The third confirmed interstellar comet, **3I/ATLAS** (discovered by the ATLAS telescope in Chile on July 1, 2025), will make its closest approach to Earth tomorrow, **December 19**, at a distance of approximately **1.8 AU** (270 million km / 168 million miles)—a safe distance and no threat.
This rare guest from outside our solar system will be gone forever after passing Jupiter in March 2026, on a hyperbolic path.
Mysterious anti-tail feature
Images from Hubble (July and November 2025) and ground-based telescopes show a persistent **anti-tail**—a sun-pointing dust structure that defies the rules of normal comet physics (tails usually point away from the sun). Recent observations (mid-December) suggest that it extends **500,000 km**, perhaps due to large debris or a unique structure. Hypotheses include light scattering by ice cubes or the effects of delayed radiation pressure; Research is ongoing.
how to see
It is faint (magnitude ~12-13), not visible to the naked eye. It will be best seen before dawn in the eastern sky, below **Regulus** in the constellation Leo. Use binoculars or a telescope; Clear, dark skies are essential.
live stream
**The Virtual Telescope Project** is hosting a free online observation from **December 18 at 11 pm EST** (0400 UTC / December 19 at 9:30 am IST), weather permitting. Check it out on their YouTube channel.
This transient interstellar object provides unique information about the formation of distant planets.
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