We have a melange of photos today, but will start with Stephen Barnard’s documentation of the eaglets growing in Idaho:
Lucy (?) and a fast-growing chick:
The nestlings are exercising their wings.
Nearby lives a Great Horned Owl (Bubo virginianus):
Anne-Marie Cournoyer found what appears to be a mating aggregation of garter snakes (Thamnophis sirtalis) in the Parc du Mont-St-Bruno outside Montreal:
And nearby, a miracle!!! Explain this if you can:
Black-capped chickadee (Poecile atricapillus). The Cornell bird site notes that it is “a bird almost universally considered ‘cute’ thanks to its oversized round head, tiny body, and curiosity about everything, including humans.”
Mourning dove (Zenaida macroura):
And finally, a space photo by reader Don McCrady:
Here is an image of M101, also known as the Northern Pinwheel Galaxy, which forms a neat triangle with the last two stars in the handle of the Big Dipper. It is a large face-on spiral galaxy that lies about 20 million light years away. Its grand spiral shape is deformed by the gravitational attraction of other galaxies in its vicinity, including the dwarf galaxy NGC 5477 seen near the left edge of the image. As you can see, the galaxy is literally dotted with bright active nebular regions called HII regions, brought out in this image with the addition of 2 hours of separate Hydrogen-alpha exposures. Seven of these bright knots actually have their own designations in the New General Catalog (NGC).
Total exposure time for this image was over 7 hours, with over 2 hours of luminance, 3 hours of RGB colour data, plus 2 hours of Hydrogen-alpha. The image was captured through a Stellarvue SVS130 f/5 apochromatic refractor and a SBIG STL4020M camera, taken from my backyard in Redmond, WA. The final image was upsampled 2x.
Very fun photos!
The cross shadow: Geometry.
You see simple geometry but a closer look reveals even more evidence that god came to earth so he could sacrifice himself to himself because a lady ate an apple. It is just so obvious if you are willing to see it.
That galaxy represents your spiral into hell if you don’t believe, the birds are the dinosaurs Jesus used to ride and the snakes are straight out of Genesis. Hallelujah!
That is a breath-taking photograph of the Pinwheel Galaxy. Congratulations. You are a patient man, Don.
Thanks Darwinwins. I actually took the luminance part of this image on April 1st, then the RGB a few days later, and then had to wait a month before I could take the H-alpha.
The Flickr page for this is https://www.flickr.com/photos/djmccrady/26524684140/in/dateposted-public/.
I presume that the telescope has some kind of computer controlled tracking mechanism to take account of the Earth’s rotation during suchong exposures?
Fat fingers…”such long exposures”
The telescope mount (Takahashi EM-200) has a clock drive that is very accurate and moves the telescope to compensate for the earth’s rotation. Exposures of up to 2 minutes are possible using just the mount’s clock drive.
For longer exposures, the imperfections of the clock drive need to be compensated. That’s why I have it auto-guided by a separate camera/guidescope. The autoguider takes pictures of a star every 3 seconds and commands the mount to speed up or slow down to keep the star precisely centered during the exposure. Using this I can expose for 20 – 30 minutes.
I don’t know Don’s processing pipeline, but typically many short exposures (a few minutes each, adding up to many hours ; Don says 20-30 mins) are ‘stacked’ together using alignment software to improve the signal-to-noise ratio. These tools locate several point sources in the image then rotate/ align each image before adding up the brightness values for each pixel. If the telescope is misaligned (kicked, clock drift, earthquake) between shots, then that’s not a problem. Also, a shot with a meteor, passing plane, drifting cloud – are there glow worms in Don’s locale? simply gets left out of the pipeline, which also improves the SNR. And at the edges of the final stack, there will be areas that don’t have the normal number of exposures stacked together. So you crop them.
Which isn’t to belittle Don’s work – it’s still hundreds of images to acquire, process and combine, not to forget the interminable series of dark and flat calibration frames to be applied to every image before the stacking. IME, the post-imaging pipeline typically takes pretty much as much time as the actual imaging – and that’s for single-colour “science” (OK, college) imaging, not the balancing of the four different colours (RGB and luminance) that goes into presentation imagery like this. Excellent work!
Aiden pretty much nailed it. The luminance and RGB exposures are limited to 5 minutes each, otherwise my local light pollution starts to overwhelm the image, and so 2 hours of that adds up to 24 luminance shots. Three hours of RGB is one hour per channel, and at 5 minutes per exposure that’s 36 images.
The Hydrogen alpha is the strongest filter which is why I need at least 20 minutes per exposure (and I’ll try to tune my system to get to 30 minutes if possible). But since the exposures need to be so long, 2 hours of H-alpha only adds up to an extra 6 images.
So the whole thing is a total of 66 sub-exposures. (And there’s 66 books in the bible… coincidence?)
All aligned and co-added with dark and flat frame calibration, and then tons of post-processing to get rid of background gradients and bring out the colour.
The removal of background gradients and “bringing out the colour” were issues we didn’t cover in the “Practical Astronomy” course, which was focussed (sorry, I’m wearing the pun lenses again) on stellar photometry, eclipsing binaries, etc.
A dark and a flat for each image, or (say) every half hour during a photography session? Enough pipeline to attract the unhealthy attention of the local plumbing regulators.
Thank you both for the excellent explanations. Clearly a great deal of work required but the result is super, Don!
Thanks for sharing! So far, I have never been able to see the Pinwheel galaxy with my reflector. I have just learned that my chances are better with M33, the Triangulum galaxy, and so I will look for that when it becomes available.
You need a dark sky to see it because of its low surface brightness. The Triangulum galaxy will also be tough without a dark sky because it also has a low surface brightness.
That is definitely my problem.
Shining a security light at the galaxy will help. Maybe.
Miraculous, indeed, but like most things of this bent it is accomplished with the play of shadows (instead of smoke and mirrors…).
…or Photoshop?
It’s not Photoshopped
Miracle?? The top section of the shadow is caused by the depth of the square post the sign is attached to. The top of the sign/post is not a uniform thickness.
If the sign portion was attached on a board the same thickness as the post, it would be quite obvious why the shadow is the way it is.
Calm down Michael I think Prof Coyne was being ironical.
Personally I could have used a trigger warning. No, not the snakes. Those Black-capped chickadees scare the living crap out of me. Lovecraftian monstrosities!
That is correct, combined with fact the ground is sloping away from the sign stretching the shadow. I confirmed it with a little wood model, a piece of paper, and a flashlight. (Too much time on my hands.) Note the high sun angle from the shadow of the sign on the post and the fact the post is leaning in the direction of the sun and the ground away.
In reference to the cross, I used to walk over a motorway bridge with a heavy wrought iron balustrade, straight lines but following an arc and sturdy. But, when you noticed the shadow on the concrete footpath in parts it looked decrepit and not very trustworthy, this amused me. I can see the same with this signpost, the effect coming from the ground being uneven.
The footpath on the bridge looked smooth and even but the shadows made a liar of that assumption. The angle of sunlight also stretched the shadow and accentuated the imperfections in the path itself, giving it that rickety look.
Here, the top of the post has been highjacked by the light angle/ direction to look as though it is a continuation to the length of the post not it’s flat top, making it look like a cross… beware the shadows, beware the brain looking at the shadows.
Anyhow, the pinwheel galaxy is not a shadow but can I believe your play with light here Don, that it is real, does the camera lie? It matters little, it is an incredible sight, nice work.