Ceres was the first asteroid or minor planet to be discovered. It was found completely by accident by Giovanni Piazzi from his Palermo Observatory in Sicily on the evening of 1st January 1801. In respect of his patron, the then Sicilian monarch Ceres Ferdinandea, Piazzi named this new planetary body after him. Almost immediately this long name fell out of vogue and was soon shortened to just Ceres.
Ceres is the largest of the inner asteroids averaging about 950 kilometres across. Later measures have found the size to be more like of 975 by 909km (2005). Ceres is mostly visible in small binoculars, but still remains star-like in all amateur telescopes. It takes 4 years 7 months or 4.599 yr. to orbit the Sun, whose orbits lies in the main asteroid belt between the orbits of Mars and Jupiter at the mean solar distance of 2.766 AU or roughly 410 million kilometres. This distance also varies throughout the orbit - aphelion to perihelion - by about 66 million kilometres or 0.44 A.U.
Ceres crosses on average about four different constellations each year, but does not necessarily remain aligned to the familiar twelve zodical constellations. This is caused by Ceres having an inclination to the ecliptic of about 10.5o - indicating possible maximum declinations of +34o or -34o.
CERES DATADiscoverer : Giovanni Piazzi : 01 Jan. 1801 Satellites : 0 Diameter : 975x909 km. Flattening : 0.0700 Polar Tilt : 29.56o Period (P) : 4.599 years Synodic Period : 443.5 days Orbital Velocity 17.88 kms-1 Eccentricity (e) : 0.0792 Inclination (i) : 10.587o Mass : 9.5 x1020 kg. Mean Density : 2.08 g.cm-3 Mean Distance : 2.776 AU or x 4.13 x109 km Sidereal Rotation : 09 hr. 04.8m Mean Sidereal Rotation : 0.3781 d. Maximum Diameter : ″ (arcsec) Minimum Diameter : ″ (arcsec) Maximum Magnitude : +6.8 |
Ceres’ orbit appears slightly elliptical at an eccentricity of 0.0792, whose inclination is 10.59o to the ecliptic. This allows the observable range of possible declinations to vary between +34.1o and -34.1o, placing this minor planet often within constellations away from the zodiac. During 2006, for example, Ceres appears in the southern constellations of Microscopium and Piscis Austrinus, while in 2007, the first discovered minor planet can be found in Cetus for more than half the year.
So far over sixty-three oppositions have been observed between 1830 and 2006, making the true orbit fairly well established. Over the decades, Ceres’s calculated predicted positions suffers greatly from the gravitational perturbations of nearby planetary bodies, which slowly change the ephemerides. These perturbations effects are mainly influenced by Jupiter, and to a much lesser extent, by both Mars and Pallas.
During certain oppositions, Ceres may brighten to about 6.8v magnitude, making the planet readily visible in binoculars as a bright star. When approaching its near yearly conjunction with the Sun, the brightness may drop to about 9.5 magnitude.
In 2004, from the same observation made by Hubble to measure Ceres’ diameter, was discovered a very bright white spot on the surface. This spot was likely caused by a cometary collision sometime in the past, whose signature appears to conclude that it is made mainly of frozen water ice. (See Ceres Image above). It is this bright surface feature that causes small fluctuations in light, whose variability was first found by Johann Schröter in 1811. This has lead to the observed rotational period of 09 hours 4.5 minutes (0.3781 dy) and poles being tilted by 29.6o.
During mid-August 2006, a sub-committee of the International Astronomical Union (IAU) proposed Ceres be promoted to planet status, decided under new definitions for planets - being massive enough to remain spherical. Ceres in this case is the only known body in the inner asteroid belt that is even close to spherical by its gravity. Had this been adopted both Pluto’s moon Charon and UB 313 (aka Xena) would have been promoted to fully-fledged planets, making twelve (12) planets in our Solar System. This idea however only lasted until 24th August 2006 when the vote was taken in the 26th I.A.U. Conference in Prague, and the idea was rejected.
Instead an additional criteria for planet status was required, that is; Presently, the IAU has classified Ceres as a dwarf planet - though there is an uneasy disquiet among some of the IAU Commission delegates aboout changing this.
