In astronomy, the term “nebula” refers to an interstellar cloud (as in the word “nebulous”) and can take several forms. An emission nebula is formed of ionized gases that emit light of various colors (as in a neon sign). The primordial element in the cosmos is hydrogen, and a hydrogen emission nebula is seen as red. Reflection nebulae are clouds of less intensive energy, but still sufficient to scatter the light. As in the sky, blue is the color with the shortest wavelength; as the sky is blue, so are many reflection nebulae. Finally, there are dark (or absorbtion) nebulae, basically a dust cloud that obscures the light behind it. In the picture of the Horsehead Nebula, we have both a n emission nebula and a dark nebula (which just happens to resemble a horse’s head). The Horsehead Nebula (also known as Barnard 33) is located in the constellation Orion and is about 1500 light years from Earth. Due to its form, it is probably the most identifiable nebulain the Cosmos. The Horsehead Nebula is within the Orion Molecular Cloud Complex ( the Orion Nebula) where intense star formation is taking place; this stellar nursery (not the Horsehead, which requires a telescope) can easily be seen by the naked eye as the “fuzzy” patch beneath Orion’s Belt. The Barnard 33 designation is from the Barnard Catalog of Dark Objects (dark nebulae).
BARNARD 33 - THE HORSEHEAD NEBULA
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NGC 7635 (more commonly called the Bubble Nebula) is within an emission nebula (see above) in the constellation Cassiopeia and about 7000 light years away. The "bubble" is created by what is called the stellar wind from a massive hot star located within the bubble (left of center, lower half). Basically the high temperature of the star causes glowing gasses (called a plasma) to escape at over 4 million miles per hour, driving the colder gasses in front of it and forming the edges of the bubble as it expands. In 2016, to mark the 26th anniversary of the Hubble Telescope launch in 1990, an image of the Bubble Nebula was posted and can be found on the NASA website; you can search for (what many have referred to the image as) the “Hubble Bubble” – I have anyway.
NGC 7635 - THE BUBBLE NEBULA
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The Trifid Nebula (Messier 20 or M20) is a beautiful, deep sky object located about 5000 light years away in the constellation Sagittarius (the Archer, but to most of us it resembles a teapot). The name “Trifid” means tri-lobed as it appears to be so dissected by blackish dust lanes. It is a unique combination of three types of nebulae (see the description above in the Horsehead Nebula section). The red areas are a star-forming emission nebula, while the blue area on the left is a reflection nebula. The dark areas that trisect the object are dust lanes, comprising a dark nebula. Finally, below center there is an open star cluster. The Trifid Nebula – a favorite object of astronomers – both stargazers and image makers. I think it resembles a rose, just about to bloom.
M20 - THE TRIFID NEBULA
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The Eagle Nebula (Messier 16 or M16) is a large emission nebula and associated open star cluster about 7,000 light years away in the Constellation Serpens. While a popular object for astronomers for some time, the Eagle Nebula took on truly cosmic fame after the spires (dark stalagmite-looking silhouettes sometimes referred to as “The Star Queen” seen just below center) above were photographed by the Hubble Space Telescope (HST) in 1995 and labeled the “The Pillars of Creation”. These awesome spires of gas and dust are topped with dense structures known as Bok Globules (or protostars). The image is shown so often in astronomy magazines that some people sort of expect to see it through a pair of binoculars. Truth be told, they are probably not there at all according to information from the Spitzer Space Telescope. It takes the light from M16 about 7,000 years to reach Earth and apparently a few thousand light years ago, a nearby Supernova explosion probably blew away the pillars; we’ll know for sure in another thousand years or so. Part of the fascination with astronomy and astrophysics is that when you view a galaxy or nebula, you are looking back in time.
