Interstellar Comet 3I/ATLAS — Spring 2026 Visibility

What this countdown tracks

The clock counts down to the spring 2026 visibility window for interstellar comet 3I/ATLAS (designation C/2025 N1) — only the third confirmed interstellar object ever observed in our Solar System, after 1I/'Oumuamua (2017) and 2I/Borisov (2019). The comet reached perihelion on October 30, 2025 and remains observable through the northern-hemisphere spring of 2026.

About this celestial event

3I/ATLAS was discovered on July 1, 2025 by the ATLAS (Asteroid Terrestrial-impact Last Alert System) survey from telescopes in Hawaii and Chile. Within weeks its hyperbolic orbit — far in excess of the escape velocity from the Solar System — made clear that the comet originated outside our system. The "3I" designation marks it as the third interstellar object on record; the "C/2025 N1" designation reflects its discovery date.

3I/ATLAS is significantly larger and more chemically active than its predecessors. 1I/'Oumuamua (2017) was a small, asteroidal-looking object that showed no visible cometary coma; 2I/Borisov (2019) was clearly cometary but only briefly bright. 3I/ATLAS has a clearly visible coma and a developing tail, and at peak brightness is expected to reach magnitude 12–13 — within reach of any 8-inch amateur telescope from a dark site.

The comet's hyperbolic orbit means it makes only one pass through the Solar System: it came in from the Sagittarius region, looped around the Sun in October–November 2025, and is now heading out toward Cassiopeia and beyond. Once it leaves the Solar System in the late 2020s it will not return.

Best viewing

Following October 30, 2025 perihelion, 3I/ATLAS slowly fades but remains observable through northern-hemisphere spring 2026. The comet's morning-sky position favours pre-dawn observation — visible low in the east before astronomical twilight — through January, February and March 2026, with observability shifting to the evening sky from April onward as Earth's geometry changes. By June 2026 the comet will be too faint for amateur telescopes.

Best observation requires a 6- to 8-inch (150–200 mm) amateur telescope from a dark site, ideally Bortle 4 or better. The comet will appear as a small, fuzzy patch with a slight tail; binoculars (15×70 or larger) may show it from the darkest sites at peak brightness. Astrophotographers with tracking mounts and a 200 mm or longer lens can produce the best images.

The comet's chemistry is being studied intensively because interstellar objects offer the only direct samples of material from other planetary systems. Spectroscopic observations have already detected water and CO2 production, with some unusual spectral features that distinguish 3I/ATLAS from typical Solar-System comets.

Past interstellar visitors

• 2I/Borisov (C/2019 Q4) — discovered August 2019, perihelion December 2019; first clearly cometary interstellar object
• 1I/'Oumuamua (1I/2017 U1) — discovered October 2017; small (100 m), elongated, no coma; subject of intense ongoing scientific debate
• Several pre-discovery candidates have been proposed for older interstellar visits but none confirmed

How to observe

The Minor Planet Center publishes orbital elements and ephemerides; NASA JPL HORIZONS provides high-precision positions. Stellarium, SkySafari and Cartes du Ciel show the comet's position in real time. Live observations are coordinated through the Comet Observation Database (COBS) and the British Astronomical Association's Comet Section. The Virtual Telescope Project, Subaru Telescope, ESO and major university observatories run scheduled imaging campaigns.

Related countdowns

3I/ATLAS is the headline comet event of the spring 2026 sky alongside Lyrid meteor shower 2026, Eta Aquariid meteor shower 2026 and March equinox 2026. The NASA Roman Space Telescope launch 2026 is the other major space-science event of 2026.

FAQ

What is 3I/ATLAS? The third confirmed interstellar object ever observed in our Solar System; discovered July 1, 2025 by the ATLAS survey. When can I see it? Through northern-hemisphere spring 2026 (January–April), in the pre-dawn sky in the east, fading after May. What equipment do I need? A 6- to 8-inch amateur telescope under dark skies; binoculars from the darkest sites at peak. Where did it come from? Its hyperbolic orbit traces back to the Sagittarius direction; its parent star system is unidentified.