What did you see in the sky tonight?

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Re: What did you see in the sky tonight?

Post by Nitpicker » Mon Apr 07, 2014 5:45 am

Chris Peterson wrote:
Nitpicker wrote:I find I can very easily get confused if I try to discuss colours too much. This has now become one of those times. I only (think I) understand the technical side of colour theory in terms of the simple RGB colour model. In other words, red, green and blue are the only components of colour in my simple world, and intensity is derived from that. For example, in normalised coordinates (1,0,0) is the most intense red and (0.5,0,0) is a less intense red. As such, I don't quite understand your meaning.
Yes, it does get confusing. What I meant is that if you take a light source with some particular combination of wavelengths defining it, your retinal L, M, and S cones (roughly, RGB) will respond in some ratio. If you simply change the intensity of the source, not only will the absolute response of the cones change, but so will the ratios. At a physiological level, the two generate very different signals. The color you perceive, however, may be the same or different, depending on many factors. This is the basis of many color and intensity optical illusions, where we are fooled into believing that different colors are the same, or that the same colors are different.
Ah, I see. I was skipping over the whole physiological bit, as I'm pretty sure the conscious part of my brain is blissfully unaware of it. I was merely talking about how my conscious brain perceives graduated shades of a colour. I have probably trained my brain to think this way about colours after years of using and programming computers for engineering design purposes. In this context you often (but not always) decide that any two colours which are close to each other photometrically (if that is a word), are next to useless practically, and may as well be considered the same colour. So grey with a touch of orange and grey with a touch of blue, both become grey. Maybe one day I will re-train my brain to perceive colours like an artist. It might just help to keep the dementia at bay.

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Re: What did you see in the sky tonight?

Post by Nitpicker » Mon Apr 14, 2014 2:03 am

I saw lots of rain clouds over the weekend. This afforded me an opportunity to review some of my older images. One of the fun things I'm discovering about building up a collection of my own images, is in spotting interesting comparisons (even if none of the individual images are fantastic). Here is an animation of two waxing crescent moons, taken three months apart last year, both showing a disc ~25% illuminated. The images have been scaled and aligned such that their illuminated portions overlap. (And I've decided I really like looking at crescent moons in this orientation, especially the limbs.) Quite a lot of libration can be seen:
Crescent_Libration.gif
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Re: What did you see in the sky tonight?

Post by geckzilla » Tue Apr 15, 2014 7:08 am

I am able to see plenty of live online eclipse images. So far I've heard the color described as peachy and warm. If I hear the hackneyed, hyperbolic "blood red" adjective again I might get angry.
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Re: What did you see in the sky tonight?

Post by Nitpicker » Tue Apr 15, 2014 7:18 am

I was going to say "blood orange", hoping that it might keep everyone happy. Hope I didn't just make you angry, geck.

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Re: What did you see in the sky tonight?

Post by Chris Peterson » Tue Apr 15, 2014 7:22 am

geckzilla wrote:I am able to see plenty of live online eclipse images. So far I've heard the color described as peachy and warm. If I hear the hackneyed, hyperbolic "blood red" adjective again I might get angry.
Extremely red from here. One of the reddest eclipses I've seen.
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Re: What did you see in the sky tonight?

Post by geckzilla » Tue Apr 15, 2014 7:37 am

Nitpicker wrote:I was going to say "blood orange", hoping that it might keep everyone happy. Hope I didn't just make you angry, geck.
I think blood orange is actually a good description of the real fruit. It does look kinda bloody. As a color swatch and not as a fruit, I'm not sure why people chose that out of all of the silly, silly names given to colors.
Chris Peterson wrote:Extremely red from here. One of the reddest eclipses I've seen.
And you are on a mad streak. I'm not sure I believe anything you say lately. :lol2:
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Re: What did you see in the sky tonight?

Post by Chris Peterson » Tue Apr 15, 2014 8:04 am

geckzilla wrote:
Chris Peterson wrote:Extremely red from here. One of the reddest eclipses I've seen.
And you are on a mad streak. I'm not sure I believe anything you say lately.
Perhaps I should say one of the most colorful eclipses I've seen. Objectively, it's a red-orange color.
E7_22425p.jpg
The moonrise was very nice, too.
E7_22292p.jpg
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Re: What did you see in the sky tonight?

Post by BDanielMayfield » Tue Apr 15, 2014 9:06 am

Very nice, and I got to see something with my own eyes for a change, thanks to the strong cold front that swept through yesterday.

I liked the color contrast between the orange moon and the star to the lower right of it, which to the eye looked much bluer than this same star looks in Chris' photo. By the way, what star is that, and is it really all that blue or is this just a perception effect due to the shadowed Moon's proximity?

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Re: What did you see in the sky tonight?

Post by Ann » Tue Apr 15, 2014 9:19 am

BDanielMayfield wrote:
By the way, what star is that, and is it really all that blue or is this just a perception effect due to the shadowed Moon's proximity?
I think it is Spica, so it is pretty blue. But in case it is Spica, then Mars should be not too far away.

