A Journey to the Dark Site of the Earth: Down Under offered these observers their best views of some dramatic, deep-sky sights.
Arkaroola Wilderness Sanctuary
During the (Northern Hemisphere's) spring of 2016, we decided to spend our next vacation ''Down Under," in one of those amazing places in the Australian Outback. We chose the Arkaroola Wilderness Sanctuary, which has a small settlement that had enchanted the second author of this article during a short visit back in 2011. Arkaroola Wilderness Sanctuary (arkaroola.com.au) lies in the northern part of Ikara-Flinders Ranges National Park, about 700 km north of Adelaide, the capital of South Australia. To get there, a four-wheel-drive vehicle is recommended, because the last 150 km of the 700-km road from Adelaide is unsealed (i.e., dirt). A nearby airfield makes it possible to get there by small aircraft as well. The sanctuary's remote location can cause problems not only with transportation, but also with regard to electricity, which is locally produced by a small generator. This relative scarcity, however, does have a good side effect: Limited access to power creates a truly dark observing site.
Arkaroola is a mecca for bushwalkers, four-wheel-drive enthusiasts, and nature and wildlife lovers. In fact, Arkaroola is a resort and a tourist shelter for active trans-Australian travelers who stay there for a few days before continuing their journeys across the continent. And, since the owner Doug Sprigg is an avid amateur astronomer, the sanctuary also sports three fully equipped observatories for visitors. Two dome observatories each house a motorized 14-inch Schmidt-Cassegrain telescope, and a roll-off-roof observatory boasts a 16-inch Go To Dobsonian, a 12-inch Dobsonian, a Meade ETX-125, and two motorized chairs equipped with 20x100 binoculars.
The first author of this article is foremost an astrophotographer, so he took along a lot of photographic equipment: an HEQ-5 mount, two DSLR cameras, a bunch of lenses, and an 80-mm apochromatic (APO) telescope. One can imagine that there wasn't much space left in the luggage for the usual things taken on a 3-week trip! Luckily, we didn't need to bring a counterweight on the plane as we were able to use one from the Arkaroola inventory. The second author brought quality 2-inch eyepieces: a 31-mm Nagler and a 17-mm Ethos to be used with the 16-inch Dobs of Arkaroola. He also packed two DSLR cameras for wide-field, tracked photographs and ultra-wide time lapses.
Since Australia is in the Southern Hemisphere, July is a winter month with very long nights. Astronomical night begins around 7 o'clock in the evening and ends around 6 o'clock in the morning. This timeframe coincides with good visibility of the Milky Way in both hemispheres. In South Australia, winter also means better temperatures. While we were there in July and August the temperature reached a comfortable 20[degrees]C (68[degrees]F) during the day, while at the end of the night only very rarely did it plummet down to a bit under 0[degrees]C (32[degrees]F). We spent a total of 17 days in Arkaroola, and out of those we managed to observe on 13 nights. It's true that it rained one night, but in the morning there was no evidence of any precipitation.
It's Really Dark Here
The view of the winter Milky Way from-30[degrees] latitude is truly impressive. The center of the galaxy lies right on the zenith. The stories that say the Milky Way can cast a shadow are not exaggerated--raising a hand above the ground easily proved this. In Arkaroola, there's absolutely no sign of any light pollution that would show on "all-sky" (180[degrees] fisheye-lens) images. The sky transparency was also excellent, with stars visible all the way to the horizon. A Sky Quality Meter (SQM) confirmed the extreme darkness of the night sky, showing a brightness of 21.92 magnitudes/square arcsecond when the Milky Way was setting. (For comparison, Howard Banich measured a SQM of 21.76 with the wide-angle meter at the 2017 Oregon Star Party.) When the Milky Way was at the zenith, we measured a SQM of 21.55, which appeared to be the natural difference caused by the brightness of our galaxy's center at the zenith.
