Messier 15 – M15 - Globular Cluster

M15 is one of the brightest and finest globular clusters in the northern section of the sky and the best deep-sky object in the constellation of Pegasus. It is only marginally fainter and smaller than M13, the finest northern globular cluster. M15 is relatively easy to find, located 4 degrees to the northwest of magnitude +2.4 star Enif (Epsilon Pegasi - ε Pegasi) and positioned on one edge of a right-angled triangle made up of stars of 6th, 7th and 8th magnitudes.

M15 Globular Cluster (NASA, ESA, and The Hubble Heritage Team (STScI/AURA))

Finder Chart for M15

Finder Chart for M15 - pdf format

Finder Chart for M2 (also shown M15)

Finder Chart for M2 (also shown M15) - pdf format

Approaching naked eye visibility under excellent conditions, this globular cluster is easily observed with binoculars or finder scopes, appearing as a magnitude +6.2 fuzzy star. A 100mm (4-inch) telescope at low power (40x) reveals a uniformly lit disk while high powers (>100x) hint at resolution of some of the outer stars. When viewed through a larger 200mm (8-inch) telescope, M15 appears as a large bright diffuse ball surrounding a dense compact centre region, with many individual stars resolved in the outer halo. The brightest of these stars are of magnitude +12.6. Larger telescopes do even better. A 300mm (12-inch) scope resolves many stars across the complete disk, creating a spectacular 3-dimensional effect. In total, the globular has an apparent diameter of 18 arc minutes, however in amateur telescopes it appears somewhat smaller, perhaps only 8 arc minutes visually.

M15 is one of the most densely packed globulars known in the Milky Way galaxy. Its core has undergone a contraction known as "core collapse" resulting in an enormous number of stars surrounding what may be a central black hole. It is also unusual in that it is one of only four known globulars (along with M22, NGC 6441 and Palomar 6) that contains a planetary nebula. The planetary nebula is named Pease 1.

The cluster was discovered by Italian born French astronomer Jean-Dominique Maraldi on September 7, 1746 and is located 33,600 light-years from Earth. With an age of at least 12.0 billion years, it's thought to be one of the oldest known Milky Way globular clusters.

M15 Data Table

Object TypeGlobular Cluster
Distance (kly)33.6
Apparent Mag.6.2
RA (J2000)21h 29m 58s
DEC (J2000)12d 10m 00s
Apparent Size (arcmins)18 x 18
Radius (light years)88
Age (years)12000M

Sky Highlights - October 2015

Comet Catalina (C/2013 US10)
Comet Catalina (C/2013 US10) edges towards naked eye visibility

Mercury at its best in the morning
Mercury reaches greatest elongation west on October 16, 2015

Uranus at opposition
Uranus reaches opposition on October 12, 2015

The Planets
This Month's Guide

Northern Hemisphere
Southwest:- Saturn (mag. +0.6)
Southeast:- Neptune (mag. +7.8)
East:- Uranus (mag. +5.8)
Southwest:- Neptune
South:- Uranus
West:- Uranus
East:- Venus (mag. -4.5), Mars (mag. +1.8), Jupiter (mag. -1.8), Mercury (mag. -0.9 after 1st week)

Southern Hemisphere
West:- Saturn
East:- Neptune, Uranus
Northwest:- Neptune
North:- Uranus
West:- Uranus
East:- Venus, Mars, Jupiter

Deep Sky
Binoculars/small scopes:-
Messier 31 - M31 - Andromeda Galaxy (Spiral Galaxy)
NGC 869 and NGC 884 - The Double Cluster - Open Clusters
NGC 457 - Owl Cluster - Open Cluster
Messier 52 - M52 - Open Cluster
Messier 15 – M15 - Globular Cluster
NGC 752 - Open Cluster
Messier 39 - M39 - Open Cluster
Messier 29 – M29 – Open Cluster
Messier 57 - M57 - The Ring Nebula (Planetary Nebula)
Messier 27 - M27 - The Dumbbell Nebula (Planetary Nebula)
47 Tucanae - NGC 104 - Globular Cluster

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