We Are Family

I didn’t grow up with a sister (although I now have an awesome sister-in-law named Debbie). I guess that’s one of the reasons I find the Pleiades (PLEE-uh-deez) star cluster, aka the Seven Sisters, so intriguing. The idea of having six sisters is a difficult notion around which to wrap my imagination.

Right now, you can contemplate the Seven Sisters every evening, because about an hour after sunset when it’s good and dark, you’ll find them overhead, near the meridian.

They’re the sparkly little cloud of stars northwest (to the upper right) of the constellation Orion the Hunter. Lying between Orion and the Pleiades, you may notice a prominent, golden or pumpkin-colored star. This is Aldebaran (al-DEBB-uh-rahn), an orange giant that marks the eye of Taurus the Bull, the constellation within which the Seven Sisters reside.

Orion and Taurus, oriented with south at the bottom

Star maps created with Your Sky

The Pleiades are an open cluster, a group of stars that formed around the same time in the same nebula, or cloud of gas and dust. You may wish to think of an open cluster as a family group. There are several hundred members of this cluster, although you can see but a fraction with the naked eye.

Hobby astronomers use the Pleiades to test their visual acuity. Most people can pick out six separate stars when looking at the cluster naked-eye. Of course, amateurs try to push the envelope. The record for anyone of my acquaintance is 11 stars, seen at a very dark national park by a 20-something female astronomer. Yes, young eyes are a definite advantage; I’ve seen young adults easily pick out six or seven stars in light-polluted urban environments.

How many can you see? Test yourself at a dark location with no line-of-sight lights. To maximize your night vision, be sure to dark adapt first, that is, avoid all white light for a minimum of 20 minutes before attempting. To squeeze out every last star you can, also try averting your vision. In addition to looking directly at the cluster, try looking both slightly above and slightly below it. Sometimes additional stars will pop into view while using averted vision. This is because our peripheral vision is better than our straight-ahead vision.

Under a dark sky and with good observing conditions, you may notice a fuzziness or haziness associated with the Pleiades. No, you’re not imagining it. Not unlike car headlights moving through a patch of fog, the cluster is currently passing through an interstellar cloud of gas and dust called the Merope Nebula.

The Seven Sisters moniker by which most of the Western World knows the cluster refers to Greek legend: they’re the seven daughters of the giant Atlas (most famous for holding up the world) and the nymph Pleione (from whom the Pleiades get their name).

The named stars of the Pleiades
(oriented with south at the bottom)

Parents and daughters are immortalized in the names of the nine brightest stars in the cluster: Atlas and Pleione together to the east, and to the west, Alcyone (al-SIGH-oh-nee, the brightest star of the cluster), Merope (MERR-uh-pee, after which the nebula is named because it is densest near that star), Electra, Maia, Asterope, Taygeta, and Celaeno. The six that most people see naked-eye are Atlas, Alcyone, Merope, Electra, Maia, and Taygeta.

Known since antiquity, mentions of the Pleiades have been found in the written record as far back as several thousand years BCE. Nearly every ancient culture ascribed a mythological or folkloric identity to the celestial swarm. The Hindus saw a flame in the starry pattern--a symbol of their fire god. The Greek poets spoke of a flock of pigeons. In the French countryside, the cluster was known as the "Mosquito Net," a fact I’m sure you'll never see on a tourism brochure. The desert-dwelling Arabs imagined a herd of camels, and Hebrew writers memorialized a hen and her chickens. Natives of the Tonga Islands in the South Pacific named the object “Little Eyes.”

Many modern naked-eye observers of the Pleiades see the pattern of a little water dipper and mistakenly think they have found the much larger Little Dipper, the central asterism (star pattern) of the northern constellation Ursa Minor the Little Bear. Personally, I always see a little cluster of grapes. At recent public outreach events, people have told me they see items ranging from a lollipop to a microphone!

What do you see?

Unfortunately, my sister-in-law lives on the other side of the country, so I get to see the Pleiades more often than I get to see her. Sometimes, miles trump light years. But she’s often in my daily thoughts, and with the marvels of modern electronic communication, she’s always just an email away. As for those ladies of the night, my low-tech binoculars bring them— all seven— into sharp focus.

I’ve got all my sisters with me.

Cassie's Cluster

Note: There will be no September 17 post so that I may prepare for the STAR-HOPPERS weekend workshop in astronomy for grandparents & grandkids. Enjoy the September 10 post or browse my older posts. I'll be back with a new post on September 24.

