Messier 107 (M107) is a remarkable globular cluster located in the constellation Ophiuchus, often depicted as the Serpent Bearer. This large constellation straddles the celestial equator, making the cluster visible from both hemispheres during specific times of the year.
M107 was discovered in 1782 by French astronomer Pierre Méchain and later added to Charles Messier’s catalogue of comet-like objects. Although not initially listed in Messier’s primary compilation, M107 gained recognition as a notable deep-sky object due to its unique characteristics.
Age and Composition
M107 is a typical example of a globular cluster, a tightly bound group of stars that orbit the Milky Way’s core. Globular clusters like M107 contain stars that are among the oldest in the galaxy, offering crucial clues about the early history of star formation.
Unlike some globular clusters, M107 is classified as loosely concentrated, meaning its stars are more spread out rather than densely packed. This looser structure sets it apart from clusters with intense central densities.
Astronomers estimate M107 to be about 13 billion years old, making it one of the oldest known clusters in the Milky Way. Its stellar population predominantly consists of Population II stars, which are old, metal-poor stars with low levels of heavy elements. The cluster spans an apparent diameter of 10 arcminutes, corresponding to a physical size of approximately 80 to 100 light-years. M107 is located about 20,900 light-years from Earth, residing within the galaxy’s dense bulge region.
The “Crucifix Cluster”
M107 is sometimes referred to as the “Crucifix Cluster” due to the distinctive arrangement of its brighter stars in the central region. Under optimal viewing conditions, this arrangement can resemble a cross-like shape, giving the cluster its evocative nickname. This feature is particularly striking through medium-sized telescopes, making M107 a visually rewarding object for observers.
Magnitude and Visibility
The apparent magnitude of M107 is 8.1, meaning it is not visible to the naked eye but can be observed using binoculars or small telescopes under dark skies. When viewed through binoculars, M107 appears as a faint, diffuse patch of light. Telescopes with larger apertures can resolve individual stars, particularly near the outer regions of the cluster.
Its relatively low surface brightness, combined with its loose structure, makes it slightly more challenging to observe than denser globular clusters. However, the cross-like feature in its core adds a unique element to its appeal for amateur and professional astronomers alike.
Observation
In the Northern Hemisphere, Ophiuchus becomes visible in the evening sky during spring, with its prominence peaking during summer months. The optimal observation period for M107 in this region is from May to August, when the cluster is well-positioned high in the southern sky.
In the Southern Hemisphere, Ophiuchus rises during the winter months, offering similarly ideal viewing conditions from May to August. Observers in southern latitudes benefit from the constellation being higher in the sky, providing clearer views of M107 with less atmospheric interference.
Clear, dark skies and minimal atmospheric turbulence are crucial for observing the cluster, as its faintness can be easily obscured by light pollution or poor weather conditions. Viewing is best when the cluster is highest in the sky, typically around midnight, to reduce the effects of atmospheric distortion.