The Horsehead Nebula (Equine Elegance)

The Horsehead Nebula, located in the constellation Orion, is one of the most easily recognizable and most photographed nebulae in the sky. Found just below Alnitak, the left star of the three stars that define Orion's belt, the Horsehead is a dark nebula. A dark nebula is an extremely dense interstellar cloud, so dense that light from surrounding stars will not pass through the cloud. It is within the inner regions of dark nebulae that stars are born.

Photo Credit and Copyright: Jean-Charles Cuillandre (CFHT), Hawaiian Starlight, CFHT

The Horsehead, or as it is also called Barnard 33, is visible to us due the bright nebula IC 434 behind it. The pinkish/red glow typically associated with the Horsehead is caused by hydrogen gas ionized by Sigma Orionis, a bright star that is close by. The bright spots seen in the base of this magnificent nebula are stars preparing to emerge.

Approximately 1500 light years away, the Horsehead Nebula was first identified in 1888 on photographic plate B2312 by Williamina Fleming, who was working at the Harvard College Observatory as an assistant to Edward Charles Pickering.

The Hubble Space Telescope Institute, in 2001, conducted a  public survey on which formation in the heavens people would most like the Telescope to observe for its eleventh Birthday - the Horsehead Nebula was the runaway winner. Over 5,000 registered their votes online, including astronomers, both amateur and professional, teachers and students.

Many amateur astronomers and astrophotographers use the Horsehead Nebula as a test for their detection skills and equipment quality. This nebula can be difficult to find and will require at the least a high-end amateur telescope. Fortunately for those of us who do not possess professional equipment, others do and are willing to share the beauties of our night sky!

Author Resource: Written by Starr Hendon

The Trifid Nebula (Greenhouse in the Sky)

Within the nebula-rich constellation of Sagittarius lies the Trifid Nebula (M20 or NGC 6514). The word trifid means 'divided in three'. This stellar nursery has been a favorite of amateur astronomers for years, as it is a bright, colorful object when viewed through a small telescope.

Photo Credit: NASA, JPL-Caltech, J. Rho (SSC/Caltech)

The nebula was first observed by Charles Messier in June 1764; the hazy, glowing object was listed as simply M20 in the Messier Catalogue. The English astronomer John Herschel, while observing the nebula some 60 years later, noticed the dust lanes that seem to separate the cloud into three separate lobes. Herschel then named the nebula Trifid.

Trifid, unlike most nebulae, is actually a rare combination of three different types of nebulae, in addition to open star clusters.

In the upper left corner of Trifid is a reflection nebula. Reflection nebulae, as the name implies, are dust clouds that merely reflect the light that is emitted by nearby stars. These nebulae tend to be light and wispy, somewhat similar to the airiness of a mare's tail cloud. As these reflection nebulae are not dense, stars can be seen through the cloud's dust. Star formations have been known to develop within reflection nebulae.

The area that appears orange in the picture above and pink in the pictures below, is an emission nebula. Emission nebulae are clouds made up of ionized gas. A hot star emitting high-energy photons close to a nebula is one of the most common sources of ionization. The emission nebula within Trifid is an H II region, an area that has shown recent star formation.

The bands seen within Trifid are dark nebulae. Dark nebulae are so dense that light from surrounding stars and other nebulae cannot be seen through the cloud that makes up the nebula. These clouds which make up dark nebulae are the breeding ground of new stars and planets.

This combination of three different star-breeding nebulae within Trifid is akin to a greenhouse. Over time, many new stars will undoubtedly emerge from this hotbed of stellar activity.

Photo Credit: ESO

To the left of the "heart" of Trifid is a finger-like cloud formation (seen clearly in the two lower pictures) which points to the star that powers the nebula. This gas protrusion from the cloud is a well-defined example of an "EGG", or evaporating gaseous globule. The white spot at the tip of the "finger", resembling a star, is actually an extremely dense knot of gas; so dense that it is able to avoid being obliterated by the massive radiation put out by Trifid's central star.

