First Asteroid Ceres Discovered New Year’s Night 212 Years Ago

Giuseppe Piazzi

Happy New Year! May you have as pleasant a start to the new year as Giuseppe Piazzi did on January 1, 1801. That night the Italian monk and amateur astronomer was at work in his observatory on the island of Sicily compiling a catalog of the stars in the constellation Taurus. Using an earlier catalog as his reference, he noticed a star that was out of place and not included among its pages. The next night he returned to check it and to his surprise, the star had moved!

Piazzi suspected it might be a “new star” but still cautious, he observed it on a third and even a fourth night – noting it had moved the same distance each night – before sending news of the discovery by letter to colleagues at other European observatories.

He initially reported the object as a comet, similar to what William Herschel did when he discovered Uranus back in 1781, but added in a letter to an astronomical friend:

“I have announced the star as a comet. But the fact that the star is not accompanied by any nebulosity (haziness) and that its movement is very slow and rather uniform has caused me many times to seriously consider that perhaps it might be something better than a comet. I would be very careful, however, about making this conjecture public.”

Front Cover of Piazzi’s book on the discovery of what we now know is the dwarf planet Ceres. Astronomers thought it was the planet hypothesized to orbit between Mars and Jupiter.

Piazzi wrote a similar letter to Johann Bode, director of the Berlin Observatory. Because Napoleon’s invasion of Italy disrupted communications at the time, Bode didn’t get the letter until March 20, nearly 3 months later. But one look at the figures convinced him Piazzi had found something brand new.

Could it be the missing planet astronomers had hypothesized must lie between the vast and apparently empty gap between Jupiter and Mars?

Unfortunately, Piazzi had been the only person to observe the new object before it’s conjunction with the sun and disappearance in the solar glare. When predicted to reappear in the morning sky several months later, astronomers were ready with their telescopes, but no one could find the object.

Because of bad weather and illness, Piazzi hadn’t made enough observations earlier that year to allow astronomers of the day to establish an orbit. Without an orbit, predicting the “planet’s” position after solar conjunction was impossible.

A young German mathematician named Carl Friedrich Gauss became aware of the problem and worked for months to produced a new, more accurate method of orbit determination. He applied it to Piazzi’s handful of positions and confidently predicted where to look for the new “planet” in December 1801. And wouldn’t you know it, one Baron Franz Xaver von Zach , a Hungarian astronomer, found it within 1/2 of a degree of Gauss’ predicted position on December 31, 1801, almost exactly one year after Piazzi’s discovery.

Zach was famous for organizing a group of astronomers nicknamed the Celestial Police, whose mission was to find the putative planet predicted by Bode’s Law to lie between Jupiter and Mars.

Hubble Space Telescope photos of Ceres. At 580 miles in diameter, it’s the largest asteroid (dwarf planet) in the Main Belt between Mars and Jupiter. NASA’s Dawn spacecraft will study it up close beginning in 2015. Credit: NASA/ESA

Piazzi named the new object Ceres Ferdinandea, after the Roman goddess of agriculture and grain crops and King Ferdinand IV of Naples and Sicily. The Ferdinand was later dropped (thank you!) leaving us with Ceres.

Ceres became the first – and largest – of the asteroids, a collection of small, rocky bodies orbiting in a broad belt between Mars and Jupiter. Stirred up by Jupiter’s gravity, they never glommed together to form a planet.

Ceres was recently reclassified as as a dwarf planet, joining erstwhile-planet Pluto and icy asteroids Eris, Makemake and Haumea. Three more asteroids – Pallas, Juno and Vesta – were discovered in the next few years. In the early 19th century, it was believed these objects were actual planets; you’ll see them referred to as such in books of the time.

As the discovery pace quickened in the 1840s and beyond, astronomers soon realized there were too many to be considered in the same class as planets. Instead they named them asteroids from the Latin aster or “star”, referring to their appearance in the telescope. It’s estimated there are between 1.1 and 1.9 million asteroids in the main belt 0.6 miles across and larger and millions more smaller ones. While these numbers sound impressive, if you could crunch all the asteroids in the main belt together they’d only form a sphere less than half the size of the moon!

Ceres’s story continues into the present. After departing Vesta this fall, NASA’s Dawn space probe will visit the dwarf planet for a year starting sometime in early 2015. Based on density estimates, astronomers suspect it harbors water beneath its crust. The Hubble picture reveals a pink surface and mysterious white spot.

Piazzi, we’ve only begun to know the world you found that New Year’s night.

16 Responses

  1. Bob Crozier

    A few questions, if I may:
    1) In the link you included for Bode’s Law, Neptune is missing on the table. Is that because it doesn’t fit pattern?
    2) Why does this pattern work? Why would planets exist at these distances and not some other distances? For example, (referencing the link) why do we have to “add 4” instead of adding 1 or 2 or 10? And does this same pattern seem to work in other stellar systems for the planets that we are now finding?
    3) If all the asteroids were pulled together into one ‘planet’ which would end up being less than half the size of the moon, that would still be a dwarf planet, wouldn’t it? Does that still meet the prediction of Bode’s Law?

    Thanks for writing all this stuff. I’m a newbie here and a newbie to the world through my telescope. Much appreciated!

    1. astrobob

      Hi Bob,
      It’s unclear why Bode’s Law seems to work … at least out to Uranus. After that, it doesn’t. Although it’s called a “law” there’s no hard physical theory behind it. No one’s even sure it has a physical basis. I’ve heard the suggestion that it may possibly have something to do with gravitational resonances between the planets.
      There are several estimates of the mass of asteroids in the main belt – anywhere from a quarter to half the moon or ~500 to 1000 miles across. An object that size and close to spherical in shape would quality as a dwarf planet. Since Bode’s Law dealt with planet-sized bodies, I don’t think the prediction works, especially considering how many other similar if smaller bodies there are in the asteroid belt. Looking at other multiple planet extra-solar solar systems, Bode’s Law would not work very well, since multiple large planets have been found orbiting very close to their host suns.

  2. Giorgio Rizzarelli

    Interesting story Bob (and also the comments about Bode’s law), thanx for sharing. Happy New Year!

    1. astrobob

      Thanks Giorgio. Italy has always been at the forefront of astronomy starting with, of course, Galileo.

      1. Giorgio Rizzarelli

        Speaking about events now at year’s beginning, check email.. I sent you a picture comparing the sun disc size in photos I did yesterday at perihelion and 6 months ago with same instrumentation. Sun disc today is sensibly bigger and I used the comparison picture to measure Earth’s eccentricity, getting the exact value of 0.017! You may wish to publish it on your blog. See email for details

  3. lynn

    Hi Bob
    What does that all mean from Georgio’s comment, what does the exact value mean etc, just wondering and just for us stupid one’s that don’t understand it lol and what happen’s when the sun’s disc is bigger what does that entail. Thanks 🙂

    1. astrobob

      Those were the best available photos at the time (January 1, 2013). They were taken by the Hubble Space Telescope. At that time Dawn was still much too far from Ceres to shoot anything approaching the Hubble.

    1. astrobob

      Hi Paul,
      NASA has been sharing the best images possible. Remember, the spacecraft is still moderately far from Ceres. Later this spring we will see photos with 100 times the resolution of the best ones taken to date once the spacecraft reaches its close mapping orbit.

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