  Macroscopic dark matter is almost unconstrained over a wide "asteroid-like"
mass range, where it could scatter on baryonic matter with geometric cross
section. We show that when such an object travels through a star, it produces
shock waves which reach the stellar surface, leading to a distinctive transient
optical, UV and X-ray emission. This signature can be searched for on a variety
of stellar types and locations. In a dense globular cluster, such events occur
far more often than flare backgrounds, and an existing UV telescope could probe
orders of magnitude in dark matter mass in one week of dedicated observation.