Messier 52 in the constellation Cassiopeia the Queen is one of my favorite open clusters. I like its rich star field and its somewhat fan-shaped appearance. I also consider it a big plus that it’s easy to find.

An open cluster is a loose collection of stars that formed around the same time in the same nebula (cloud of gas and dust). You might think of an open cluster as a sort of family group.

Messier 52, or M52 as it is commonly known, is one of the 110 celestial objects in the catalog of famed 18th century French astronomer and comet-hunter Charles Messier (pronounced MESS ee yay). This catalog is used extensively by amateur astronomers as an observing list, since it contains some of the “best and brightest” deep-sky objects in the night sky. Messier discovered M52 in 1774, while “chasing” a nearby comet.

M52 is easy to find because you can use the distinctive Lazy W asterism (star pattern) of Cassiopeia to locate it. Grab your binoculars, and let’s take a look at Cassie’s cluster.

1) About an hour after your local sunset time, face north. 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 left shoulder to the west, and you’ll be facing approximately north.

Looking north to Cassiopeia's Lazy W
Star maps created with Your Sky

2) Look for a W-shaped group of stars east of the meridian. This is the central asterism of Cassiopeia, the Lazy W. Cassiopeia is a circumpolar constellation, one that circles the North Celestial Pole, the imaginary fixed point in the sky directly above the North Pole. Luckily for us, there is a star extremely close to that point in the sky, which serves as a navigational marker. This is Polaris, the North Star.

Cassiopeia and the other circumpolar constellations appear to make a complete counterclockwise circuit around the North Star, over the course of one day. But they’re not really spinning around the North Star. This apparent motion, or the way they appear to move in our sky, is caused by the rotation of the Earth, as it spins on its axis like a top, 24/7.






3) From Shedar (SHEDD-er), the lower right star of the W, draw an imaginary line through Caph (KAFF), the upper right star of the W. Then extend that line the same distance again past Caph, plus a skosh. Train your binoculars on that spot, and you should see a fuzzy patch. With a small telescope, you’ll be able to resolve the stars in the cluster, that is, they’ll separate into distinct points of light.

M52 lies around 5,000 light years from Earth. One light year is the distance light travels in one Earth year, nearly six trillion miles. The cluster is estimated to contain 200 members.

The open cluster M52
Credit: AURA/NOAO/NSF

Two hundred family members in one place at the same time makes for quite a reunion. Pass the potato salad, please.







Astronomy Essential: The universe began with the Big Bang.

The Big Bang is a widely accepted scientific theory of the origin of the universe. It postulates that about 13.7 billion years ago, the visible universe was extremely dense and extremely small— about the size of a dime. This singularity suddenly expanded to create the large-scale universe, which continues to expand today.

Many astronomers accept that a Big Bang event is the best current explanation for some key observable features of the universe, such as: its continuing expansion from a smaller, denser state; the microwave radiation “glow” that is present throughout the universe; a consistent abundance of simple elements such as hydrogen and helium throughout the universe, even in the oldest objects; and a limit on the age of stars in the cosmos.

Messier’s Lagniappe

As a young child growing up in Louisiana, I couldn’t help but assimilate a few Cajun words into my lifelong vocabulary. One of my favorites is lagniappe. A lagniappe (LANN-yapp) is a little something extra for free. Consider the thirteenth donut in a baker’s dozen, and you’ve got the idea.

Everybody likes something for free. And for stargazers, a freebie in the sky is simply irresistible.

In the 18th century, the French astronomer Charles Messier (MESS-ee-yay) produced a catalog of over 100 celestial objects that might be mistaken for comets. He was a dedicated comet hunter and didn’t want to waste time looking at fuzzy things that weren’t comets. The resulting Messier catalog has become a staple of amateur astronomy and is typically the first observing list new telescope owners work their way through.

Charles Messier

The catalog object Messier 46, also known as M46, lies in the constellation Puppis the (ship’s) Stern. Puppis (PUH-piss) lies east and south of the well-known winter constellation Canis Major (KAY-niss) the Big Dog, prominent now in the southern sky. M46 is a visually pleasing star cluster— with a lagniappe.

For this exercise, I’d recommend a reflector telescope with at least six inches of aperture (mirror diameter). Let’s go collect our cosmic freebie, shall we?

1) Wait at least one hour after sunset to begin observing, so your sky is good and dark.

