Zodiacal Light and the Gegenschein: August 2013

Any trip away from home is an excuse to find dark skies and interesting locations for night sky photography, and a trip to the Australian Astro Imaging Conference (AAIC) was no exception, despite its Gold Coast location. While planning the trip, I considered that it was almost the ideal time of year (in the southern hemisphere) to capture the zodiacal light in the west, with brilliant Venus set to be blazing in the middle of it. And a trip up north from Melbourne would further increase the angle of the zodiacal light, putting it almost vertical to the horizon with the Milky Way running overhead across the sky at the end of twilight as well. Later in the night the Gegenschein (counter-glow) would rise, in a dark part of the sky well separated from the Milky Way.

Magellenic Clouds (left), Milky Way plus Venus and the Zodiacal Light Maranoa Wetlands, Queensland, Monday 26th August, 2013 Canon 6D, 24mm lens, Panorama of 27 images, each 30 secs, f2.8, ISO3200

And so a plan was hatched to look for dark skies, to capture the best image I could of the entire Zodiacal Band, with the strongest Zodiacal Light in the west at the end of twilight and the fainter parts around to the Gegenschein up high later in the night just before moonrise. I also wanted to compare some modestly high altitude observing sites (we don’t have big mountains in Australia) to see if the increased transparency would enhance the view of the zodiacal light, particularly low in the western sky. What are the Zodiacal Light and the Gegenschein I hear you ask? The solar system is full of dust, mostly orbiting the Sun in the same plane as all the planets. In the sky, that plane that the planets all move along is called the ecliptic and under very dark skies we can see that it is brighter than the background sky because of the sunlight reflecting back off all that dust. The effect is strongest in the western sky just as it gets dark or in the eastern sky before dawn as that is when we see the strongest reflection of sunlight, which is what we call the Zodiacal Light. However, at the position directly opposite the Sun (the anti-solar point) on the ecliptic we also get a slightly stronger reflection due to back-scattering. This oval shaped patch of faint reflected sunlight along the zodiacal band is called the Gegenschein, a German name meaning counter-glow or counter-shine.

Little Llangothlin Nature Reserve, Guyra, New South Wales

After much Google Earth location scouting and monitoring of the cloud forecasts during the previous days, I left the AAIC conference at morning tea on Sunday morning, picked up the hire car, collected (lots of) bags and gear at the hotel and headed inland through the hills to Warwick. After 450km and several sections of road works for ongoing flood repairs, I arrived at Little Llangothlin Nature Reserve in the late stages of twilight. This was a good deal later than I would have liked, given that I still needed to unpack bags, reassemble tripods, prepare camera gear and then hike 1.5km round to the other side of the lake in the dark. At an altitude of just under 1400m, it was already a very cold night. Nonetheless, I kept warm initially carrying two tripods and a pack full of gear as I dashed off along the rough paths and through the scrub around the perimeter of the reserve. Eventually I decided I had gone far enough and cut back in towards the lake to find the water’s edge. Before I could even see the water, I noticed the ground underfoot getting boggy, with tall tussocky grass growing in very slushy ground. By the time I got to the edge, there was more water than there was grass. Now I don’t mind the cold, but wet feet in damp, frosty conditions was not my idea of ideal observing!

Zodiacal Light and Milky Way with strong green and red airglow Little Llangothlin Nature Reserve, New South Wales, Sunday 25th August, 2013 Canon 6D, 14mm lens, Panorama of 18 images, each 30 secs, f2.8, ISO3200

But I didn’t have much choice at that point, so I setup my two tripods, one with the panorama head for the all-sky panoramas and one with the eMotimo TB3 timelapse motion control unit (contact me for a discount if you’re interested in purchasing one!). I then precariously danced around the panorama head as I executed two all-sky panoramas with different lenses over the next half hour, stepping from one grass tussock to the next in a futile attempt to keep my feet dry, but eventually even the tussocks themselves were sinking into the water. By any measure, this was a dark sky location. But any benefit of transparency at this higher altitude site appears to have been lost on this night by strong airglow (with a dramatic colour change from green in the south to red in the north). But even accounting for that, the transparency does not seem especially good, which I think was due to very high moisture content in the air around the lake, which became mist and fog not much later in the night. I had intended to stay out with the cameras until moonrise two hours later, but instead left the timelapse running and took my wet feet back to the car. After moonrise, I returned to collect the timelapse gear and heavily frosted tripod before finally removing my soaking wet shoes and crawling into a relatively comfortable and dry bed in the back of the car.