Ceres, in the Roman mythology, is the daughter from the union of Saturn and Rhea, and is also the wife and sister of Jupiter. Ceres’ mythological name is the Greek goddess Demeter, whose convoluted origin comes from the ancient celebrated Sicilian, and later the Roman, goddess of the harvest and grain. She is ritually worshipped for the increasing needs of food supply and towards the labourers in the fields who careful tended to the crops. One of Ceres significant roles in the Roman mythology was with the important relationship of Ceres and her young daughter Proserpina - Queen of the Underworld, whose equivalent story is aligned with the Greek goddess Persephone - the celebrated ancient goddess of Spring. This ancient story goes something like;
This popular story has real symbolic meaning regarding the growing of the annual crops - something that was increasingly important at the time to the large growing city population of Rome and surrounding its regions. In later times, the Romans became inordinately dependant on cereal and grain production, especially as most of the grain crops at first came from Sicily. By the 2nd and 1st Centuries B.C. this soon extended with with the importation of grain from Spain and even North Africa. If it were not for these distant regions, Rome would have not been able to support its large population.
Ceres honour for this reason became mainly worshipped by mainly the plebeians, either once every four years, or later annually. Here secret rituals by her followers occurred during the spring festival known as the Cerialia. Both the Romans and Sicilians vigourously venerated her in the hope of continuing bountiful crops and to avoid any possible crop failures during times of severe drought or hardship. Her worship is believed to have reached its pinnacle around 496 BC.
Ceres, by some, is astronomically represented in the sky as the outline of the zodiacal constellation of Virgo, the virgin. Some have also attributed Virgo to the goddess Astraea - the 5th discovered minor planet. Her name is synonymous to the Greek goddess, Demeter.
Ceres is mentioned in the Roman “The Satyricon” by Petronius Arbiter: Chp. 106
Several observers in the 18th Century were first to note of the relationship between the planets and the mean planetary distances, even before “Bode Law” was posulated. Even Johannes Kepler (1571-1630) in 1596 “Misterium Comographicum” had noted the inordinately large gap between Mars and Jupiter, but this was merely commented. The first was the Oxford Professor David Gregory (1659-1708) in his work “Astronomae elementa” (1702), followed by the German popularist Christian Freiherr von Wolff in 1741. This latter claim was examined by Johann Daniel Titus (1729-96), who was first to notice the planetary “gap” missing in the orbital relationships. This was first published in “Comptemplation de la nature” in 1766. Here Titus modified Gregory”s relationship (now known as Bode’s Law) to produce the famous relationship;
Here each more distant planet, has added the geometrically increasing numbers of 0, 3, 6, 12, 24, 48, 96, etc., to the value of 4, and always only doubling the last numbers. From this sequence produces the known planetary distances, which are convert to astronomical units (A.U.) by dividing by ten. When appling this rule, the succession of values follow Table 1.
******************************* Planet A.U. Calculation ******************************* Mercury 0.4 4+ 0 = 4 Venus 0.7 4+ 3 = 7 Earth 1.0 4+ 6 = 10 Mars 1.5 4+ 12 = 16 ?? ??? 4+ 24 = 28 Jupiter 5.2 4+ 48 = 52 Saturn 9.5 4+ 96 = 100 Uranus 19.2 4+192 = 196 Neptune 29.9 4+384 = 388 *******************************
Clearly the Earth and all then five known planets conveniently fitted this rule, except of course between Mars and Jupiter. After William Herschel discovery of Uranus in 1781, the planetary position automatically fitted so-called Bode’s Law, then the only irresistible conclusion that could be deduced was that there was probably another planet between Mars and Jupiter.
Towards this particular relationship, the missing gap was again further extended in 1772 by the investigations of Johann Elert Bode (1747-1826), who wanted to respond to Gregory’s “nonsense” proposal that the missing object might be just a moon of Mars. In 1776, Bode’s strong objection soon convinced him that another planet existing between the orbits of Mars and Jupiter that also drove him to further speculations into other possible trans-Uranian planets. [By the time of Neptune’s discovery in 1847, the sequence became questioned as the distances did not correspond to the law. Some interpreted this as being evidence of a planetary body beyond Neptune in the depths of the Solar System]
This curious equation came very popular in both the astronomical community and among the general public., as it was believed to have some real cosmic significance. The eventual formation of these “Celestial Police” became the positive reinforcement for some serious search of these missing planetary bodies. von Zack immediately attempted to predicted various theoretical orbits in 1785, then beginning some rudimentary searches during 1787 - without any success. By 1799, von Zack had requested the meeting of some of his prominent German colleagues that soon lead to the formation of the “Celestial police“ Society. At the very first formal meeting, this small observational group began organising its systematic search programme along the ecliptic by hoping to stumble upon this new undiscovered planet.
