Astro Session: June 30, 2018
The Eagle Nebula (Messier 16, NGC 6611, Star Queen Nebula) is an open star cluster and emission nebula in the constellation Serpens, about 7000 lightyears away from us. Imaging Info: 96 x 240 sec. Ha + 42 x 240 sec. OIII frames stacked in DSS, processed in PSCC2018. These frames were taken over several nights. You can see the numbers are a bit unbalanced, but the clouds moved in during the OIII sequence last night, and there was nothing I could do. I went ahead and stacked and processed them as they are. I'll probably come back to this one in the future with more oxygen-3 (and maybe sulphur-2) to achieve something like the actual proportional levels of light from the nebula across these bandpasses. Equipment: William Optics ZS61, Atik 414EX mono CCD, 12nm Astronomik Ha filter, 12nm Astronomik OIII filter, CEM25P EQ Mount, ZWO ASI120MM-S Guide Cam + Orion TOAG, INDI/KStars/Ekos control software. Location: Stratham, New Hampshire, Bortle: 4, SQM: 20.62 https://www.astrobin.com/353803
Posted June 30, 2018
Astro Session: June 22, 2018
The view from my backyard, with the right equipment focused on a particular part of the sky: Cygnus Wall region of NGC 7000, the North America nebula, imaged in narrowband Ha and OIII. The way narrowband imaging works is by filtering out all light except for an allowed narrow bandpass at specific locations in the electromagnetic spectrum. A hydrogen-alpha (Ha) filter will only allow light to pass through to the camera sensor around 656 nanometers, which is out at the red end of the spectrum, and an oxygen-3 (OIII) filter will only allow light to pass through around 501nm, which is in the middle of the blue and green ranges. When I say red, green, blue, I'm talking about where these bandpass lines fall within the scope of the visible spectrum, which starts around 390 and goes to 700 or so (for humans). I shot the oxygen-3 sub-exposures last week, and the hydrogen-alpha subs last night. When you process these separately filtered images into one color image, you may get the Ha coming out vivid red to rust red, and the OIII coming out in blues and greens. The Cygnus Wall is that bright, rolling line across the middle where you have a lot of concentrated star formation, but this area of NGC 7000 also has lot of dust and debris drifting in front of it--the dark reddish-brown regions across the top and right side. (Imaging info: 42 x 300 second subs in OIII, 40 x 300 sec. subs of Ha. + 20 dark frames stacked in DSS, processing in PSCC2018 + Astronomy Tools actions & Annie's Astro actions. Equipment: William Optics ZS61, Atik 414EX mono CCD, 7nm Optolong 2" Ha filter, 8.5nm Baader 2" OIII filter, CEM25P EQ Mount, ZWO ASI120MM-S Guide Cam, https://www.astrobin.com/352528).
Posted June 22, 2018
Astro Session: June 16, 2018
It was narrowband time last night in the backyard. I took a couple hours of hydrogen-alpha (Ha) sub-exposures of M17, the Swan Nebula in the constellation Sagittarius. M17 is about 5,500 light-years away. It's also called the Omega Nebula, Checkmark Nebula, and sometimes the Horseshoe Nebula, but all I see is a swan--with a black beak, neck arched forward, and wings outstretched. The bright region in the middle is the swan's chest. I started to take a few OIII frames on the 16th, but by that time M17 was heading back toward the southern horizon, and so I jumped over to the "Cygnus Wall" in NGC 7000 (North America Nebula). I captured several hours of OIII data there, amazing stuff, and I've already posted the finished image in Ha and OIII. I came back to M17 on the 21st, and took another 40 x 300 second subs in OIII. (M17 info: Ha 16 x 300 second + 82 x 120 second exposures + 20 dark frames, OIII 40 x 300 second exposures + 20 dark frames, stacked in DSS, William Optics ZS61, Atik 414EX mono CCD, 7nm Optolong 2" Ha filter, 8.5nm Baader 2" OIII filter, CEM25P EQ Mount, QHY5III178 guide cam with the Orion TOAG, https://www.astrobin.com/352947).