2) Face south. 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.

Star maps created with Your Sky

3) First locate the Hourglass asterism (recognizable star pattern) of the constellation Orion the Hunter, on or near the meridian. It 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) Now let’s locate Canis Major. The stellar landmark that helps us find the Big Dog is blue-white Sirius, the brightest star in the night sky.

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.

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. In ancient star lore, Canis Major was considered one of Orion’s hunting dogs. Sirius marks the location of the dog’s snout.

5) East or left of Sirius, about double the distance between Sirius and the star Mirzam (which is just to its right, or west), lie two star clusters, M46 and M47. Both are open clusters. An open cluster is a loose collection of stars that formed around the same time in the same nebula (cloud of gas and dust).

Point your scope at the spot shown on the map above. Of the two clusters, M46 is the one farthest east. Both clusters will be around the same size in your field of view, but M47 is a bit brighter. However, M46 is our target, and you’ll know you’re looking at the correct cluster when you spot what looks like a fuzzy donut or smoke ring in it. This is the planetary nebula NGC2438— and our lagniappe.

A planetary nebula is the nebula formed when an average-sized star dies and ejects a gaseous shell of stellar material into surrounding space. Despite their name, planetary nebulas have nothing to do with planets; some of them simply resembled planets when viewed in earlier telescopes.

In the case of NGC2438, our dying star does not belong to the M46 cluster. Although we say it is “in” M46, the nebula is actually a foreground object, lying a little more than halfway to the cluster. At several billion years old, the disintegrating star is much older than the relative youngsters of the cluster. The stars of M46 are estimated to be 300 million years old.

M46 with planetary nebula in foreground

Although the American French word “lagniappe” didn’t come into use until the mid 19th century— nearly 30 years after Messier’s death— I like to call the planetary nebula in M46 “Messier’s Lagniappe.” I think that would have made the good Frenchman smile.

Astronomy Essential: There’s a black hole at the center of our galaxy.

It’s a supermassive black hole, to boot, estimated at four million times the size of our Sun. A black hole is an extremely dense object with gravity so strong that not even light can escape it.

Our Milky Way galaxy is not, at its heart, unique. Black holes are thought to reside at the center of most galaxies. Astronomers think that black holes may be a critical component in galaxy formation, providing the mass needed to create an environment where stars can form.

You’ll never see our galaxy’s black hole, because its extreme gravity traps the light that might illuminate it. Astronomers have to watch the behavior of stars near it to infer its existence. And at 27,000 light years away, you’re not likely to make it there in your spaceship. Just one light year is nearly six trillion miles!

Fishing for Scorpion

Scorpius the Scorpion is one of those rare constellations whose prominent star pattern actually resembles the figure it represents. The ancient Greeks, Arabs, Persians, and Turks all saw a starry scorpion in the pattern. It’s easy to see why. The long, lazy curl of stars that punctuates the constellation at its southern end looks like a scorpion’s toxic tail. Although this dramatic feature is easy to spot, it may not be wholly visible to skywatchers in the far northern latitudes, because Scorpius sits low in the south.

Image by Jim Kalisch

In Greek mythology, the scorpion was the infamous creature that stung Orion the Hunter to death. The prodigious huntsman had boasted that he could and would kill every wild animal in existence. This angered the gods, who dispatched the stealthy scorpion to do their dirty work. Afterwards, king of the gods Zeus placed both Orion and Scorpius in the sky, ensuring that the Hunter (winter constellation) was never in the sky at the same time as the Scorpion (summer constellation). They chase each other around the celestial sphere for eternity.

Scorpius in 19th century star atlas

Let’s see if we can spy the scorpion, while avoiding the business end of that sinister tail.

1) You’ll need to face south. 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 that twilight’s over and your sky’s good and dark. On Thursday the 24th, you’ll have a couple dark hours to stargaze before the gibbous Moon rises. The Moon is considered gibbous whenever its face is more than half illuminated but not fully illuminated. On Friday the 25th, the Moon’s phase will be Last Quarter (commonly called a “half moon”), and it’ll rise around midnight. Each night for the rest of our observing week, the Moon will rise a bit later with its illuminated part continuing to shrink or wane.

3) Looking due south, you should see a tall curve of stars that hooks over to the left (east) after it skims the horizon. This is the asterism (recognizable star pattern) known as the Fishhook. It’s also the torso and tail of the mythological scorpion.







