M99, mag. +10.2, is a spiral galaxy situated in the southern part of the constellation of Coma Berenices. It's a member of the Virgo cluster of galaxies and appears almost face-on from our perspective. This galaxy was discovered by Pierre Mechain on March 15, 1781 and on this night he also discovered M98 and M100. The discoveries were reported to Charles Messier who measured their positions before adding them to his catalogue on April 13, 1781. This was just prior to the release of the third and final published edition of the catalogue.
The 3rd Earl of Rosse, William Parsons, first identified the spiral structure of M99 in 1846 using his 72-inch (1.83 m) reflecting telescope at Birr Castle in Ireland. At the time, Rosse was using the world's largest optical telescope and the galaxy was one of the first to have its spiral structure identified.
M99 is located 55 Million light-years from Earth. It covers 5.3 x 4.6 arc minutes of apparent sky, which corresponds to a spatial diameter of 85,000 light-years. The galaxy is positioned 7 degrees east of bright star Denebola (β Leo - mag. +2.1) and just less than 1 degree southeast of star 6 Comae Berenices (mag. +5.1). Tenth magnitude edge-on spiral galaxy, M98, lies 0.5 degrees west of 6 Comae Berenices.
Finder Chart for M99 - pdf format (credit:- freestarcharts)
M99 is visible through small telescopes as a faint roundish glow with a brighter core. Of course aperture helps and it's much easier to detect with a medium size telescope or larger. Through 200mm (8-inch) reflectors, the galaxy appears as a fuzzy patch of light with a noticeably brighter centre. On dark nights the outer haze hints at the spiral structure, which is easily seen at high powers through 250mm (10-inch) scopes. Even larger instruments bring out finer details such as dust bands and subtle details in the spiral surface. It's a testament to the quality of today amateur scopes that the spiral shape can easily be seen.
While not classified as a starburst galaxy, there is a high activity of star formation occurring in M99. To date, four supernovae have been recorded in the galaxy. They are SN 1967H (mag. +14), SN 1972Q (mag. +15.6), SN 1986I (mag. +14) and SN 2014L (mag. +15.4).
M99 and the other Virgo cluster galaxies are best seen during the months of March, April and May.
M99 Data Table
| Messier | 99 |
|---|---|
| NGC | 4254 |
| Object Type | Spiral galaxy |
| Classification | SA(s)c |
| Constellation | Coma Berenices |
| Distance (light-years) | 55 Million |
| Apparent Mag. | +10.2 |
| RA (J2000) | 12h 18m 50s |
| DEC (J2000) | +14d 25m 01s |
| Apparent Size (arc mins) | 5.3 x 4.6 |
| Radius (light-years) | 42,500 |
| Number of Stars | 150 Billion |
| Notable Feature | Three supernovae have been observed in this galaxy. |