Looking up with unaided eyes gave us a clear impression that we were observing a spiral galaxy "edge on," from the inside. At the beginning of the night, we were always greeted by strong zodiacal light in the west, which gradually faded as the night progressed before reappearing in the east as dawn approached. It was interesting to note that just a two-day journey by car could take us to the latitude of Melbourne, where auroras can sometimes be spotted.
Though Arkaroola is very arid, dew started to form on the optics by the end of the night. This could have been a troublesome factor, particularly for the long, wide-field time lapses we planned. Fortunately, we came prepared with dew heaters, which were turned on for longer photographic sessions. Apart from this, e.g., for visual observations or exposures of just a few minutes, dew wasn't a problem.
A Few North, A Few South
We carried out more serious astrophotography with the 80-mm APO, focusing on astronomical objects that are impossible, or very difficult, to photograph from northern latitudes. Prior to the trip, we compiled a "top 20" list of objects to image so we'd have a plan to follow. Even though Europe and the contiguous United States share large portions of the sky with the Southern Hemisphere, objects that are typically near zenith (when viewed from the south) are significantly easier to image than when they are just 10[degrees] or 20[degrees] above the horizon (when viewed from the north). That's why we added quite a few targets that are also visible from northern latitudes to our "top 20" list.
One of those objects was the Rho Ophiuchi cloud complex, which can't be successfully photographed from far northern latitudes. From Arkaroola, it was a piece of cake, requiring only two hours of exposure. The same was true with Omega Centauri, which we easily saw from the Canary Islands a few years earlier. From Arkaroola, it was even higher and thus brighter. A very easy target!
We had a wonderful opportunity to compare two of the brightest globular clusters in the sky to M13 in Hercules, which, as seen from Europe, is considered "bright." This was a no-contest comparison, to say the least. Even on paper Omega Centauri and 47 Tucanae are by far brighter and larger, but when you see the difference with your own eyes, it's obvious they dwarf Ml3. In particular, the telescopic view of Omega Centauri, which is almost as big as the full Moon, overwhelmed us and left a long-lasting impression.
We spent time with a few other southern objects including Centaurus A (a galaxy known for its particular radio activity), the Jewel Box cluster (NGC 4755), and the Eta Carinae Nebula with its yellowish star within. An obvious southern target was the Large Magellanic Cloud. Its internal structure is so delicate and complicated that browsing it with the 16-inch and a wide-field eyepiece was a source of great pleasure.
In summary, our top three visual southern objects were Omega Centauri, Centaurus A, and 47 Tuc. It's no surprise that two of them are globular clusters. Indeed, these massive aggregates of stars, when viewed with large telescopes from a truly dark location, gained a lot and become more comparable to long-exposure photographs. Centaurus A, on the other hand, looked exactly like it does in popular photographs--a rare situation for galaxies viewed through the telescope.
In addition to the typical southern targets, we could see all the deep-sky objects of Sagittarius and Scorpius close to the zenith during July and August from Arkaroola. These usually require binoculars in Europe, but they suddenly became naked-eye targets! At the end of the night, our familiar winter constellation, Orion, and its bright M42 nebula could be seen at an altitude not possible from Europe or the continental United States. This, combined with the extremely good weather conditions in Arkaroola, made it possible for us to view the nebula directly in living color!
One night we tried for one of the difficult objects of the Northern Hemisphere, the famous Helix Nebula (NGC 7293). We located the object with the 16-inch and 31-mm eyepiece. We were, however, a bit confused, because at about 50x magnification and a very wide field of 1.6[degrees], the object appeared too big for the planetary nebula, and the expected "donut" shape didn't seem to have a hollow. We exchanged the eyepiece for the Ethos 17-mm (88x), and we're happy to report that the Helix returned to its normal donut shape.
Later the same night we tried for another stunning object hardly visible from latitude 50[degrees] north, where it lies about 7[degrees] degrees above the horizon. This was the famous Great Sculptor Galaxy (NGC 253), also known as Silver Coin Galaxy. From Arkaroola, it was almost at the zenith. What an amazing, detailed view we had using the 16-inch Dob with the 17-mm Ethos. The same could be said for our view of the nearby, smaller Milkweed Seed Galaxy (NGC 247).