4) Let’s begin our survey of the Fishhook at the top, with the stunning red supergiant star Antares (pronounced ahn-TAHR-eez), brightest star in Scorpius. Due to its deep red color and its position in the imaginary scorpion’s body, Antares is commonly called the Scorpion’s Heart.

The name Antares is from the Greek for like Mars. Planet Mars periodically enters Scorpius and passes near Antares. The red planet and the red star can easily be mistaken for one another.

Luminous Antares is 10,000 times brighter than our Sun and much larger. If Antares were dropped into our solar system in place of the Sun, it would extend beyond the orbit of Mars, engulfing that planet along with Mercury, Venus, and Earth. Immense Antares is a candidate for death by supernova, a cataclysmic explosion that occurs when a massive star reaches the end of its life cycle.

5) Below Antares, nine bright stars wind around to form the Fishhook before it terminates in a glowing barb composed of a close-set pair of stars. This terminal pair is an asterism called the Cat’s Eyes. It’s also the stinger of the legendary scorpion. The eastern star in the pair is the second brightest star in Scorpius, Shaula (pronounced SHOWL-uh). Shaula is Arabic for stinger. The fainter western star is Lesath (pronounced LESS-utt), Arabic for sting. Although Shaula and Lesath appear cozy from our two-dimensional viewpoint, they’re more than 150 light years apart and don’t interact. We often forget to apply the third dimension of depth when we see visually pleasing star patterns.

6) The third brightest star in Scorpius is Girtab, riding low on the Fishhook where it turns up toward the Cat‘s Eyes. Girtab (pronounced GRRR-tahb) is from the Sumerian for scorpion. This yellow-white giant star can’t be seen from above 50 degrees north latitude, so folks in Spokane, Washington and Utica, New York will see an interrupted Fishhook dip below the horizon.






7) If you’re observing from a dark-sky location, try this naked-eye challenge. Can you spot the two star clusters just northeast of the Cat’s Eyes? They should look like fuzzy patches of light. They’re both open clusters. An open cluster is a family group of sorts, a loose collection of stars that formed around the same time in the same nebula, or cloud of gas and dust.

The cluster closest to Shaula, known as Messier 7 (pronounced MESS-ee-yay) or Ptolemy’s Cluster, is also the brighter of the two. It contains approximately 80 stars and was named for the ancient Greek astronomer Ptolemy (pronounced TAHL-uh-mee), who wrote about it in the year 130.

The naked-eye cluster slightly north and west of Messier 7 is called Messier 6 or the Butterfly Cluster. This whimsical cluster also contains around 80 stars whose arrangement, when viewed through binoculars, suggests a butterfly. The fainter Butterfly Cluster glimmers from nearly twice the distance of Ptolemy’s Cluster.

Ptolemy’s Cluster (lower left) and Butterfly Cluster (upper right)
Copyright T. Credner, AlltheSky.com

8) Our expedition wouldn’t be complete without a dip in the Summer Milky Way. Can you see the misty stream that rises from the southern horizon, winds behind the Fishhook and the two clusters, and then stretches northward across the sky? What we call the “Summer Milky Way” is only one arm of the pinwheel-like galaxy we inhabit. The hazy, mottled arm is a horde of stars too numerous and faint to be resolved into pinpoints with the naked eye. Because the southern part of that arm--the Sagittarius Arm--lies in the direction of the dense galactic core, Scorpius occupies an area of the sky teeming with deep-sky delicacies ready to be hooked with telescope and binoculars.

Gone fishing.

A Crab, Two Jackasses, and 350 Bees

The constellation of Cancer the Crab holds a special place in my heart, because it’s my astrological sun sign. To be sure, I consider astrology a recreational pursuit rather than a scientific one. Nevertheless, I can’t help but feel somewhat possessive toward the little celestial crustacean as he scuttles across the spring sky.

Cancer is a constellation of the zodiac, following Gemini the Twins to its west and preceding Leo the Lion to its east. The zodiac is the band of twelve constellations that straddles the ecliptic, as seen from Earth. The ecliptic is the imaginary line that represents the path the Sun appears to take across the sky, as seen from Earth. Because the Earth, the Moon, and the planets all lie in roughly the same plane as they orbit the Sun, the ecliptic also represents the plane of the solar system.

The name Cancer is, appropriately, from the Latin word for crab. In Greek myth, Cancer was the crab that pinched strongman Hercules’ foot as he fought the giant water snake Hydra, a monstrous creature with nine heads. During this skirmish, Hercules crushed the crab under his foot, and the gods placed the feisty but unlucky crab in the heavens.

