|| Prarabdh Research Desk : Information about some of the common galaxies and Nebulae in...........

When we look up at the night sky much things that we see are the pretty ancient stuff. Although objects look very close but actually vast distances apart. We see so many things in space including galaxies, stars, stars groupings and nebulae. But there are many more objects that exist in universe such as planets, satellites, comets and forms of radiation.

Some of the things are discussed below

• Galaxies

 A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. Galaxies, averaging an estimated 100 million stars,[3] range in size from dwarfs with less than a hundred million (10^8) stars, to the largest galaxies known - supergiants with one hundred trillion (10^14) stars each orbiting its galaxy's center of mass.

1) Milky Way Galaxy

The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. The term Milky Way is a translation of the Latin via lactea, from the Greek (galaktikos kýklos), meaning "milky circle".  

Earth lies inside the spiral arms of the Milky Way, the few hundred billion stars of our home galaxy appears as bright band of stars across the night sky. Dark splotches among the stars are massive globs of intersteller dust and gas that blocks the light from the stars behind them. The nearest star to us in Milky Way is Sun.

2) Sombrero Galaxy

The Sombrero Galaxy (also known as Messier Object 104, M104 or NGC 4594) is a peculiar galaxy of unclear classification in the constellation borders of Virgo and Corvus, being about 9.55 megaparsecs (31.1 million light-years) from the Milky Way galaxy. It is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster.It has a diameter of approximately 15 kiloparsecs (49,000 light-years),three-tenths the size of the Milky Way.

Viewed from sides, this spiral galaxy bulges in middle like sombrero (mexican hat). Scientists suspects that black hole as massive as 1 billion suns may lie at the centre of the galaxy. Around its center lie billions of old, faint stars that form the enormous bulge of light.

3) Andromeda Galaxy

The Andromeda Galaxy, also known as Messier 31, M31, or NGC

224 and originally the Andromeda Nebula, is a barred spiral galaxy with diameter of about 46.56 kiloparsecs (152,000 light-years) approximately 2.5 million light-years (770 kiloparsecs) from Earth and the nearest large galaxy to the Milky Way. The galaxy's name stems from the area of Earth's sky in which it appears, the constellation of Andromeda, which itself is named after the princess who was the wife of Perseus in Greek mythology.

The Milky Way and Andromeda galaxies are expected to collide in around 4–5 billion years, merging to form a giant elliptical galaxy or a large lenticular galaxy.

The virial mass of the Andromeda Galaxy is of the same order of magnitude as that of the Milky Way, at 1 trillion solar masses (2.0×10^42 kilograms).

4) Whirpool Galaxy

The Whirlpool Galaxy, also known as Messier 51a, M51a, and NGC 5194, is an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus.It lies in the constellation Canes Venatici, and was the first galaxy to be classified as a spiral galaxy.Its distance is 31 million light-years away from Earth.

Whirlpool Galaxy was discovered on October 13, 1773, by Charles Messier while hunting for objects that could confuse comet hunters, and was designated in Messier's catalogue as M51.

The Whirlpool Galaxy lies 31 million light-years from Earth and has an estimated diameter of 76,000 light-years.Overall the galaxy is about 43% the size of the Milky Way. Its mass is estimated to be 160 billion solar masses, or around 10.3% of the mass of Milky Way Galaxy.

5)Triangulum Galaxy

The Triangulum Galaxy is a spiral galaxy 2.73 million light-years

(ly) from Earth in the constellation Triangulum. It is catalogued as Messier 33 or NGC (New General Catalogue) 598. With the D25 isophotal diameter of 18.74 kiloparsecs (61,100 light-years), the Triangulum Galaxy is the third-largest member of the Local Group of galaxies, behind the Andromeda Galaxy and the Milky Way. It is one of the most distant permanent objects that can be viewed with the naked eye.

The galaxy is the smallest spiral galaxy in the Local Group (although the smaller Large and Small Magellanic Clouds may have been spirals before their encounters with the Milky Way), and is believed to be a satellite of the Andromeda Galaxy or on its rebound into the latter due to their interactions, velocities, and proximity to one another in the night sky. It also has an H II nucleus.

• Nebula

A nebula is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust

Some common nebula-

1)Eagle Nebula

The Eagle Nebula (catalogued as Messier 16 or M16, and as NGC

6611, and also known as the Star Queen Nebula) is a young open cluster of stars in the constellation Serpens, discovered by Jean-Philippe de Cheseaux in 1745–46. Both the "Eagle" and the "Star Queen" refer to visual impressions of the dark silhouette near the center of the nebula, an area made famous as the "Pillars of Creation" imaged by the Hubble Space Telescope. The nebula contains several active star-forming gas and dust regions, including the aforementioned Pillars of Creation. The Eagle Nebula lies in the Sagittarius Arm of the Milky Way.

2)Omega Nebula

The Omega Nebula, also known as the Swan Nebula, Checkmark

Nebula, Lobster Nebula, and the Horseshoe Nebula (catalogued as Messier 17 or M17 or NGC 6618) is an H II region in the constellation Sagittarius. It was discovered by Philippe Loys de Chéseaux in 1745. Charles Messier catalogued it in 1764. It is by some of the richest starfields of the Milky Way, figuring in the northern two-thirds of Sagittarius.

The Omega Nebula is between 5,000 and 6,000 light-years from Earth and it spans some 15 light-years in diameter. The cloud of interstellar matter of which this nebula is a part is roughly 40 light-years in diameter and has a mass of 30,000 solar masses. The total mass of the Omega Nebula is an estimated 800 solar masses.

3)Lagoon Nebula

The Lagoon Nebula (catalogued as Messier 8 or M8, NGC 6523,

Sharpless 25, RCW 146, and Gum 72) is a giant interstellar cloud in the constellation Sagittarius. It is classified as an emission nebula and as an H II region.

The Lagoon Nebula was discovered by Giovanni Hodierna before 1654 and is one of only two star-forming nebulae faintly visible to the eye from mid-northern latitudes. Seen with binoculars, it appears as a distinct cloud-like patch with a definite core. Within the nebula is the open cluster NGC 6530.

The Lagoon Nebula is estimated to be between 4,000–6,000 light-years away from the Earth. In the sky of Earth, it spans 90' by 40', which translates to an actual dimension of 110 by 50 light years. Like many nebulae, it appears pink in time-exposure color photos but is gray to the eye peering through binoculars or a telescope, human vision having poor color sensitivity at low light levels.

4) Horsehead Nebula

The Horsehead Nebula (also known as Barnard 33) is a small dark

nebula in the constellation Orion. The nebula is located just to the south of Alnitak, the easternmost star of Orion's Belt, and is part of the much larger Orion molecular cloud complex. It appears within the southern region of the dense dust cloud known as Lynds 1630, along the edge of the much larger, active star-forming H II region called IC 434.

The Horsehead Nebula is approximately 422 parsecs or 1,375 light-years from Earth. It is one of the most identifiable nebulae because of its resemblance to a horse's head.

The nebula was first recorded in 1888 by Scottish astronomer Williamina Fleming on a photographic plate taken at the Harvard College Observatory.

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