ARLINGTON, VA - NOVEMBER 17: Charles Jones fixes Thanksgiving dinner ahead of time at his apartment ... [+]
If you’re preparing to cook a turkey for Thanksgiving, you’re probably already thinking about temperature, so this is a great time to pause and remember Anders Celsius, born on November 27, 1701.
As the son of an astronomer and the grandson of a mathematician, Celsius followed family tradition and became a scientist; officially, he worked as a professor of astronomy at Sweden’s Uppsala University, but his research also included physics, geography, and mathematics. (We can only imagine what the conversations were like at Celsius family holiday dinners, but there was probably some heated debate about the latest research.)
In 1936, a few years after becoming a full-fledged professor, Celsius set out on an expedition to Lapland, in the far north of Finland, to measure a degree of latitude. His team compared the distance to another team’s measurement of a degree of latitude in Peru, near the equator, and the results proved Isaac Newton’s theory that the Earth isn’t a perfect sphere; instead, it’s mostly round but a bit squashed, so it’s flatter at the poles. Celsius also noticed that auroras are related to Earth’s magnetic field; he observed hundreds of nights of auroras and noticed that his compass seemed to be a bit off-kilter anytime the lights appeared in the sky.
And in 1742, two years before his death, Celsius proposed a new temperature scale, with the melting point of ice at 100⁰ and the boiling point of water at 0⁰. If that sounds backwards to you, don’t panic – but don’t try to bake your turkey at -70⁰C, either. A colleague reversed Celsius’ scale the next year, putting the freezing point of water at 0⁰ and its boiling point at 100⁰, which should sound more familiar. Over the next decade or so, several scientists came up with their own versions of more-or-less the same scale, but Celsius seems to have been the first, and he’s the one we remember today.
A few decades after Celsisus’ death, revolution swept across neighboring France, 1900 km (1180 miles) away from Uppsala. The revolution’s leaders, steeped in the ideas of the Enlightenment, wanted to relieve France not only of its monarchs and aristocrats, but its outdated and chaotic system of measurements. They proposed the metric system, with units based on natural phenomena (a meter was originally one ten-millionth of the distance from the North Pole to the Equator, and a kilogram was originally the mass of a cubic liter of water) and divided into multiples of ten. The centigrade temperature scale became part of the metric system in 1790, the year after the beginning of the French Revolution.
Today, most countries use a version of the metric system called the International System of Units, or SI. Many of the original units have seen some slight revisions over the years – a meter is still recognizable as a meter, but in 1960 scientists redefined it based on a number of wavelengths of an isotope of krypton (so much for simplicity), and in 1983, it became the distance light travels in 1/299,792,458th of a second. It’s the same distance by any of these definitions.
And Celsius’ centigrade scale has received the same treatment. In 1948, the centigrade scale was renamed Celsius in honor of the scientist who first invented it. And in 1954, the definition of a degree Celsius changed. Instead of the freezing point of ice at 0⁰C, the scale is now technically based on pinning 0.01⁰C to the triple point of water – the temperature and pressure at which water can be either a solid, a liquid, or a gas. It works out so that a single Celsisus degree equals a single kelvin – a temperature scale often used to describe the extreme heat and cold of objects in space – but the scales are offset from each other.
In case you’re wondering what Celsius even means, it’s a Latin version of Anders Celsius’ family estate name, which means “mound” in Swedish. “Celsus” means “mound” in Latin. Of course, it may not matter, because if you live in the U.S., you’re probably baking your turkey in degrees Fahrenheit. Just in case, though, you should roast that 11kg (24 pound) turkey at around 205⁰C (478.15 kelvin) for about 4.5 hours.
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