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What's in a Name

Things are often not what they seem. Many astronomical discoveries are not named for - or by - their discoverers. Here are some of them.

Comet Halley
Halley didn't discover Comet Halley.

There were sightings of the comet over two thousand years ago and comets weren't routinely named for their discoverers until the 20th century. So you might wonder what Halley did to get it named after him.

Edmond Halley (1656-1742) used Isaac Newton's new physics and records of previous comet sightings. From this he worked out that several known comets were, in fact, the same one. He predicted its return in 1758, but didn't live to see the sensation caused by the comet's being spotted on Christmas Day 1758.

Bode's Law
Bode's Law was neither Bode's nor a law. It was a formula to work out the distances of the planets from the Sun. When German astronomer Johann Bode (1747-1826) first published this relationship, he forgot to mention that it had been done six years earlier by Johann Titius. (It is sometimes called the Titius-Bode Law.)

The formula works surprisingly well. The discovery of Uranus supported it and it predicted a planet where the Asteroid Belt was eventually found. Bode didn't live to see Neptune defiantly break the law in 1846. It was found at a distance much closer than that given by the formula.

Powerful patrons
The favor of those in power was helpful, and naming celestial discoveries for them was more impressive than dedicating books.

Galileo, the Medicis and Marius
Jupiter's four largest moons are known as the Galilean moons after Galileo Galilei (1564-1642). He discovered them early in January 1610 and published his findings. Galileo called them the Medicea Sidera (Medici Stars), numbering them I-IV. The Medicis were a wealthy and powerful family that ruled Florence.

However Galileo's discovery was disputed by German astronomer Simon Marius (1573-1624). He claimed to have seen the moons first and proposed names for them from Roman mythology. Although the moons collectively bear Galileo's name, individual names for them were adopted in the mid 19th century - the ones which Marius had proposed.

A planet named George
When William Herschel discovered Uranus in 1781, he named it Georgium Sidus (George's star) after George III who later supported Herschel's astronomical work. If the king had had a Facebook page, William would certainly have clicked "LIKE", but the king was short of fans elsewhere, particularly in France and America. Johann Bode suggested the name Uranus after the father of Saturn in Roman mythology. This name was finally adopted, though the Herschels stubbornly continued to refer to it as "the Georgian planet."

The What? Belt
The Kuiper Belt is located between 30 and 55 astronomical units from the Sun. (An astronomical unit is the distance between the Earth and The Sun.) It's similar to the Asteroid Belt, but bigger and colder. The numerous small objects that comprise it are icy bodies, not rocky ones.

It's not clear how the belt got named after Dutch-American astronomer Gerard Kuiper (1905-1973). Although he had said there might once have been such a belt, he also said that it didn't exist anymore. In the decades following the discovery of Pluto in 1930, there were various people who proposed such a belt, including Irish astronomer Kenneth Edgeworth (1880-1972). It's sometimes called the Edgeworth-Kuiper belt, but this ignores the work of many others who contributed to understanding it.

It's somewhat ironic that with all the people who were serious about this belt, it was named after someone who said it didn't exist.

Leavitt's Law
Most people have never heard of Leavitt's Law. Yet it is one of the most important relationships in astronomy, as it lets astronomers determine distances in space. Edwin Hubble relied on it in the work which showed that Andromeda was a separate galaxy, not part of the Milky Way.

Some stars are variable, meaning their brightness changes. Leavitt discovered that a type of star called a Cepheid variable pulsates in a regular way and that the period of pulsation depends on how luminous it really is (intrinsic luminosity). Light gets dimmer in a predictable way as the distance increases, so if you know how bright a star is, you can work out the distance to it by comparing the actual brightness with the apparent brightness.

Henrietta Swan Leavitt (1868-1921) had been hired by Harvard Observatory as a computer (someone who did measurements and calculations in pre-electronic days). Nonetheless she devised what became the international standard for determining the magnitudes of stars in photographs. She also discovered over a thousand variable stars, half of those known in her lifetime. And she discovered what was called the period-luminosity relation, not Leavitt's Law. However in 2009 the American Astronomical Society did officially agree to encourage people to call the relationship the Leavitt Law and that has become somewhat more common.

References:
IAU Central Bureau, "IAU Comet-naming Guidelines" http://www.cbat.eps.harvard.edu/cometnameg.html
International Comet Quarterly, "What is improper about the term 'Kuiper belt'?" http://www.icq.eps.harvard.edu/kb.html

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