Ceres

Ceres is the largest object in the asteroid belt and the only dwarf planet in the inner solar system, orbiting the Sun at 2.77 AU between Mars and Jupiter. With a diameter of 946 km, it contains roughly one-third of the total mass of the entire asteroid belt. Ceres is composed of a mixture of rock and water ice, with a thin outer crust, a possibly icy mantle, and a rocky core. Its surface is generally dark (albedo 0.09) but features over 300 bright spots — the most famous being the dazzling deposits in Occator Crater, which turned out to be sodium carbonate salts left by briny water that seeped up from a subsurface reservoir and evaporated.

At opposition, Ceres reaches about magnitude 6.7 — just at the limit of naked-eye visibility under perfect conditions, but easily visible in binoculars. It appears as a star-like point; even in large amateur telescopes, its 0.84-arcsecond disk is too small to resolve. Like Pluto, the key to identifying Ceres is its motion — plot its position over several nights using a detailed chart and look for the 'star' that moves. Ceres travels through the zodiacal constellations and reaches opposition roughly every 15.5 months. Its brightness varies between magnitude 6.7 at the best oppositions and about magnitude 9.3 when farthest from Earth. A go-to mount with asteroid tracking makes finding it straightforward.

Ceres was the first asteroid ever discovered, found by Giuseppe Piazzi in Palermo, Sicily on January 1, 1801 — the very first night of the 19th century. Piazzi initially thought it was a comet, but its orbit revealed it as a new class of object orbiting between Mars and Jupiter, fulfilling the prediction of the Titius-Bode law. Ceres was considered a planet for about 50 years before being reclassified as an asteroid as more similar objects were found. In 2006, it was reclassified again as a dwarf planet. NASA's Dawn spacecraft orbited Ceres from 2015 to 2018, mapping its surface in detail and discovering the bright salt deposits in Occator Crater.