Gloucester Area Astronomy Club

h 3945 Canis Majoris
by Glenn Chaple

What is the most colorful double star in the night sky? Most amateur astronomers would vote for β Cygni (Albireo). Others might cite γ Andromedae (Almach), ι Cancri, ξ Bootis, or η Cassiopeiae. Sadly overlooked is a double star that might challenge them all – h 3945 in Canis Major. It is arguably the most colorful double star in the winter sky and, in fact, has been nick-named the “Winter Albireo.”

h3945 (aka 145 Canis Majoris) is one of more than 5500 double stars catalogued by John Herschel (William’s son) in the early 1800s. The magnitude 5.0 primary is accompanied by a 5.9 magnitude companion 26.8 arc-seconds away. Their spectral types (K0 and F0) give rise to a stunning color contrast. In her book Double Stars for Small Telescopes, Sissy Haas writes, “Showcase pair: A bright, wide, and easy pair with deep colors. The stars are bright citrus orange and royal blue; these colors are seen vividly and in strong contrast.” In early 2008, 3945 was the subject of a forum on the Cloudynights website. The general consensus was that this is one of the most beautiful double stars in the night sky. That was my thought when I included h3945 in a “Top 100 Doubles” series written for Deep Sky Magazine in 1983.

Despite these kudos, h3945 still gets the cold shoulder from most backyard astronomers. In the February, 1980, issue of Deep Sky, I described h3945 as “one of the most colorful, yet underrated, double stars in the heavens.” Richard Dibon-Smith, on his Constellation Web Page (www.dibonsmith.com) concurs, noting that, “h3945 is a gorgeous yet rather unknown binary.” In the Cambridge Double Star Atlas, co-author James Mullaney laments that h3945 is “Largely unknown & unobserved – a pity!”

Why would such a beautiful double star be so grossly ignored? There are two parts to the answer – h3945 is in a southerly location, and it isn’t as bright and easily seen as Albireo or Almach. The first isn’t a problem if your observing site affords a clear view of the lower half of Canis Major. As for finding h3945, just trace a line from ο1 CMa past ο2 CMa and extend it about 3 degrees beyond (see finder chart).

Sissy Haas, Richard Dibon-Smith, James Mullaney, your truly, plus a batch of backyard astronomers on the Cloudynights website have all raved about h3945. Now it’s your turn to experience one of the night sky’s true gems.

Your comments on this column are welcome. E-mail me at gchaple@hotmail.com

β Orionis (Rigel)
by Glenn Chaple

You won’t need a finder chart to locate this month’s featured sky object. It’s the first magnitude star β Orionis, better known by its proper name Rigel. Seventh brightest star in the night sky, Rigel dazzles us with a diamond-white color; especially striking when compared with Orion’s other first-magnitude star, the ruddy-hued Betelgeuse.

Many backyard astronomers are unaware that Rigel is a double star. Its companion (Rigel B) lies 9 arc-seconds away – a gap that should be easily breached by the smallest of telescopes. Unfortunately, it shines at magnitude 6.8, 400 times fainter than the primary. As a result, the little star often hides in the glare of its master.

In 1822, the first reliable measure of the Rigel system indicated a separation of 8.9” and a position angle of 201o, the latter meaning that Rigel B lay south and slightly west of the main star. Not much has changed in nearly two centuries. In 2004, the separation and P.A. had increased slightly to 9.4” and 204o. Because Rigel A and B share a common proper motion, astronomers believe they form a physical binary separated by a whopping 2500 AU – a distance over 60 times greater than the gap separating Pluto from the sun. Their orbital period is thought to exceed 25,000 years. The last time Rigel B was in its current orbital position the earth was in the grip of the Ice Age!

Because of the large disparity in brightness between its components, Rigel offers a similar challenge to the one presented by the notoriously difficult Sirius. While Sirius and its white dwarf companion the “Pup” require absolutely steady seeing conditions and an 8-inch or larger telescope, Rigel may be split with a 6-inch under normal sky conditions. Years ago, on an evening of unusually steady skies, I managed to glimpse Rigel B with a 3-inch f/10 Edmund reflector (the classic model sold back in the 50s and 60s) and a magnifying power of 120X. I cheated, first spotting the companion with a 6-inch reflector. Knowing where to look, I had no trouble capturing Rigel B with the 3-inch. It appeared as a tiny bluish speck just outside the brilliant sparkle of the main star.

