Thursday, February 28, 2008

Leaping Lepus

As it is Leap Year--and Friday the 29th, Leap Day--let’s visit a constellation with some spring in its step: Lepus the Hare. This unassuming little constellation is one of my favorites, because it features a couple fine telescope objects.

Lepus (pronounced LEEP us) is in perennial flight from the hound dogs of the hunt, Canis Major and Canis Minor. He is well equipped for the chase. Hares, long-eared cousins of the rabbit, have been known to attain speeds of around 45 miles per hour.

Lepus in 17th century star atlas
Courtesy of
Linda Hall Library of Science, Engineering and Technology

If you’re out under the night sky for a few hours, you’ll notice that Lepus and his canine pursuers travel from east to west over time. The stars are not actually moving west. We see this apparent motion because Earth is turning on its axis 24/7, toward the east. In the case of the hare and hounds, the effect is quite theatrical. The hare manages to stay a hop and a skip ahead of the dogs, but after midnight is relentlessly hounded right over the western horizon.

Unfortunately, the stars in Lepus are not terribly bright. Stargazers in the far northern latitudes may have some difficulty spotting the hare as he scampers under Orion’s feet, low near the southern horizon.

Let’s leap!

1) You’ll need to face south, so if you don’t know the cardinal directions at your location and you don’t have a compass, make note of where the sun sets on the horizon. That spot is approximately west. Stand with your right shoulder to the west, and you’ll be facing approximately south.

2) Wait at least one hour after sunset to begin observing, so your sky is nice and dark. During this observing week, the moon is waning (shrinking) and will not rise to wash out the sky with its bright light until after midnight. You’ll have plenty of ‘prime time’ observing hours.

3) Locate Orion the Hunter by spotting his hourglass-shaped asterism (recognizable star pattern). One hour after sunset, Orion is nearly due south. He hangs halfway to two-thirds of the way up from the southern horizon toward the zenith (the point directly above your head).

4) Below the blue supergiant star Rigel, at the lower right corner of the Orion hourglass, look for a small triangle of faint stars. These represent the Hare’s Ears. Below and to the left of the ears are the two brightest stars in Lepus, which are in the hare’s body.

Lepus star map

5) The top star of the two is Arneb, the brightest star in Lepus. Arneb (pronounced AHR neb) is a red supergiant whose name is Arabic for hare.

6) The bottom star of the two is Nihal (pronounced nih HALL), from the Arabic for camels beginning to quench their thirst. Nihal--along with Arneb and the two fairly bright stars to the left of them--form an ancient Arabic star grouping that represented four camels drinking from the ‘river’ of the Milky Way. Nihal is a yellow star, a giant version of our Sun.

7) If you have a telescope, or access to a telescope, take a look at one of my favorite globular clusters, Messier 79 (pronounced MESS ee yay). M79, as it is commonly known, is a dense ball of gravitationally bound stars. There are 150 globular clusters in the Milky Way, our home galaxy. I like M79’s whimsical star streamers. I hope you do too.

You’ll need a clear view of the southern horizon to claim this globular, since it sits low in the sky below the figure of the hare. A small scope like the Starblast Astro will snare the object, and it will look like a small fuzzy blob. Using a larger scope like a six-inch reflector, you’ll begin to resolve the fuzz into pinpoint stars. Point your telescope at the spot marked M79 on the Lepus star map above.

8) Another must-see deep-sky object in Lepus is Hind’s Crimson Star, named after the astronomer who discovered it. This is one of the most spectacular red stars in the sky. Hind’s Crimson Star is a carbon star, and as the term suggests, it has an unusually high carbon content. This carbon abundance results in the signature deep-red color. Carbon stars are among the coolest in temperature and are considered rare.

You’ll need a telescope for this object also. Try making an imaginary equilateral triangle with the bottom star and the top right star of the Hare’s Ears, with the third point out to the right of those two. Then use your telescope to search for Hind’s Crimson Star (aka R Leporis) near that third point. Make small, ever-widening circles with your telescope until you find it. Yes, it will be a bit of a challenge to target, but there will be no mistaking its brilliant color.

Courtesy of Ad-Libs Advertising, Inc. (dba Astronomics and/or Christophers, Ltd.)

Call me mad as a March hare, but I think you’ll find this object worth the extra effort.

Thursday, February 21, 2008

Two Dog Night

As Orion the Hunter strides purposefully across the winter sky, he is not alone. With him are his two faithful hunting dogs, represented by the constellations Canis Major (Big Dog) and Canis Minor (Little Dog).

