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Why do astronomers take repeated telescope images when searching for near-Earth objects?

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The Chicxulub asteroid — Earth impact hazard An artist's rendering of the impact of a near-Earth object 66 million years ago in what is today the Caribbean region. Many scientists think that the collision of a large asteroid or comet nucleus with Earth triggered the mass extinction of dinosaurs and many other species near the end of the Cretaceous Period.

Astronomers take repeated telescope images of the same region of the sky to identify near-Earth objects (NEOs) by detecting motion. By capturing three or more images over a short period—typically spanning tens of minutes—researchers can compare the frames to spot objects that have shifted position against the background of fixed stars.1

This process is essential because the distance an object travels between these images, combined with its brightness, provides critical clues regarding its size and proximity to Earth; for instance, bright objects that appear to move rapidly are likely very close to our planet. Historically, astronomers have used tools like a blink comparator to view these images in rapid succession, which highlights moving bodies against the static field. While these initial observations help identify potential threats, they are only the first step; astronomers must eventually acquire an "arc" of data over several days to compute an accurate orbit and predict the object's future path.12