Nebulae Named After Land Animals

The Fox Fur Nebula in Monoceros

In a previous post we mentioned that nebulae of all types are among the most spectacular, scary, complex, and sometimes least understood objects in the entire Universe, and how we perceive them often depends on our skill in manipulating photographic images, rather than our observing skills. In fact, most of the structure of many nebulae are invisible to our eyes, and we only become aware of their existence when imaging experts assign false colors to various emissions or components of the nebula.

Put simply, nebulae are vast regions of interstellar dust and ionized gases which form stars due to a process called gravitational accretion. This whole turbulent and complex process results in unusual and exotic gas shapes being formed, often making them look like something produced by a very imaginative artists.

In this list, we present a selection of nebulae of various types, including the planetary, emission or dark nebulae variety, that with one or two exceptions bear a striking resemblance to animals or parts of animals. Note though that these similarities only apply to optical images and that in other frequencies, the nebulae shown here may either be invisible, or look nothing like the optical image. Let us now start our tour of the celestial menagerie:

Cat’s Eye Nebula

Cat's Eye Nebula
Image Credit: Nordic Optical Telescope / Romano Corradi

-Nebula type: Planetary nebula
-Constellation: Draco
-Coordinates: RA 17h 58m 33.423s |17h 58m 33.423s
Distance: 3,262 light years
-Apparent Diameter: – 5 minutes of arc (including extended halo)
-Magnitude: 9.8
-Other designations: NGC 6543, Snail Nebula, Sunflower Nebula, (includes IC 4677), Caldwell 6

While most images show only the bright inner 0.2 light-year wide part of this planetary nebula as the cat’s eye, the image shown here is of the entire “eye”, with the “pupil” glowing brightly in the centre.

Although The Cat’s Eye Nebula was discovered by William Hershel, its non-stellar nature was first demonstrated by William Huggins, who used the spectra of nebula to prove that these object were gaseous in nature. This particular nebula was incidentally the first planetary nebula to have its nature determined through studies of its spectrum.

Nonetheless, the Cat’s Eye is among the most intensely studied planetary nebulae in astronomy, and recent observations have shown that the bright inner core has an effective temperature of between 7,000K and 9,000K, while the outer halo is significantly hotter at about 15,000K. Spectroscopic studies have also shown that the extremely energetic central stars’ solar wind leaves the star at a speed of about 1,900 km/sec, and is blowing material out of the nebula at the rate of about twenty trillion tons per second.

Monkey Head Nebula

Monkey Head Nebula
Image Credit: Bill Snyder

-Nebula type: Emission nebula
-Constellation: Orion
-Coordinates: RA 06h 09.7m|Dec. +20° 30′
-Distance: ± 6,400 light years
-Apparent Diameter: 40 minutes of arc
-Magnitude: 6.8
-Other designations: NGC 2174

It is not hard to make out the outline of a monkey head in this confused jumble of clouds, pillars, and glowing gas located in the constellation Orion. However, it is not certain if the designation NGC 2174 refers to the entire nebula, its brightest part, or to the star cluster that is contained within the nebula.

What is certain though is that the image above shows a violent and turbulent star-forming region in which stars are being formed at a furious pace on a “first-come-first-served” basis. The violence has to do with the fact that while there is enough material present to form hundreds of stars, the first ones to emerge from their birth cocoons blow away much of the material, and the younger and more massive the star, the more material is blown away.

This feeding frenzy results in bright filaments of material emerging from the dark mass, which are streamers of dust and gas being blown off the main mass by the strong solar winds of newborn stars located behind the clump of dark material.

Dark Horse Nebula

Dark Horse Nebula-Nebula type: Dark nebula
-Constellation: Ophiuchus
-Coordinates: RA 17h 21m|Dec. -21° 07′
-Distance: Uncertain
-Other designations: Great Dark Horse

Seeing the shape of a galloping horse silhouetted against the rich star fields of the upper regions of the Milky Way’s central bulge requires no imagination. Like other dark nebulae, the Dark Horse Nebula consists of material that is dense enough to prevent light from background stars penetrating them, thus making them stand out against the star fields behind.

The rump and hind legs of the Horse are also known as the Pipe Nebula, which is itself made up of three distinctly separate nebulae, designated B77, B78, and B59, respectively, with the “B” in each designation referring to the astronomer E.E. Barnard, who made it his life’s work to find and describe dark nebulae. Note that the ability to see the Dark Horse without optical aid is generally taken as a sign that the sky is very dark, in the sense that there is no light pollution at the observing site.