Next time you turn your telescope skyward to admire the Orion Nebula, take a side trip to Rigel. Unlike the legions of backyard astronomers who have marveled at the great nebula, you’ll be among a much smaller group of observers who have admired Orion’s brightest binary star.

Your comments on this column are welcome. E-mail me at gchaple@hotmail.com

omicron Ceti (Mira, the “Wonderful”)
By Glenn Chaple

Last month, we looked at the prototypical eclipsing binary beta Persei (Algol). This month, we turn to another prototype, the classic long-period variable (LPV) omicron Ceti. This star boasts a rich history, having been discovered by David Fabricius on August 13, 1596. Johann Bayer added it to his Uranometria star catalog as a 4th magnitude star. When it became apparent that this star would miraculously appear and disappear (a stellar behavior unheard of in those days), astronomers gave omicron Ceti the nick-name Mira “the Wonderful.” Mira’s periodicity was first described by Johann Holwarda, who determined a period of 11 months – a figure is close to today’s standard.

Mira is the prototype of a class of pulsating variable stars called “long-period variables (LPVs).” The typical “Mira-type” star is a red giant with a range of 5 or 6 magnitudes and a period of several months to one or two years. The brightest of LPVs, Mira typically varies from magnitude 3 to 9 in a 331 day cycle. At times Mira will rise to 2nd magnitude, and in 1779 was observed by William Herschel to rival the first magnitude star Aldebaran.
With modest means, you can follow Mira through a complete cycle. Naked eye observations will cover magnitude 5 and brighter, binoculars will work for magnitudes 5 through 8, while a small rich-field telescope can handle Mira at minimum. A small scope magnifying 50X will also uncover Mira’s 9th magnitude optical companion, situated 120 arc-seconds away.

In November, Mira reached a peak brightness of about magnitude 3.5. The star has begun to fade, but should still be visible to the naked eye throughout December and the early part of January. The accompanying chart should help you make rough estimates of Mira’s brightness. If you want to follow it into the domain of binoculars and small telescopes, log on to www.aavso.org. First, click on “Make a Chart.” In the box labeled “NAME,” type on “omi Cet.” Next to the “Plot a Chart of this Scale” prompt, scroll to “B” (the scale used for relatively bright variable stars). Click on “Plot Chart” and – voila! – you have a “B” chart for Mira.

Last month, I noted that observing and recording an eclipse of Algol should be on every backyard astronomer’s “to-do” list. Add Mira the Wonderful to that list.

Your comments on this column are welcome. E-mail me at gchaple@hotmail.com.

Ursid Meteor Shower
By Glenn Chaple

You’re quite likely familiar with the Geminid meteor shower. One of the year’s most prolific, with hourly rates often exceeding 100 meteors, the Geminids reach peak activity on the evening of December 13-14. With the moon close to new phase, the 2009 Geminid display should be spectacular.

Less known is a meteor shower that occurs about a week later – the Ursids. Discovered a little over a century ago, the Ursids are associated with the comet P8/Tuttle. There are two reasons why this meteor shower is so little observed. For one thing, it’s rather sparse. Although there have been reports of short outbursts of 100 Ursids per hour, the hourly rate rarely reaches double figures. Couple that with the fact that the Ursids climax near the peak of the Holiday season (predicted maximum activity is scheduled for the evening of December 21-22), and you have a meteor shower few backyard astronomers have ever observed.

That includes me. In years when I’ve made plans to view the Ursids, either clouds or a bright moon got in the way. Other times, I got so wrapped up in Holiday hysteria, I either forgot or was too tired to bother. On the one clear, moonless evening I did give the Ursids a try, I saw virtually nothing for 15 minutes, got bored, and went back inside – behavior NOT worthy of a so-called avid amateur astronomer!

Here’s my game plan for Ursids 2009 – one that I encourage you to try. Some time towards the middle of the night when the waxing crescent moon has set, I’ll bundle up and go outside with a thermos of hot chocolate. Since the Ursids appear to radiate from the vicinity of the star Kochab (β Ursae Minoris) I’ll set up a lawn chair in a part of my back yard that affords a clear view of the northern sky. Then I’ll sit and wait. No copping out after a quarter hour! I’ll watch for at least an hour, or until I’ve spotted 5 or 6 Ursids, which ever comes first. Who knows – I might be fortunate enough to catch one of those rare Ursid outbursts. It’s the uncertainty of meteor showers that makes them so fascinating.

