Palomar Testbed Interferometer

The Palomar Testbed Interferometer was a research facility featuring three small telescopes that worked together to measure stellar details with high precision. The instruments were aligned to capture light from two stars simultaneously, allowing researchers to determine their size, shape, and mass.

The instrument was developed by Caltech and the Jet Propulsion Laboratory, operating at Palomar Observatory from 1995 to 2008. Its creation marked an important advance in interferometry techniques for astronomical observation.

Scientists at the facility produced over 50 academic papers examining stellar masses, diameters, and shapes through advanced interferometric techniques.

The facility was located on the grounds of Palomar Observatory in the hills east of San Diego. Visitors can tour the observatory to learn about its installations and exhibitions, though the interferometer itself is no longer operating.

The interferometer made a striking discovery about the star Altair, revealing that it has a flattened shape at its poles because it spins so rapidly. This observation was one of the breakthroughs that became possible with this technology.