By September 1799, now only four months prior to Ceres’ discovery, there was a Society meeting at the observatory of the famed German visual observer, Johann Schröter’s. They had already realised that the search looking for these planets was mammoth undertaking, so they decided to align more recruits to help with their searching tasks. One of these observers they desired was Piazzi Giuseppe, who was the head astronomer of the Sicilian Palermo Observatory. They directly considered his nomination as important especially because of the much better observing conditions in Sicily. Piazzi was also the natural choice for this project as he was doing regular observations in the production of an extensive new star catalogue. Within days a letter was dispatched.
It must have been bitterly disappointing to all that this introductory letter about their group had still been in transit to Piazzi at the time of discovery. Although ‘losing their prize’ to someone ouside the group was upsetting, there was still much work to do. Although Ceres had been found on the 1st January 1801, it was soon became clear that it would soon be lost in the solar glare of the subsequent conjunction. At first Piazzi thought the new celestial body was merely some comet, but be the next night he observed that the star had moved and showed no indication of a tail. The timing of the discovery proved hard to ascertain it common motion, especially as the curved arc of its motion happened to coincide near the end of the observed retrograde motion of January 13. Piazzi observed Ceres again on the 11th January, but was unable to do further observations after this date because he become sick and bedridden. His uncertainty soon continued to diminished as Ceres closed on the Sun - but realised the new body’s movement against the background sky seemed far too slow for any comet. Yet without enough supporting observations computation of the orbit was not possible; and so Ceres disappeared in the sun’s rays without knowing where it would appear in the morning sky to be recovered.
Within three months, the new minor planet was again found by one of ‘The Police’. It was rediscovered based only on the seemingly intuitive orbital calculations of the mathematician and astronomer, Karl Gauss (1777-1855). Gauss had amazingly and accurately predicted Ceres’ new position to the extent that it was within the general field of any medium powered eyepiece. He was also first to calculated the orbit of Ceres, doing all the positional reductions himself. Now Ceres could always confidently be followed and recovered after its next and subsequent conjunctions with the Sun.
The reality of their presumed single ‘missing planet’ was soon to posing too many unanswered questions - Ceres seemed much too faint and too small. At the same time, Sir William Herschel also stated that Ceres diameter was merely “ ...at under 100miles” ( >161km), whose conclusion was based on the body always appearing star-like even using high magnifications. This small estimated size was soon confirmed using both orbital calculations and by the apparent magnitude of the minor planet. In fact, Ceres diameter was not really determined or approximated until the 20th Century. In 1994 this diameter was determined from ground radar as 930km, which was only improved in 2004 by the Hubble Space Telescope (HST) as 975x905 km.
After about 1803 AD, this general view had been totally accepted by them - Ceres was simply not big enough to be “planet-sized”. Herschel’s diameter was no better than a poor approximation, but amazingly, this value for the diameter wasn’t really questioned and never changed for many decades.
To solve this apparent dilemma of the missing planetary mass, Heinrich Wilhelm Matthäus Olbers began suggested that Ceres might be among several more of these small bodies. Soon planetary observers were earnestly searching for more of these planetary bodies, soon resulting in the discovery of Juno and Vesta in 1804 and 1807, respectively.
Perhaps the biggest observational evidence for these bodies not being true planets was the discovered by Schröter. In his written letter to Heinrich Olbers, he clearly states that his visual magnitude observations of Ceres and Pallas seemed to show unusually variablity. Here Olbers correctly assumed that; “...these asteroids are irregular rather than round figures.”, Since then, nearly all the other minor planets between Mars and Jupiter has confirm this statement as true. Ceres so far seems to be the only one near to being actually spherical! As stated before in the introduction to this page, the variability in this instance is mainly caused by bright white spot on Ceres’ surface.
