Dwarf Planet 1 Ceres will reach opposition (the point at which it is directly opposite the Sun when observed from the Earth) at 5.37 pm GMT on Tuesday 21 March 2023, when it will also be at the closest point on its orbit to the Earth, 1.60 AU (i.e. 1.6 times as far from the Earth as the Sun, or about 239 207 000 km), and be completely illuminated by the Sun. While it is not obvious to the naked eye observer, asteroids have phases just like those of the Moon; being further from the Sun than the Earth, 1 Ceres is 'full' when directly opposite the Sun. As 1 Ceres is only about 939.4 km in diameter, it will not be visible to the naked eye, but with a maximum Apparent Magnitude (luminosity) of 6.9 at opposition, it should be visible in the Constellation of Coma Berenices to viewers equipped with a good pair of binoculars or small telescope, with the best visibility being at about 1.20 am local time from anywhere on Earth.
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Because Ceres is further from the Sun than the Earth, its orbital period is much longer than ours, with the Dwarf Planet completing one obit every 1683 days (4.65 years), on an eccentric orbit tilted at 10.6° to the plane of the Solar System. The orbit of Ceres places it within the inner part of the Main Asteroid Belt, but due to its large size, with a diameter of 939.4 km, it is considered to be a Dwarf Planet rather than an asteroid.
Ceres was discovered on 1 January 1801 by Giuseppe Piazzi, a Catholic priest at the Academy of Palermo, Sicily. It was the first body to be discovered in the Main Asteroid Belt, and at the time when it was discovered an international search was underway for a presumed 'missing planet' between the orbits of Mars and Jupiter (although Piazzi was studying stars when he first observed Ceres, and initially presumed he had found a new comet). Ceres was for a long time considered to be the largest asteroid in the Solar System, but in 2006 was re-classified as a Dwarf Planet, as part of a revision of the classification of Solar System bodies driven by the discovery of a growing number of bodies in the Outer Solar System which are too large to be considered asteroids or comets yet to small to be considered to be planets. Of the nine bodies currently classified as Dwarf Planets, only Ceres is located within the Main Asteroid Belt, with five lying in the Kuiper Belt (Orcus, Pluto, Haumea, Quaoar, and Makemake), two lie within the Scattered Disk (Gonggong and Eris), and one within the Detached Region on the outer fringe of the Solar System (Sedna).
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