A Tour of the Night Sky as Seen from San Pedro de Atacama, Chile
by Jeff Kanipe
This month, we have a wonderful surprise for you—a tour of the southern sky, as seen from Chile, by Jeff Kanipe, author of the highly regarded series, Annals of the Deep Sky. His report covers the Large and Small Magellanic Clouds and other objects in their vicinity, all of which are below our horizon here in Denver. Jeff made his observations in November–they’re included here now, because the area is southeast (“to the left and DOWN”) of the summer sky we see in Denver, helping us to imagine the objects’ placement. (It also allows observers enough lead time to plan a November trip for themselves!) —Ed.
As a young amateur astronomer growing up on the Texas coastal plain, I could see the star Canopus from my backyard in early February evenings—and from atop the old 100-foot radar tower acquired by our local astronomy club as an observing base, I could see the northern half of the Southern Cross transiting the meridian in early May. But it always frustrated me that the Magellanic Clouds (MCs) were, and would always be, below my horizon, and I vowed that I would one day see them with my own eyes.
My chance came as I was preparing to write about the Clouds for my book series, Annals of the Deep Sky. I couldn’t very well write about something as important as the MCs without observing them myself. That would be like a birdwatcher describing a bird never seen, or a rockhound a rock never collected. So, as I commenced my preliminary research on the Clouds, I also began preparing for a trip to the Southern Hemisphere.
The logistical planning took only about six months, but there was a lot to consider during that time, among them accommodations, observing site, access, and, of course, cost. Obviously, the destination is somewhere in the Southern Hemisphere, but not just anywhere. I wanted to observe the Clouds at a decent altitude from a location where clear skies were practically guaranteed.
I found such a place a few kilometers south of the town of San Pedro de Atacama, in the Chilean Andes. The Atacama is no ordinary desert; it has the reputation for being one of the driest places on Earth (after the McMurdo Dry Valleys in Antarctica) with an average rainfall of 15mm (0.6 inches) per year. According to astrobiologists, the Atacama’s arid environment is the closest analogy we have to Mars on Earth; and certainly, the extensive and desolate vistas stretching out to the horizon reminded me of some of the Martian panoramic images captured by the robotic rovers.
My accommodations were provided by San Pedro de Atacama Celestial Explorations (SPACE) and my host was Alain Maury, an indefatigable former professional astronomer with a long list of asteroid and comet discoveries to his name. Maury’s enterprise offers tours of the night sky every clear night of the year. He told me over 17,000 people attend each year. He also rents telescopes to amateur astronomers; mine was a 20-inch (50-centimeter), f/4 Dobsonian reflector, a stout, not-very-handsome, aluminum-and-metal contrivance with massive bearings and an excellent mirror. The telescope, which I nicknamed “the Battleship,” is permanently mounted, and its primary mirror protected from the pervasive desert dust by two shutters over the mirror box.
My wife, Alex, and I arrived the evening of November 5th, after a nine-hour flight from Houston to Santiago, a four-hour layover there, and another two-hour flight to the town of Calama, followed by an hour’s drive to San Pedro. It was close to 9 PM when we finally put away our gear and, despite being exhausted, went outside to take in the stars.
What greets northern observers who have never observed from such a southern latitude is, in effect, a totally different, and yet familiar, sky. To the north, neither Dipper was visible, but Cassiopeia was in upper culmination, on the horizon.
Floating just 45° above the northern horizon and galloping off to the west was Pegasus, which sits on the south side of the zenith back home in Colorado. To the southwest, the base of the Scorpion’s tail wriggled straight up from the horizon, and the teapot asterism of Sagittarius was poised on its spout, as though to pour out its very last drop. Both constellations were high enough to be observable—that in itself is striking, because at this time of year, Scorpius would have set in before Denver’s astronomical twilight was over, and Sagittarius would be very low.
