Ceres
Published on Aug 12, 2006 at 12:16 am.
6 Comments.
Filed under asteroids.
Not only is this weekend the peak of the Perseid meteor shower, but it also happens that this year Ceres is at opposition today. Ceres is the first asteroid discovered, and the largest body in the asteroid belt. August 12, 2006, Earth is passing between Ceres and the Sun, so Ceres will be opposite the Sun in the sky. That means that it will rise at sunset, be highest in the sky around midnight, and set at sunrise. As the weeks and months to by, it will be rising earlier and earlier, eventually rising around noon, and high in the sky at sunset, and then setting at midnight. In about half a year, we’ll be on the other side of the Sun from Ceres, so it will rise at sunrise and set at sunset — in other words we won’t see it at all. But, this weekend is the ideal time to see Ceres (through a telescope or with binoculars), since we will be closest to it.
Ceres was the first asteroid discovered. Italian astronomer Giuseppe Piazzi accidently found Ceres in 1801. Interestingly enough, at that time, a team of astronomers were actively searching the sky for a “missing planet” believed to lie between Mars and Jupiter. A number of years earlier, a mathematician, Johann Titius, had devised a sequence of numbers that seemed to sort of fit the orbital spacings of the planets, with the notable exception of a number for an orbit between that of Mars and Jupiter. The Titius sequence is rather fudged, at best, and the first two numbers don’t even conform, but people tended to ignore that. No one much listened when Titius proposed his sequence. However, several years later, a famous astronomer by the name of Johann Bode published the Titius law, but without acknowleging its author, so for nearly two hundred years this relationship has been known mainly as Bode’s Law. Bode and Baron von Zach decided to conduct a search for the missing planet that they believed was between Jupiter and Mars. Quickly, they realized how daunting the task was, so they enlisted the aid of nearly two dozen astronomers. Piazzi was not asked to participate, and he didn’t even know abou this group who called themselves the “Celestial Police”. So, you can imagine their consternation when someone from outside their group found a body with an orbit nearly where they had been looking! They belatedly asked Piazzi to join them, declaring that the invitation had been delayed in transit to Italy.
Ceres is the biggest asteroid in the asteroid belt, at nearly 950km in diameter. It rotates in just over 9 hours, and is actually an oblate spheriod. It is one of only a couple of asteroids whose gravity is sufficient to pull itself into a roughly spherical shape, a situation known as isostasy. Though the largest object in the asteroid belt, it is not the largest minor planetary body. Several objects in the Kuiper Belt beyond Pluto are somewhat larger. Though the largest body in the asteroid belt, Ceres falls far short of planetary status. It, like every body in the universe, has gravity, but not much. In fact, you would only weigh about 2.8% of your normal weight on Ceres. I for example, would weigh only just over 4 pounds on Ceres! Imagine how high that you could jump there. Wow. I could finally dunk a basketball!
And it is so small, that you could fit nearly 50 Ceres sized objects inside our Moon. This sort of dispels the idea that the asteroids are somehow some sort of planet the blew up. There simply isn’t enough material there to make a planet of any consequence. More likely, Jupiter’s gravity never allowed the material to come together to form a planet. Being small, Ceres isn’t very bright. It is too dim to see with the naked eye, though it is well within the grasp of binoculars, if you know where to look. Also, being small means that it is too small to see any detail from Earth. In fact, for all but the very largest telescopes, Ceres is just a dot. Even the Hubble telescope has a tough time with Ceres. The best images every taken were taken with the Hubble from late 2003 to early 2004. I put one of them above. This image is actually fabricated from combining data from multiple images. The best view of Ceres would come from NASA’s Dawn spacecraft, if it ever actually is launched. Dawn has been on the budget chopping block. The bright spot on the image above is likely ejecta from an impact crater, but no one really knows for sure — not until we get a closer look.
Ceres is currently in Pisces Austrinus, Southeast of Capricornus, and just west of the bright star Fomalhaut. A finder chart can be found here. Though Earth will be passing between Ceres and the Sun on August 12, Ceres will still be about 184,000,000 miles away. But, as I said, Ceres is bright enough to see in binoculars from a dark sky. However, the trick is knowing which little dot in the field of view is Ceres. That is the hardest part! Next week, we are doing a star party, and I think that pointing a telescope at Ceres might be interesting. Well, sort of interesting, that is. It would be interesting to astronomers and people pretty interested in astronomy. Most of the general public would be bored with seeing just dots. Still, some of the people who come to my star parties are a bit more serious than the average person walking off the street.