We wondered: Which splendid northern deep-sky objects cannot be seen from here? It appears that only three such objects could be named without doubt: the two compan ion galaxies of the Big Bear, M81 and M82, and the Great Andromeda Galaxy (M31). The latter can be seen from Arkaroola, but it's very low on the horizon, while it's a magnificent binocular object when close to the zenith from northern latitudes (August-October). So, the southern skies seem to have more, and more interesting, objects to offer stargazers. The other clear advantage of the southern skies is that the entire shape of the Milky Way is better seen during the long nights of the Australian winter.
Of course, we didn't leave out Saturn, which was ruling the zenith with Scorpius in July-August 2016. Through the 16-inch Dob, the ringed planet was steadier and sharper than we had ever seen it before. The Cassini division was apparent all the way around, and one could clearly see seven bands on the planet's "surface" in color. A simple Dobsonian was enough--no need to use the expensive 15-cm APO.
After 17 days of pure astronomical pampering at Arkaroola, we returned to Adelaide, where boarded our plane to fly back to Europe via Doha. We were very pleased with our astro-vacations in the Southern Hemisphere and promised ourselves we'd return one day to experience the Australian wilderness together with truly dark skies.
JURIJ STARE is an experienced astrophotographer who runs a software firm dealing with GIS in Slovenia. He's also an activist for the International Dark-Sky Association. ZBIGNIEW ZEMBATY is a professor at Opole University of Technology in Poland, where he conducts research in civil engineering and geophysics. A life-long amateur astronomer, he uses a 20-inch Dobsonian for visual observations. Whenever possible, he travels to stargaze from remote locations with truly dark skies.
FURTHER READING: For more astro images taken from Arkaroola by Jurij Stare, see https://is.gd/AustraliaObserving.
Caption: SOUTHERN PEACE A thin crescent Moon pairs with a lustrous Venus in this 2.5-second exposure taken from Arkaroola Wilderness Sanctuary.
Caption: MAP Hop in your all-terrain rig and hit the road for Arkaroola Wilderness Sanctuary. Head north from Adelaide until you run out of pavement, then enjoy two more hours of driving on "unsealed" roads.
DESERT VISTA The Arkaroola Wilderness Sanctuary nestles in the hills of the Flinders Ranges about 700 km north of Adelaide.
Caption: ALL-SKY SPLENDOR From a vantage point in the Southern Hemisphere, with no light pollution to interfere, the Milky Way comes into its own, as proven in this 180[degrees] view of the sky above Arkaroola captured through a fish-eye lens.
Caption: CLOUD CONGREGATION The globular cluster NGC 6723 (upper right of center) lies some 30,000 light-years past the dramatic nebula complex of NGC 6726, NGC 6727, NGC 6729, and IC 4812 in Corona Australis.
Caption: STELLAR FLAMBOYANCE Although visible from northern climes, it takes a trip to the Southern Hemisphere to truly appreciate the resplendent Rho Ophiuchi cloud complex. The first author captured the colors of this star-forming region in twenty-four 2-minute exposures and twelve 5-minute exposures using a DSLR camera with a 200-mm lens at f/4.
Caption: WORTH THE TRIP The Eta Carinae Nebula tops the list of "most desired targets" for almost every amateur astronomer, but at a declination of-60[degrees], it requires northern observers to hit the road to see it. This stunning view was captured with forty 5-minute exposures with a DSLR mounted on an 80-mm apochromatic refractor.
Caption: DOUBLE THE FUN The Magellanic Clouds, Large and Small, are members of the Local Group and orbit our own Milky Way Galaxy. Separated by 21[degrees] on the sky, the duo is visible to the naked eye. A telescope reveals not just more of the galaxies' structure, but a wealth of deep-sky objects to explore as well.
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|Title Annotation:||DARK SKY DOWN UNDER; Arkaroola Wilderness Sanctuary|
|Author:||Stare, Jurij; Zembaty, Zbigniew|
|Publication:||Sky & Telescope|
|Date:||May 1, 2018|
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