Pluto

Pluto is the largest known dwarf planet in the Kuiper Belt, orbiting the Sun at an average distance of 39.5 AU. With a diameter of 2,376 km — about two-thirds the size of Earth's Moon — Pluto is a small, icy world composed of roughly 70% rock and 30% water ice, with a surface covered in nitrogen, methane, and carbon monoxide ices. Its most striking surface feature is Tombaugh Regio (informally 'the Heart'), a vast heart-shaped plain of nitrogen ice roughly 1,000 km across. Pluto has five known moons, the largest being Charon (1,212 km diameter), which is so large relative to Pluto that the two are sometimes considered a binary system — they orbit a common center of gravity that lies between them in space.

At magnitude 14.0, Pluto is a challenging but achievable target for experienced amateur astronomers. You need at least a 10-inch telescope under dark skies, a detailed star chart, and patience — Pluto appears as nothing more than a faint star indistinguishable from its surroundings. The key technique is to sketch or photograph the field on two or more nights and look for the one 'star' that has moved. A go-to telescope with accurate pointing helps enormously. CCD imaging makes the task much easier than visual observation. Pluto currently moves through the rich star fields of Sagittarius, which makes identification more difficult due to the dense stellar background. Even in the largest amateur telescopes, Pluto shows no disk — only its motion reveals its planetary nature.

Pluto was discovered by Clyde Tombaugh at Lowell Observatory on February 18, 1930, after a systematic photographic search motivated by Percival Lowell's prediction of a 'Planet X.' It was considered the ninth planet for 76 years until the International Astronomical Union reclassified it as a dwarf planet in 2006, following the discovery of similar-sized Kuiper Belt objects like Eris. NASA's New Horizons spacecraft flew past Pluto on July 14, 2015, returning stunning images that revealed a geologically complex and surprisingly active world — nitrogen glaciers, mountains of water ice, and a thin but dynamic atmosphere.