April 2011 – The Amazing Sky

April 25, 2011

Springtime Cluster #3: Diamond Tresses in the Sky

Unlike most deep-sky objects, this one is obvious to the unaided eye. The Coma Star Cluster is so big it barely squeezes into the frame of the wide field telescope I used to take this image. To see it for yourself just look up and due south on northern spring evenings. To the left of Leo, off his back end, shines this loose and scattered grouping of stars obvious to the unaided eye on a dark night. Indeed, I think in olden times this bunch of stars was drawn as the tuft of hair at the end of Leo’s tail.

But now we picture this cluster of stars as the tresses of hair of the late dynasty Egyptian Queen Berenice II, placed in the sky to honour her loyalty to her husband, the Pharaoh Ptolemy. The story has it that the group did not become officially recognized as a constellation until the 16th century.

The constellation of Coma Berenices (hair of Berenices) extends over a larger area of sky than just this grouping, but the Coma star cluster is certainly the most obvious feature of the constellation. Binoculars frame it well (taking in a bit more sky than this image) and are the best way to view it. With their narrow field, telescopes look right through this object.

The cluster is spread over nearly five degrees of sky and contains about 40 stars, so a rather sparse gathering to be sure. Many open clusters, like M67 pictured a couple of blogs back, contain hundreds of stars. Coma is so big in our sky because it is one of the closest star clusters to us, only 288 light years away, and above us toward the north pole of our Galaxy.

Its size and scattered appearance actually meant it hid in plain sight for centuries – yes, it was given a name and people saw it, but astronomers didn’t give it status as an official star cluster until 1938. In 1915 astronomer P.J. Melotte had listed it as object number 111 in his catalogue of star groupings. And so today, we usually refer to this cluster as Mel 111, the most famous entry in “Mel’s” catalog!

I took this shot with the same gear used for the M67 and Beehive M44 shots earlier, so it’s easy to see just how much bigger the Coma Cluster is than just about every other star cluster in the sky. This is a stack of four 6-minute exposures at ISO 1600 with the Canon 7D camera and the 92mm TMB apo refractor.

April 24, 2011April 24, 2011

Easter Sunday Space Station

What a picture perfect pass this was, on Easter Sunday evening, April 24, 2011. The International Space Station (ISS) rose out of the west right on time, passed almost directly overhead, the flew off to the east, fading out just as it approached the horizon. The sky was a deep blue in the late twilight, with the spring stars beginning to appear. As it usually does, the Space Station outshone them all, including Arcturus, the brightest streak at right. The Station also passed just north of the handle of the Big Dipper at the top of the frame.

I took this with the 15mm lens that takes in a field of view from the horizon to almost straight up.

Because the sky was still bright, one long exposure wouldn’t work with this shot. The Station took nearly 3 minutes to traverse the frame. The only way to avoid overexposing the sky would have been to stop the lens way down or use a very slow ISO speed, either of which would have meant the Station and stars might not have recorded very well, especially the fast-moving Station.

So instead, I used what turned out to be thirteen short 15-second exposures at f/4 and ISO 400, taken 1 second apart. Each one is exposed correctly, and the aperture and ISO speed are fast enough to pick up stars and the moving satellite. The trick is to then stack the images in Photoshop. To do this I import the images first from the memory card using Adobe Bridge, then process them in Adobe Camera Raw. ACR provides most of the processing necessary for shots like these – sharpening, noise reduction, some contrast boost, and the usual Vibrance and Clarity. Once processed, I use Bridge’s “Import into Photoshop Layers” command to automatically create a single image with all the processed frames stacked on top of each other in layers. Then it’s a matter of turning the Blend mode of each layer from Normal to Lighten, and voila! – the frames turn transparent and appear merged together, all properly exposed. The result is a single exposure effectively 3 minutes long, long enough that the stars also trail.

In this shot, the 1-second interval between exposures creates the gaps in the ISS trail. I could do a little Photoshop trickery to eliminate those but I think they give a sense of the speed of the ISS as it flies overhead quite quickly when it is closest, then slows down in apparent motion as it flies away into the distance.

A great help in planning a shot like this is Starry Night software – it loads in the latest satellite orbit data and shows the exact path of the satellite across your local sky. So I was ready and waiting with the camera all framed up, knowing just where it would appear, then started the camera firing as the ISS came overhead and into the field of the camera. It was a fine sight on an Easter Sunday.

April 24, 2011April 24, 2011

Springtime Cluster #2: Ancient M67

Poor old M67. Does anyone ever look at this cluster? I tend to ignore it, in favour of its brighter and bigger brother, the Beehive Cluster just to the north. Yet, this smaller cluster ranks with the best of the sky’s open star clusters for richness and brilliance. Only a few showpiece star clusters, like the Beehive and the Pleiades, beat M67.

Located in Cancer, M67 really deserves more respect – even a name! – as it stands out as one of the few prominent deep-sky objects in the otherwise sparse spring sky, at least sparse for bright targets for binoculars or a small telescope. Yes, if you love galaxies, the spring sky is heaven! There are thousands of galaxies to hunt down in spring, but most need a decent-sized telescope to do them justice. By contrast, M67 looks just fine in a small telescope. With a few hundred stars packed into an area the apparent size of the Full Moon this is one rich cluster.