UPDATE: The Swan Nebula (M17) bi-color narrowband with the WilliamOptics ZS61 and the Atik 414EX. I shot the hydrogen-alpha frames on June 16th (16 x 300 second exposures + 82 x 120 second exposures) and I came back on the 21st to shoot 40 x 300 second exposures in oxygen-3. I decided not to shoot sulphur-2 frames based on the wonderful result with bi-color for my Cygnus Wall image set (6.8 hours of Ha + OIII). For the Swan Nebula (this post) and Cygnus Wall (last post) images I used the Hydrogen-alpha/Oxygen-3 bi-color process developed in an article by Travis Rector, et. al. in The Astronomical Journal here: https://doi.org/10.1086/510117, and detailed here: https://www.starrywonders.com/bicolortechniquenew.html
Posted June 16, 2018
Astro Session: June 8, 2018
How about a little Voldemort with your Astronomy? Here's Barnard 104, the Fish Hook Nebula (backward checkmark nebula was already taken?), just left of the star beta Scuti in the constellation Scutum--along with several other absorption nebulae in the Barnard Catalogue, 113, 111, 110, 107, and B106. (See the image below). These are the dark cloudy regions across the middle, which stand out against the glow of a billion stars in this area of the Milky Way Galaxy. (Okay, I'm being a bit deceptive with the drama there. It's probably more like 5 or 10 billion). Oh, and let's not forget NGC 6704, the open star cluster toward the bottom in the center. A note on the "Barnard Catalogue", which is what I've always called it: I just found out the official name for it is the very Harry Potter sounding, Barnard Catalogue of Dark Markings in the Sky. Go home, Death Eaters! The star gazing geeks got here first! (ZWO ASI071MC cooled CMOS camera at -10°C, iOptron CEM25P EQ mount, William Optics ZenithStar 61 f/5.9, 12 x 120 sec. sub exposures, stacked in DSS. Location: Stratham, New Hampshire, US. Bortle 4).
So, all in all, a successful night of astronomy stuff, even with the clouds rolling in around 2 am. Here are a couple more wide-field shots from the session, the Eagle Nebula and the Sadr Region--the diffuse nebula (IC 1318) around gamma Cygni, also called Sadr (center star in the constellation Cygnus).
I spent a few hours last night dialing in the Orion "TOAG" or Thin Off-Axis Guider, which I bought a couple years ago, but have never been able to get working properly. I've tried seven or eight times, added it to my imaging train a couple times a year, attempting to get things working without success. Well, I went at it again last night, and you know what? It came together. I still have some weirdness to tinker with--to work out, but for the first time I wasn't guiding with a separate scope. I was guiding at the same focal length as the ZS61 using a pick-off prism that directs a portion of the field of view up into the guide camera. Here's the setup I used last night to dial-in the distance between the primary camera and guide camera, and then bring everything into focus. I ended up with some pretty cool shots, but my main purpose was to get Off-Axis Guiding (OAG) adjusted and working--and that was with me slewing around the sky to clear areas between banks of clouds to find some halfway interesting targets. In this setup I'm using my trusty ZWO ASI120MM-S for guiding, and the ZWO ASI071MC cooled color camera for the primary. The goal here is to be able to guide (track the motion of the earth against the star field to a very fine degree, and make small incremental adjustments to the EQ mount) so that I can take long exposures without worrying about the external guidescope issues I know all of you care deeply about, like field rotation and differential motion between a guide scope and imaging telescope. I have been able to take 20 minute exposures with a guidescope and camera, but the stars are not as sharp as I would like--think pressing down the button of your camera and holding the shutter open for 20 or 30 minutes and have everything in the field of view remain in sharp focus. That's essentially what the guiding system accomplishes, taking continuous images of the stars and feeding them to some pretty sophisticated software that controls the motion of the equatorial mount (that's the white z-shaped device with the black boxes on which the telescope is fastened and balanced).
Posted June 8, 2018
Astro Session: June 2, 2018
The Crescent Nebula (NGC 6888) with two channels, hydrogen-alpha and oxygen-three. 4 x 1200 second exposures for the Ha (mostly red channel), and 10 x 600 second exp. for the OIII (mostly blue channel). I didn't get nearly enough of the blue halo around the Crescent as I would have liked. I'll probably need to go to 20-minute exposures in OIII next time--or more 10 minute ones.
Posted June 2, 2018
Astro Gear: May 30, 2018
Narrowband imaging on the cheap?
It's tempting to say "here's what you can expect from a $129 Hydrogen-alpha filter", but it's never as simple as that, is it? Perspectives and opinions vary, but I consider this a pretty good H-alpha narrowband shot of the Crescent Nebula (NGC 6888), with some great contrast--the Crescent structure itself stands out, and I still managed to bring in a lot of the surrounding dust and clouds of ionized hydrogen. I used an Astronomik 1.25" 12nm Ha filter, an Atik 414EX mono CCD, iOptron CEM25P EQ mount, and I took 4 x 1200 second subs + 15 dark frames, all stacked in DSS. I shot these frames from my backyard, on a clear night with good seeing (Bortle 4, SQM: 20.62 mag/arc sec² according to https://www.lightpollutionmap.info). I've never shot deep space objects with 6, 5, or 3nm bandpass filters, but a 2" Baader 7nm used to be my primary Hydrogen-alpha filter--and I loved it. When I started out in astrophotography I was thinking long-term and went with 2" filters for everything--and it cost me a bunch. A couple years ago I switched to 1.25" filters, both for cost savings and pairing with the smaller Atik 414EX sensor--2" wasn't necessary. It also allowed me to get the Atik EFW2 with the 9-position filter wheel, so I can run with LRGB, Clear, Ha, OIII, SII, near-IR all in one neat motorized package. Because I was looking to save to money I went with a cheap Ha filter--the Astronomik 12nm H-alpha runs around $130 USD. Very inexpensive when compared to the $300 2" Baader I used to use regularly, and nowhere near the $900+ Astrodon 3nm 2" filter. I'm sure the Astrodon kicks ass--they're one of the premier filter manufacturers. But do you need a $900 filter to shoot narrowband? If you have fairly dark skies in your neighborhood (or within driving distance), I would say absolutely not. Will it make things easier when it comes to increasing SNR in light polluted skies? Absolutely. Will it make things easier when it comes to increasing contrast and pulling in those fainter wisps of dust and hydrogen? Probably. But I wouldn't hold off on narrowband imaging just because you can't afford the best. There are just too many cool targets in the night sky that you're not going to pick up with RGB. And that's one of the advantages of our hobby. You can shoot forty subs tonight, stack, process, and post them, and then come back tomorrow, next week, or next year and reshoot the same target with a different camera, faster scope, or better filters. Some targets never get old, and if they do, there are mysterious absorption nebulae and integrated flux nebulae--and even crazier things in the night sky to pursue. Beyond that, there are always interesting new wonders below the horizon--or above, depending on which hemisphere you spend most of your time.