M16 - THE EAGLE NEBULA
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The Ring Nebula (Messier 57 or M57) is a Planetary Nebula in the northern constellation of Lyra and is just over 2,000 light years away. Some explanation is necessary regarding Planetary Nebulae, and I’ll try to do it in a simplified, yet accurate, manner. When a star “lights up”, the illumination is energy given off (as in Einstein’s famous equation) from a nuclear fusion reaction (4 atoms of helium fusing into 1 atom of hydrogen). It’s not exactly that simple, but close enough. The expansion of the star is due to released pressure which just balances the gravitational collapse of the core; you thus have thermodynamic equilibrium that can go on for millions, even billions of years. In the case of our Sun, the expected lifetime is 10 billion years; the Sun is currently at the midpoint of its lifetime. Contrast this with a nuclear explosion that lasts for a few brief moments. The long lifetime of a star is truly amazing, but at the end it runs out of fuel. What happens next depends on the size (mass) of the star. For a star roughly the mass of the Sun and up to about 8 solar masses, the star goes through a cycle of growing to the Red Giant stage and then slowing becoming a Planetary Nebula with a White Dwarf star in its center. Now, the term Planetary Nebula is confusing, because the object has nothing to do with a Planet; it just looks like a ringed planet. What has happened is that the star is no longer in thermodynamic equilibrium. In the core of the star, gravity is winning and the core is contracting; in the outer regions of the star, pressure is winning and the outer shell of ionized gas starts expanding. The rate is extremely slow, but it is going on. In the case of M57, the rate is about 1 arcsecond per century. Now, the Moon is 30 arcminutes in diameter (half a degree) and if you took 1 arcminute, it is composed of 60 arc seconds. As I said, slow. The result is a beautiful deep sky object, both colorful and uniquely formed - one of the favorites of viewers and certainly for astroimagers. You can actually see the White Dwarf in the center of the ring. And it does look like a ring! What happens to larger stars when they run out of fuel? They have a violent ending, exploding suddenly in an event called a Supernova. If the star originally had about 10-25 Solar masses, the result of the Supernova would be a Neutron Star; if the star had more than 25-30 Solar masses, the result would be a Black Hole. Nuff said.
M57 - THE RING NEBULA
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The Owl Nebula (Messier 97 or M97 ) is a Planetary Nebula (see the section above for a definition/ description of Planetary Nebulae) located approximately 2,000 light years away in the constellation Ursa Major (what we call the Big Dipper). The shape of M97 and the two dark patches that look very much like eyes, give us the look of an owl face, maybe a Barn Owl. The original star (as it was collapsing) expelled matter (jets of ionized gas and dust) to both sides, with the dust blocking enough light in just the right places to “give us the eyes,” one a bit fainter than the other. The White Dwarf star (which can be seen in the photo between the eyes) lights up the Owl Nebula, but not a whole lot; the appearance through an eyepiece is faint; the image through a sensitive CCD camera appears a lot brighter
M97 - THE OWL NEBULA
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The Little Dumbbell Nebula (Messier 76 or M76) is a Planetary Nebula (see the Horsehead Nebula above for a definition) is located about 2,500 light years from Earth in the constellation Perseus. It’s called the “Little Dumbbell” because it does have a weightlifting dumbbell shape but also to distinguish it from a similar object – the Dumbbell Nebula (M27), another Planetary. The shape of M76 is quite interesting; it’s a bilaterally symmetrical structure, viewed side-on; if it were turned, the shape of 2 rings would be more obvious. Originally, astronomers thought there were two distinct objects and assigned two different NGC numbers to it. Now, bilaterally-shape objects like M76 are classified as Bipolar Planetary Nebulae. Here, one finds a unique magnetic field or fields involved that spreads the ionized gasses around both poles of the star; a current theory is that there is a companion (binary) star involved in Bipolar Planetary Nebulae. In fact, the White Dwarf in the center of M76 is a binary pair (one in the red spectrum and the other blue). With the progress of technology in astronomy, I suspect this will be sorted out in the near future. As a final note, the Little Dumbbell is difficult to view through an eyepiece unless a moderate diameter telescope (8 inches or more) is used; M76 is listed as the dimmest of all Messier objects. Imaging the object is not a problem; processing the data is typically the greatest challenge in astrophotography.
M76 - THE LITTLE DUMBBELL NEBULA
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The Cat's Eye Nebula or NGC 6543, is a Planetary Nebula about 3,000 light years from Earth in the northern constellation of Draco (the Dragon, lying between the Big Dipper and Little Dipper). The central eye is beautiful surrounded by a complex spider web filamentary structure. I was taken by the complexity as much as the beauty, but I had no idea how complex this object was – and is. The morphology is still not understood. The images from the Hubble Space Telescope (HST) in 1994 and interpretation shed some light but also add to the mystery. Apparently, the original star emitted the complex shell (consisting of knots, bubbles, and ionized gas jets) in a series of pulses every 1,500 years or so. Not typical at all. Explanations included intermittent magnetic activity (like Sunspots) and/or the action of a Binary Star (or more than a Binary); thus far, we are still looking for the Binary companion(s). This is really good stuff. I am now thinking of reimaging in the future, possible using an OIII filter and longer exposure times to get more detail in the complex mosaic surrounding the eye
NGC 6543 THE CAT'S EYE NEBULA
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M1 THE CRAB NEBULA
Chinese astronomers watching the sky on July 4, 1054, noted the appearance of a bright “apparition” in the sky within the constellation Taurus (the Bull); this event was also observed by the Anasazi people of the American Southwest. The “new Star” was visible during daylight hours for nearly a month and was a naked eye object at night for almost 2 years. It turns out that this was the first documentation of a massive and sudden collapse (implosion) of a Star far larger than the Sun – this was a Supernova; material rushed outwards of a speed of over 3 million mph (930 miles/ sec.) and is still expanding. At the core of this Supernova remnant, located 6,500 light years from Earth, is a small ultradense Neutron Star, rapidly-rotating. It has a strong magnetic field and gives off pulses (30 per second) of electromagnetic radiation every revolution. If the Earth is in the path of these radiated beams (which it is in this case), we classify it as a “Pulsar”. When we first detected these clockwork pulses in the 1960’s (including the energetic one from the Crab Nebula), there were limited explanations regarding their source, and the rumor of a “contact” from an alien civilization was spread.
