Gloucester Area Astronomy Club

The Milky Way
by Glenn Chaple

This month, we explore the galaxy most of us are familiar with – the Milky Way. Many astronomers regard the Milky Way, viewed with the unaided eye on a dark, moonless night, as the most awe-inspiring heavenly sight of all. During late summer, it arches overhead, from Cassiopeia to our north, through Cygnus above, then down to Sagittarius on the southern horizon.

Studying the Milky Way with a standard telescope is akin to exploring the Mississippi River by placing a drop of its water under a microscope. You’ll do better by sailing the Milky Way with the most practical vessel possible – binoculars.

On an evening and location (preferably one that affords an open sky) where dark skies prevail, set up a reclining lawn chair or lay down a blanket. Relax and direct your binoculars towards Cassiopeia, the departure point for your “cruise.” Take your time and enjoy the scenery. Maintain a course through Cygnus and onward to Sagittarius. Along the way, you’ll encounter a dazzling cosmic vista – myriads of stars interspersed with an occasional cluster or nebula.

When finished, begin again. Unlike a traditional ocean cruise, this one doesn’t cost a penny and the scenery is far more spectacular.

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

NGC 6207
by Glenn Chaple

Unless you’re a rank beginner, you’ve no doubt marveled at the spectacular stellar swarm that is M13. Taking on the appearance of a spoonful of sparkling sugar dropped on a sheet of black velvet, the great globular cluster in Hercules is one of the night sky’s most dazzling sights.

Most backyard astronomers are so entranced by M13, that they fail to notice a small, faint oval patch of light a half degree to the northeast. This is the 11th magnitude galaxy NGC 6207. Years ago, I was just able to glimpse this 2’ by 1’ smudge in a 3-inch f/10 reflector. Most of the time, NGC 6207 will require a 4 to 6 inch scope, or larger.

M13 and NGC 6207 may appear close together, but they’re light years apart – literally! While M13 is a “mere” 23 thousand light years away, the light from NGC 6207 comes from a distance of 46 MILLION light years – two thousand times more distant!

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

Izar (ε Bootis)
by Glenn Chaple

Most of us are familiar with the novel Moby Dick, whose protagonist Captain Ahab relentlessly hunts a great white whale. I can sympathize with the obsessive Captain. For several years back in the late 1970s, I pursued an astronomical white whale- the double star epsilon (ε) Bootis. Instead of the Pequod, my vessel of pursuit was a 3-inch f/10 reflector.

Trying to capture Izar with a 3-inch reflector is like attempting to harpoon a whale from a rowboat. The difficulty lies in the magnitude difference between the components (2.6 and 4.8) and their closeness (2.9 arc-seconds). On numerous evenings I tried to resolve Izar’s component stars without success. Notching this stellar duo became an overpowering obsession. On the evening when I at last split Izar, skies were remarkably steady and I used the highest practical magnification (120X) my little reflector could handle. Even then, the companion played hide-and-seek in the diffraction ring of the primary.

A larger telescope and magnifying power of 200X will readily split Izar and reveal a striking color contrast between the golden yellow primary and its bluish companion. The Russian astronomer Wilhelm Struve, who conducted a double star survey in the late 1820s and early 1830s (Izar became Σ1877 in his double star catalog), nick-named it “Pulcherrima” (The Most Beautiful).

But Izar is more than just a close pair of stellar specks. The main component is a K0 spectral class giant 30 times as large as the sun. Its A2-type companion is twice the sun’s size – a virtual twin to Sirius. Separated by 180 Astronomical Units, the two undergo a slow gravitational dance, their orbital cycle encompassing perhaps a thousand years.

Imagine that Izar were moved from its current location 250 light-years away to a distance equal to that separating us from Sirius. The star would be a dazzling sight, rivaling Venus in brilliance. Viewed with even the smallest telescopes, the magnitude -3.6 and -1.4 components, separated by 85 arc-seconds, would be an absolutely magnificent sight.

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

M40 – the “Unknown” Messier Object
by Glenn Chaple

What is the most most-observed deep-sky object in the Messier Catalog? Some might suggest the Orion Nebula (M43) or Andromeda Galaxy (M31), both cosmic showpieces. More likely, it’s the Pleiades (M45), a striking and easily observed naked eye cluster.

What about the other end of the spectrum – those Messier objects that receive scant attention? The least-observed might well be Messier 40. Arguably the oddest member of the Catalog, M40 isn’t a cluster, nebula, or galaxy. It’s a double star! We might well label M40 “Messier’s Mistake.”

Messier stumbled upon this stellar duo while searching for a nebulous object reported to be in the area. For some reason, perhaps because it might appear nebulous at low power or in an inferior instrument, he added it to his Catalog. A century later, another comet hunter, Friedrich Auguste Theodor Winnecke, rediscovered the object. He correctly catalogued it as a double star, and it bears the alternate identity Winnecke 4.

Finding M40 isn’t a problem. Start at delta (δ) Ursae Majoris, then move about a degree northeast to 70 UMa. In the same low-power field a quarter degree further northeastward is M40. As double stars go, M40 isn’t a very inspirational sight. Its magnitude 9.7 and 10.1 component stars are separated by over 52 arc-seconds. Quite likely, it’s an optical pair. It may not be one of the night sky’s spectacles, but the path to observing all of the Messier objects goes through M40.

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

Sirius
by Glenn Chaple

An unwritten law in astronomy states that you should avoid observing any sky object when it’s near the horizon. First of all, incoming light has to pass through a greater amount of earth’s atmosphere when approaching from a low altitude. Secondly, ripples from escaping ground heat create turbulence that’s most troublesome near the horizon.

However, if you want to experience one of the night sky’s loveliest treats, ignore that law and look at Sirius when it’s low in the sky. When the night sky’s brightest star is situated high above the southern horizon as it is after sunset on February and March evenings, it’s a magnificent sight. A gleaming, sparkling diamond, Sirius captivates the beholder, no matter whether viewed with unaided eye, binocular, or telescope.

Sirius is now on the wane, setting soon after sunset. As it nears the horizon, something magical happens. That same atmospheric turbulence that wreaks havoc on sky objects refracts the light from Sirius, causing it to sparkle in a dazzling array of gemlike hues. Its diamond like radiance is interrupted by flashes of ruby red and emerald green – a visually entrancing sight.

Next time you set out to do some “serious” astronomy, try a moment to make a “Sirius” observation. You’ll be delighted you did.

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

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.