Cancer the Crab in 18th century star atlas
Courtesy of Linda Hall Library of Science, Engineering and Technology

How did a word that means crab come to refer to a group of cellular diseases? Early physicians noticed that tumors and the distended blood vessels around them formed a pattern that resembled a crab. Around the 17th century, they began applying the word “cancer” to the diseases that caused these tumors.

A dark sky--well away from city and suburban lights--is required to commune with the Crab. The faint constellation would be inconspicuous if it weren't for the renowned naked-eye star cluster at its heart: the Beehive. Even the brightest stars in Cancer are somewhat dim. If you see anything bright in Cancer, rest assured it’s a planet just passing through.

Grab your long-handled net, and let’s go crabbing!

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 that twilight’s finished and your sky’s good and dark. This observing week, you’ll have plenty of gazing time before the Moon floods the sky with light. It rises well after midnight on Friday the 25th and even later each night after that.

3) As you face south, tilt your head back slowly and move your gaze from the southern horizon up to the zenith, the spot directly above your head. Look for a fuzzy patch. It'll be almost as high as the zenith if you live in the southern latitudes of the continental U.S. If you live in the northern latitudes, it'll be slightly lower, up to a quarter of the way from the zenith down toward the southern horizon. It'll also be slightly west of due south. Find it? Excellent! This is the famous Beehive cluster.






If you’re having trouble finding it, first make sure you’re dark adapted. Avoid all white light for a minimum of 20 minutes. This will improve your night vision and help you see faint objects. Second, try to locate the Sickle, a prominent asterism (recognizable star pattern) in Leo. It looks like a big, backwards question mark. Right now the bright golden planet Saturn is hanging out at the base of the Sickle. The open end of the Sickle’s curving top points toward the Beehive. Also, if you can locate reddish planet Mars near the Gemini twin stars (Castor and Pollux) and draw a line between Saturn and Mars, it will cross the Beehive.

M44, the Beehive cluster

The Beehive is an open cluster, a loose grouping of stars that formed around the same time from the same gas cloud. It contains around 350 stars. It is alternately known as M44 and as Praesepe (pronounced pree SEE pee). The former is shorthand for Messier 44, the object’s designation in the catalog of famed 18th century French astronomer Charles Messier (pronounced MESS ee yay). The latter, Praesepe, is the oldest of these names and is Latin for manger. The origin of the whimsical Beehive name is unknown.

4) Once you’ve found the Beehive, look for two faint stars that bracket it on the left (east). The top star is Asellus Borealis and the bottom one, Asellus Australis. These are Latin for Northern Ass and Southern Ass. These two stars form the asterism known as the Donkeys or the Asses. In ancient mythology, the asses participated in a battle between the Greek gods and some giants. After helping the gods prevail by spooking the giants with their obnoxious braying, they were rewarded with a place in the sky next to a well-stocked feed trough, also known as a manger. Aha! Now we see why the Beehive originally had the name Praesepe.

5) The star Acubens, Arabic for the claw, marks the southernmost crab claw. Just south of Acubens (pronounced ak oo BENZ) is a circlet of stars--the asterism known as the Hydra’s Head, in the constellation Hydra. The water snake and the crab huddle together in the sky, sworn enemies of Hercules.

6) Al Tarf, the brightest star in Cancer, is an orange giant. Its name is from the Arabic for the end, and it marks one of the crab’s southern legs.

7) The only other star in Cancer with a traditional name is Tegmine (pronounced TEG-min-uh). It's Arabic for in the covering, referring to the crab’s shell. Tegmine is west of the Beehive.

8) The Beehive is a great binocular object. In fact, binoculars--rather than a telescope--usually give the most satisfying magnified view of a large object like this. If you have access to a pair of binoculars of any size, use them to peer at the fuzzy patch. The magnified patch will resolve, separating into distinct points of light.

Wander around in the cluster and notice how brilliant and sharp the stars are. I like to contrast this object with the Pleiades or "Seven Sisters" open cluster in Taurus. The Pleiades (pronounced PLEE uh deez) cluster is currently crossing paths with a nebula, a cloud of gas and dust. This makes its stars appear to be wrapped in cotton candy. In contrast, the sparkling Beehive is a visual 'palate cleanser,' not unlike a refreshing sorbet served between courses at a fancy banquet.