February 24, 2017
From the time I was a young kid growing up under the dark skies of rural Canada, I dreamed of owning an eight-inch Schmidt-Cassegrain telescope. Glossy advertisements in astronomy magazines promised me that a “C8” would give me the aperture I would need to peer deeply into the cosmos, the portability that would encourage me to peer often, and the robotic gizmos that would unfailingly point me in the right direction. It was an irresistible combination . . . except for the (fittingly) astronomical price. Someday, somehow, I thought, I’d get a good job and save up enough to buy one.
That day arrived late last year, when I found a C8 optical tube assembly (OTA) on sale for a price that seemed hard to beat. And not just any OTA: this was an Edge HD, quite possibly the best mass-produced Schmidt-Cassegrain on the market today. I snapped up the telescope – with a little help from my employer – and waited until I could use it. I waited long, because in cold weather, Schmidt-Cassegrains can take a long time to reach "thermal equilibrium:" the same temperature as the air around them. Until they do, air currents inside their tubes disrupt the view. In the winter, you have to leave your Schmidt-Cassegrain outside for quite a while before using it, and since I currently observe in urban parks that just isn’t possible for me. So I waited for warmer temperatures. Fortunately, they come early in Washington, DC. Tonight, with temperatures in the upper teens, I stepped out with my Edge HD for the first time.
Aside from the temperature, conditions were far from ideal. The wind gusted from the southwest, so the “seeing” was far from perfect, and the transparency of the atmosphere also left something to be desired. Wisps of cloud drifted by from time to time, the first signs of a storm system that should be with us tomorrow morning. Yet it was a comfortable night overall, and I looked forward to observing with no risk of frost bite.
I set up in my usual observing spot: out behind a police station, in a community garden. Bright street lights are far too close, so I can never develop proper night vision. Yet since I observe in the heart of a little vegetable labyrinth, I'm usually shielded from prying eyes and barking dogs. I have two mount/tripod assemblies that I can use with my C8: the Twilight I setup that I use with my lighter AR 102, and a Nexstar SE computerized mount that came with my (now dearly departed) C6. Both can theoretically handle weights up to around 18 pounds, but in practice neither can quite accommodate the 14-pound Edge HD, with its finder and eyepieces. Still, both are light and small enough for me to walk them the five or so minutes it takes for me to reach my observing sites.
This time, I decided to roll out the Twilight I. I wanted to see what I could see with my OTA, and I just didn’t have the patience to deal with occasionally finicky electronics. To minimize the wobbling that usually plagues big telescopes on flimsy mounts, I placed my tripod on Celestron vibration pads. To my surprise, it actually worked fairly well. The telescope shuddered when I moved it and especially when I focused it, but that shudder was not as bad as I’d feared.
After unpacking my telescope, I waited around 10 minutes before I lost patience and decided to observe, thermal equilibrium be damned. I snapped in a cheap, 30 mm Plössl eyepiece and wheeled my telescope over to the Orion nebula. The first think I saw when I looked through the telescope was a satellite streaking by. An auspicious start! When it left my view, the Orion Nebula emerged from the inky background. As you might expect, the difference between the Edge HD and my AR 102 was immediately striking. Where the little refractor shows a little arc of misty grey-green light, the bigger Schmidt-Cassegrain reveals delicate tendrils of nebulosity in a giant crescent around the Trapezium Cluster.
Next, I reached for in a new purchase. I recently sold my Celestron refractor and used the money to buy a new diagonal and my first quality eyepiece: a 14 mm Explore Scientific 82°. After plugging in the eyepiece and thereby boosting my magnification, I turned to Venus. I was astonished. The AR 102 shows a small, flickering crescent blurred and distorted by chromatic aberration. At 145x, the Edge HD, by contrast, gave a razor-sharp view, even before it reached thermal equilibrium. Since Venus is nearing its closest approach to Earth, when it will be between the Sun and our planet, its crescent is even narrower now than when I last observed it. That made the effect of my sharp, Edge HD optics even more pronounced.
There’s no sign of false color with the Schmidt-Cassegrain, so I could fully enjoy the pale, yellow-white atmosphere of Venus. I used a barlow lens to double my magnification to a whopping 290x – the highest I’ve ever used – and somehow the atmosphere (largely) obliged. The crescent flickered in the turbulence but overall remained razor sharp. Although it now filled much of my view, it lost little of its brightness.
The view was now truly breathtaking. The atmosphere of Venus looks largely featureless, yet there was an almost magical quality to the zoomed-in crescent. It was amazing to think that this is a world roughly the same size as our own, but with an atmosphere so thick, and so choked with greenhouse gases, that a car would crumple and then melt on the surface. A hell-world deceiving me with the beauty of that delicate crescent.
Mars is near Venus right now in the night sky, but it is actually much farther from Earth. As a result, it is roughly 200 times dimmer than Venus, and less than a tenth of the bigger planet’s apparent size. When I trained the Edge on Mars, I was not surprised to find a tiny, featureless globe. The wind picked up, and as it did the seeing worsened. The little red planet seemed to bob and weave across my view. I marveled at how small the disk looked, even at nearly 300x. Space is big.
