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 Pegasus. It's only marginally fainter and smaller than M13, the finest northern globular cluster. M15 is relatively easy to find. It's located 4 degrees to the northwest of Enif (ε Peg - mag. +2.4) and at one edge of a right-angled triangle made up of 6th, 7th and 8th magnitude stars.

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

Finder Chart for M15 (credit:- freestarcharts)

Finder Chart for M15 - pdf format (credit:- freestarcharts)

Finder Chart for M2 (also shown M15) (credit:- freestarcharts)

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

Approaching naked eye visibility under excellent conditions, M15 is easily seen with binoculars or finder scopes appearing as a mag. +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) scope, M15 looks like a large bright diffuse ball of light with a dense compact centre. Many stars are resolved in the outer halo, the brightest of which shine at mag. +12.6. Larger instruments 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, it visually appears somewhat smaller, perhaps only 8 arc minutes across.

M15 is one of the most densely packed globulars known in the Milky Way. 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's also unusual in that it's one of only four known globulars (along with M22, NGC 6441 and Palomar 6) that contain a planetary nebula. The planetary is named Pease 1.

The cluster was discovered by Italian born French astronomer Jean-Dominique Maraldi on September 7, 1746. It's located 33,600 light-years distant. With an age of at least 12.0 billion years, this is one of the oldest known Milky Way globulars.

M15 Data Table

Messier15
NGC7078
Object TypeGlobular Cluster
ConstellationPegasus
Distance (light-years)33,600
Apparent Mag.+6.2
RA (J2000)21h 29m 58s
DEC (J2000)+12d 10m 00s
Apparent Size (arc mins)18 x 18
Radius (light-years)88
Age (years)12 Billion

Sky Highlights - February 2017

Comets
Comet Encke (2P/Encke) now visible in the western sky during evening twilight
Now is the last good chance to see comet 45P/Honda-Mrkos-Pajdusakova before it dramatically fades

Conjunction
Mars passes less than 1 degree north of Uranus on February 27th

Minor Planet
Vesta now visible with binoculars and small telescopes.

The Planets
This Month's Guide

Algol Minima
Algol eclipse dates and times for February 2017

Northern Hemisphere
Evening
Southwest:- Venus (mag. -4.8), Mars (mag. +1.1 to +1.3), Uranus (mag. +5.9)
Midnight
East:- Jupiter (mag. -2.1 to -2.3)
Morning
South:- Jupiter
Southeast:- Saturn (mag. +0.6)

Southern Hemisphere
Evening
West:- Venus, Mars, Uranus
Midnight
East:- Jupiter
Morning
North:- Jupiter
East:- Saturn, Mercury (mag. -0.2 - first half of month)

Deep Sky
Naked eye / binoculars:-
Messier 45 - M45 - The Pleiades (Open Cluster)
The Hyades - Open Cluster
Messier 44 - M44 - The Praesepe (Open Cluster)
Messier 35 - M35 - Open Cluster
Messier 42 - M42 - The Great Orion Nebula (Emission/Reflection)

Small telescopes:-
Messier 36 - M36 - Open Cluster
Messier 37 - M37 - Open Cluster
Messier 38 - M38 - Open Cluster

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