A Window in the Stars

In this part of the sky the Milky Way takes on a surprising palette of hues. And it’s all due to dust.

The centrepiece of this shot is a bright star cloud in Sagittarius called, well, the Sagittarius Star Cloud! But not the Large one. This is the Small Sagittarius Star Cloud, a.k.a. Messier 24, a mass of stars with a single black eye. The dark spot, called Barnard 92, is a dense and opaque cloud of dust. Stardust — clouds of carbon soot blown out by aging stars — weaves all through this scene, creating the dark canyons winding through the stars. Obscuring dust also dims much of the background stars and discolours most of this part of the Milky Way a yellowish brown. It’s the same effect that dims the setting Sun a deep orange or red, as its light shines through haze and dust in the sky.

But here, the Star Cloud looks bluish and “cleaner.” That part of the Milky Way has less dust in front of it. And yet it is much farther away than the yellow dusty starfields around it. When we look toward the Small Sagittarius Star Cloud we are looking through a dust-free window, allowing us to see unencumbered right past our Galaxy’s nearby Sagittarius-Carina spiral arm to glimpse a dense part of the more distant Norma Arm, an inner spiral arm of our Milky Way Galaxy about 12,000 to 16,000 light years away.

To the lower right of M24 is M23, a rich cluster of stars 2,000 light years away, nearby by galactic standards, and so sits suspended in front of the fainter star background. The pinkish nebula at top is Messier 17, the Swan Nebula.

I took this shot May 2 from Chile, using the Canon 7D and 135 lens, for a stack of six 2-minute exposures.

— Alan, June 7, 2011 / Image © 2011 Alan Dyer



Here Comes the Sun!

I can count on one hand how many shots of the Sun I’ve taken in the last decade that weren’t at an eclipse, or a sunrise/sunset. I just don’t do much solar shooting. But today I had to resurrect some old gear to get this shot. The Sun was putting on a fabulous show this afternoon (Sunday, June 5, 2011) with an army of huge prominences rimming the edge of the Sun. Very impressive. And looking very HOT!

After 2 to 3 years of record low activity, the Sun is picking up, returning to its normal self, with sunspots and prominences a daily occurrence. But these were especially dramatic. Each of these prominence “flames: towers tens of thousands of kilometre above the surface of the Sun. The Earth would be a dot next to one of them.

To get this shot, I created a masked composite in Photoshop of two exposures, a short 1/13s second shot to record the disk detail, and a long 1/2 second shot to record the fainter limb prominences. For a telescope I used my little Coronado PST H-alpha scope, a special scope just for solar viewing that filters out all but a narrow wavelength of red light, allowing the prominences to be seen.

Trouble is, my DSLR cameras won’t reach focus on the Coronado scope. So I dusted off the little 2003 vintage Sony DSC-V1 point and shoot camera and a Scopetronix 40mm eyepiece and “afocal” adapter, so the camera was screwed onto and looking into the eyepiece which was then inserted into the scope. I hadn’t used an afocal setup like that since the Venus transit in 2004.

It was tough to focus the stack, so focus was a bit of a guess — it was helped here with a liberal application of Photoshop’s Smart Sharpen filter! In all, it is a crude system but in a pinch it does work. Maybe I’ll have to get better gear just to take solar shots. With the Sun becoming more active, there certainly will be lots more to shoot.

— Alan, June 5, 2011 / Image © 2011 Alan Dyer


Saturn Sidles Up to a Star

If you look up this week, to the southwest, you’ll see a bright star in the evening twilight that, upon close inspection, is really a tight double star. The fainter companion becomes obvious as it gets dark. The bright member of the pair is actually Saturn, and its fainter companion is the star Porrima, a.k.a. Gamma Virginis. And they are unusually close!

This week Saturn (at bottom here) sidles up to Porrima (at top), getting so close both are contained in a high-power telescope field, which is what this shot depicts. I took it Saturday night, June 4, when Saturn was about 1/4° (16 arc minutes) from Porrima. But by June 10 their separation will be a tad less, at 15 arc minutes apart. This week Saturn stops its annual retrograde motion just shy of Porrima.

The pairing made a wonderful sight in the telescope tonight, especially because of the “good seeing” — so Saturn looked very sharp. And Porrima, itself a very tight double star, was easy to split at 200x, appearing like a pair of headlights at high power. (The photo doesn’t split Porrima.)

But the nicest view is just naked eye — Saturn and Porrima are forming a rare and temporary double star easy to split with no optical aid but looking much more striking than any other naked eye double. The pairing won’t last long — Saturn turns around near Porrima this week, then begins to head east again away from its stellar partner.