Want to know more about the Geminids and Ursids? Check out Gary Kronk’s www.meteorshowersonline.com. And don’t forget the section on meteor showers in Guy Ottewell’s annual publication Astronomical Calendar.

Your comments on this column are welcome. E-mail me at gchaple@hotmail.com.

β Persei (Algol, the “Demon Star”)
By Glenn Chaple

Are you ready for the eclipse of November 13th? I’m not talking about the sun or moon. I’m referring instead to an eclipse of the fascinating star β Persei (Algol).

Algol is arguably the best-known example of an eclipsing binary. Every 2.867 days like clockwork, Algol dims from magnitude 2.1 to 3.4. The entire fade-away and return to normal brightness takes about 10 hours. Algol’s variability was first described by Italian astronomer Geminiano Montanari in 1667. However, its Arabic name (from Al Ra’s al Ghul “The Demon’s Head”) suggests that Algol’s odd behavior was noted centuries earlier.

Algol is comprised of a bright B8 main-sequence star orbited so closely by a fainter K-type subgiant that the two appear as a single star. Because their orbital plane is nearly edge-on to our line-of-sight, the faint member periodically passes in front of the primary, the eclipse causing a temporary dimming of the system’s light.

There are two windows of opportunity for viewing an Algol eclipse. First, you’ll need an evening from mid autumn to late winter when Perseus is well-placed in the sky. Next (unless you’re a night owl who doesn’t mind being out during the wee hours of evening) you’ll want an eclipse that begins after sunset and winds down around midnight.

According to the RASC Observer’s Handbook 2009, a favorable Algol eclipse will occur on Friday, November 13th, with mid-eclipse predicted for 8:21 pm, EST. Although the complete event takes about ten hours, most of the action can be seen within a 6-hour span. Starting about 3 hours before mid-eclipse (around 5:20 pm, or as soon as darkness permits), record your initial magnitude estimate. Use the accompanying chart, which shows the magnitudes of nearby comparison stars (to the nearest tenth, with decimals omitted). Continue at 15-minute intervals until Algol has returned to its original brightness. Special equipment won’t be necessary – Algol is readily visible to the unaided eye. One hint: go outside an evening or two before the eclipse to identify Algol and its comparison stars. You’ll avoid a lot of confusion and wasted time on eclipse night.

Observing an eclipse of Algol is a great group project for an astronomy club. I took part in one a few years ago with members of the Boston ATMs. Between estimates we had time to conduct regular skygazing through our telescopes – a combination which made for a fun and fast-paced evening. Should clouds prevail on the 13th, you can scout out future Algol eclipses by consulting the Observer’s Handbook or a current issue of Sky and Telescope. Observing and recording an eclipse of Algol should be on every backyard astronomer’s “to-do” list.

Your comments on this column are welcome. E-mail me at gchaple@hotmail.com.

NCG 7293 – the “Helix Nebula”
By Glenn Chaple

NGC 7293, the Helix Nebula, is the nearest planetary nebula (distance ~ 450 LY) and largest in apparent size (12 by 16 arcminutes). Moreover, it’s a 7th magnitude object. An easy telescopic target? Hardly! The magnitudes listed for deep-sky objects are often misleading, and the Helix Nebula is a prime example. Were you to defocus a 7th magnitude star until the image covers half a moon diameter, you’d have an idea of the visual appearance of the Helix. In Visual Astronomy of the Deep Sky, author Roger N. Clark notes that its average surface brightness is 20.8 magnitudes per square arcsecond.

Despite its faintness, the Helix Nebula can be readily observed. On a clear, moonless night in dark-sky areas, it may be glimpsed with binoculars. In fact some keen-eyed observers in extremely remote locations have spotted the Helix with the unaided eye! The key to viewing the Helix by telescope is to use a telescope/eyepiece combination that can produce a field about one-half to a full degree across. Because of its southerly location, you’ll want to select a viewing site with an open southern horizon, free of any sky glow.