Courtesy of Linda Hall Library of Science, Engineering and Technology

I sometimes wonder which breeds the ancient Greeks envisioned these two dogs to be when they memorialized them in the sky. The star atlas illustrations of the 17th and 18th centuries aren’t consistent on this point and tend to cast Canis Major as a bulldog. I’m not buying it. The bulldog most likely originated in early England, and it became well known throughout Europe primarily as a fighting dog.

Canis Major in Hyginus star atlas
Courtesy of
Linda Hall Library of Science, Engineering and Technology

I prefer the woodcut print in Hyginus’s 1482 star atlas, Poeticon Astronomicon. Now that dog could be a Greek hunting hound--a Cretan Hound, to be exact. Slender and swift like a greyhound, this carefully cultivated Greek breed has been known since antiquity as a champion hare hunter. And let’s not forget who scampers in the sky just ahead of the Big Dog, at Orion’s feet. You betcha: Lepus the Hare.

Courtesy of Linda Hall Library of Science, Engineering and Technology

Canis Minor is a small, scrappy underdog of a constellation. The depictions in the well-known Bayer and Flamsteed star atlases are a bit unsatisfactory; their Little Dogs look like coiffed, pampered pets.

Canis Minor in Bayer's star atlas
Courtesy of
Linda Hall Library of Science, Engineering and Technology

Canis Minor in Flamsteed's star atlas
Courtesy of
Linda Hall Library of Science, Engineering and Technology

Instead, I picture Canis Minor as terrier-like: energetic and feisty, with a natural hunting instinct for small game. In my opinion, another venerable Greek breed fits the bill: the Alopekis. Its name, meaning small and foxlike, appears to suit this compact, resourceful dog. Now this is a pooch with the stamina to keep up with both Orion and a fleet-footed Cretan Hound.

Come on outside, and let’s shake paws with these two admirable canines.

1) You’ll need to face south, so if you don’t know the cardinal directions at your location and you don’t have a compass, make note of where the sun sets on the horizon. That spot is approximately west. Stand with your right shoulder to the west, and you’ll be facing approximately south.

2) Wait at least one hour after sunset to begin observing, so your sky is nice and dark. The waning (shrinking) Moon will be big and bright this week as it is just past Full Moon. However, it will rise later each night, so your dark-sky observing window after sunset will increase as the week goes on. Plus, even with the Moon in the sky, you should still be able to see the bright stars of Canis Major and Minor.

3) Locate Orion the Hunter by spotting his hourglass-shaped asterism (recognizable star pattern). One hour after sunset, Orion is nearly due south. He hangs halfway to two-thirds of the way up from the southern horizon toward the zenith (the point directly above your head). Now locate Orion’s Belt, a diagonal line of three evenly-spaced stars cinching the middle of the hourglass.

4) The stellar landmark that helps us find Canis Major is blue-white Sirius, the brightest star in the night sky. Because Sirius (pronounced SEER ee us) follows Orion across the sky, ancient peoples called it the Dog, and it has come to be known as the Dog Star. Within Canis Major, it marks the location of the dog’s snout.

Find Sirius by drawing an imaginary line through the three stars of Orion’s Belt, moving from upper right to lower left, and continuing on until you come to a very bright star. This is spectacular Sirius. As star distances go, Sirius is considered quite close to Earth. At only 8.6 light years away, it is the fifth closest star to us in the Milky Way. It’s the combination of its proximity to Earth and its extreme luminosity that makes Sirius appear so bright.

Sirius is from the Greek word for scorching. Since Sirius joins the Sun in the daytime sky during July and August, the hot days of late summer have been known for centuries as the dog days. (Modern culture sidebar: remember the wonderfully quirky 1975 film “Dog Day Afternoon,” set on a hot summer day in Brooklyn?)

5) Now that you’ve found Sirius, you can find the Upside Down Y asterism that includes four of the five brightest stars in Canis Major. Sirius marks the bottom of the Y. So look below Sirius, toward the southern horizon, and you should spot three fairly bright stars that form the top of the Y.

Wezen (pronounced WEZZ en), the star at the fork of the Y, is a yellow supergiant. Its name is from the Arabic word for weight. The star at the bottom of the left fork is Aludra (pronounced al UDE rah), a blue-white supergiant whose name means virginity. The end star of the right fork is Adhara, Arabic for the virgins. Adhara (pronounced ad HAR ah) is a blue giant radiating a tremendous amount of ultraviolet light. It’s been said that if our eyes could see in ultraviolet, Adhara would be the brightest star in the sky!

