M100, mag. +9.5, is a spiral galaxy located in the southern part of constellation of Coma Berenices. It's one of the brightest members of the Virgo cluster of galaxies appearing almost face-on from our perspective. M100 exhibits prominent well-defined spiral arms and is therefore regarded as an example of a grand design spiral galaxy; other notable galaxies that fall into this category are M51, M74, M81 and M101.

M100 was discovered - along with M98 and M99 - by Pierre Méchain on March 15, 1781. Charles Messier subsequently observed all three objects and added them to his catalogue on April 13, 1781. He described the galaxy as faint without stars. It was not until 1850 that the spiral nature of M100 was first detected. Ango-Irish astronomer William Parsons the 3rd Earl of Rosse was the person to achieve this. He included M100 in a list of 14 spiral nebulae he had observed.

Finding the area of sky where M100 is positioned is not so difficult once one is familiar with the location of Virgo cluster. The centre of the cluster is located close to supergiant elliptical galaxy M87 about halfway along a line connecting Denebola (β Leo - mag. +2.1) with Vindemiatrix (ε Vir - mag. +2.8). M100 is positioned towards the northern section of the group, 2 degrees southeast of star 11 Com (mag. +4.7).

The Virgo cluster galaxies are best seen during the months of March, April and May.

M100 Spiral Galaxy (J. Trauger/JPL/NASA/ESA)

Finder Chart for M100 (also shown M49, M53, M58->M60, M64->M66, M84->M91, M98 and M99)

Finder Chart for M100 (also shown M49, M53, M58->M60, M64->M66, M84->M91, M98 and M99) - pdf format

At mag. +9.5, M100 is within the range of 7x50 or 10x50 binoculars. However, since the galaxy appears face it suffers from low surface brightness and therefore a difficult object. It's easier to spot through larger 11x80/20x80 binoculars or small telescopes, where it appears as a faint hazy patch of light with an uneven texture. A medium size 200mm (8-inch) scope reveals a bright core surrounding by an envelope of shady nebulosity. With large amateur instruments some dust structure is visible but only on dark nights of excellent seeing. In total, M100 covers 7.5 x 6.1 arc minutes of apparent sky although it appears visually smaller.

The galaxy is located 57.5 Million light-years distant. It has an actual spatial diameter of 125,000 light-years and is estimated to contain 400 Billion stars. Two satellite galaxies - NGC 4323 and NGC 4328 - are present within M100.

To date, five supernovae have been observed in M100. They are SN 1901B (mag. +15.6 - March 1901), SN 1914A (mag. +15.7 - Feb 1914), SN 1959E (mag. +17.5 - Aug 1959), SN 1979C (mag. +11.6 - April, 1979) and SN 2006X (mag. +15.3).

M100 Data Table

Object TypeSpiral galaxy
ClassificationSAB (s)6c
ConstellationComa Berenices
Distance (kly)57500
Apparent Mag.9.5
RA (J2000)12h 22m 55s
DEC (J2000)15d 49m 21s
Apparent Size (arc mins)7.5 x 6.1
Radius (light-years)62,500
Number of Stars400 Billion
Notable FeatureOne of the first spiral galaxies to be discovered.

Sky Highlights - March 2017

Comet 41P/Tuttle-Giacobini-Kresak now visible with binoculars as it heads towards perihelion

Mercury heading towards greatest elongation east

Minor Planet
Vesta now visible with binoculars and small telescopes.

The Planets
This Month's Guide

Algol Minima
Algol eclipse dates and times for March 2017

Northern Hemisphere
West:- Venus (mag. -4.8 to -4.1 - first half of month), Mars (mag. +1.3 to +1.5), Uranus (mag. +5.9), Mercury (mag. -1.5 to -0.4 - second half of month)
Southeast:- Jupiter (mag. -2.3 to -2.5)
Southwest:- Jupiter
Southeast:- Saturn (mag. +0.5)

Southern Hemisphere
West:- Venus (first half of month), Mars, Uranus
North:- Jupiter
East:- Saturn
West:- Jupiter
Northeast:- Saturn
East:- Neptune (mag. +8.0 - second half of month)

Deep Sky
Naked eye / binoculars:-
Melotte 111 - Mel 111 - The Coma Star Cluster (Open Cluster)
Messier 44 - M44 - The Praesepe (Open Cluster)

Messier 67 - M67 - Open Cluster
Messier 51 - M51 - The Whirlpool Galaxy (Spiral Galaxy)
Messier 97 - M97 - The Owl Nebula (Planetary Nebula)
Messier 101 - M101 - The Pinwheel Galaxy (Spiral Galaxy)
Messier 65 – M65 – Spiral Galaxy
Messier 66 - M66 - Intermediate Spiral Galaxy
Messier 95 - M95 - Barred Spiral Galaxy
Messier 96 - M96 - Intermediate Spiral Galaxy
NGC 4244 - Spiral Galaxy
NGC 4565 - Needle Galaxy - Spiral Galaxy

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