Arp-Madore 1

Arp-Madore 1 (also known as AM 1) is a globular cluster visible in the constellation Horologium, located 123.3 kpc away from Earth. It is one of the most distant known globular clusters of the Milky Way galaxy's halo; its distance gives it interest as a test case for gravitational theories. AM 1 has a visual magnitude of 15.07.

It is named after Halton Arp and Barry F. Madore, who identified it as a distant globular cluster in 1979, using the UK Schmidt Telescope, after previous researchers at the European Southern Observatory had observed its existence but not its classification.