I kept my magnification high and turned to Rigel, a blue supergiant star some 863 light years from us that shines with the almost unimaginable brightness of some 200,000 (!) Suns. Several million years from now, it will explode in a brilliant supernova and its core will become a black hole.
Rigel is actually at the heart of a solar system that contains several smaller stars. At 290x, I spotted one of its companions for the first time: Rigel B, actually another star system that orbits the bigger Rigel – Rigel A – at a distance equivalent to 2,200 times the distance between Earth and the Sun. Rigel B consists of two stars between three and four times the mass of the Sun, and one of these might actually be yet another star system consisting of two stars. It’s hard to imagine looking up from the surface of a planet orbiting Rigel Bb, with so many bright blue suns in the sky. Anyway, the Rigel B system is hard to spot with a telescope of six inches or less, so I was happy to glimpse it this time.
I finished by taking another look at the Orion Nebula. I kept my magnification at 290x and screwed in my narrowband filter that, you'll remember, only lets in light that shines at the wavelengths of emission nebulae. Now the view was just overwhelming. My eyes were not fully night adapted, and yet: the detail in the nebula around the zoomed-in Trapezium Cluster was just incredible. Boiling grey-green mist.
A few closing thoughts. First: this telescope hugely outperforms my AR 102. I expected as much, of course, and the comparison really isn’t fair given the very different roles (and costs!) of both telescopes. Yet I was surprised not so much by how much brighter objects appear through the Edge, but how much sharper they look. Second, the Twilight I mount can hold my C8 in a pinch. The view did wobble at high magnifications, especially during gusts of wind, but this is not a bad grab-and-go setup. It’s pretty amazing that such a powerful telescope can be so portable. Third: I’m beginning to grasp the appeal of “splitting” or “resolving” binary star systems. That’s good, because binaries are some of the few deep space objects that are easy to observe from urban locations. Finally: it sure feels great to have a really high quality eight-inch Schmidt-Cassegrain. I think I’ll keep it.
February 2, 2017
After ogling the Orion Nebula in my new observing site on January 7, I got a little overzealous and made the mistake of returning with my AR 102 just after a rainstorm, on a humid night that soon clouded over. Hunched over in the mud, I could barely make out anything, and I soon enjoyed the company of a big, barking dog. Someone turned on some really bright spotlights at Sidwell Friends School that I can't remember seeing last time, so observing any deep space objects was out of the question. All in all: a disappointment.
On a partly cloudy night roughly a week later, I stepped out with my 15x70 binoculars and returned to the park. The lights were on again, but I found a dark shadow under hill that shielded me from the glare. I reclined on the hill and had ethereally beautiful view of the Pleiades and Hyades open clusters, which are now too near zenith to be easy targets for my refractor. Of the two, the Hyades cluster impressed me more, both because I know it's relatively near Earth (just a 150 light year trip!), and because bright, crimson Aldebaran contrasted strikingly with the surrounding stars.
Over a week went by before the sky cleared again. Tonight, on February 7, I ventured out with my AR 102 to catch a glimpse of the Moon, Venus, and Mars. It was windier than I expected so the seeing was quite poor, and it again so cold that my hands quickly turned into claws. Nevertheless, the waxing crescent Moon was striking even at 20x. I tried to take a picture using my iPhone and a little gadget I picked up that fastened the phone to my eyepiece. However, the results were disappointing, and I found it hard to keep the phone positioned over the eyepiece. Money poorly spent, it seems.
Before long, I wheeled my telescope from the Moon to Venus, which was beginning to approach the western horizon. Venus is nearing inferior conjunction, which means that it's getting close to the Earth. It is, therefore, both extremely bright and fairly big through the eyepiece. I have always found Venus disappointing, since uniformly bright clouds shroud the planet and prevent visual observers from seeing much more than a featureless crescent. This time, I could make out that crescent just fine at 132x, but it bobbed and flickered in the turbulent atmosphere, and chromatic aberration surrounded it with a purple halo. Not the best view. Mars was little better: it's now so far from Earth that it's just about impossible to see any surface features using my little refractor.
Yes, the seeing was poor, but I wondered whether my optics were also a little soft. It seemed hard to focus the telescope. I turned to a really bright star - the white giant Sirius - and decided that the view was, indeed, a little fuzzy. I from my old eyepieces to a brand new, variable magnification eyepiece and suddenly noticed that the view was a bit sharper. Maybe I'll have to clean those older eyepieces.
My hands were about to freeze off, so I turned to give the Moon a last look before packing it in. Using the variable magnification eyepiece at 83x, the view was just spectacular. In fleeting moments of good seeing, the mountains on the crater rims suddenly popped out in razor sharp detail. It felt like I was tumbling down towards them from an unimaginable height. With my telescope and eyepiece cooled down, I could make out no chromatic aberration at all.
All in all, two satisfying observing nights and one disappointment. Urban observing isn't easy, and with my telescopes it's all but pointless for most deep space objects. Still, it's hard to describe the magic of those stunning views of the Moon, or the standout Winter star clusters.