Andromeda Galaxy

Constellation              Andromeda

Right ascension            00h 42m 44.3s

Declination                +41° 16' 9"

Redshift                   −301 ± 1 km/s

Distance                   2.54 ± 0.06 Mly (778 ± 17 kpc)

Type                       SA(s)b

Apparent dimensions (V)    190' × 60'



Apparent magnitude (V)     3.4

The Andromeda Galaxy (also known as Messier 31, M31, or NGC 224; often referred to as the Great Andromeda Nebula in older texts) is a spiral galaxy approximately 2.5 million light-years away in the constellation Andromeda. It is the nearest spiral galaxy to our own, the Milky Way. As it is visible as a faint smudge on a moonless night, it is the farthest object visible to the naked eye, and can be seen with binoculars even in urban areas.

Andromeda is the largest galaxy of the Local Group, which consists of the Andromeda Galaxy, the Milky Way Galaxy, the Triangulum Galaxy, and about 30 other smaller galaxies. Although the largest, it may not be the most massive, as recent findings suggest that the Milky Way contains more dark matter and may be the most massive in the grouping. However, recent observations by the Spitzer Space Telescope revealed that M31 contains one trillion (1012) stars, greatly exceeding the number of stars in our own galaxy. 2006 estimates put the mass of the Milky Way to be ~80% of the mass of Andromeda, which is estimated to be 7.1×1011 solar masses.

At an apparent magnitude of 4.4, the Andromeda Galaxy is notable for being one of the brightest Messier objects, making it easily visible to the naked eye even when viewed from areas with moderate light pollution. It appears quite small without a telescope because only the central part is bright enough to be visible, but the full angular diameter of the galaxy is seven times that of the full moon.

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Antennae Galaxies

Constellation                      Corvus

Right ascension                    12h 01m 53.0s / 12h 01m 53.6s

Declination                        -18° 52' 10" / -18° 53' 11"

Redshift                           1642 ± 12 / 1641 ± 9 km/s

Type                               SB(s)m pec / SA(s)m pec

Apparent dimensions (V)            5'.2 × 3'.1 / 3'.1 × 1'.6

Apparent magnitude (V)             11.2 / 11.1

Notable features                   Interacting galaxies

The Antennae Galaxies (also known as NGC 4038/NGC 4039) are a pair of interacting galaxies in the constellation Corvus. They were both discovered by Friedrich Wilhelm Herschel in 1785.

The Antennae are undergoing a galactic collision. Located in the NGC 4038 group with five other galaxies, these two galaxies are known as the 'Antennae' because the two long tails of stars, gas and dust thrown out of the galaxies as a result of the collision resemble the antennae of an insect. The nuclei of the two galaxies are joining to become one giant galaxy. Most galaxies probably undergo at least one significant collision in their lifetimes. This is likely the future of our Milky Way when it collides with the Andromeda Galaxy. Two supernovae have been discovered in the galaxy: SN 2004GT and SN 2007sr.

A recent study finds that these interacting galaxies are closer to the Milky Way than previously thought—at 45 million light-years instead of 65 million light-years.

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Seyfert's Sextet Galaxy

Constellation(s)              Serpens

Right ascension               15h 59m 11.9s

Declination                   +20° 45' 31"

Number of galaxies            4

Brightest member              NGC 6027

Seyfert's Sextet is a group of galaxies about 190 million light-years away in the constellation Serpens Caput. The group appears to contain six members, but one of the galaxies is a background object and another "galaxy" is actually a separated part of one of the other galaxies. The gravitational interaction among these galaxies should continue for hundreds of millions of years. Ultimately, the galaxies will merge to form a single giant elliptical galaxy.

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Sombrero Galaxy

Constellation           Virgo

Right ascension         12h 39m 59.4s

Declination             -11° 37' 23"

Apparent dimension (V)  8'.7 × 3'.5

Apparent magnitude (V)  8.98

Type                    SA(s)a

Helio Radial velocity   1024 ± 5 km/s

Redshift                0.003416 ± 0.000017

Galactocentric Velocity 904 ± 7 km/s

Distance                29.3 ± 1.6 Mly (9.0 ± 0.49 Mpc)

The Sombrero Galaxy (also known as M104 or NGC 4594) is an unbarred spiral galaxy in the constellation Virgo. It has a bright nucleus, an unusually large central bulge, and a prominent dust lane in its inclined disk. The dark dust lane and the bulge give this galaxy the appearance of a sombrero. The galaxy has an apparent magnitude of 9.0, making it a galaxy that can easily be seen with amateur telescopes. The large bulge, the central supermassive black hole, and the dust lane all attract the attention of professional astronomers.

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Milky Way Galaxy

Type                               SBbc (barred spiral galaxy)

Diameter                           100,000 light years

Thickness                          1,000 light years (stars)

Number of stars                    200 to 400 billion

Oldest star                        13.2 billion years

Mass                               5.8×1011 M

Sun's distance to galactic center  26,000 ± 1400 light-years

Sun's galactic rotation period     220 million years (negative rotation)

Spiral pattern rotation period     50 million years

Bar pattern rotation period        15 to 18 million years

The Milky Way is a barred spiral galaxy that is part of the Local Group of galaxies. Although the Milky Way is one of billions of galaxies in the observable universe, the Galaxy has special significance to humanity as it is the home galaxy of the Solar System. The plane of the Milky Way galaxy is visible from Earth as a band of light in the night sky, and it is the appearance of this band of light which has inspired the name for our galaxy.

Some sources hold that, strictly speaking, the term Milky Way should refer exclusively to the observation of the band of light, while the full name Milky Way Galaxy, or alternatively the Galaxy should be used to describe our galaxy as an astrophysical whole. It is unclear how widespread the usage of this convention is, however, and the term Milky Way is routinely used in either context.

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