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That small dot moving left to right is 3I/ATLAS. It's a comet that was discovered on 1 July 2025. It's travelling at 58 km PER SECOND and isn't gravitationally bound to the Sun. Which means you're looking at a comet that formed around another star, passing through the Solar System.

3I/ATLAS was discovered with the NASA-funded Asteroid Terrestrial-impact Last Alert System (ATLAS) survey telescope in Chile. Its nucleus size is uncertain because of the comet's coma, but is likely substantially smaller than 24 km in diameter.

This video sequence was posted on 2 July 2025 by astrafoxen ‪(astrafoxen.bsky.social‬), and spans 41 minutes. The comet itself is point-like since the telescope tracked its movement; the smears are background stars, and the tiny images are hot pixels.

With RUBIN up and running, I wonder how many more of these we'll detect.