Geminga

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 Geminga (PSR J0633+1746) — Gamma-Ray Pulsar at RA 06h 33m 54.15s, Dec +17° 46′ 12.9″ within Gemini, 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

First detected in 1972 by NASA's SAS-2 satellite and mapped by Europe's COS-B mission as the second-brightest high-energy gamma-ray source in the sky, Geminga baffled astronomers for two decades because no radio or bright optical counterpart existed at its position in Gemini. Italian astrophysicist Giovanni Bignami coined the name 'Geminga' both as an acronym for 'Gemini gamma-ray source' and as a play on the Milanese dialect phrase gh'è minga ('it's not there'). Only in 1992 did ROSAT X-ray observations and EGRET gamma-ray timing uncover its 237.1-millisecond rotation period, proving it is an isolated neutron star.

Geminga serves as the prototype of radio-quiet gamma-ray pulsars: its narrow polar radio beam sweeps past Earth without intersecting our line of sight, whereas its fan-like outer-magnetosphere gamma-ray beam washes across us with every 0.237-second rotation. Ground-based Cherenkov arrays such as HAWC and Milagro also discovered an extended multi-degree halo of multi-TeV gamma rays around Geminga, produced as relativistic positrons and electrons escaping the pulsar scatter cosmic microwave background photons—providing a potential local source for the positron excess measured near Earth.

With a characteristic spin-down age of 342,000 years and a distance of roughly 815 light-years, Geminga's progenitor supernova exploded inside the solar neighborhood during the Pleistocene epoch, likely helping reheated and inflate the low-density Local Bubble surrounding the Sun. As the neutron star plows supersonically through the interstellar medium at ~200 kilometers per second, Chandra X-ray images trace three comet-like bow-shock tails stretching behind it.

Practical Visual Observing Guide

• Completely invisible to optical amateur telescopes (V = 25.5) and nearly silent at standard radio frequencies.
• Exhibits a large proper motion of ~170 mas/yr across northern Gemini as a result of its proximity and supernova kick velocity.
• Ranks alongside the Vela and Crab pulsars among the brightest persistent GeV gamma-ray objects in the sky.

Catalog Cross-Identifications & Aliases

Common Aliases: PSR J0633+1746 · 2CG 195+04 · 1E 0630+178

Related Objects, Comparisons & Guides

Scientific Sources & Dataset Provenance

• SIMBAD Astronomical Database (CDS) (2026-10 release): Wenger, M., et al. 2000, A&AS, 143, 9 (The SIMBAD astronomical database) — Centre de Données astronomiques de Strasbourg