Short thread on this topic at Cloudy Nights: https://www.cloudynights.com/topic/612314-7nm-vs-12nm-h-a-filter
The general conclusion is get the narrowest bandpass you can afford, which is the right answer, especially if you have any light pollution problems.
Posted May 30, 2018
Astro Session - May 24, 2018
Fourteen stacked frames through the powerlines: The Lagoon Nebula (M8, NGC 6523) and Trifid Nebula (M20, NGC 6514). We have a couple sets of transmission lines running east-west south of our property, and unfortunately they interfere with the amazing stuff in the constellation Sagittarius, which is even lower on the horizon than Serpens (also amazing). Transit for M8 is 23°, compared with 33° or so for the Eagle Nebula. We really need to take a trip south to get a better view of these beautiful ionized hydrogen structures. At the middle and lower left I also captured two globular clusters, NGC 6544 and NGC 6553. That's a very bright section of the milky way lighting up the whole lower left of the frame. Yes, there are stars running through the long bands of power lines, because over the 16 or so minutes of exposure time the earth rotated about four degrees. So, those stars were not obscured by the lines in some of my exposures, but when I stack them all together, aligning all the stars, they're going to appear where they were when camera caught them. That's also why the powerlines appear blurry--they're actually smeared out across the frame. They are much narrower and sharper than that in the individual subs. What's funny--to me, anyway--is that I was shooting the Eagle Nebula, and after 30 or so exposures I started to wonder if I had a chance to get the Lagoon Nebula. I slewed even lower toward the horizon, took a test frame, and saw the powerlines running through it...and thought what the hell, maybe the lines will look kind of cool in the foreground.
North America Nebula (NGC 7000) 50 stacked frames from the ZWO071MC camera.
The Eagle Nebula, Messier 16, sometimes called Star Queen is a diffuse nebula in the constellation Serpens. M16 was only 22° above the horizon to the southeast when I was taking these subs, low enough to have the atmosphere and some light pollution from Hampton affect the result. Even so, I'm here in New Hampshire at 43° latitude, and I'll take any chance I can get to shoot the Eagle Nebula.
Swan Nebula (M17, Checkmark Nebula, Omega Nebula, NGC 6618) is another H II region in the constellation Sagittarius.
The Great (and powerful) Globular Cluster in the constellation Hercules (M13) with a hint of the spiral galaxy NGC 6207 at the top. Last night was my first night out with the William Optics ZenithStar 61, and as I expected, it's just a brilliant little refractor. Paired with the ZWO ASI071MC cooled camera and the WO 0.8x Flat/Reducer F6-A, you get a spectacular 4.7° × 3.1° field of view--that's a big chunk of the sky. If you're looking for a pretty fast widefield apochromatic, this is it. It's not the best choice for the Hercules cluster, but I was just slewing all over the sky, taking pictures, and waiting for the North America Nebula to get above 30 degrees.
Posted May 24, 2018
Astro Session - May 18, 2018
We have not had a really clear night for a month, and last night was still fairly poor for imaging. Even so, I set up the ZWOASI071C paired with a Nikon 24-85mm lens to see what I could capture for a wide-field shot centered on the star Deneb in the constellation Cygnus. This area of the Milky Way just happens to be surrounded by some distinctive clouds of ionized hydrogen, including the North America Nebula (NGC7000) and the Pelican Nebula (IC 5070). Both of these are pretty faint, but they are large, so if you stack enough frames you can bring out enough to see why NGC7000 was given its name. For size comparison, the North America Nebula is four times the size of a full moon. (122 stacked 30 sec. frames, ZWO ASI071MC cooled CMOS camera, iOptron CEM25P EQ mount, Nikon 24-85mm F/3.5-4.5 ED lens @ 85mm. Location: Stratham, New Hampshire, US. Bortle ~4)
