BOOMERanG experiment (Balloon Observations Of Millimetric Extragalactic Radiation And Geophysics) was an experiment that flew a telescope on a (high-altitude) balloon and measured the cosmic microwave background radiation of a part of the sky during three sub-orbital flights.

By using a telescope which flew at over 42,000 meters high, it was possible to reduce the atmospheric absorption of microwaves to a minimum.

This allowed massive cost reduction compared to a satellite probe, though only a tiny part of the sky could be scanned.

The BOOMERanG team was led by Andrew E. Lange of Caltech and Paolo de Bernardis of the University of Rome La Sapienza.

Only a tiny fraction of the sky can be seen concurrently, so the telescope must rotate to scan the whole field of view.