If you remember Charles Messier (discussed above), of Comet and catalog fame, the Crab Nebula was his first entry, duly noted as M1. It received the name “Crab” Nebula by a Lord Rosse in 1844 for its tentacle-like structure.
If you remember Charles Messier (discussed above), of Comet and catalog fame, the Crab Nebula was his first entry, duly noted as M1. It received the name “Crab” Nebula by a Lord Rosse in 1844 for its tentacle-like structure.
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The Cone Nebula is found in the Constellation Monoceros (the unicorn, Greek), about 2,700 light years from Earth. It is an object quite similar to its nearby neighbor, the Horsehead Nebula (see above) in Orion; they are both combinations of a Dark Nebula (a dark cloud of gas and dust) in front of a bright, hydrogen-rich Emission Nebula that is actually a vast stellar nursery. The contrast in color is beautiful; a narrow-band Hydrogen Alpha filter enabled the camera to "see" the glowing ionized hydrogen plasma. The giant pillar of gas and dust is certainly cone-shaped, although it is also seen by many as either a surreal creature or a religious figure. The pillar is buffeted by strong winds generated by a nearby young Star in its growth process; it is a dynamic, turbulent region of the sky, causing the Cone Nebula to slowly erode. Once the Cone Nebula is found using a medium-size telescope, it is easy to find the Christmas Tree Cluster located just above it; depending on the size of the scope, both objects can be viewed together.
NGC 2264 THE CONE NEBULA
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The Flame Nebula is found in the Constellation Orion, about 1200 light years away. It is similar to the Cone and Horsehead Nebulae (a Dark Nebula of gas and dust in front of an Emission Nebula) although there is a Reflection Nebula (the blue) on the left as well. The Flame is very close to the Horsehead Nebula and to Orion’s Belt. With a larger field of view, the easternmost Belt Star (Alnitak) would create quite a bit of glare, and I avoided it in this image. In terms of orientation, Alnitak would be to the right of the image and the Horsehead Nebula would be to the right of, and just beneath, Alnitak. The Flame Nebula has a primeval look to it; I picture early man, wearing skins, rejoicing with arms wide in front of his first fire. This one could have many interpretations.
NGC 2024 THE FLAME NEBULA
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Another primeval image; it looks more like the Running Sasquatch. The Running Man is found in Orion, very close to the Great Nebula under the 3 Belt Stars, in the area known as the sword; it is about 1,5000 light years from Earth. The hot young Stars in the Great Nebula do not give off quite enough heat to fully ionize the surrounding hydrogen gas, but they are bright enough to cause the scattering effect characteristic of a Reflection Nebula, hence the bluish coloration. It’s not quite that simple, as the combination of dust (Dark Nebula) and some degree of ionization (Emission Nebula) is also evident. The Running Man Nebula is a favorite object for astrophotographers, but difficult to perceive visually through most small (6”) to medium-sized (14”) telescopes.
NGC 1977 THE RUNNING MAN NEBULA
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The Flaming Star Nebula is found in the Constellation Auriga (the Charioteer) and is about 1,500 light years away. It’s another of those Emission/ Reflection/ Dark Nebula combinations, and it’s quite colorful and visually interesting, with all the dust lanes. The hot blue stars are quite dominant in this area, and give rise to both the Emission (Red) and Reflection (Blue) coloration. It’s another favorite for astrophotgraphers.
The origin of the IC catalog is fairly straightforward. The New General Catalog (NGC) of celestial objects was updated towards the end of the 19thcentury, through 1907, with an Index Catalog (IC) of Nebulae and Star Clusters. Over 5,000 addditional objects were referenced in two editions; most of these additional objects were “seen” through photography.
The origin of the IC catalog is fairly straightforward. The New General Catalog (NGC) of celestial objects was updated towards the end of the 19thcentury, through 1907, with an Index Catalog (IC) of Nebulae and Star Clusters. Over 5,000 addditional objects were referenced in two editions; most of these additional objects were “seen” through photography.
IC 405 THE FLAMING STAR NEBULA
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