I first saw the Helix on July 31, 1981 from the clear skies of Stellafane. Through my 3-inch f/10 reflector at 30X, it appeared as a “large, tenuous glow.” Stellafane regular Peter Kandefer peeked into the eyepiece and confirmed my sighting. More recently, I had no trouble spotting the Helix with a 4-inch f/8 reflector. The key in both instances was to know exactly where to look. The accompanying finder chart pinpoints the Helix Nebula’s location in the southern part of Aquarius about 1 ½ degrees west of the 5th magnitude star Upsilon Aquarii.

The Helix Nebula offers three challenges:
1. Capture it with binoculars or small telescope
2. Discern its annular form with medium to large-sized telescopes
3. Spot its 13th magnitude central star
Are you up to the challenge? On the next clear, moonless autumn night, try your luck with NGC 7293, the Helix Nebula.

Your comments on this column are welcome. E-mail me at gchaple@hotmail.com.

Epsilon Pegasi – the “Pendulum Star”
By Glenn Chaple

This month, we’re going to pay a visit to epsilon Pegasi (Enif), the “Pendulum Star.” It’s an optical double star comprised of magnitude 2.5 and 8.7 component stars separated by 144 seconds of arc. Pairs this wide usually don’t merit much consideration, but wait! Epsilon Pegasi has a surprise for us.

After centering this pair in the eyepiece field (60 – 100X is the recommended magnification), mentally trace a line between them. While keeping your eye at the eyepiece, gently jigglethe telescope back and forth so that the two stars move at right angles to the imaginary line. While the golden yellow primary (a K-type star) travels serenely back and forth, the little companion seems to swing wildly to and fro, like a clock pendulum. It’s one of the most amazing telescopic optical illusions you’ll ever witness.

What’s happening? According to Sir John Herschel, who was among the first to describe the “Pendulum Star,” the oscillations are due to the longer time it takes light from the faint star to affect the retina. We detect the motion of the primary a split second earlier, so the companion seems to lag behind. Rapid back and forth movement of the telescope generates the illusion of pendulum-like motion.

The Pendulum Star received plenty of recognition in astronomy guidebooks written in the late 19th and early 20th century – a time when double stars enjoyed tremendous popularity. Nowadays, with attention directed towards nebulae, clusters, and galaxies, epsilon Pegasi receives scant notice.

The finder chart shows the location of epsilon Pegasi. If you hunt down deep-sky objects by the star-hop method, you may recognize it as a pointer (with nearby theta Pegasi) to the globular cluster M15. Next time you plan to visit M15, take a moment to check out epsilon Pegasi. This star will put on a show that’s sure to dazzle!

Your comments on this column are welcome. E-mail me at gchaple@hotmail.com.

“Chaple’s Arc”
By Glenn Chaple

Forgive me for the apparent ego trip, but this month I’m going to introduce you to an amazing little asterism called “Chaple’s Arc.” I stumbled upon the Arc in the mid-1970s while looking for the double star h1470. Instead of one double, I found four arranged in an arc 1/2o across. So smitten was I by its extraordinary appearance that I eventually wrote about it in the September 1980 issue of Deep Sky Monthly. New York amateur astronomer John Pazmino viewed the group and dubbed it “Chaple’s Arc.”

A quarter century later, I decided to introduce the Arc to a much larger audience by featuring it in my “Observing Basics” column in Astronomy. To my amazement, I saw the same group described in the British magazine Sky at Night. The writer called it the “Fairy Ring.” Uh-oh! Had I missed something?

After a little detective work and an assist from Sky and Telescope’s Sue French, I learned that the Arc had been seen by Utah amateur astronomer Kim Hyatt in the early 1990s. Like me, he found it during a search for h1470. Because he was using a larger telescope than I had, he was able to view some faint pairs that, along with my four, formed a ring of double stars. Not knowing about Chaple’s Arc, he and a friend christened it the Fairy Ring.

This summer you can view a famous Ring (M57) for the gazillionth time, or you can be one of the few to glimpse a much lesser-known Ring (the Fairy). Here’s how to find it. Using a low-power eyepiece, trace a line from eta Cygni to 25 Cygni and extend it a half degree beyond to the Arc.

For an interesting discussion on Chaple’s Arc/the Fairy ring, Google “Chaple’s Arc” and look for the Cloudynights thread in the subject. Whether you call it Chaple’s Arc or the Fairy Ring, this is one asterism that will astound and delight you.