Photo Credit: Hunter Wilson

Just half a degree south of Trifid is the Lagoon Nebula, another favorite of astrophotographers, also located in the constellation Sagittarius.

*** Note: Although the colors are markedly different between the top and two bottom pictures, these are all pictures of the Trifid Nebula. The color variances are due to a number of factors, including the equipment used for taking the photographs and filters that may have been applied during the taking of the pictures.


For Help Locating This Object in the Sky: Use the Interactive Messier Map in the upper right hand corner. Objects are listed numerically. Click on the object you wish to view (ex. The Crab Nebula is M1) and a map will be displayed showing that object's location.

Author Resource: Written by Starr Hendon

The Dumbbell Nebula (Expanding Planetary Nebula)

In 1764, Charles Messier discovered the first planetary nebula - the Dumbbell Nebula (M27 or NGC 6853). Located in the constellation Vulpecula, the Dumbbell, being a very bright planetary nebula, is easily visible when viewed through binoculars or amateur telescopes. This is the type of nebula that will be produced by our Sun when it runs out of the nuclear fuel that makes up its core, estimated to occur in 5-8 billion years.

Photo Credit: Joe & Gail Metcalf, Adam Block, NOAO, AURA, NSF

Planetary nebulae, unrelated to our solar system's planets, were designated as such due to the similarities they appear to share with the giant planets when seen through smaller telescopes. These nebulae have a relatively short life span; only in the tens of thousands of years as compared to the typical lifetime of a star, generally several billions of years. The estimated age of the Dumbbell Nebula is somewhere between 3,000 and 4,000 years, just a baby in space time.

The Dumbbell was formed when its central star, similar to our own Sun, began running low on the hydrogen that is necessary to fuel its life. As the hydrogen is depleted, the star begins burning other gases within its nuclei, including oxygen, helium and carbon. The stellar core is compacted and the outer layers begin to expand. During unstable periods, the star may eject these layers completely. What is left in place of the original core is a white dwarf star. The white dwarf in the Dumbbell is the largest known white dwarf in the solar system.

The newly-formed white dwarf star is small but extremely hot due to nuclear burning. The energy from this nuclear burning radiates away from the star, causing the ejected layers, or shells, to fluoresce. The Dumbbell's shell is expanding outward at roughly 17 miles per second, as found by Bohuski, Smith and Weedman in 1970. This expansion will continue for billions of years until all of the energy has been depleted, leaving a black dwarf in place of the star.

For Help Locating This Object in the Sky: Use the Interactive Messier Map in the upper right hand corner. Objects are listed numerically. Click on the object you wish to locate (ex. The Crab Nebula is M1) and a map will be displayed showing that object's location.

Author Resource: Written by Starr Hendon

The Lagoon Nebula (Home of Bok Globules)

Located in the constellation Sagittarius is a vast interstellar cloud known as the Lagoon Nebula (M8 or NGC 6523). Being relatively close to Earth, at approximately 5,700 light years away, the Lagoon Nebula is a favorite among amateur astrophotographers. This rich region in the sky contains numerous objects that can be easily seen with home telescopes. The Trifid Nebula (M20) is found only half a degree north of the Lagoon. With a high-powered telescope, you may be able to discern the remote globular cluster NGC 6544 one degree southeast of the Lagoon.

Photo Credit: Hunter Wilson

French astronomer Guillaume Joseph Hyacinthe Jean-Baptiste Le Gentil de la Galaisière is credited with discovering the Lagoon in 1747; however, it appears that John Flamsteed noted the nebula as early as 1680, as did Philippe Loys de Chéseaux in 1746.

As with many other nebulae, the Lagoon appears pink in time exposure color photos but is gray when viewed with the naked eye or binoculars and smaller powered telescopes. This is due to our human eyes not being able to process colors very well at low light levels. A nebula or light-pollution filter is needed to bring out the full complexity of this star-forming nebula.

