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Binocular Universe: South for the Winter
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This year marks the 30th anniversary of the passage of Halley's Comet. But the universe played a trick on us back in 1986. Instead of swinging past on the Earth-facing side of the Sun, as it did previously in 1910, the comet passed perihelion on the far side. Adding insult to injury, the best viewing opportunity was to be had from the southern hemisphere. Many amateurs traveled down under to see the comet at peak brightness. My plans, however, were far more modest. With our 18-month-old daughter in tow, my wife and I trekked to the Florida Everglades at 25° North latitude. We wouldnt have a perfect seat behind home plate, but at least we were in the bleachers.
Truth be told, I found Halley disappointing. Most people did. Even from those spectacularly dark Floridian skies, all that was visible was a modest fuzz ball with a hint of a fan-shaped tail.
While Halley left me wanting, the surrounding southern sky...WOW! I had done enough reading and research ahead of time to know that there were going to be many fine sights awaiting me. But I was not prepared how amazing the view would be.
As I write this in 2016, the outside temperature is well below freezing and a cold wind is howling. But reminiscing about that trip to Flamingo, Florida, at the tip of the 'Glades still warms my heart.
If you also have a bad case of the "Winter Blues, lets take a trip south for the winter. It might be to this month's Winter Star Party in the Florida Keys. Or how about a stay on a Caribbean island? Then again, there is always southern California or Hawaii. The choice is up to you!
As you head south, everyday constellations rise higher above the southern horizon. Because their light is now piercing less of our earthly atmosphere, familiar objects take on an exciting, more spectacular appearance. At the same time, new and exotic star patterns begin to appear below. What wonders of the universe do these unfamiliar regions hold?
Here is a tour guide to some of these unsung southern beauties. While old favorites such as the Orion Nebula should be outstanding from southern vantage points, I have restricted the objects in this tour to between -35 degrees and -55 degrees declination. They represent the best of what the Deep South has to offer.
Above: Winter star map from Star Watch by Phil Harrington.
Above: Finder chart for this month's Binocular Universe.
Chart adapted from Touring the Universe through Binoculars Atlas
Let's begin at the brilliant star Canopus. Also known as Alpha Carinae, Canopus is a white-hot F0 supergiant. At magnitude ‑0.72, it holds the distinction of being the second brightest star in the night sky. Though normally considered a far southern target, Canopus can be seen from as far north as +35° latitude given an unobstructed southerly view. Astrometric data from the European Space Agency's High Precision Parallax Collecting Satellite (Hipparcos) space mission found that Canopus lies 313 light-years away. That's significantly farther away than Sirius, which is only 8.6 light years from our solar system.
Canopus' home constellation, Carina, is the southernmost of three separate constellations formed from the long-retired star group Argo Navis. Recall from your mythology lessons that Argo was the ship used by Jason and the Argonauts as they searched for the elusive Golden Fleece. The constellation Argo Navis dates to ancient Greece, but was scuttled by Nicolas Louis de Lacaille in 1763 when he divided it into Carina, the ship's Keel; Puppis, the Poop Deck; and Vela, the Sails.
Scattered amongst the stars of the Keel is a veritable treasure trove of stunning deep-sky objects. Our first port of call is NGC 2516, an impressive open cluster not far from Canopus. On dark, clear February nights, it is visible as a soft, gray smudge spanning about a moon's diameter. With the slightest optical aid, however, it erupts starlight! Seven-power binoculars resolve about a third of the 100 stars that make up NGC 2516. A trio of orange orbs dominate the scene of otherwise pure white stars. NGC 2516 spans better than 15 light years and is 1,300 light years from Earth.
Another stunning open cluster that most Northerners miss out on is NGC 3114. Three 6th-magnitude beacons rule over another 170 or so stellar citizens in this brilliant galactic blaze. NGC 3114 covers 35' of arc. I could only stare in silent awe when I saw NGC 3114 through my 11x80 when I first spied it thirty years ago.
You'll have to stay up late to catch our next Carinian targets, but they are well worth it. The Eta Carinae Nebula, NGC 3372, is one of the most amazing objects in the entire sky. For those heading south for the winter, it is a "must see!" The view of this huge glowing cloud is exquisite even in the most modest optical equipment. Dark rifts divide the nebula into several distinct regions, with the most prominent patch clearly teardrop shaped.
Entombed within this cloud is the namesake star Eta Carinae. Johan Bayer recorded it as 4th magnitude on his Uranometria star atlas of 1603. Edmund Halley was the first person to view Eta telescopically in 1677; he too estimated Eta as magnitude 4. By 1730, it had brightened to magnitude 2, but fell back to 4th over the next fifty years. It continued to fluctuate until 1843, when in mid-March, it suddenly soared to magnitude -0.8, brighter than Canopus. It quickly dropped below naked-eye visibility, but started to brighten around 1940. It peaked above magnitude 4.5 in 2014.
