The existence of heavy compact objects has been suggested many times throughout the years. In terms of sizes, they would belong to the realms of nuclear or atomic physics, but in terms of masses could extend to the macroscopic world, reaching kilograms, tones or more. The most notable candidates are nuclearites - hypothetical lumps of strange quark matter, Q-Balls, magnetic monopoles or primordial black holes. These objects may have originated in the early universe or could be produced by some stellar phenomena. Especially in the first case, they could be a component of dark matter.

If they exist, it is likely that they reach our planet at high speeds and cross the atmosphere, leaving behind a trail of light in the air. We present results of a search for such objects in visual photographs of the sky taken by the ``Pi of the Sky'' experiment, exemplified with the most stringent limits on the flux of incoming nuclearites of the masses spanning between 100 g and 100 kg.