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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.

Hubble Telescope image of Ceres in 2004 (NASA,ESA and J. Parker (Southwest Research Institute))

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

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

Detailed chart showing Ceres during late November and December 2012

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

Ceres Data Table

DateRA (J2000)DEC (J2000)Apparent Magnitude
November 26,201206h 06m 02s23d 48m 11s7.4
November 27,201206h 05m 18s23d 52m 11s7.4
November 28,201206h 04m 32s23d 56m 11s7.3
November 29,201206h 03m 45s24d 00m 11s7.3
November 30,201206h 02m 57s24d 04m 13s7.3
December 01,201206h 02m 07s24d 08m 14s7.3
December 02,201206h 01m 17s24d 12m 16s7.2
December 03,201206h 00m 24s24d 16m 18s7.2
December 04,201205h 59m 31s24d 20m 20s7.2
December 05,201205h 58m 36s24d 24m 21s7.2
December 06,201205h 57m 41s24d 28m 22s7.1
December 07,201205h 56m 44s24d 32m 22s7.1
December 08,201205h 55m 47s24d 36m 21s7.1
December 09,201205h 54m 48s24d 40m 19s7.0
December 10,201205h 53m 49s24d 44m 15s7.0
December 11,201205h 52m 49s24d 48m 10s7.0
December 12,201205h 51m 48s24d 52m 04s6.9
December 13,201205h 50m 47s24d 55m 55s6.9
December 14,201205h 49m 45s24d 59m 45s6.9
December 15,201205h 48m 42s25d 03m 33s6.8
December 16,201205h 47m 40s25d 07m 18s6.8
December 17,201205h 46m 37s25d 11m 01s6.8
December 18,201205h 45m 33s25d 14m 41s6.7
December 19,201205h 44m 30s25d 18m 18s6.7
December 20,201205h 43m 27s25d 21m 53s6.8
December 21,201205h 42m 23s25d 25m 25s6.8
December 22,201205h 41m 20s25d 28m 54s6.8
December 23,201205h 40m 17s25d 32m 20s6.9
December 24,201205h 39m 14s25d 35m 43s6.9
December 25,201205h 38m 12s25d 39m 03s6.9
December 26,201205h 37m 10s25d 42m 19s7.0
December 27,201205h 36m 09s25d 45m 33s7.0
December 28,201205h 35m 08s25d 48m 43s7.0
December 29,201205h 34m 08s25d 51m 50s7.1
December 30,201205h 33m 08s25d 54m 53s7.1
December 31,201205h 32m 09s25d 57m 54s7.1