We now know that Eta Carinae is a stellar system containing at least two stars. The primary sun is a strange beast similar to a luminous blue variable (LBV). It once had a mass 150 greater than our Suns, but exhausted 20% of after losing hydrostatic equilibrium. This caused that sudden flare in brightness in the mid-19th century, an event now known as the Great Eruption.
Its companion is thought to be spectral class O and contain between 30 to 80 times the mass of the Sun. Those facts are somewhat tentative because the entire system is fully engulfed by the Homunculus Nebula, an expanding cloud of material ejected by the primary sun during the Great Eruption.
Studies, however, do reveal a great abundance of heavier elements in the primary star, leading many theorists to believe that this is a good candidate for the next Milky Way supernova. Exactly when that will happen remains unknown. It could be millions of years from now. Or it could be tonight!
Eta Carinae is the brightest member of the star cluster Trumpler 16. Trumpler 16 contains 90 stars hidden among the clouds of NGC 3372. No fewer than five additional open clusters are also seen superimposed onto the nebula. These include Trumpler 14 and 15, Bochum 10 and 11, and Collinder 228. All appear as tight clumps of few stars. Many fine open clusters surround the Eta Carinae Nebula. The close-up chart here spans just 10°, only a little more than the field of 7x50 binoculars. Look at all there is to see!
Above: Close-up chart centered on Eta Carinae.
Chart adapted from Touring the Universe through Binoculars Atlas
Though it is difficult to say which one is best, many favor NGC 3532. Discovered by Lacaille in 1751, NGC 3532 is an outstanding gathering of stars clumped within 50' of arc. Over 60 cluster suns are bright enough to be seen through 7x50 binoculars, with more than 150 visible giant binoculars. En masse, the cluster appears wedge shaped elongated east to west, with many of the stars set in long intertwining lines and curves. One visit to NGC 3532 and you surely will feel as John Herschel did when he described it as the most brilliant cluster he had ever seen. No one can argue with that!
West of the Eta Carinae complex is another standout open cluster. NGC 3293 is a tightly-packed swarm of 90 stars from 6th to 13th magnitude. Most binoculars show only the brightest ten or so surrounded by the gentle glow of unresolved starlight. Photographs show a vivid cloud of nebulosity engulfing the group. Seeing it visually, however, requires great skies and great eyes.
Here's a full list of the objects plotted on the Eta Carinae chart above. Click the list to open a printable PDF version in a new window.
Sailing onward, we will next examine Vela, the Sails. The brightest star in Vela is Gamma Velorum, a fine multiple star made up of at least four suns. Binoculars reveal the system's "B" star, a 4.2-magnitude type-B sun, about 41" to the southwest of Gamma A, which shines at magnitude 1.7. Both of these stars are spectroscopic binaries. While far too close to split individually, Gamma A is comprised of a blue spectral class O supergiant and a massive Wolf-Rayet star. Although they were once classified within spectral-class O, Wolf-Rayet stars are now separately noted as spectral-class W. They are well known for their high intrinsic luminosity.
Two other suns are believed to be gravitationally linked to the Gamma system. Gamma C, at 7th magnitude, lies 62" to the southeast of the primary, while Gamma D is 9th magnitude and is separated from Gamma A by 93" to the southeast.
Drop 3° southward from Gamma to find the open cluster NGC 2547. Over 110 stars make up this dazzling cast, with more than a dozen shining brighter than 9th magnitude. Many of the suns appear to form lines and curves; all told, they strike me as a crooked cruciform lying on its side.
Just north of Delta Velorum is another beautiful open cluster. IC 2391 can be seen with the unaided eye on a good evening, and is easy in binoculars. My 11x80s show a large, coarse gathering of many bright stars, including several doubles. Its brightest sun, 5.5-magnitude Omicron Velorum, looks like a brilliant sapphire set among a glistening backdrop. Binoculars are definitely the instrument of choice since the cluster spans the equivalent width of two Full Moons.
Scan about a degree due east of IC 2391 to find yet another open cluster. NGC 2669 contains about 90 stars, with the brightest half dozen forming a trapezoidal pattern. On its own, NGC 2669 is not especially impressive, but add to it the magnificent environs, and you have a ringside seat to a wonderful star-studded show for binoculars.
I'm not sure what I miss most about the 1980's -- it certainly isn't the mullet haircut! -- but as far as discovering undiscovered astronomical treasure, my trip to see Halley's Comet had to be the highlight. Armed with binoculars, that experience fueled my passion and certainly cemented in my mind the idea that "two eyes are better than one!"
About the Author:
Phil Harrington is a contributing editor to Astronomy magazine and author of 9 books on astronomy, including Touring the Universe Through Binoculars. Visit his web site at www.philharrington.net to learn more.
Phil Harrington's Binocular Universe is copyright 2016 by Philip S. Harrington. All rights reserved. No reproduction, in whole or in part, beyond single copies for use by an individual, is permitted without written permission of the copyright holder.
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