Palomar 15

Lore & Background

Palomar 15 is one of the 15 Palomar globular clusters, all discovered in the 1950s on the survey plates of the first Palomar Observatory Sky Survey (POSS). These clusters were discovered late because they are very faint, heavily obscured, remotely located, or have few member stars. The 48-inch Schmidt camera at Palomar was used to find them.

Among the Palomar globulars, Palomar 15 is regarded as the most difficult to observe. Visual observation of Palomar globulars generally requires dark skies, excellent seeing conditions, and high power (at least 200 power magnification). Many Palomars are small objects requiring precise sky navigation and averted vision. Some Palomar globulars are small and compact, while others are very sparse and hard to distinguish from foreground stars.

Reader's Guide

Palomar 15 is notable as the most challenging Palomar globular cluster for visual observers. The article states that overall, there is great variability in the level of difficulty to observe these objects, and Palomar 15 is explicitly identified as the most difficult. Successful observation of any Palomar globular requires skies with no light-pollution, excellent seeing conditions, and high power (at least 200 power magnification). Many Palomars are small objects and require the observer to know how to navigate the sky precisely, relying on averted vision when needed. In some Palomars, visual observers can resolve individual stars, while others look hazy. The Palomar globulars were discovered fairly late due to being very faint, heavily obscured, remotely located, or having few member stars. They were discovered only with the enormous 48-inch Schmidt camera at Palomar. Some of the astronomers who identified these objects as globular clusters include George Abell, Fritz Zwicky, Edwin Hubble, Halton Arp, and Walter Baade.

Did You Know?

• Palomar 15 is one of 15 Palomar globular clusters.
• All Palomar globulars except Palomar 7 and Palomar 9 had never been seen before their discovery on POSS plates.