a star. It was not until March 13th, 1781, when William Herschel observed it from his garden house in Bath, that Uranus’ true nature began to be revealed.

Discovery:

Herschel’s first report on the object was recorded on April 26th, 1781. Initially, he described it as being a “Nebulous star or perhaps a comet”, but later settled on it being a comet since it appeared to have changed its position in the sky. When he presented his discovery to the Royal Society, he maintained this theory, but also likened it to a planet.

As was recorded in the Journal of the Royal Society and Royal Astronomical Society on the occasion of his presentation:

“The power I had on when I first saw the comet was 227. From experience I know that the diameters of the fixed stars are not proportionally magnified with higher powers, as planets are; therefore I now put the powers at 460 and 932, and found that the diameter of the comet increased in proportion to the power, as it ought to be, on the supposition of its not being a fixed star, while the diameters of the stars to which I compared it were not increased in the same ratio. Moreover, the comet being magnified much beyond what its light would admit of, appeared hazy and ill-defined with these great powers, while the stars preserved that lustre and distinctness which from many thousand observations I knew they would retain. The sequel has shown that my surmises were well-founded, this proving to be the Comet we have lately observed.”

While Herschel would continue to maintain that what he observed was a comet, his “discovery” stimulated debate in the astronomical community about what Uranus was. In time, astronomers like Johann Elert Bode would conclude that it was a planet, based on its nearly-circular orbit. By 1783, Herschel himself acknowledged that it was a planet to the Royal Society.

Name and Meaning:

As he lived in England, Herschel originally wanted to name Uranus after his patron, King George III. Specifically, he wanted to call it Georgium Sidus (Latin for “George’s Star”), or the Georgian Planet. Although this was a popular name in Britain, the international astronomy community didn’t think much of it, and wanted to follow the historical precedent of naming the planets after ancient Greek and Roman gods.

Consistent with this, Bode proposed the name Uranus in a 1782 treatise. The Latin form of Ouranos, Uranus was the grandfather of Zeus (Jupiter in the Roman pantheon), the father of Cronos (Saturn), and the king of the Titans in Greek mythology. As it was discovered beyond the orbits of Jupiter and Saturn, the name seemed highly appropriate. As he would later write in his 1784 book, “From the Newly Discovered Planet“:

“Already in the pre-read at the local Natural History Society on 12th March 1782 treatise, I have the father’s name from Saturn, namely Uranus, or as it is usually with the Latin suffix, proposed Uranus, and have since had the pleasure that various astronomers and mathematicians, cited in their writings or letters to me approving this designation. In my view, it is necessary to follow the mythology in this election, which had been borrowed from the ancient name of the other planets; because in the series of previously known, perceived by a strange person or event of modern times name of a planet would very noticeable. Diodorus of Cilicia tells the story of Atlas, an ancient people that inhabited one of the most fertile areas in Africa, and looked at the sea shores of his country as the homeland of the gods. Uranus was her first king, founder of their civilized life and inventor of many useful arts. At the same time he is also described as a diligent and skilful astronomers of antiquity … even more: Uranus was the father of Saturn and the Atlas, as the former is the father of Jupiter.”

There were some holdouts to this new name, largely in Britain, where the name Georgium Sidus remained popular. Nevertheless, Herschel’s proposal would become universally accepted by 1850. Uranus was the only planet in the Solar System named after a god from Greek mythology, rather than using the Roman counterpart’s name. 

Other Names:

While Uranus remains the widely-recognized name for the Solar System’s seventh planet (and third gas giant), other cultures have recognized it by various other names. For example in traditional Chinese astronomy, it is known as Tianwángxing, which means literally “Sky King Star”.

The same name is recognized in the Korean, Japanese and Vietnamese astronomical traditions. To the Aztecs (and other Nahuatl-speaking peoples), Uranus was known as “Ilhuicateocitlalli” – named after the word for “sky” (“ilhuicatl”) – and also as “Xiuhteuccitlalli”, the Aztec god of fire, day, and heat. Many other cultures recognized Uranus in their mythological traditions and assigned various names.

The discovery of Uranus was one of several that would follow from the 18th century onward. In time, Neptune, the Asteroid Belt, Ceres, Vesta, Pluto and the Kuiper Belt would be added to the mix, thus creating a model of the Solar System that would endure until the early 21st century – when new bodies were discovered beyond the orbit that Neptune that would lead to the nomenclature debate.

We have written many interesting articles on Uranus here at Universe Today. Here’s The Planet Uranus, Ten Interesting Facts About Uranus, Why is Uranus on its Side?, Tilt of Saturn, and Who Discovered Uranus?

For more information, here’s an article from the Hubble educational site about the discovery of Uranus, and here’s NASA’s Solar System Exploration page on Uranus.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

Sources:

• NASA: Solar System Exploration – Uranus
  
• Wikipedia – Uranus
• Views of the Solar System – Uranus
• Space Facts – Uranus