Messier 14 Distance Calculated Using RR Lyrae Variable Stars
Astronomers calculate the distance to the globular cluster Messier 14 at roughly 30,000 light-years from Earth using RR Lyrae variable stars, Svábhegyi Csillagvizsgáló reported. Located in the constellation Ophiuchus, the cluster spans about 100 light-years across and contains more than 150,000 stars. Charles Messier originally discovered the celestial object in 1764, logging it as a round, nebulous patch of light because early telescopes could not resolve individual stars within the dense grouping.
Stellar Pulses Reveal Cosmic Distances
Measuring distances within globular clusters relies heavily on RR Lyrae variables, which astronomers often call cluster variables due to their high frequency in these stellar systems. These stars change brightness periodically over intervals lasting from eight hours to roughly one day. Their absolute magnitude—the intrinsic brightness a star would display at a standard distance of 10 parsecs—remains roughly constant regardless of pulsation period. By comparing this absolute brightness against the apparent brightness observed from Earth, researchers calculate the distance to Messier 14.
Julia Balázs investigated the physical mechanisms behind RR Lyrae pulsations, publishing her theoretical work in 1959 using the same telescope visitors now use at the Budapest dome. Modern observations catalog more than 173 variable stars within Messier 14, including numerous RR Lyrae and W Virginis types. W Virginis variables also shift in brightness periodically, though their pulsation cycles stretch much longer, typically lasting 10 to 20 days.
Historical Nova Discovery in Messier 14
A nova erupted inside the cluster during the summer of 1938, marking only the second such event discovered within a Milky Way globular cluster. Nova outbursts occur within close binary systems where a white dwarf star pulls material from a companion. Hydrogen accumulates on the white dwarf surface until a sudden thermonuclear reaction triggers, boosting the system’s brightness by up to 10,000 times before it fades over several months.
Astronomers did not catch the outburst in real-time. Helen Sawyer Hogg captured photographic plates of the cluster, revealing the transient star across eight exposures taken in June 1938 that appeared on no prior or subsequent plates. Amelia Wehlau identified the nova decades later while examining those historical photographic plates between 1963 and 1964.
Observing Messier 14 from Earth
Stargazers face specific challenges when targeting Messier 14 due to its location and surface brightness. The cluster shines at magnitude 7.6 in the constellation Ophiuchus, but it does not climb very high in the sky from Hungary. Observers require a clear southern horizon free from tall terrain obstructions. High humidity or light pollution severely degrades viewing odds because the cluster’s large 11-arcminute apparent diameter spreads out its light, making the faint object blend easily into a bright background sky.
Another globular cluster, NGC 6366, sits just over three degrees southwest of Messier 14. Although dimmer, NGC 6366 complicates amateur stargazing sessions because inexperienced observers can easily mistake the two neighboring deep-sky objects.
How large is Messier 14 and how to view it?
How large is Messier 14 compared to other clusters?
Messier 14 has a physical diameter of approximately 100 light-years and contains over 150,000 stars, making its shape noticeably more elongated than typical globular clusters.
What equipment is needed to see individual stars in Messier 14?
While Charles Messier saw only a fuzzy patch through 18th-century instruments, medium-sized amateur telescopes today easily resolve the cluster into a multitude of individual stars.
When was the Messier 14 nova found on photographic plates?
Amelia Wehlau identified the 1938 nova outburst on historical photographic plates taken by Helen Sawyer Hogg during an examination conducted between 1963 and 1964.
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