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Re: What did you see in the sky tonight?

Post by Nitpicker » Tue Apr 15, 2014 11:50 am

I got the tail end. It rose in full eclipse for me, but I couldn't get a clear shot until slightly later:
Moon_20140415_0831Z_to_0926Z.jpg
Edit: next morning, in daylight, I realise my choice of images last night was much better suited to my dark-adjusted eyes. Oops. :oops:
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Last edited by Nitpicker on Wed Apr 16, 2014 12:17 am, edited 1 time in total.

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Re: What did you see in the sky tonight?

Post by Chris Peterson » Tue Apr 15, 2014 3:51 pm

Ann wrote:I think it is Spica, so it is pretty blue. But in case it is Spica, then Mars should be not too far away.
The star and planet colors aren't very intense because of saturation and not enough pixels. By blurring the background and adding it back in we get a much better representation of the visual appearance of Spica and Mars. (You need to look at the full size image to see it best.)
E7_22430p.jpg
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Re: What did you see in the sky tonight?

Post by Nitpicker » Wed Apr 16, 2014 1:27 am

I put a little more thought into this lot, and it is better for daytime eyes:
Lunar_Eclipe_20140415.gif
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Re: What did you see in the sky tonight?

Post by Ann » Wed Apr 16, 2014 4:41 am

Chris Peterson wrote:
Ann wrote:I think it is Spica, so it is pretty blue. But in case it is Spica, then Mars should be not too far away.
The star and planet colors aren't very intense because of saturation and not enough pixels. By blurring the background and adding it back in we get a much better representation of the visual appearance of Spica and Mars. (You need to look at the full size image to see it best.)
E7_22430p.jpg
Interesting, Chris. Now that you've blurred it, I think Spica looks more non-blue than in your first picture.

There is, on the other hand, a very blue-looking star quite close to Mars. I think that is Theta Virginis.

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Re: What did you see in the sky tonight?

Post by Chris Peterson » Wed Apr 16, 2014 4:59 am

Ann wrote:
Chris Peterson wrote:
Ann wrote:I think it is Spica, so it is pretty blue. But in case it is Spica, then Mars should be not too far away.
The star and planet colors aren't very intense because of saturation and not enough pixels. By blurring the background and adding it back in we get a much better representation of the visual appearance of Spica and Mars. (You need to look at the full size image to see it best.)
Interesting, Chris. Now that you've blurred it, I think Spica looks more non-blue than in your first picture.
On my monitor, it looks more blue. But there's not a lot to work with, since most of the pixels it is captured on are saturated, and therefore white. Only a few unsaturated pixels accurately record the color, but when they're mixed with the saturated ones the overall color saturation is reduced. Maybe tomorrow I'll go through the images I took and see if there's a shorter exposure (I made many bracketed shots). That should give a Moon that's underexposed, but also a Spica that's unsaturated.
There is, on the other hand, a very blue-looking star quite close to Mars. I think that is Theta Virginis.
I think you're right about that. Since it's 23 times dimmer than Spica, it's not saturated and we get color. It does seem a little too blue for its temperature, but when I look at the raw image, it's actually white, so I think the blue is some sort of processing artifact. I probably should have masked out other areas when I did the blurring and other processing to try and bring out the color in Spica and Mars.
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Re: What did you see in the sky tonight?

Post by Nitpicker » Sun Apr 27, 2014 2:45 am

Before dawn last Friday, I managed to drag myself out of bed and photograph my first ever waning crescent moon. (I'm not normally a morning person.) The gaps in the trees on the eastern side of my yard, coincided nicely with some good, steady seeing conditions. This monochrome image was produced from a stack of the best 240 of 400 full resolution subs, with a Nikon D5100, through a 6" SCT at f/10 prime focus.
SSO_LD_Wan_Cres_210_20140425_0530+10.jpg
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Re: What did you see in the sky tonight?

Post by owlice » Sun Apr 27, 2014 3:33 pm

That's a nice pic, Nitpicker!

I looked at the sky last night and saw.... clouds.
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Re: What did you see in the sky tonight?

Post by Nitpicker » Mon Apr 28, 2014 12:55 am

owlice wrote:That's a nice pic, Nitpicker!
Thanks owlice. Happy to take constructive criticism from anyone, too. For instance, what is a good way to remove the white edge around the limb, introduced as an artefact from (arguably too much) wavelet sharpening in Registax? I produced several versions of this image, sharpened to varying degrees, and decided that this one showed the most fine detail.

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Re: What did you see in the sky tonight?

Post by Chris Peterson » Mon Apr 28, 2014 1:07 am

Nitpicker wrote:
owlice wrote:That's a nice pic, Nitpicker!
Thanks owlice. Happy to take constructive criticism from anyone, too. For instance, what is a good way to remove the white edge around the limb, introduced as an artefact from (arguably too much) wavelet sharpening in Registax? I produced several versions of this image, sharpened to varying degrees, and decided that this one showed the most fine detail.
In Photoshop, I copy the image to a new layer and only sharpen one of them. Then I use the Darken method of blending the two layers. That removes bright halos but leaves most of the sharpening.
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Re: What did you see in the sky tonight?