The other bright star in Canis Major is not in the Upside Down Y asterism. It can be found just to the right (west) of bright Sirius. It is called Mirzam, which means announcer, perhaps a reference to its rising before Sirius and heralding its arrival. Mirzam (pronounced MERE zam) is a blue giant star.

Regrettably, observers in the far northern latitudes may have difficulty seeing the entire Y asterism as it doggy paddles in atmospheric murk near the horizon. When near the horizon, even bright Sirius can be affected by atmosphere, often twinkling furiously in a kaleidoscope of colors.

Winter Triangle

6) To find the little dog Canis Minor, first locate Betelgeuse, the red supergiant star at the upper left of the Orion hourglass. Draw an imaginary straight line connecting Betelgeuse and Sirius. Now, look for a bright star left (east) of Betelgeuse that, when connected to both Betelgeuse and Sirius with straight lines, would complete an equilateral triangle. Found it? Great! You have located Procyon, the brightest star in Canis Minor and the eighth brightest star in the night sky. Plus, the equilateral triangle you inscribed is the asterism called the Winter Triangle.

Procyon’s name is from the Greek for before the dog, a reference to its rising just before Sirius. Procyon (pronounced PRO see ahn) is a yellow-white subgiant star. Can you see its slightly golden color? Now compare it to brilliant, bluish Sirius.

The only other notable star in the Little Dog is Gomeisa, Arabic for little bleary-eyed one. Gomeisa (pronounced go MAY sah) is a rapidly spinning blue-white star. Look for it just northwest of Procyon.

7) If you’re observing under a dark sky, try to spot the winter Milky Way winding between the two dogs. I like to think of it as a cool, clear stream they might need to splash through a few times on their galactic romp with their master.

Milky Way marked with swirling gray band

Thursday, February 14, 2008

A Cosmic Valentine

My significant other is fond of saying that Valentine’s Day isn’t a day, it’s a season. This gives him the latitude to spread dinners and small gifts over the course of a week, rather than cramming it all onto February 14. Of course, I fully support this seasonal approach. I ain’t no fool (and neither, apparently, is he).

Since our observing week begins on Valentine’s Day, I will also take the ‘seasonal’ approach with my cosmic valentine to you. Here are seven romantic delights from the cosmos to spread over your week. They’re all visible in the current night sky, and they’re 100% guaranteed to make your heart flutter.

1) Messier 37. I think jewelry is always an appropriate valentine. With a single red giant star near its center, this sparkling star cluster in the constellation Auriga the Charioteer has been called “a ruby in a field of diamonds.” To find Auriga, look for a pentagon-like shape just north of the bright red planet Mars. Mars is nearly overhead about an hour after sunset. You’ll need binoculars to see this cluster. Train your binos on the spot marked M37 on the map below.

By the way, “Messier 37” is the name given to this object in the catalog of the famed 18th century French astronomer Charles Messier (pronounced MESS ee yay).

2) Rosette Nebula. May I offer you a red rose from the heart of space?

In the constellation Monoceros the Unicorn, ESE of the red supergiant Betelgeuse in Orion, lies one of the loveliest objects in the winter sky. This nebula (cloud of gas and dust) is a star-forming region, and the cluster of young stars in the center formed from the nebula only four million years ago. A small, wide-field telescope like the inexpensive Starblast Astro is a good match for this large nebula. You will need a dark sky and good transparency (atmospheric clarity) to see the nebulous ‘petals’ around the star cluster. Don’t expect to see any color in the petals; the red signature of this hydrogen-rich nebula can only be captured photographically.

An hour after sunset, you will find Orion in the south, about halfway between the southern horizon and the zenith, the point directly above your head.

3) Messier 79. What’s a Valentine’s Day celebration without a little sugar to sweeten the experience? Under Orion’s feet in the constellation Lepus the Hare is what looks like a galactic sugar pile. It is the globular cluster M79, a dense ball of gravitationally bound stars. There are 150 known globular clusters in the Milky Way, our home galaxy. This is one of my favorites; I like its whimsical star streamers. I hope you do too.

You will need a clear view of the southern horizon and a telescope to claim this globular. A small scope like the aforementioned Starblast Astro will net the object, and it will look like a small fuzzy blob. Using a larger scope like a six-inch reflector, you will begin to resolve the fuzz into pinpoint stars.