The shot also picks up four of Saturn’s moons: Dione very close to Saturn, then Tethys, and Rhea in a row from left to right, and bright Titan below the trio.

This a stack of five 5-second exposures at ISO 1600 with a Canon 7D attached to my 130mm Astro-Physics refractor with a 2x Barlow, giving an effective focal length of about 1600mm and f/12. I took this in twilight to add the blue sky.

— Alan, June 5, 2011 / Image © 2011 Alan Dyer


The Seven Sisters of the South

Down in the south sit many austral equivalents to namesake northern sky objects: the Southern Cross, the Southern Beehive, the Southern Pinwheel. This is the “Southern Pleiades,” a match to the famous Pleiades star cluster prominent in our northern hemisphere sky. Since our Pleiades also carries the moniker the “Seven Sisters,” I suppose that makes this object the “Seven Sisters of the South.”

The field here again duplicates what binoculars would show, and this is a lovely object for binos. Its resemblance to the northern Pleiades comes from this star cluster’s bright but scattered appearance, and the blue colour of its sorority of stars. Like its northern counterpart, the Southern Pleiades is a cluster of hot young stars which shine furiously blue in their energetic youth. This group is perhaps no more than 50 million years old, and like the northern Sisters, shines quite close by, just 480 light years away, putting it a stone’s throw away down our own galactic spiral arm.

Officially catalogued as IC 2602, and also dubbed the Theta Carinae Cluster, this clutch of blue stars shines just below the Carina Nebula (you can see both together in my earlier blog The Best Nebula in the Sky). A couple of other fainter star clusters also populate the field.

I took this shot with the Canon 7D and 135mm telephoto lens and stacked five 2-minute exposures. Stacking helps smooth out background noise, though in a wide field shot like this, the sheer number of stars tends to overwhelm any camera noise.

— Alan, June 4, 2011 / Image © 2011 Alan Dyer




An Island in a Sea of Stars

This image looks toward the inner spiral arm of our Milky Way called the Norma Arm, where stars bunch together to form the rich Norma Starcloud, a prominent patch in the southern Milky Way. What you see here is all stars, lots and lots of stars.

Seemingly embedded in the sea of stars is an island of brighter stars called the Norma star cluster, or more prosaically NGC 6067. It’s about 6800 light years away, much closer to us than the more distant stars behind it. It is literally floating in front of the background sea of stars.

As with the previous image, this is a wide field shot, taken with the 135mm telephoto, to frame the field much as it would appear in binoculars. This shot is a stack of six 2-minute unguided exposures at ISO 1250 with the Canon 7D riding on the little Kenko tracking platform. It’s one of a couple of dozen fields I shot the first night of shooting on Chile in May.

— Alan, June 4, 2011 / Image © 2011 Alan Dyer





Rose of the Southern Sky

It’s been a month since my last post, a month with no new astrophotos from home. But I’ve got a backlog of RAW files to work through from the Chile trip a month ago. Here’s a new image from that shooting expedition. It’s of an area of the southern sky that lends itself to every focal length and framing variation — you can’t go wrong with the Carina Nebula!

This wonderful nebula in the deep-south Milky Way rewards any astrophotographer. For this shot I used a 135mm telephoto (Canon’s wonderful f/2 L-series lens) and the Canon 7D camera. The 7D is what I call a “stock” camera, used just as it comes off the dealer shelf. The 7D does a superb job capturing the red nebulosity and its faint outlying bits and pieces. It tends to record these clouds of glowing hydrogen as magenta in tone. By comparison, my other Canon camera is a “filter-modified” 5D MkII. You can see a shot of this same area of sky taken with the 5D MkII a few blogs back under The Best Nebula in the Sky, posted May 6. The 5D MkII’s modification (which replaces the filter in front of the sensor with a new astro-friendly one) allows it to record deep-red wavelengths and picks up more faint nebulosity, registering it more as red in tone. But both images look good and presentable.

This field is rich in objects — not only the main sprawling nebula but nearby star clusters and patches of dark dust clouds. It is one of the finest fields in the sky for binoculars, and this shot approximates the field of view of typical binos. I like to shoot a lot of objects with telephoto lenses — while the main subject is not frame-filling and in your face, it does match (at least in field of view) what you can see in binos, useful for illustrations and observing articles. Of course, the camera picks up  more stuff and colours even your bino-aided eyes can’t see.

This shot is a stack of five 2-minute exposures at f/2.8 with the 135mm telephoto, on the Canon 7D at ISO 1250. I used the little Kenko Sky Memo tracking platform for this, letting it track without any added guiding. It’s tracking was spot on, with nary any star trailing as it followed the target for 20 minutes or so.

— Alan, June 3, 2011 / Image © 2011 Alan Dyer