M104, more commonly known as the Sombrero Galaxy, is a spectacular almost edge-on spiral galaxy in Virgo. At magnitude +8.4, it appears in binoculars as a small patch of nebulosity. Its most striking feature, which is visible in medium/large size amateur scopes, is a ring of thick dust encapsulating the galaxy bulge that gives it the appearance of a Sombrero hat. Many astronomers regard M104 as the finest of all the Virgo galaxies.
Pierre Méchain discovered M104 on May 11, 1781. A couple of years later he described it in a letter to Johann Bernoulli and later it was published in the Berliner Astronomisches Jahrbuch (Berlin Astronomy Year Book). Charles Messier made some hand-written notes about the galaxy and five other objects, but none were included in his final published catalogue. It was finally added to the "official" catalogue in 1921 and the remaining "missing" items, (M105 to M109), were included a few years later.
In 1912, M104 was one of the first galaxies to have its spectra and velocity measured by Vesto Slipher. He noted that the object was redshifted and therefore receding from us. The current accepted rate is 900 km/s. Slipher's calculations along with measurements from other galaxies pointed towards an expanding Universe, providing a key piece of evidence for the Big Bang Theory.
The Sombrero Galaxy is located very close to the constellation boundary with Corvus. It's positioned 11.5 degrees directly west of Spica (α Vir - mag. +1.0) and 6 degrees northeast of delta Corvi (δ Crv - mag. +2.9). Just north of M104 is a faint naked-eye triangle formed by stars chi Virginis (χ Vir - mag. +4.7), psi Virginis (ψ Vir - mag. +4.8) and 21 Virginis (mag. +5.5).
It's best seen during the months of March, April and May.
Through 7x50 or 10x50 binoculars, M104 is visible under dark skies as a small round patch of nebulosity. The galaxy is easy to observe with almost any telescope. A 100mm (4-inch) scope under good seeing conditions hints at dark markings within the structure. When seen through larger 200mm (8-inch) reflectors, M104 appears as a flattened saucer with a large centre bulge bisected by the dark dust lane. Even larger amateur instruments of the order of 250mm (12-inch) aperture or greater reveal a bright nucleus, extensive halo and the dark dusk lane which extends outwards on both sides. On good nights, the Sombrero Galaxy is a spectacular sight.
M104 covers 8.6 x 4.2 arc minutes of apparent sky. It's located 30 million light-years distant, which corresponds to an actual diameter of 75,000 light-years. The galaxy is estimated to contain about 100 billion stars. It also contains a reasonable large number globular clusters (approx. 2,000). It's the dominant member of a small group of galaxies known as the M104 group or NGC 4594 group.
M104 Data Table
|Object Type||Spiral galaxy|
|Classification||Sa (s) a|
|Distance (light-years)||30 Million|
|RA (J2000)||12h 39m 59s|
|DEC (J2000)||-11d 37m 23s|
|Apparent Size (arc mins)||8.6 x 4.2|
|Number of Stars||100 Billion|