M77 is a notable 9th magnitude face-on barred spiral galaxy in the constellation of Cetus. The nucleus of the galaxy contains at its core an Active Galaxy Nucleus (AGN), which although obscured from view by astronomical dust at visible wavelengths is detectable due to strong emissions in the infrared, ultraviolet, and X-ray regions of the electromagnetic spectrum. This type of galaxy is known as a Seyfert galaxy, named after 20th century American astronomer Carl Seyfert who first identified the class in 1943, of which M77 is the brightest example. They are believed to be home to a supermassive black hole of between 10 and 100 million solar masses.

M77 was discovered by Pierre Méchain on October 29, 1780. He described the object as a nebula and subsequently reported it to Charles Messier who then added it to his catalogue. Messier and later William Herschel both described M77 - incorrectly - as a star cluster.

The galaxy is located about 1 degree southeast of magnitude 4.1 star delta Cet (δ Cet) and a few degrees to the northeast of famous long period variable star Mira. The constellation Cetus in Greek mythology represented a "Sea Monster" although today it's often referred to as "the Whale" or "the Shark". It's the fourth largest constellation in the sky covering 1231 square degrees and is bordered by Aries, Pisces, Aquarius, Sculptor, Fornax, Eridanus and Taurus.

Messier 77 barred spiral galaxy by the Hubble Space Telescope (ESA/NASA/André van der Hoeven)

Finder Chart for M77

Finder Chart for M77 - pdf format

Although it shines at magnitude +9.1, M77 is a compact galaxy with a bright center and therefore a relatively easy target for large binoculars (15x70s or 20x80s) and small telescopes. It can even be spotted with 10x50 binoculars from dark sites with excellent seeing conditions. A 80mm (3.1-inch) scope shows the galaxy as a condensed ball of fuzzy light with a slightly brighter central core. A 100mm (4-inch) telescope enhances the view, with the galaxy displaying an oval shaped halo surrounding a bright central region. When viewed through a 200mm (8-inch) scope the details are pronounced with the central core of the galaxy evident and almost stellar like. The large surrounding diffuse halo is prominent. A bright star lies nearby to the east of M77.

M77 is a magnificent galaxy and one of the largest in Messier's catalogue. It's estimated to be at least 47 Million light-years distant, with an apparent size of 7.1 x 6.0 arc minutes this corresponds to an actual diameter of 100,000 light-years. The galaxy is probably even larger still, as evidence suggests of faint outer spiral extensions. The stars in the inner region of M77 are young while those away from the centre tend to be older.

It is one of the first recognized spiral galaxies, and listed by Lord Rosse as one of 14 "spiral nebulae" discovered to 1850. When Vesto Slipher was working on galaxy spectra, M77 was one of two galaxies in which he detected large redshifts (the other being M104, the "Sombrero").

This interesting barred spiral galaxy is best seen during the months of September, October and November.

M77 Data Table

Object TypeBarred spiral galaxy
Distance (kly)47,000
Apparent Mag.9.1
RA (J2000)02h 42m 41s
DEC (J2000)-00d 00m 47s
Apparent Size (arc mins)7.1 x 6.0
Radius (light-years)50,000
Number of Stars>300 Billion
Other NameArp 37
Notable FeaturesBrightest Seyfert galaxy and one of the largest Messier galaxies.

Sky Highlights - April 2017

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