4) Saturn. Why should I give you just one friendship ring, when I can give you hundreds with a single object? Planet Saturn’s complex ring system is composed of billions of ice and rock particles, with each ring of rubble traveling in its own orbit. The ring system is remarkably thin: only half a mile thick compared to 175,000 miles wide!

You can spot golden-yellow Saturn with the naked eye. Around two hours after sunset, you should be able to spot it rising due east. It will be the brightest object near the eastern horizon, and its golden color should distinguish it from the stars in the vicinity.

5) Shooting Stars. Get thee to a dark site, away from city lights, to await your next cosmic valentine. You can see meteors, aka ‘shooting stars,’ every night of the year. A meteor is the streak of light we see in the sky when a bit of dust or space debris hits Earth’s atmosphere at high velocity. Increase your chances of seeing a meteor or two by lying on the ground or on a lounge chair, so that you can scan the greatest area of sky.

When you do spot one, make a wish. Think of it as a gift certificate from space; you can spend it however you like.

6) Venus. Since I can’t give you the Sun and the Moon, I’ll give you the next best thing: the next brightest object in the sky. Planet Venus, named for the Roman goddess of love, is currently lighting up the pre-dawn sky. The blue-white beauty rises in the ESE about an hour and a half before sunrise. Don’t confuse it with planet Jupiter, which rises from the same spot on the horizon, but about an hour earlier than Venus. Venus is also noticeably brighter than Jupiter.

7) Total Lunar Eclipse. Let’s finish out our observing week with an uncommon treat: a total lunar eclipse. A total lunar eclipse occurs when the Sun, Earth, and Moon are aligned just right during a Full Moon, so that the Sun casts the Earth’s shadow onto the surface of the Moon. On Wednesday, February 20, a total lunar eclipse will occur from 6:43 p.m. to 10:09 p.m. Mountain Time (adjust as needed for your time zone). Totality--when the Moon is entirely in the Earth’s shadow--will occur from 8:01 to 8:51 p.m. MT. The eclipse will be visible everywhere in the continental United States, and you can view it naked eye. Just watch the eastern horizon for the rising Full Moon, and then watch the shadow of the Earth creep across the Moon.

So what’s so valentine-ish about this, you ask? Well, during totality, the Moon will turn red! That’s right, red. It might be dull brick red or it might be scarlet, depending on atmospheric quality. The more dust and ‘gunk’ in Earth’s atmosphere, the redder the Moon will look. This blushing moonface occurs because some indirect light from the Sun still reaches the Moon’s surface, even though the Moon is in the Earth’s shadow. On its way to the Moon, this light first skims through Earth’s atmosphere, which filters out most of the blue. The remaining light, therefore, is red or orange.

Season’s greetings.

Thursday, February 7, 2008

The Sword of Orion

Last week we took a naked-eye tour of the constellation that owns the winter sky: Orion. Our heavily-armed hunter's most impressive weapon is his sword, dangling from the diagonal three-star belt that's recognizable even to novice stargazers. The sword also appears to be composed of three stars, but upon closer examination, we see this is a trick of light.

If you have binoculars or a telescope, go outside tonight and look at the Sword of Orion to discover just how much more is going on there than meets the (naked) eye.

1) Yes, we pay through the nose for these crisp, clean winter night skies: with face-freezing temperatures. But do try to dark adapt before observing by avoiding all white light for at least 20 minutes. It will make a big difference in the acuity of your night vision and how much detail you can see. You can always isolate yourself with the lights off in a heated room that's adjacent to an exit, or in a heated car with the dash lights turned all the way down.

2) Begin observing at least one hour after sunset, for good sky darkness. The Moon will be a waxing (growing) crescent this week, culminating in a First Quarter Moon (aka "half moon") on February 13. It will be easier to observe the Sword of Orion earlier in our observing week, while the Moon is still small and sets fairly early. The Moon will set around three hours after sunset on the evening of Saturday the 9th and four hours or so after sunset on the evening of Sunday the 10th. After Sunday, the Moon may set too late for comfortable evening viewing of the sword, unless you're a night owl and very cold hardy.

3) Here's a nifty tip for targeting sky objects with binoculars, so that when you look through your binos, the object you’re seeking is in the field of view or very close by. This becomes especially important when you’re wandering around in dense star fields where there are lots of distractions.