Cat’s Paw Nebula

Cat's Paw Nebula
Image Credit: ESO/Digitized Sky Survey 2 – ESO,

-Nebula type: Emission nebula
-Constellation: Scorpius
-Coordinates: RA 17h 19m 58s|Dec. -35° 57′ 47s
-Distance: 5,500 ± 970 light years
-Apparent Diameter: ± 80 light years
-Other designations: ESO 392-EN 009, Sharpless 8, RCW 127, Gum 64

Also known as the Bear Claw Nebula, the three lobes at bottom left form the actual structure named after its resemblance to the pads on the animal’s paw. In scientific terms, the Cat’s Claw Nebula is only a minute fraction of the much larger NGC 6334, a complex arrangement of nebulae and star forming regions in which the Cat’s Paw Nebula is more precisely identified as NGC 6334A. The heat being produced by the hot young stars in this active star forming region is what is causing the hydrogen gas surrounding them to glow red.

Fox Fur Nebula

Fox Fur Nebula
Image Credit APOD / NASA

-Nebula type: Combination of diffuse emission and dark nebulae
-Constellation: Monoceros
-Distance: 2,700 light years
-Other designations: NGC 2264, Sh2-273

With some imagination, it is possible to see the head and front legs of a red fox, and to some observers the dark, reddish area to the right of the bright blue nebulosity resembles a stole (vestment) made from red fox fur, hence the informal name of this confused jumble of dust and gas.

The close-up image of a small part of the much larger Christmas Tree star cluster (which also includes the Cone Nebula) shown here, highlights the reddish region of the cloud complex in which embedded stars are illuminating their surroundings with their own UV light. However, the blue parts shown here consist of a different type of dust that reflects mainly the blue light from the same stars that illuminate the reddish parts of the cloud complex.

Horse Head Nebula

Horsehead Nebula
Image Credit: Ken Crawford

-Nebula type: Dark nebula
-Constellation: Orion
-Coordinates: RA 05h 40m 59.0s|Dec. -02° 27′ 30.0″
-Distance: 1,500 light years
-Diameter: 7 light years
-Other designations: Barnard 33, LDN 1630,

Like the Dark Horse Nebula, the shape of a horses’ head in the Horse Head Nebula is similarly apparent. Located just below the star Alnitak, the eastern-most of Orion’s belt stars, the Horse Head is an enormous pillar of dust in the giant Orion Molecular Cloud Complex that is obscuring the light from stars behind it. In fact, the Horse Head is so dense that it casts a shadow, which can be seen towards its lower left in the image above.

This part of the Orion Molecular Cloud Complex is an enormous star-forming region in which the area immediately surrounding the Horse Head is filled with localized pillars and filaments of gas and dust, which results in alternating regions of transparency and opacity. The pinkish glow in almost all images of this region is caused by emissions from heated and ionized hydrogen gas, while the streaks in the background are caused by magnetic fields arranging gas being blown out of the region by energetic stars into lines that correspond to the magnetic fields.

Note that while the Horse Head Nebula is very easy to photograph, it is notoriously difficult to observe optically.

Snake Nebula

Snake Nebula
Image Credit: Friendlystar

-Nebula type: Dark nebula
-Constellation: Ophiuchus
-Coordinates: RA 17h 23m 30s|Dec. -23° 38′
-Distance: 650 light years
-Apparent Diameter: 37 × 17 minutes of arc
-Other designations: Barnard 72

Another easily recognized dark nebula, the Snake Nebula is in fact a part of the Pipe Nebula, which is in turn, a part of the Dark Horse Nebula, neither of which is shown here.

In telescopic views under dark and clear skies, the Snake’s body varies between 2′ and 3′ in thickness, and runs from the northwest to the southeast for about 6’. Note that the bright spots on the Snake’s “body” are foreground stars. The three dark blotches under the Snake are unrelated, small dark nebulae that are designated Barnard 69, Barnard 70, and Barnard 74, respectively.

