Ceres
Reference data for dwarf planet 1 Ceres: 4.60-year orbit at 2.77 AU, 939.4 km diameter from Dawn, Occator crater salt deposits, and visual magnitude.
Provenance-Backed Scientific Measurements
Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.
| Parameter | Value | Uncertainty | Method & Epoch | Quality Status | Source Archive |
|---|---|---|---|---|---|
| Opposition Magnitude (V) | 7.4 mag | ± 0.65 mag | Brightens to V = 6.64 at perihelic opposition and fades to ~9.3 at conjunction. | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Sidereal Orbital Period | 1680.5 d | ± 0.1 d | Equivalent to 4.601 Julian years. | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Semi-Major Axis | 2.7675 AU | ± 0.0001 AU | JPL Horizons DE440/441 planetary and satellite ephemeris solution | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Orbital Eccentricity | 0.0758 dimensionless | ± 0.0001 dimensionless | JPL Horizons DE440/441 planetary and satellite ephemeris solution | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Mean Volumetric Radius | 0.0736 R⊕ | ± 0.0001 R⊕ | Dawn orbiter mean radius of 469.7 ± 0.2 km (diameter 939.4 km). | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Mass | 0.000157 M⊕ | ± 0.000001 M⊕ | 9.3835 × 10²⁰ kg, representing roughly 31% of the total mass of the main asteroid belt. | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Ceres (1 Ceres) — Main-Belt Dwarf Planet Data at RA 13h 25m 00.00s, Dec +02° 15′ 00.0″ within Virgo, alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.
Astrophysical Context & Structure
Spotted on the night of January 1, 1801, by Sicilian astronomer Giuseppe Piazzi from Palermo Observatory at the exact orbital gap between Mars and Jupiter predicted by the Titius-Bode relation, Ceres was initially hailed as a missing planet, later designated asteroid 1 Ceres, and classified as a dwarf planet alongside Pluto and Eris in 2006. Spanning 939.4 kilometers in mean diameter and orbiting at 2.768 astronomical units every 4.60 years, it contains nearly one-third of the entire mass of the main asteroid belt and is the only main-belt body large enough to have relaxed into a nearly spherical hydrostatic ellipsoid.
When NASA's Dawn spacecraft orbited Ceres from 2015 to 2018, gravity and spectroscopic measurements revealed a low bulk density of 2.162 grams per cubic centimeter and a dark surface rich in ammoniated phyllosilicates (clays) and carbonates—implying that Ceres accreted in the volatile-rich outer Solar System or preserved an ancient subsurface ocean. Inside the 92-kilometer Occator Crater, Dawn resolved dazzlingly bright patches (Cerealia and Vinalia Faculae) composed of sodium carbonate and ammonium chloride salts left behind by recent cryovolcanic brine percolation from deep underground reservoirs, along with Ahuna Mons, a 4-kilometer-high cryovolcanic dome.
Despite a low geometric albedo of 0.09, Ceres's large cross-section brings it to visual magnitude 6.6–7.5 at opposition, making it an easy binocular target as it loops through the zodiac.
Practical Visual Observing Guide
- Reaches magnitude V = 6.64 at favorable perihelic oppositions—just bright enough to be glimpsed with the naked eye under pristine dark skies and easy in 7x50 binoculars.
- Subtends an angular diameter up to 0.84 arcseconds at close opposition, resolvable as a tiny non-stellar disk in 14-inch+ telescopes under superb seeing.
- Rotates once every 9.074 hours with a tiny light-curve amplitude of ~0.04 magnitudes.
Catalog Cross-Identifications & Aliases
Common Aliases: 1 Ceres · A801 AA
| Catalog Authority | Identifier |
|---|---|
| SIMBAD | Ceres |
Related Objects, Comparisons & Guides
Vesta (4 Vesta) — Brightest Asteroid Profile
Reference data for protoplanet 4 Vesta: V = 5.1 naked-eye opposition brightness, 525 km diameter, Rheasilvia impact basin, and HED meteorites.
Pluto (134340 Pluto) — Kuiper Belt Dwarf Planet
Reference data for Pluto: 247.9-year resonant orbit, 2,376.6 km diameter from New Horizons, Charon binary dynamics, and nitrogen glaciers.
Jupiter (Gas Giant & Galilean Moons)
JPL orbital parameters (5.2038 AU, 11.862 yr), opposition magnitude −2.94, 50.1″ angular disk, Galilean moons, and observing guide for Jupiter.
Apparent vs Absolute Magnitude Explained
Understand the logarithmic Pogson astronomical magnitude scale, apparent visual magnitude (m), absolute magnitude (M at 10 parsecs), and bolometric corrections.
Angular Size, Separation & Field of View
How angular diameter (degrees, arcminutes, arcseconds), spherical angular separation, and small-angle physical diameter relate to telescope field of view.
Scientific Sources & Dataset Provenance
- NASA/JPL Solar System Dynamics & Planetary Fact Sheets (DE441 (2021/2026)): Park, R. S., et al. 2021, AJ, 161, 105 (The JPL Planetary and Lunar Ephemerides DE440 and DE441) — NASA Jet Propulsion Laboratory / GSFC