Barnard's star

Barnard's Star is the second-closest stellar system to the Sun (after Alpha Centauri) and the closest single star, a red M4 V dwarf 5.96 light-years away in Ophiuchus, magnitude 9.6. Despite its proximity it is far too faint for naked-eye view. Its claim to fame is the largest proper motion of any known star — 10.36 arcseconds per year, equivalent to one full Moon diameter every 180 years.

Easy in any telescope of 80mm or more from a dark site. Use a finder chart from the AAVSO or a good atlas centred on RA 17h 57m 48s, Dec +04° 41′ — Barnard's Star sits in a sparse field between Beta and Mu Ophiuchi. Sketch its position against background stars, then observe again a year later: the star will have moved noticeably, by more than three arcseconds. Few amateur observations bring the dynamism of stellar motion home as vividly.

E. E. Barnard discovered the high proper motion in 1916 from photographic plates taken at Yerkes Observatory, instantly recognising it as a record-breaker. Peter van de Kamp of Sproul Observatory claimed in the 1960s to have detected one or two unseen Jupiter-mass planets via tiny astrometric perturbations, but the result was a famous case of systematic plate-measurement error. A real super-Earth candidate, Barnard b (3.2 Earth masses, 233-day orbit), was announced in 2018 from radial-velocity work, then largely retracted after re-analysis in 2021. As of 2024 a sub-Earth-mass planet on a 3-day orbit has been confirmed by ESPRESSO.