Space for the Earthbound - A Journey Through the Universe

Explore the endlessly fascinating world of outer space from the comfort of your home


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 Perseids (August's Annual Meteor Shower)

August is upon us and that means it's time once again for the Perseid meteor shower.

Animation Credit: NASA MSFC

The Perseids are without a doubt one of the most popular meteor showers of the year for stargazers, largely due to the fact that the shower occurs in August. The peak date for the Perseids is Thursday, August 12, 2010. As the new moon for August is on the 10th this year, it should prove to be a very exciting shower. This is one of the longest meteor showers of the year, beginning July 17 and lasting until August 24. Even if your weather is unfavorable for meteor viewing on the peak date, there are plenty of chances to catch these "shooting stars" before the shower ends.

The full moon this year falls on the last day of the shower, August 24. Although a full moon will diminish meteor viewing to a slight degree, the full moon of August will be the most distant moon of the year. This distance makes the August moon the smallest of the year. Very definitely a plus for night sky watchers!

The best viewing for the Perseid meteor shower is as far from city light pollution as possible. Look to the northeast after midnight in the Northern Hemisphere. The best viewing will come in the hours closest to the dawn. The Perseids are named as such because they appear to come from the constellation Perseus, which at this time of year is just a bit to the east of the constellation Cassiopeia.

The meteors seen during the Perseid shower are actually debris left by the comet Swift-Tuttle as it continues on its 130-year orbital path around the Sun. Although the meteors appear to be fairly large to the naked eye, the debris causing them is generally about the same size as a grain of sand; however, a few may be similar in size to a marble or a pea. This stream of debris is known as the Perseid cloud and the majority of the dust within this cloud is approximately one thousand years old. There is also within this cloud a fairly new filament of dust left by Swift-Tuttle in 1862. Meteors originate from this filament at a much higher rate than from the rest of the debris stream.

Activity from the Perseid meteor shower was first recorded in the Chinese annals, which state that in the year 36 AD "more than 100 meteors flew thither in the morning". This August shower is also known as the "tears of St. Lawrence", since there is an abundance of meteors at the time of the festival in Italy for St. Lawrence on August 10.

The peak of the shower on August 12 should show, under optimal conditions, somewhere around 60 meteors per hour. The first hourly count, also called the ZHR (Zenithal Hourly Rate), was provided in 1839 by E. Heis from Münster, Germany. Lambert Adolphe Jacques Quételet of Brussels, Belgium, is credited with the actual discovery of the shower. In 1835, Quételet reported the activity that appeared to be emanating outward from the constellation Perseus.

So, grab a lawn chair or a blanket, find a nice, dark location and relax and enjoy the show! Binoculars can be helpful in locating faint meteors and tails but the best viewing is done with just your eyes. These meteors move extremely fast, traveling at speeds of up to 133,200 mph (60 kps) and many could be missed while using any visual aids.

Photo Credit: Nick Ares

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