********************************************************* 0h UT R.A. Decl. Mag Δ r El. Con DATE (J2000) V A.U. A.U. o ********************************************************* --2005-- 31 Dec 18 34.9 -25 31 8.7 3.858 2.876 002.8 Sgr --2006-- 14 Jan 19 00.0 -25 25 8.9 3.847 2.886 010.5 Sgr 28 Jan 19 24.6 -25 07 9.1 3.808 2.895 019.1 Sgr 11 Feb 19 48.6 -24 39 9.2 3.740 2.904 027.8 Sgr 25 Feb 20 11.7 -24 03 9.2 3.646 2.912 036.6 Cap 11 Mar 20 33.6 -23 22 9.2 3.528 2.920 045.6 Cap 25 Mar 20 54.2 -22 39 9.2 3.389 2.928 054.7 Cap 08 Apr 21 13.2 -22 00 9.2 3.231 2.935 064.1 Cap 22 Apr 21 30.3 -21 27 9.1 3.059 2.942 073.8 Cap 06 May 21 45.1 -21 06 9.0 2.878 2.948 084.0 Cap 20 May 21 57.2 -21 02 8.9 2.694 2.954 094.7 Cap 03 Jun 22 06.2 -21 20 8.7 2.513 2.959 106.1 Aqr 17 Jun 22 11.3 -22 02 8.5 2.345 2.964 118.3 Aqr 01 Jul 22 12.1 -23 10 8.3 2.197 2.969 131.4 Aqr 15 Jul 22 08.3 -24 39 8.0 2.081 2.973 145.1 Aqr 29 Jul 22 00.1 -26 18 7.8 2.008 2.976 158.5 PsA 12 Aug 21 48.7 -27 50 7.6 1.985 2.979 166.2 PsA 26 Aug 21 36.5 -28 57 7.8 2.016 2.982 159.1 PsA 09 Sep 21 26.0 -29 30 8.0 2.097 2.984 145.8 Mic 23 Sep 21 19.2 -29 28 8.3 2.221 2.985 131.8 Mic 07 Oct 21 17.1 -28 55 8.5 2.378 2.986 118.5 Mic 21 Oct 21 19.8 -28 00 8.8 2.557 2.987 105.9 Mic 04 Nov 21 26.8 -26 45 8.9 2.747 2.986 094.1 Cap 18 Nov 21 37.4 -25 16 9.1 2.941 2.986 083.0 PsA 02 Dec 21 50.7 -23 36 9.2 3.130 2.985 072.4 Cap 16 Dec 22 06.1 -21 46 9.3 3.309 2.983 062.4 Aqr 30 Dec 22 23.1 -19 48 9.3 3.472 2.981 052.7 Aqr *********************************************************
Ceres is well placed for southern observers during 2006. This dwarf planet for the first half of the year is placed in the southern portions of Sagittarius, Capricornus and Aquarius, as a morning object, before reaching opposition on 12 August. The current 2006 apparition is unfavourable, where the brightness will only reach 7.6 magnitude, but at least will be readily visible in binoculars. Only during the oppositions of September 2011, January 2008 and August 2020 will Ceres again be this faint. Ie. 7.7, 8.8 and 7.7, respectively. The 2006 opposition distance will be about 1.98 AU. or 297 million kilometres.
After the beginning of August, as a evening object, where Ceres will move into the northern portion of Piscis Austrinus and then into northern Microscopium - staying there until November. During late September this now classified dwarf planet reaches its most southerly declination of -29o 31′, which will not occur this far south again until early 2015. After the opposition of the 12 August, the magnitude slowly drops, decreasing to 9.3 mag. by years end, where it will be placed in the western sky just after sunset within the constellation of eastern Aquarius.
************************ Opposition Conjunction ************************ 12 Aug 2006 22 Mar 2007 09 Nov 2007 28 Jun 2008 24 Feb 2009 31 Oct 2009 18 Jun 2010 30 Jan 2011 16 Sep 2011 26 Apr 2012 17 Dec 2012 17 Aug 2013 15 Apr 2014 10 Dec 2014 25 Jul 2015 03 Mar 2016 20 Oct 2016 05 Jun 2017 31 Jan 2018 07 Oct 2018 29 May 2019 14 Jan 2020 28 Aug 2020 07 Apr 2021 *************************
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