Here are some outstanding photos of the Lagoon taken by amateur astrophotographers, including information on the equipment used for the majority of the pictures. Why these are considered amateur is beyond me, several of these shots rival those taken by professionals.

Located within the Lagoon are several Bok globules, dark clouds comprised of dense dust and gas where star formations sometimes begin. Discovered by Dutch-American astronomer Bart Jan Bok in the 1940's, these clouds have been described as "similar to insects' cocoons", giving birth to new stars and star clusters. While still somewhat of a mystery, Bok globules continue to be studied intensely.

The Lagoon Nebula is home to a rather massive structure resembling a pair of funnels or tornadoes, caused by heated and ionized gases emitted from O Herschel 36, the hot star pouring out ultraviolet light seen in the lower right corner of the picture below.  

Photo Credit: A. Caulet (ST-ECF, ESA) and NASA

For Help Locating This Object in the Sky: Use the Interactive Messier Map in the upper right hand corner. Objects are listed numerically. Click on the object you wish to locate (ex. The Crab Nebula is M1) and a map will be displayed showing that object's location.

Author Resource: Written by Starr Hendon

Spectacular Nebulae

A Nebula, from the Latin word for cloud, is a large cloud of plasma, interstellar hydrogen gas and dust. Nebula was long-used as a generic term for any extended cloud-like mass prior to the invention of the telescope. The first working telescopes were invented in the Netherlands in 1608 by Hans Lippershey, Zacharias Janssen and Jacob Metius. Galileo and Isaac Newton both made major contributions to the improvement of earlier telescopes. The telescope enabled us to correctly identify objects such as star clusters and galaxies from actual nebulae.

Nebulae are typically classified as either bright or dark. Bright nebulae must be fairly close to nearby stars to glow. Dark nebulae require a brighter backdrop, such as a star cluster, to be visible. One of the most well-known dark nebulae is the Horsehead Nebula in the constellation Orion. There is also what is known as a reflection nebula, which is simply a dark nebula that reflects the light of nearby stars.

Nebulae are not just incredibly beautiful formations in the sky. They play a very important role in the evolution of the galaxies. Nebulae can be involved in both the birth and the death of stars.

Stars are extremely dense objects and if a nebula is to be a star’s origin the dust particles and gas that make up the nebula must unite and be concentrated into a small “ball” of matter. Gravity pulls the gas and dust inward until the core of the nebula heats up and begins to rotate. This condensed material is what will become stars. A nebula can contain a large number of newly formed stars, causing a dark nebula to radiate with the light. A perfect example of this is the Cone Nebula, which is currently an active star formation.

One type of star death causes a planetary nebula, named as such because these nebulae are rounded and resemble planets. An aging star running low on hydrogen will begin to burn helium and swells to massive proportions. After the surface cools, this “red giant” is unstable. The outer layers of the star are thrown off, forming a planetary nebula. The core is a bluish-white color due to extremely high temperatures. It is the heat from this core that causes the nebula to glow. The Eskimo Nebula, discovered in 1787 by William Herschel, is an excellent example of a planetary nebula.

When a high-mass star dies, it will die not as a red giant but as a supernova. It this case, the star collapses inward on itself. The gas coming back into the inner layer of the star gets so super-heated that it is bounced back out in a major explosion, forming a visible nebula. The most studied supernova is the Crab Nebula, discovered by Arab and Chinese astronomers in 1054. The supernova became so bright that for 23 days it was visible even during the day. It remained visible to the naked eye for approximately two YEARS.

The Hubble Telescope has been instrumental in helping us to better understand nebulae, along with the outer reaches of space we didn’t even know existed many years ago. Imagine what will be learned over the next hundreds or thousands of years as technology continues to improve and expand our horizons.

The following is a small collection of nebulae from the NASA archives.

Author Resource: Written by Starr Hendon