Look directly at the point in the sky that you want to view through binoculars. Don't take your eyes off that point as you slowly bring the binoculars up to your eyes. I repeat: do NOT take your eyes off that point as you move your hands up toward your face. If you look at the binoculars, you will lose your focus on the target in the sky. Keep your eyes glued to your sky target until the bino eyepieces touch your face. Your target should be in the field or very close by. This takes a little practice, because the impulse is to glue your eyes to the binoculars first and then sweep around until you (maybe) find the object. You'll be amazed at how efficient your targeting becomes when you master this little trick.

Bottom of the Sword

4) The bottom sword 'star' that you see naked eye is actually the combined light from three stars. In my petite 10x24 binoculars, I can see two of those stars, which are the brightest in the field of view. The dimmer of the two is actually two stars, but they are so close together I can't split them with either my binoculars or a friend's beefier 10x50s.

The Running Man Nebula

5) The top sword 'star' that you see naked eye is actually the combined light from two stars, amplified by the nebula (cloud of gas and dust) that surrounds them and reflects their light. This cloud is known as the Running Man Nebula, because of its whimsical shape. Amateur astronomers with large telescopes and very good sky conditions can see the Running Man Nebula visually, and he's a favorite target of astrophotographers. Can you pick out the two brightest stars in your field of view?

With my 10x24s, I see a faint smudge above the two stars, in line with the rest of the sword. When I switch to the 10x50s, which have much more light-gathering capability, I see that the smudge is really a star cluster, also known as an open cluster. An open cluster is a loose grouping of stars that formed around the same time in the same nebula. You may want to think of them as a 'family unit.' This open cluster has the unromantic name of NGC 1981, but I like to call it the "Sword Hilt Cluster," to give it a little more flair.

Open cluster NGC1981
Image from
Sloan Digital Sky Survey

6) The middle 'star' of the sword isn't a star at all. It's one of the finest objects in the Milky Way: the Great Orion Nebula, a massive dust and gas cloud where stars are born. In binoculars, it reveals itself as a fuzzy glowing blob with some stars in it. In the 10x24s, the blob looks rather homogenous, but in the larger 10x50s, I begin to see tendrils of hazy material fanning out from the bright core.

What illuminates this bustling stellar nursery is a combination of the huge, hot stars being born there and their impact on the surrounding material. Ultraviolet radiation from these stars excites the cloud's atoms, which then emit energy in the form of light. It is the nebula's distance from Earth, 1350 light years, that makes it appear so small and star-like when we gaze at it naked eye. After all, just one light year, the distance light travels in one Earth year, is nearly six trillion miles!

The Sword of Orion

7) Let's switch now to a telescopic view. In a modest refractor telescope at 40x magnification--a significant bump up from the 10-power binoculars--more is revealed. You can now split the two clingy stars at the bottom of the sword that looked like one dim star in binoculars. You should also begin to see nebulosity (foggy-looking haze) around the brightest star of the trio.

Moving up the sword to the Great Orion Nebula, you should now see three bright stars near the dense core of the nebula. If you increase magnification to at least 65x, you’ll see that the brightest of the three is actually a tight cluster of four stars. This famous group is known as the Trapezium (a trapezium is a four-sided geometric figure). It was our old friend Galileo who first discovered the Trapezium was a star cluster, using what we'd call a primitive telescope.

Compared to our five-billion-year-old Sun, the 300,000-year-old Trapezium stars are young whippersnappers. They were born from the material of the Orion Nebula, just as stars have been born throughout the history of the universe--with the ignition of nuclear fusion in ultra-dense, ultra-hot clumps inside a hydrogen-rich nebula.

8) No matter how limited your equipment, you can see that even a modest bit of magnification on the Sword of Orion reveals far more than you can see naked eye. The more aperture (diameter of the lens or mirror) and magnification you can muster, the more you will see. Go as deep as you dare.

The most amazing view I ever had of the Orion Nebula was through my friend Gordon's 20-inch (diameter) reflector telescope, a 'cannon' that requires a tall ladder and a nosebleed to get to the eyepiece. He pumped up the magnification to eleventy-eleven-gazillion, and I felt like I was floating inside the nebula. Pinpoints of light--newborn stars--were embedded everywhere I looked, like sequins scattered in the folds of fabric. The more I looked, the more I saw. It was a cosmic experience.

The moral of my story? If you don't have a big telescope, make friends with someone who does!