Sunday, August 23, 2015

A Few Hours In The Dark...

Unfortunately, clear skies through Arizona's monsoon season come rarely, typically only a few times through the 10 weeks from 1 July into mid-September. And I don't count the times it clears at 2 or 3 am - that happens almost daily with rains in the early evening, and clear skies by dawn the next morning. Who has the schedule to wait till the hours before dawn to think about observing? I'm talking about the rare times the monsoon circulation is disrupted and we get some rare nights that are clear throughout.

Well, it happened last week. and we finally had some blue AND dry skies in the afternoon. Melinda had been to the dentist earlier in the day with a tooth extraction, and she was resting comfortably at home, so I ran out towards Kitt Peak for a few hours in the evening. It wasn't going to be a late night - I needed to be at work the next morning. With the sun setting about the time I reached the Kitt Peak turnoff, the interesting clouds I'd been watching revealed themselves - I believe that they weren't clouds at all, but smoke from the California fires some 400 miles to our west. Shown at left, something way over our horizon was casting crepuscular rays from the well-set sun, but the line of smoke stayed low with the crescent moon above it.

With most of the telescopes still in summer shutdown, there was little activity on the mountain, and I set up in an out-of-the way corner of the public parking lot. I've always got a project or two in mind, and I set up two different tracking platforms - an Astrotrac system I've had nearly 2 years, and a Vixen Polarie for shooting wider fields. Those who know me know I love to image dark nebulae, and this is prime time for dark clouds - dust and gas seen not from incandescence or fluorescence, but from their silhouette against the star clouds of the Milky Way. My main goal was to go after the area of the Pipe Nebula in the constellation Ophiuchus with a 200mm lens (Canon 70-200 @ 200mm, F/3.2 w/XSi) to put together in a mosaic. By shooting with a telephoto, you can retain the resolution of the original frames, with the mosaic revealing the wider view.

The result is shown at left - I ended up taking 5 frames in the mosaic, each 5 exposures of 3 minutes each. There was enough overlap that Photoshop assembled the mosaic just fine. As you can imagine, the "pipe" of the nebula has the mouthpiece at right, and the intention is smoke ascends from the bowl at the left side with more dark clouds. Also noticeable if you click on the image is that the "Snake Nebula", B72, is visible as an "S" shaped dark cloud at top center. The "B" designation is from the Barnard catalog of dark nebula, from E.E.Barnard, who discovered and listed 369 such dark clouds from his initial photographic exploration of the Milky Way.

While that was my primary object through the evening, I used a 20mm wide angle lens to shoot another mosaic at left on the Polarie tracker. This one is produced from 2 frames from 6 or 8 two minute exposures at F/4 with the old film-era Nikon lens. Even with only 12 minutes total exposure (of the lower half) there were quite a few deep sky objects visible. I made a labeled version posted at right to show objects in subsequent images, as well as show the position of the Pipe Nebula in the grand scale of the Summer Milky Way. This wide-field much better matches the naked-eye view, with much of the Pipe Nebula and other dark clouds seen against the Milky Way glow in the dark mountaintop skies.

But like a telescope or binoculars show much more of the sky details that can be seen by eye alone, a longer telephoto lens shows much more than the wide field. Seen here is a 3-frame stack taken with a 135mm lens (another film-era Nikon lens shot at F/4 with a Canon 20Da). Besides star and dark clouds and star clusters, also visible are a pair of luminous hydrogen clouds, illuminated by internal fluorescence from bright stars within. Part of the Charles Messier catalog of "fuzzy objects" (he was looking for comets, and is best known for his catalog!). These are labeled as M17 and M16 on the labeled version at right. While the couple-decade-old Nikon optics do an adequate job, if you look at the brighter stars, some of the blue ones have blue disks around them, and some of the red stars have red disks, indicating the color correction isn't really sufficient. Someday I'll update to newer lenses, or use the 70-200 zoom which is quite excellent, but was in use on the other mount.

Finally I close with the last frames of the night. On the Polarie and 135 lens, I shot a few frames of the Lagoon and Triffid Nebulae (M8 and M20), shown at left. Unfortunately, that tracking mount isn't beefy enough to shoot my "newish" 300mm lens to try for astronomy. But with the Pipe Nebula mosaic frames ending on the Astrotrac, the final frames of the same field were shot with the 300 at F/4.5. It looks to me that the lens has very good potential, almost needing use of an autoguider, as even the Astrotrac was barely adequate for this pair of 2.5 minute exposures... These nebulae have been featured here before, most notably at a Kitt Peak "Star-B-Que" 5 years ago, a close-up of the Triffid featured in a first-outing of the TEC140 last year, and both these nebulae and M16, 17 above were all featured in a post on "snapshots" with the Hyperstar on the C14. I really like this area, not only for the bright glows of the gas clouds, but also because of the interplay of involved dark nebula as well. But this pair has not been featured together as well as the 300mm shot at right, so a deeper excursion might be called for in a future outing.

I was a little tardy getting home - originally I was planning on a Midnight arrival, but it was closer to 1am when pulling in. Still, that isn't too much later than our normal bedtime, so made it to work the next morning just fine. I was glad I didn't put it off till Tuesday night as it was nearly overcast, though rain-free. So you've got to get out for those little moments when you can catch them! Unfortunately, in another month as the monsoons wind down, the Summer Milky way will be another twelfth of the way around the sky, lower in the west, and soon after that in conjunction with the sun. I'm glad I got out, if just for a few hours...


John Dolby said...

Welcome back! And very stunning photographic work, as usual. I love your pic's of the "Pipe Nebula" and "S" nebula. A 200mm lens seems to be the perfect optic for these structures. It's difficult to give in to the re-naming of our beloved objects of yesteryear, but I have to admit that the "Dark Horse" has usurped the Pipe Nebula in my opinion. The Pipe is now merely the back leg of the Horse. On the other hand, there are some new names that I refuse to accept. For instance, the Black-Eye Galaxy, M64. It's a perfect name. I will never accept "Sleeping Beauty Galaxy" as a replacement for that one!

Dean said...

Hi John-
Thanks for the comments. While the "Pipe" is considerably larger than fits in the 200mm (thus the mosaic), smaller objects like the Snake benefit from a longer focal length, like these images taken with the C14 and Hyperstar back when I first started using it.

John Dolby said...

Yes, the C14 and Hyperstar make a great combo. Nice!

I've been lying to myself for years that with digital imaging we don't need to go to dark-sky sites anymore. We can stay at home and shoot from our back yards in Tucson.

Back in the 1980's and 1990's, we would drive down to Empire Ranch and shoot with Konica 3200. Remember those fun times? But it was a lot of driving and extra work for setup and take-down. It's so much easier in the back yard.

Lately, I've been out to the Kartchner Caverns area at night and it's shocking to see a dark sky with so many stars. The Milky Way looked like bright, billowing clouds, rather than a wimpy band. I've forgotten how it feels to stand under a dark night sky.

I would love to start taking my scope out to dark-sky country again, but Border Patrol has become super-aggressive. One night, I pulled off to the side of the road and shut off my car engine, but before I could even get my binoculars out and open my door, a Border Patrol agent pulled up beside me, got out, and had his flashlight shining in my eyes.