Everything to know about New General Catalogue (NGC)

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Everything to know about New General Catalogue (NGC)


Many of us have heard or read about astronomical objects whose official names are starting with NGC, like NGC 1976, NGC 1952 etc. But what actually this NGC means? NGC is one of the most historic catalogues of deep space objects ever created in history. The New General Catalogue of Nebulae and Clusters of Stars (NGC) is a list of deep space astronomical objects created by John Dreyer. This catalogue has 7,840 astronomical objects listed including galaxies, nebulae, black holes, clusters etc. It's obvious that Dreyer himself has not discovered all the 7,840 objects. The journey was started many years ago by William Herschel and his sister Caroline. They both located and observed more than 1000 objects in the deep space. They published the first catalogue which contained around 2500 objects. John Herschel, Willian's son also located and discovered many astronomical objects. He catalogued objects even more than his father's discovery. He published his catalogue which contains around 5079 objects. 

This historic catalogue (the NGC) has far space objects discovered by Herschel siblings and different astronomers around the globe. Dreyer after publishing NGC realised that this list is just the beginning of astronomical observation. Many more objects are yet to study. So he published the first volume of IC (Index Catalogue) in 1895 and the second volume in 1905. In both the ICs he added another 5,386 new objects. 

Many amateur astronomers start their journey with Messier Catalogue, but as they start expanding these visions they shift to NGC. For many observers, locating the objects in ICs is a bit difficult than that in NGC and Messier catalogue. Dreyer and many contemporary astronomers faced many challenges while locating these objects due to the lack of advanced telescopes and technology. However, with modern astrophotography, today astronomers have discovered and studied many more astronomical objects far beyond the boundary of NGC and IC.

NGC was far from perfection. There were many mistakes in the catalogue as Dreyer cannot check the existence of objects. Some of them were not possible to locate due to the limitation of telescopes. There were many missing and misplaced objects. In 1973, William Tifft and Jack Sulentic make an attempt to rectify the NGC.  They published the Revised New General Catalogue (RNGC). The RNGC had major improvements over the NGC. 

However, the RNGC was also not perfect. Around 300 objects including star clusters and galaxies were misidentified or were not located in the RNGC. In 2009, the Revised New Catalogue and Index Catalogue (RNGC/IC) was published by Wolfgang Steinicke. By 2019, the catalogue was updated with 13,957 objects. Many objects are common in the NGC, RNGC, IC and Messier Catalogue. 

Out of ~8000 objects listed in the NGC, here are the 10 most amazing and well-known objects of the NGC.

NOTE: At the end of this article, links to download original HD images of all these 10 objects are given.

(1) NGC 7635 or The Bubble Nebula:

NGC 7635 is a beautiful and amazing emission nebula located in the constellation Cassiopeia. The name 'bubble' is given because the bubble-shaped cloud of gases and dust are formed due to the hot, massive, young star located at the centre of the nebula. The nebula was first discovered and listed by William Herschel. The nebula has a diameter of 6 to 10 light-years and is located about 10,000 light-years away from the Earth. The bubble is expanding at a rate of 7 million km/hr. 

(2) NGC 6543 or The Cat's Eye Nebula:

Located in constellation Draco, NGC 6543 is a planetary nebula discovered by William Herschel. It is the first nebula whose spectrum was observed for detailed study. It was only the spectrum study that showed that the nebulae are gaseous in nature and not stellar. The nebula is located 3300 light-years away from the Earth. The nebula is expanding at a rate of 60,000 km/hr. X-ray observations showed that the nebula must a massive bright star at the centre, expected to be about 10,000 to 100,000 times more luminous than the Sun.

(3) NGC 2392 or The Eskimo Nebula:

NGC 2392 was also discovered by William Herschel. Also known as the Clown-faced Nebula or the Lion Nebula, it is located about 6500 light-years away from the Earth. This planetary nebula is given the name Eskimo because it resembles a person's head wearing a parka hood. The nebula is surrounded by bright young stars.

(4) NGC 7293 or The Helix Nebula:

This nebula was discovered by Karl Ludwig Harding. This planetary nebula is one of the closest nebulae to the Earth, located about 650 light-years away. It is also referred to as the "Eye of God", due to its shape. Located in the constellation Aquarius, the centre of this nebula has a white dwarf. The star is so bright that it causes nearby gases to glow and fluoresce. 