Maranoa Wetlands, St George, Queensland

My original idea was to make it to Siding Springs Observatory near Coonabarabran on the Monday night, but taking some of my own cloud forecasting advice (which I presented on at the conference), I could see that the various weather models agreed on high cloud covering a large swathe of NSW so decided instead to head back up to the Queensland side of the border, and then inland in search of dark country skies a long way from any major towns. This turned out to be a drive of just over 600km, which is perhaps a little further than it needed to be. But while the landscape was generally flat, finding anywhere moderately interesting to observe from, with good clear (ideally 360 degree) horizons and well away from the car and truck lights of the highway was not easy. So I kept going to the Maranoa Wetlands that I had identified on Google Earth that morning, 20km past the small town of St George. At least there I figured I would have good horizons from a not too busy road.

As I kept driving through the late afternoon, I was not too sure about the wisdom of this choice. But while I did not consider the ambience of the wetlands to be very exciting as I arrived and stepped over a break in the fence along a not very exciting part of the road, photographically it worked quite well and the skies were really impressive. It is not too hard in Australia to find skies that are truly dark overhead (limited by airglow rather than light pollution). But this was one of the darkest sites I had experienced in a long time, with no light domes visible all the way around a distant dark flat horizon, save for the small glow of St George itself behind some nearby trees. It didn’t take long to convince myself that the drive had been worthwhile, and that whatever this site lacked in altitude it made up for in darkness. The Zodiacal Light was very strong in the west and the Gegenschein later in the night as clear as I have ever seen it. Airglow is still clearly the limiting factor for these images, picked up very well in the wonderfully sensitive Canon 6D, but since it occurs 100km up in the atmosphere there’s not much that can be done to escape it.

All-Sky View of the Zodiacal Light and Milky Way Maranoa Wetlands, Queensland, Monday 26th August, 2013 Canon 6D, 24mm lens, Panorama of 27 images, each 30 secs, f2.8, ISO3200

Pyramid Rock, Girraween National Park, Queensland

Having largely succeeded with my plans for the first two nights (although with no idea whether the panoramas would actually stitch together into a decent final result) I decided to try something a little different for the final night, at which point I needed to be within striking distance of the Gold Coast again for the flight home on Wednesday. While I had worked out that Bald Rock National Park on the NSW side of the border did not have 360 views from the top, locals Tony and Jeanette at AAIC assured me that Pyramid Rock in the Queensland extension of the same park (Girraween) did indeed have great horizons, if I was prepared to tackle the steep and strenuous walk to the top (and back down in the moonlight!). That sounded like a perfect adventure to me, but as I returned closer to these civilised parts of the world, I noticed again what had troubled me even from the balcony of the hotel on the Gold Coast – a number of smoke columns from fuel reduction burns being conducted in the forests. That was certainly not good for sky transparency, but the image below clearly shows the Gegenschein almost overhead, so conditions weren’t too bad in the end!

Milky Way and Gegenschein (near centre of image) over smoke filled valleys Pyramid Rock, Girraween National Park (QLD), Tuesday 27th August, 2013 Canon 6D, 24mm lens, Panorama of 27 images, each 30 secs, f2.8, ISO3200

Arriving at the Girraween Campground, I bemused a few people settling in for the evening with my hectic attempt to pull all the gear out of the car and work out how much I could carry to the top of the rock (and back in the dark!). I settled on what I estimate was a 20kg backpack full of gear, only leaving one camera behind :-). I think the very occasional run I’ve been doing at home helped, but even so this was the most strenuous photo walk I’ve tackled. It was only 2km but involved a steep climb 200m up the dry and grippy side of Pyramid Rock. I paced myself on the climb, but barely paused all the way, getting to the top just in time to catch sunset at the top. The smoke from nearby burns was atmospheric but of course I did not view it favourably for my purposes. The 1000m+ altitude of Pyramid Rock helped a little, as most of the smoke was blowing out towards the coast and not penetrating very high with an inversion putting a strong ceiling on it. However, unexpected things happen on these kind of photo adventures, and not much later in the night as temperatures fell, the smoke columns collapsed and the haze spread out along the valley floors below me, extending many kilometres by the time the moon rose.

Moonlight and Milky Way over smoke filled valleys Pyramid Rock, Girraween National Park (QLD), Tuesday 27th August, 2013 Canon 6D, 24mm lens, Panorama of ~6 images, each 30 secs, f2.8, ISO3200

After catching some final images at moonrise, I packed all the gear for the last time and stepped my way carefully down the side of the rock. The rest of the walk dragged on a bit as expected, but before long I was curled up in the sleeping bag after an intense but enjoyable and satisfying three nights of night sky photography. The flight home was a slog, as was going straight to a meeting the following night, before I could finally enjoy the comforts of home again.

Map of the driving route for three nights of photography