Pluto

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.

J2000 Equatorial Sky Chart & Culmination Altitude

The chart below plots Pluto (134340 Pluto) — Kuiper Belt Dwarf Planet at RA 20h 15m 00.00s, Dec -22° 30′ 00.0″ within Sagittarius, 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

Discovered on February 18, 1930, by 24-year-old Clyde Tombaugh at Lowell Observatory using a blink comparator to inspect photographic plates of Gemini, Pluto was classified as the ninth planet for 76 years before becoming the prototype of trans-Neptunian dwarf planets in 2006. Its inclined (17.16°), eccentric (e = 0.2488) orbit carries it from 29.66 astronomical units inside Neptune's distance at perihelion out to 49.31 astronomical units at aphelion every 247.94 years, protected from close encounters with Neptune by a stable 3:2 mean-motion resonance.

When NASA's New Horizons spacecraft swept 12,500 kilometers above Pluto in July 2015, it revealed an unexpectedly dynamic world measuring 2,376.6 kilometers in diameter.Dominating the anti-Charon hemisphere is Tombaugh Regio, whose western lobe—Sputnik Planitia—is a 1,000-kilometer-wide basin filled with convecting polygonal cells of solid nitrogen, carbon monoxide, and methane ices that resurface on timescales of under a million years. Flanking the nitrogen plains are rugged 4-kilometer-high mountain ranges of bedrock water ice (such as Tenzing and Hillary Montes), reddish tholin-draped plains, and layered nitrogen-methane atmospheric hazes.

Pluto's largest moon, Charon (diameter 1,212 kilometers), has more than half of Pluto's diameter and 12.2 percent of its mass, placing their mutual barycenter outside Pluto's surface in open space as they revolve synchronously every 6.387 days. Four tiny outer moons—Styx, Nix, Kerberos, and Hydra—circle the central binary in nearly coplanar, resonant orbits.

Practical Visual Observing Guide

• At visual magnitude V ~ 14.4 in eastern Sagittarius/western Capricornus, Pluto requires at least a 10-inch to 12-inch telescope visually under dark skies.
• Best confirmed by sketching or imaging a rich star field on two consecutive nights to watch the 14th-magnitude point of light shift by ~1 arcminute per day.
• Its 0.1-arcsecond angular diameter is indistinguishable from a star in amateur telescopes.

Catalog Cross-Identifications & Aliases

Common Aliases: 134340 Pluto · Pluto-Charon Binary · Hades

Related Objects, Comparisons & Guides

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