(5) NGC 6523 or The Lagoon Nebula:

NGC 6523 is a giant emission nebula located in the constellation Sagittarius. Discovered Giovanni Hodierna, the nebula is located about 4000 light-years away from the Earth. When seen through small telescopes, it looks like an oval-shaped cloud with a core. The nebula releases a massive amount of ultraviolet light through ionizing gases. But for the human eye, the nebula is grey coloured, as our eye is not capable to interpret ultraviolet light.

(6) NGC 7742 or The Fried Egg Galaxy:

Located about 72 million light-years away, the Fried Egg Galaxy is an unbarred spiral galaxy located in the constellation Pegasus. The galaxy is 3000 light-years across. The ring is the region of new star formation while the centre holds older stars. According to the astronomers, the galaxy might be formed by a collision with the dwarf galaxy millions of years ago. 

(7) NGC 2359 or The Thor's Helmet Nebula:

Thor's Helmet is an emission nebula located about 11,000 light-years away from the Earth. The nebula is 30 light-years wide and is located in the constellation Canis Major. The nebula is similar in shape to the Bubble Nebula, but the Thor's Helmet has a bit more complex structure due to the interaction of gases with the central hot Wolf-Rayet star WR7. The different portion of the nebula is expanding at different rates ranging from 10 km/s to 30 km/s. The nebula has unionised gases which have several hundred solar masses.

(8) NGC 6357 or The War and Peace Nebula:

This strange named diffuse nebula is located in the constellation Scorpius about 6000 light-years away. It is given the name war and Peace because its western part resembles a skull and the eastern part resembles a dove. The nebula has thousands of bright, young stars shielded by discs of gases. The nebula is also known as the Lobster Nebula or the Madokami Nebula.

(9) NGC 6369 or The Little Ghost Nebula:

The Little Ghost nebula was also discovered by William Herschel. This planetary nebula is located in the constellation Ophiuchus about 5000 light-years away from the Earth. The nebula has a white dwarf at the centre which causes surrounding gases to glow and emit radiations. The nebula is about 1 light-year wide and is made up of ionized gases like oxygen, nitrogen, hydrogen etc. 

(10) NGC 2080 or The Ghost Head Nebula:

NGC 2080 is an emission nebula located in the Large Magellanic Cloud (LMC). It was discovered by Sir John Herschel, son of William Herschel in 1834. This nebula must not be confused with Little Ghost Nebula or the Ghost Nebula. The nebula is located about 160,000 light-years away from the Earth. The nebula has several clusters of young, bright stars in the eastern part. The western part also has young stars which are surrounded by bubbles of ionized gases. 

There are still many amazing galaxies and nebulae listed in the NGC, but all are not possible to show here. 

Links:

1. Bubble Nebula - https://apod.nasa.gov/apod/image/1604/ngc7635bubble_hubble26.jpg   

2. Cat's Eye Nebula - https://cdn.spacetelescope.org/archives/images/wallpaper1/heic0414a.jpg

3. Eskimo Nebula - https://www.nasa.gov/sites/default/files/images/439415main_eskim0_nebula-full_full.jpg

4. Helix Nebula - https://apod.nasa.gov/apod/image/0912/helix_spitzer_2048.jpg

5. Lagoon Nebula - https://cdn.spacetelescope.org/archives/images/large/heic1808a.jpg

6. Fried Egg Galaxy - https://upload.wikimedia.org/wikipedia/commons/e/ee/Seyfert_Galaxy_NGC_7742.jpg

7. Thor's Helmet Nebula - https://apod.nasa.gov/apod/image/2006/ThorsHelmet800.jpg

8. War and Peace Nebula - https://upload.wikimedia.org/wikipedia/commons/1/1f/Cosmic_%E2%80%98Winter%E2%80%99_Wonderland.jpg

9. Little Ghost Nebula - https://apod.nasa.gov/apod/image/0211/ngc6369_heritage_big.jpg

10. Ghost Head Nebula - https://apod.nasa.gov/apod/image/0110/ngc2080_hst_big.jpg

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