M67 is called that because it is #67 in Charles Messier’s catalog of “things not to be confused as comets.” Messier came across this object in April 1780. Messier ‘s object #67 is one of the few open star clusters not embedded in the Milky Way. Like the Beehive, M67 sits well above the disk of our Galaxy’s spiral arms. We look up out of the plane of the Galaxy to view M67, sitting some 2600 light years away, over four times farther away than its neighbour in Cancer, the Beehive. Thus, M67 looks smaller than the Beehive because it is more distant.

M67 holds the distinction of being one of the oldest star clusters known. It’s been around for over 4 billion years. Its position well above the frenzied traffic jam of our Galaxy’s spiral arms helps M67 stay intact and together, an isolated island of stars in our spring sky.

This image was taken right after the M44 Beehive Cluster shot featured in my previous blog post, using the same gear. So the image scale is the same. You can see how much smaller M67 appears than M44. Because M67 was beginning to sink into the west when I took this, I bumped the camera up to ISO 1600 and used shorter 3 minute exposures and stacked five of them to smooth out noise. The telescope was the little 92mm TMB apo riding on the Astro-Physics 600E mount and flawlessly autoguided with the Santa Barbara Instruments SG-4 autoguider. I really love the SG-4 — just press one button and it’s guiding. True “Push Here Dummy” guiding!

April 23, 2011April 24, 2011

Springtime Cluster #1: The Beehive (M44)

At last! A clear night in what so far has been an awful spring. The long-awaited arrival of mild spring nights brings a sky sprinkled with a few naked-eye star clusters. This is the most famous, and appears as a fuzzy glow in the constellation of Cancer the Crab. Indeed, to the unaided eye, there’s not much else to see in Cancer. But this cluster is a dandy in binoculars. Called the Beehive, this is one of the few deep-sky objects known since antiquity. Apparently, the Greek poet Aratos mentioned it in 260 B.C., describing it as a “little mist.” A hundred years later Hipparchus included it in his star catalog, calling it a “cloudy star.”

It wasn’t until 1609 that Galileo, using his pioneering telescope, resolved the cloud into a mass of stars. Any binoculars will do the same today. This close-up view more closely matches the view through a modern telescope, showing its subtly coloured blue and yellow stars.

In 1769 Charles Messier included it as object #44 (the Pleiades was #45) in his first catalog of what we now call deep-sky wonders. To him, however, these fuzzy spots in the sky were just distractions to his goal of hunting the fuzzy things that really mattered – comets.

The stars of M44 really do belong together in a gravitationally-bound cluster of up to 1000 stars, traveling together through space since the time about 600 million years ago when they formed out of what must have been a massive gas cloud. That’s a pretty good age for a star cluster; most break apart and scatter around the Galaxy after just a few tens of millions of years. However, the Beehive sits about 600 light years away, above the main disk of the Milky Way and its spiral arms. Its location makes it partly immune to the disruptive tidal forces of the Galaxy. Because it lies above the galactic plane we see it far off the band of the Milky Way, shining in our spring sky sparsely populated with bright stars and lacking the rich assortment of clusters and nebulas scattered along the winter and summer Milky Way.

For this exposure I used a favourite scope, the TMB 92mm apo refractor, a compact and fast little telescope perfect for imaging big binocular-class objects like this. This is a stack of four 4-minute exposures at ISO 800 with the Canon 7D camera. A Photoshop routine added the diffraction spikes, purely for photogenic value.

April 18, 2011April 18, 2011

End of an Era

The final night was inevitable – the last night we could operate the public Observing Deck at the science centre where I work. You see, we’re building a new science centre in Calgary and the old one will be closing at the end of June. But long before then, with the Sun setting later and later, it will become too light to see anything during the evening hours the science centre is open to offer any programming on the telescope deck. So, as the person in charge of the program, I looked at sunset times and moon phases and decreed that April 14 would be the last night for public viewing at the Deck.

And so it was. We went out in fine style. A facility that has served the public well since 1967 ended its public life with the best one-night attendance of the year, thankfully clear skies (after a day of snow), and a great turnout from present and past volunteers to the Deck. Staff from the science centre – the TELUS World of Science-Calgary – were on hand to present a certificate of appreciation to the members of the Royal Astronomical Society of Canada who have made the Deck program possible. It was their volunteer help that, over 44 years, allowed hundreds of thousands of people to view through telescopes and be amazed at the craters of the Moon, the rings of Saturn, and the moons of Jupiter.

Among the highlights: record line-ups for the comet crash on Jupiter in 1994, and even bigger line-ups in August 2003 for the close approach of Mars. That year we had to turn people away from 2 hour line-ups to look through the telescopes. The Deck was also one of the centrepiece venues for our 2009 Year of Astronomy programming.

Now, what has this got to do with astrophotography? Not much I suppose. But very few astrophotographers, and indeed amateur astronomers, aren’t also rabid enthusiasts for promoting astronomy to the public. Almost everyone in the hobby and profession now can look back to a moment at just such a facility or at telescopes staffed by people like these, moments when they first saw the rings of Saturn, or some other amazing sky sight. That view, and the enthusiasm of the telescope operator, got them hooked. And off they went to pursue a lifetime interest in the sky, perhaps even wanting to photograph it. I know that’s certainly the case with me. As such, so many people in the hobby feel it their obligation to give back to the community and allow others the same chance for a life-changing view through a telescope – a “Galileo moment” as we so aptly described it during the Year of Astronomy’s 400th anniversary of the telescope.

The Observing Deck at the TELUS World of Science is now closed. May its spirit of enthusiastic volunteers promoting moments of personal discovery live on.

Photo by John Mancenido