Weirdly for Colorado-based observers, Orion cartwheeled feet-first above the eastern horizon while Sagittarius was still up. Canopus, second-brightest star in the night sky, laid claim to the southeastern sky (it’s sometimes visible just above the southern horizon at Los Angeles’s latitude and never rises in Denver). Finally, above and to its right—at last!—was the Large Magellanic Cloud trailing behind the Small Magellanic Cloud, which was approaching the southern meridian.
The Magellanic Clouds are two of the Milky Way’s nearest large satellite galaxies. Observational evidence indicates they are passing by our galaxy for the first time, but only after colliding with each other some 200 million years ago. The collision resulted in the formation of the Magellanic Bridge, composed of stars stripped from both Clouds, as well as the trailing Magellanic Stream and Leading Arm, which together span at least 200° across the sky. To the unaided eye, the Clouds are easily perceptible, but they aren’t as bright as one may anticipate—which is to say they aren’t as bright as they are in the imagination. Their large apparent size on the sky belies their great distances (163,000 light-years for the Large Magellanic Cloud, or LMC; 195,000 light-years for the Small Magellanic Cloud, or SMC), making them seem closer than they truly are. (See Chart 1.)
The LMC’s long axis is probably its most prominent feature, with some vague mottling east of its southernmost extent, in the vicinity of the Tarantula Nebula; the elongation of the SMC is noticeable as well, though it is more of a wispy smudge. The SMC’s western edge cuts off sharply along the galaxy’s bar, and just “offshore” lies the brilliant, 4th-magnitude Galactic globular cluster 47 Tucanae (NGC 104), which rivals Omega Centauri in beauty. The broad eastern side tapers out toward the LMC, a feature referred to in the literature as the “wing.”
We had clear, transparent skies over the next four nights, and I managed to observe a great many objects in both Clouds. I usually began observing around 9 PM, an hour or so after sunset, when temperatures were mild enough for a sweater; I continued until about 2 AM, by which time I had donned a ragg wool hat and a parka. Temperatures usually dropped to about 40° F (4.4° C).
As mentioned, the telescope had an excellent mirror, but I was also using a Tele Vue Paracorr, which helped flatten the field of view (FOV). This was most apparent with 47 Tuc, which effervesced with sharp stars across the entire FOV. Although I had the choice of three fine eyepieces, the one I used the most was one I brought with me, my trusty 1.25-inch, 21mm Tele Vue Plössl. With the Paracorr factored in, the eyepiece rendered a magnification of 110x, but I found it sufficient to view the general field, which typically held many objects. When I wanted a closer view, I used either a 14mm or 9mm Explore Scientific ultra-wide field eyepiece for effective magnifications of 164x and 255x, respectively. I also had access to O III and UHC filters.
On our second night, I began telescopic observations of the SMC, which crossed the meridian around 10 PM. I made quick work of it, easily picking out objects using Uranometria 2000.0 finder charts as well as photographic charts. The northeastern extent of the SMC harbors the most visually interesting objects, including, from east to west, NGC 395, 371, and 346, a complex of star clusters and nebulosity. NGC 346 is brightest and, even in short exposures, appears as an extended bluish knot. The opposite end of the SMC bar is chock full of clusters, many crowded into a single field. Near the visual edge of the southwestern bar, three small clusters, NGC 231, 220, and 222, are arrayed like steppingstones from northeast to southwest, respectively. (The group lies approximately 1.8° southeast of 47 Tuc.)
An exercise in how distance affects angular size is provided by 47 Tuc and the squarish SMC globular NGC 121, which lies 35’ to the north-northeast. Though we view them along roughly the same line of sight, 47 Tuc lies in our own Milky Way Galaxy, at a distance of about 15,000 light-years, while NGC 121 sits approximately 200,000 light years from us. While 47 Tuc spans about 50’, the more distant NGC 121 is barely 1.5’ in diameter. (In truth, 47 Tuc is also more than double the diameter of NGC 121, but their size disparity pales in significance compared to their 13-time difference in distance.)