As a bit of Ceres trivia, the rare earth element Cerium (atomic number 58) was named for Ceres.
-Astroprof
Astroprof’s Page » Planets, or not planets? on August 16, 2006 at 10:01 pm: 1
[…] So, what is a planet? Sadly, astronomers have never had a real definition. In ancient times, a planet was a “star” that appeared to wander from constellation to constellation. That was the last coherent definition of a planet that we had. Copernicus showed that the planets and Earth all orbit the Sun. Soon, it became apparent that, in that case, the Earth was a planet. Giordano Bruno then extemded that idea to be that perhaps the planets were Earths. Galileo’s telescope showed that the planets, indeed, were spherical objects. Soon it became apparent that the four inner planets were much larger than the two outer ones (only six were known at the time). Eventually, a seventh was found: Uranus. In 1801, Ceres was found. At first, Ceres was declared a planet. However, no amount of magnification showed any disk, so astronomers realized that it was way too small to be a planet. It was demoted to “asteroid”, a new category devised to include Ceres and many other similar bodies. More asteroids were found. Then, in 1930, Clyde Tombaugh discovered Pluto. Early estimates of Pluto’s size were wildly too big. Pluto was declared a planet. But over the years, we learned Pluto’s real size. It is tiny. You could fit about 3.5 Plutos inside of our Moon. It is made of ice and rock, not rock like the four inner planets, nor gas like the four big planets. It doesn’t fit. For years, astronomers have argued that it was a mistake to put it on the list of planets. Then, not long ago, the object called 2003 UB313 was discovered. The problem is that 2003 UB313 is bigger than Pluto. Is it a planet? What about several objects just a shade smaller than Pluto? Are they planets? Just what is a planet. The International Astronomical Union has been working on a definition of “planet” for several years. A committee was formed to decide on a definition. It failed to do so, so a new committee was formed. This one has come up with a definition that has been proposed to the IAU for a vote. […]
Astroprof’s Page » Send your name to the asteroid belt on November 1, 2006 at 8:40 am: 2
[…] But, two of the planetessimals surviving to today are Vesta and Ceres. These are the two largest bodies in the asteroid belt are the primary targets of the Dawn mission. Understanding these bodies is important to our understanding of how our own planet formed, as well as how planets in general form. I am glad that they decided to go ahead with the mission. […]
Oops on January 5, 2007 at 9:51 am: 3
Astroprof needs to learn more about his own planet because Cerium is a very common element, more common even than Lead. It is used in the manufacture of everything from lighter “flints”, to Aluminium alloys, to carbon arc lamps.
Astroprof on January 5, 2007 at 10:25 am: 4
Hey, Oops. I never said a word about the abundance of cerium. I just said that the rare earth element Cerium was named for Ceres. Think Chemistry. Cerium is part of the Lanthanide Series. It is classified as a “Rare Earth Element.” Yes, it is the most common rare earth element, and is more common than many non “rare earth elements”, but it still falls into that chemical category. Take it up with the chemists. See under “occurance” in the following link: http://en.wikipedia.org/wiki/Cerium
Astroprof’s Page » 2 Pallas on September 3, 2007 at 7:08 pm: 5
[…] Minor planet 2 Pallas was the second asteroid discovered. It was found by Heinrich Wilhelm Olbers in March, 1802, just one year after the discovery of 1 Ceres. Olbers was one of the “celestial police,” a group of two dozen astronomers who had been scanning the sky looking for a hypothetical “missing planet” located between Mars and Jupiter. The celestial police had been searching earnestly for this hypothetical planet when word came that Giuseppe Piazzi had found a tiny body orbiting the Sun between Mars and Jupiter. This body was later named Ceres. Piazzi was quickly invited to join the celestial police after his discovery. The following year, Olbers was searching for Ceres when he found another body nearby. That was Pallas. Olbers was somewhat lucky in that Pallas happened to be near the ecliptic at the time. Most of the time it is some distance away from the ecliptic, as seen above. […]
Astroprof’s Page » Plutoids on June 11, 2008 at 12:41 pm: 6
[…] whether or not Pluto should be on the list of planets. After all, it was to these other bodies what Ceres was to the objects that became known as asteroids. Astronomers proposed several names for these […]