Your comments on this column are welcome. E-mail me at gchaple@hotmail.com.

Messier 6 and Messier 7
By Glenn Chaple

The song “Love and Marriage,” contains a line that goes, “you can’t have one without the other.” The words aptly describe the open clusters M6 and M7 in Scorpius. This cosmic “horse and carriage” lies in the southern sky above the Scorpion’s stinger.

M7 is the brighter and larger of the two. With an overall magnitude of 3.3, it spans 80’ – over twice the moon’s apparent diameter. Readily seen with the unaided eye in the absence of bright moonlight or city lights, M7 was first reported by the Greek astronomer Claudius Ptolemy nearly two millennia ago. “Ptolemy’s Cluster” is a dazzling sight in binoculars and small rich-field scopes – a striking aggregation of some 80 stars between magnitudes 6 and 10, immersed in a sparkling background of Milky Way stars. Because of its large size, M7 appears rather sparse in large-aperture scopes. Current studies indicate that M7 is 800 light-years away and is approximately 200 million years old.

Just five degrees northwest of M7 is its partner M6. This cluster, which is a magnitude fainter than M7 and one-third as large, lies just outside the glow of the Milky Way. Like M7, M6 is visible to the unaided eye and was recorded by Ptolemy. Rather than be saddled with the nick-name “Ptolemy’s Cluster II,” M6 was dubbed the “Butterfly Cluster.” The outline formed by its brightest stars does indeed resemble the outstretched wings of this insect. M6, like M7, is at its visual best when viewed with binoculars or small RFTs. With the latter, you can see about 80 stars brighter than 11th magnitude. The most luminous of the cluster’s member stars is the reddish-orange semiregular variable BM Scorpii, whose magnitude fluctuates from 5.5 to 7.0 in a cycle of roughly two years. M6 is twice as remote as M7 and half its age.

Though the splashier M7 seems to get better reviews, I found M6 to be a more attractive sight when recently observed in the 1.5o field encompassed by my 4-inch f/4 Astroscan at 35X. M6 appeared as a tight little group, while M7 seemed sparse. Oddly enough, I was more impressed by M7 when I first viewed the two clusters with a 3-inch f/10 reflector at 30X back in the summer of 1977. Compare M6 and M7 and see what you think. Now if I can just get that “Love and Marriage” melody out of my head!

Your comments on this column are welcome. E-mail me at gchaple@hotmail.com.

Finder chart for M6 and M7 From Mag-7 Star Atlas
(Copyright Andrew L Johnson)

44 Bootis
By Glenn Chaple

Rule #1: Never write about a deep-space object you haven’t seen.

Rule#2: Ignore Rule #1.

In the early 1970s, during my tenure as a “rookie” backyard astronomer, I observed double stars with relentless abandon. My instrument of choice at the time was a 3-inch f/10 reflecting telescope, made by Edmund Scientific. For a reference, I chose the 1966 edition of Norton’s Star Atlas.

One evening, I decided to dine on double stars in the constellation Bootes. According to Norton’s, one particular pair, 44 Bootis, had a separation of 2.6 seconds of arc – close, but not impossible in a 3-inch scope. To my surprise and disappointment, I couldn’t split the pair – not that night or on subsequent evenings. Had I read Norton’s more carefully, I would have seen a note describing 44 Bootis as a binary pair that was closing. I would later learn that its magnitude 5.3 and 6.2 components were separated by a mere 0.4 arc-seconds at the time of my futile attempts.

Fast forward four decades to the present. 44 Bootis, whose 210-year orbit is highly inclined to our line-of-sight, has opened up. Orbital data indicate that its component stars are separated by 2.2 arc-seconds. Time for a feast!

I haven’t yet seen 44 Bootis, at least not double. But I’ll be outside this month trying. Although a 2+ arc-second separation is within reach of a 3-inch, I’m going “loaded for bear.” My instrument of choice this time will be a 5-inch f/12 Maksutov-Cassegrain telescope, paired with an eyepiece that magnifies at least 150X. To be safe, I’ll conduct the observation on a night of above average seeing. Instead of my reporting what I ultimately see, check out 44 Bootis for yourself, and we’ll compare notes.

Your comments on this column are welcome. E-mail me at gchaple@hotmail.com.