Messier 19

Lore & Background

Messier 19 was discovered by Charles Messier on June 5, 1764 and added to his catalogue of comet-like objects that same year. It was resolved into individual stars by William Herschel in 1784. His son, John Herschel, described it as 'a superb cluster resolvable into countless stars'. The cluster is located 4.5° WSW of Theta Ophiuchi and is just visible as a fuzzy point of light using 50 mm binoculars. Using a telescope with a 25.4 cm aperture, the cluster shows an oval appearance with a 3′ × 4′ core and a 5′ × 7′ halo.

M19 is one of the most oblate of the known globular clusters. This flattening may not accurately reflect the physical shape of the cluster because the emitted light is being strongly absorbed along the eastern edge, the result of extinction caused by intervening gas and dust. When viewed in the infrared, the cluster shows almost no flattening. It lies at a distance of about 28.7 kly from the Solar System, and is quite near to the Galactic Center at only about 6.5 kly away.

This cluster contains an estimated 1,100,000 times the mass of the Sun and is around 11.9 billion years old. The stellar population includes four Cepheids and RV Tauri variables, plus at least one RR Lyrae variable for which a period is known. Observations made during the ROSAT mission failed to reveal any low-intensity X-ray sources.

Reader's Guide

Messier 19 holds significance as one of the most oblate globular clusters known, though its apparent flattening may be an artifact of extinction by gas and dust along its eastern edge, as infrared observations show almost no flattening. Discovered by Charles Messier in 1764 and later resolved by William Herschel, it was described by John Herschel as a superb cluster resolvable into countless stars. Its proximity to the Galactic Center—only about 6.5 kly away—makes it a valuable object for studying the effects of the Galactic environment on globular clusters. The cluster's age of 11.9 billion years and mass of 1.1 million solar masses place it among the older, massive clusters. Its stellar population includes Cepheids, RV Tauri variables, and at least one RR Lyrae variable, providing insights into variable star evolution. The lack of low-intensity X-ray sources detected by ROSAT adds to its observational profile. For amateur observers, it is visible as a fuzzy point in 50 mm binoculars and shows an oval core and halo in a 25.4 cm telescope.

Did You Know?

• It is one of the most oblate known globular clusters, but infrared views show almost no flattening.
• The cluster lies only about 6.5 kly from the Galactic Center.