Horseshoe Nebula

Horseshoe Nebula
Image Credit: ESO

-Nebula type: Emission nebula
-Constellation: Sagittarius
-Coordinates: RA 18h 20m 26s|Dec. -16° 10′ 36″
-Distance: 5,000 – 6,000 light years
-True Diameter: 15 light years
-Magnitude: 6.0
-Other designations: M17, Swan Nebula, Sharpless 45, RCW 160, Gum 81

Perhaps better known as M17, the Horseshoe Nebula also goes by other popular names, among which are the Omega Nebula, Checkmark Nebula, and Swan Nebula. Different observers see different things in this nebula, although the name “Horseshoe Nebula” probably derives from a description of it by John Herschel, made when he observed it from Cape Town in 1873. Part of the description refers to a horseshoe- “…In particular the large horseshoe-shaped arc.. is there represented as too much elongated in a vertical direction and as bearing altogether too large a proportion to [the eastern] streak and to the total magnitude of the object”.

Nonetheless, the Horseshoe Nebula is only a relatively small part of much larger 30,000 solar-mass cloud of interstellar material that is estimated to span an area of about 40 light years. Although the Horseshoe Nebula itself is only about 15 light years across, it has about 800 solar masses and is considered by many to be the biggest star-forming region in the entire Milky Way galaxy.

The nebula contains the star cluster NGC 6618, with the light from this 800+ member cluster responsible for the nebula’s glow, while the light from a further 1,000+ stars embedded in the outer reaches of M17 is reflected off the nebula. Although it is not apparent from the image shown here, the general geometrical shape of the Horseshoe Nebula closely resembles that of the Orion Nebula

Dragon Nebula

Dragon Nebula
Image Credit: ESO

-Nebula type: Emission nebula
-Constellation: Dorado
-Coordinates: RA 05h 35m 30.0s|Dec. -67° 35′ 00?
-Other designations: ESO 56-EN161, Dragon’s Head Nebula

The reddish structure left of centre is seen as the head and gaping mouth of a dragon bearing down on the observer, although one might need to use a bit of imagination to picture the shape as one of the mythical beats traditionally depicted in folklore.

Nonetheless, whatever an observer sees, this enormous combined nebula, and star-forming region is located just to the north of the central bar in the Large Magellanic Cloud. In fact, the entire region shown here is an exceedingly complex area of huge bright clouds of gas and dust that are alternated by dark dust clouds and lanes, the whole of which is interspersed with closely grouped stars.

Amongst the components of this structure are NGC 2029 and NGC 2032, which are active regions in which stars are forming, and NGC 2040, an ancient supernova remnant in which an open star cluster has formed.

Camel Eye Nebula

Camel Eye Nebula
Image Credit: ESA / Hubble & NASA

-Nebula type: Planetary nebula
-Constellation: Camelopardalis
-Coordinates: RA 04h 06m 59.39s|Dec. +60° 55′ 14.4?
-Distance: 4,240 light years
-Apparent Diameter: 0.863 minutes of arc
-Magnitude: 13.0
-Other designations: PK 144+6.1, PN G 144.5+06.5, GC 801, CS 14.4, H 4.53

Also known as the Oyster Nebula, the Camel’s Eye is actually located on the flank of the giraffe depicted in the constellation Camelopardalis, and not in the “head” of the animal, which makes the name “Camel’s Eye” somewhat of a misnomer.

This pretty nebula shows a complex arrangement of “bumps and bubbles” that have yet to be explained. Another interesting feature of this nebula is that it has a variable star at its centre, which glows bright orange in this image. While variable stars are not exactly uncommon, it is highly unusual for central stars in planetary nebulae to be variable, and to vary significantly over periods of only 30 minutes or so, to boot.

Elephant’s Trunk Nebula

Elephant's Trunk Nebula
Image Credit: Bob Franke

-Nebula type: Dark nebula
-Constellation: Cepheus
-Distance: 2,400 light years

The feature shown here is easy to recognize as the trunk of a cosmic elephant. However, this is only a minute part of the enormous region of ionized gas designated as IC 1396, with the area containing the Elephant’s Trunk Nebula designated as IC 1396A.

As seen in this image, the Trunk is a small, dense area known as a “globule”, which is bounded by a bright, sinuous rim. The bright rim represents the “surface”, or edge of the globule, which is being illuminated and ionized by the radiation from a massive star, designated HD 206267, and located just to the east of the Trunk. In fact, the entire region surrounding the Trunk is being ionized by the star, and the only reason the Trunk stands out is that it is dense enough to withstand the ionizing radiation better than the surrounding area. The Trunk itself is now thought to a star-forming region as a result of the stars’ radiation compressing the gas and dust on the edges of the nebula, thus creating the conditions required to cause gas clouds within the nebula to collapse.

 

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