Another Milky Way globular I should mention, 7th-magnitude NGC 362, appears along the northern periphery of the SMC. At 14’ across, it’s no match for 47 Tuc, but it has a fine spherical form with many outliers.
A trio of H II regions comprised of NGC 249, 261, and 267, located 27’ northeast of NGC 222, punctuate the southwest region of the SMC’s bar. They form a triangle and span a field of 4.5’. There are so many clusters in this part of the SMC, they are difficult to distinguish unless one meticulously slews from those that have been positively identified.
On the following evening, I scanned the SMC again, familiarizing myself with the objects I observed the night before, and added new objects to my growing list. Finally, unable to resist, I turned the telescope on NGC 2070, the Tarantula Nebula (a.k.a. 30 Doradus) in the LMC, and spent some time gawking at this highly complex object. It is a mass of knots, filaments, laminar nebulae, and dark voids that extend out of the field of view, where it adjoins numerous other star clusters and wispy nebulae.
At 195x with an O III filter this object is a jaw-dropper that resolves into a number of loops that merge with nearby H II regions. Shift the field slightly in any direction, and new structures swim into view. It is by far one of the most incredible objects I’ve ever seen in any telescope. The nebula itself contains some 2,400 massive stars and is one of the most active star-forming regions in the Local Group of Galaxies. Using the Tarantula as an anchor, I star-cluster-hopped to other objects in the immediate vicinity, chalking up one after another.
On our fourth night, I rough-sketched the Tarantula and surrounding objects without the aid of any filter. I next scanned the region in and around the northwestern portion of the LMC bar, and here is where I found the going toughest. Without a prominent anchor point like the Tarantula, the identification process was a lot slower. I had to form “constellations” out of the various cluster patterns and note distinguishing features to facilitate identifying the objects I was observing.
I began at the northwest extreme (the highest part in the sky) and slewed systematically eastward through the bar. After the eastern sweep, I lowered the tube a single field of view to the south and scanned the opposite way, towards the west. With this back-and-forth pattern, I picked up a lot of star clusters and nebulae, and by 1 AM, I was becoming familiar with the layout of the myriad clusters.
On our last night, November 9th, I returned to the northwestern bar and surrounding region to both look for more objects and to confirm what I had observed the previous night. I also set aside some time to take a few short-exposure “reference images” of the Clouds, ones that I could later use for comparison to my descriptive observations. I used an iOptron SkyTracker camera platform, which Alain set up for me and aligned with the South Celestial Pole. I was able to take a few nominal exposures using my Canon EOS T3i.
Around 1 AM, Alain invited Alex and me to view various southern sky gems through his 28-inch (71-centimeter) Dobsonian. We viewed objects in the Magellanic Clouds, as well as 47 Tucanae, Omega Centauri (NGC 5139), Centaurus A (NGC 5128), and the nearly edge-on spiral galaxy NGC 253 in Sculptor, among others. To say the least, the views through the 28-inch were spectacular in those dark and transparent skies, especially the Tarantula, which took on an eerie three-dimensional assemblage of folds of ashen-hued curtains shot through with stars. In my hyper-pareidolia, it took on the visage of some canine creature with tufted ears—a fox, perhaps, or a wolf, but certainly not an arachnid!
All in all, my southern-sky “observing run” was a success. During the day, we ate well, saw myriad guanacos and vicuñas, various species of sparrows and hummingbirds, a multitude of wild donkeys, and traversed some very alien topography, including the Valle de la Luna, El Tatio geyser field, and Salar de Atacama, the largest salt flat in Chile (and inhabited by tens of thousands of flamingos). At night, it was almost like being on another planet, with the familiar stars looking decidedly out of place. If the chance ever comes your way to see the far southern sky and the Magellanic Clouds with your own eyes, jump on it. It will change the way you look at the universe, because, as astronomer Bart Bok once wrote, “the Southern Hemisphere holds all of the good stuff.”
San Pedro de Atacama Celestial Explorations: http://www.spaceobs.com/en