Post by Nitpicker » Mon Apr 28, 2014 1:15 am

Chris Peterson wrote:In Photoshop, I copy the image to a new layer and only sharpen one of them. Then I use the Darken method of blending the two layers. That removes bright halos but leaves most of the sharpening.
Thanks. So, you save the image from Registax just prior to the wavelet sharpening step?

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Re: What did you see in the sky tonight?

Post by Chris Peterson » Mon Apr 28, 2014 2:03 am

Nitpicker wrote:
Chris Peterson wrote:In Photoshop, I copy the image to a new layer and only sharpen one of them. Then I use the Darken method of blending the two layers. That removes bright halos but leaves most of the sharpening.
Thanks. So, you save the image from Registax just prior to the wavelet sharpening step?
I don't generally like the results of wavelet algorithms, so I normally sharpen outside of Registax, but it's the same process. If you sharpen using Registax, just save an unsharpened version first, and blend the two in Photoshop. This approach also lets you sharpen harder than you otherwise would.
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Re: What did you see in the sky tonight?

Post by alter-ego » Mon Apr 28, 2014 2:59 am

Chris Peterson wrote: In Photoshop, I copy the image to a new layer and only sharpen one of them. Then I use the Darken method of blending the two layers. That removes bright halos but leaves most of the sharpening.
Thanks, Chris. That's good advice. I've not gotten serious about imaging methods and processing techniques. I like reading articles by the experts but the technique you described is easy-peasy and will fit right in with my imaging practice and experience. I'm pretty simple minded and like simple instructions!
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Re: What did you see in the sky tonight?

Post by geckzilla » Mon Apr 28, 2014 3:15 am

I saw a side-by-side comparison of sharpening done by Registax versus a program called Astra image. I think Astra image produces a nicer picture.
https://www.flickr.com/photos/avdhoeven/13998756035/

My way of learning is to pretty much find someone whose work I like and attempt to copy them shamelessly. During and after that process I of course add my own ideas and skill but it really helps to set a goal in this way and if that person has published some tutorials then that will accelerate your learning. Oh look, Andre also has some tutorials. How convenient. http://www.astro-photo.nl/lunar-and-solar-processing
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Re: What did you see in the sky tonight?

Post by Nitpicker » Mon Apr 28, 2014 3:33 am

alter-ego wrote:
Chris Peterson wrote: In Photoshop, I copy the image to a new layer and only sharpen one of them. Then I use the Darken method of blending the two layers. That removes bright halos but leaves most of the sharpening.
Thanks, Chris. That's good advice. I've not gotten serious about imaging methods and processing techniques. I like reading articles by the experts but the technique you described is easy-peasy and will fit right in with my imaging practice and experience. I'm pretty simple minded and like simple instructions!
Yep, me too. Thanks Chris.

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Re: What did you see in the sky tonight?

Post by Nitpicker » Mon Apr 28, 2014 4:02 am

Thanks geckzilla, but the difference between Registax and Astra image is so slight, compared with the results I'm getting and the results I'd prefer. I don't think I can blame Registax. :ssmile:

I'm also not really interested in building mosaics for whole disc shots of the moon. My 1500mm FL telescope and DSLR APS-C sensor size combination are really well suited to each other for whole disc shots of the moon. If I want a bit more detail, I can insert a lens to increase the focal length for a narrower, stand-alone, detail image.

The best comparable image to mine, of a waning crescent moon, that I found via a Google search was this one:
http://www.takayuki-astro.com/moon_080727.html

It has noticeably lower resolution than mine, taken with a smaller (but probably better quality) scope, and with a smaller sensor. Even though mine shows slightly more detail, I have to admit I prefer Takayuki's version.

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Re: What did you see in the sky tonight?

Post by Nitpicker » Mon May 12, 2014 2:28 am

I saw Saturn last night, with my 6" SCT, within 24 hours of its closest approach for the year. It is always a lovely sight through the eyepiece, but with my camera, I was also delighted to (just) catch the Encke Gap, for the first time, in an over-sharpened image. At 325 km wide, it presents as a target of ~0.05 arcsec, or about one twentienth of the nominal resolution of my scope.
SSO_P6_Saturn_20140511_2145+10_sharp.jpg
And here is a variant from the same data, following a slightly more aesthetic treatment:
SSO_P6_Saturn_20140511_2145+10.jpg
With luck from the weather this coming Wednesday evening, I'm hoping to see -- again for the first time -- the northern limb of the Full Moon occult Saturn.

(Not sure why these small images do not display in their native pixel scale when inserted into a post here. They are meant to appear ~1.6x bigger, and they will if you download them.)
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