Dwarf planet Ceres reaches opposition this year in the constellation of Taurus on December 18th. The largest member of the asteroid belt shines at magnitude 6.7 and is easy to find as is located only 17 degrees to the northeast of brilliant Jupiter. The brightest star in Taurus, first magnitude orange/red star Aldebaran is also close by.

This month presents a superb opportunity to catch a glimpse of Ceres. Although it never quite gets bright enough to be seen with the naked eye, the dwarf planet is at its brightest possible this month and an easy binocular or small telescope object. It is also fun to track Ceres as it moves quickly on its current retrograde motion through Taurus.

Discovery

The Titius–Bode law (sometimes termed just Bode's law) was a hypothesis that is attributed to German astronomers Johann Elert Bode and Johann Daniel Titius in middle part of the 18th century. Although an extremely simple hypothesis in terms of mathematics, it predicted to a remarkable accuracy the distance from the Sun of all the known planets at that time. Sir William Herschel then discovery Uranus in 1781 which also fit to the hypothesis. However, the rule had one notable discrepancy; it predicted the existence of a then unknown celestial object between the orbits of Mars and Jupiter, at a distance of 2.8 AU from the Sun.

The idea of an undiscovered planet existing between the orbits of Mars and Jupiter was now given enough credit, that around the end of the 18th century a number of astronomers starting systematically searching the skies for it. On January 1, 1801, Giuseppe Piazzi an Italian Catholic priest, mathematician, and astronomer discovered Ceres at the Academy of Palermo, Sicily. Originally he though it was a comet but soon realized that the object displayed no cometary activity. Once the orbit was calculated, it was determined that Ceres was located 2.77 AU from the Sun, almost exactly that distance predicted by the Titius–Bode law. The missing object had been found and Ceres was hailed as the new planet.

Ceres has a diameter of 975 kilometres (610 miles), which is much smaller than all the other planets. It was assigned a planetary symbol, and remained listed as a planet in astronomy books and tables for about half a century. During this time asteroids Pallas, Juno and Vesta were discovered and also classified as planets. Further discoveries followed and it soon became clear that many medium/small objects in the region between Mars and Jupiter existed and so they were all re-classified as asteroids. The region is now referred to as the asteroid belt. Incidentally, the Titius–Bode law was finally discredited in 1846 when the planet Neptune was discovered in a region of the solar system that was not at all predicted by the equations.

Despite its small diameter, Ceres is by far the largest of all objects in the asteroid belt and constitutes a third of the mass of the belt. In 2006, the International Astronomical Union (IAU) demoted Pluto as a planet and defined a new type of object, the "dwarf planet". Ceres was redefined for a third time as a dwarf planet along with Eris, Haumea, Makemake and Pluto. The latter are all Kuiper belt objects located in the outer regions of the solar system, with Ceres been the only dwarf plant located in the inner solar system and the asteroid belt.

Magnitude

Ceres has an apparent magnitude ranging from 6.7 to 9.3, and therefore is not a naked eye object even when at it's brightest. The dwarf planet is at its very best when opposition occurs close to perihelion, and on December 18, 2012 that is what exactly happens. On this date, Ceres will peak at magnitude 6.7 and hence easily visible in binoculars and small telescopes. Although it's the largest object in the asteroid belt, Ceres is not the brightest. That distinction goes to Vesta, which can reach magnitude 5 and hence naked eye visibility. Incidentally Vesta also reaches opposition this month, peaking at magnitude 6.4.

Location

The beautiful zodiac constellation of Taurus is where to find Ceres in December. The famous constellation represents the head and shoulders of a bull, depicted as charging at neighbouring Orion. Aldebaran denotes the magnificent red eye of the bull with Ceres located in the northeast corner of the constellation about 18 degrees from Aldebaran. Unmistakable Jupiter is a few degrees north of Aldebaran.

Ceres, Vesta and Jupiter during late November and December 2012 - pdf format

Detailed chart showing Ceres during late November and December 2012 - pdf format

Ceres Data Table