APOD: Alborz Mountain Star Trails (2018 Mar 02)

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APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by APOD Robot » Fri Mar 02, 2018 5:10 am

Image Alborz Mountain Star Trails

Explanation: Colourful star trails arc through the night in this wide-angle mountain and skyscape. From a rotating planet, the digitally added consecutive exposures were made with a camera fixed to a tripod and looking south, over northern Iran's Alborz Mountain range. The stars trace concentric arcs around the planet's south celestial pole, below the scene's rugged horizon. Combined, the many short exposures also bring out the pretty star colours. Bluish trails are from stars hotter than our Sun, while yellowish trails are from cooler stars. Near the center, the remarkably pinkish trail was traced by the star-forming Orion Nebula.

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Re: APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by awmeyer » Fri Mar 02, 2018 5:30 am

I thought APOD was an American website (NASA GSFC). Why the British spelling "colourful" rather than "colorful" (.e.g. APOD Mar. 6 2017) ?

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Re: APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by geckzilla » Fri Mar 02, 2018 5:48 am

The British spelling of color has been used quite a number of times at APOD over the years, sometimes even right next to the American spelling. Who knows?
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Re: APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by Ann » Fri Mar 02, 2018 8:00 am

Star trail pictures often make me sigh, because I feel that the astrosights are flashing by so fast that everything is smeared out into long rather meaningless lines. Imagine having to watch people that way. Talk about spaghettification!

What I'm saying is that I really , really want to identify the stars in an astropicture. Actually this picture is better than most star trail images, because Orion is so "in your face". Because Orion anchors the picture, I can also identify Sirius, which looks kind of faint to me. But what can I see in the upper right quadrant? There is an extremely white and bright line there. Is that the Hyades? Surely it isn't Capella? (Correct color, wrong position.)

There are also a lot of blue lines in the upper right corner. Could they possibly, possibly belong to the Pleiades? (Sort of correct position, wrong "cluster effect".)

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Re: APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by Case » Fri Mar 02, 2018 12:21 pm

Ann wrote:
Fri Mar 02, 2018 8:00 am
But what can I see in the upper right quadrant? There is an extremely white and bright line there. Is that the Hyades?
I think it is. :D Note the bright line is shorter than the others, which I interpret as partially overlapping lines, like one would get with a cluster.
Ann wrote:
Fri Mar 02, 2018 8:00 am
There are also a lot of blue lines in the upper right corner. Could they possibly, possibly belong to the Pleiades? (Sort of correct position, wrong "cluster effect".)
I think the Pleiades are just outside the image area. I think the three not-so-blue streaks top-right are 94 Tau, 65 Tau, and 37 Tau (4.35). The real Pleiades are 4° further out and brighter (27 Tau: 3.60). So the two very blue streaks then must be 32 Tau (5.60) and 33 Tau (6.00), halfway between 37 Tau and the brighter stars of the Pleiades.

On a different note, the mountains are lit from the West, so I guess that part of the composition is the setting Sun, as the Moon should be in the East at the EXIF time.

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Re: APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by rstevenson » Fri Mar 02, 2018 1:01 pm

awmeyer wrote:
Fri Mar 02, 2018 5:30 am
I thought APOD was an American website (NASA GSFC). Why the British spelling "colourful" rather than "colorful" (.e.g. APOD Mar. 6 2017) ?
Although Asterisk is hosted on a NASA server, and is run by our friendly neighbourhood Americans, it deals with an international--indeed, intergalactic--subject, and has (at least) an international audience. So no biggy, right?

Eventually English will descend into an international version, understood by all and, except for us old curmudgeons, spelled the same way by all. Alas, by then it will likely consist of only about 600 words.

Rob

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Re: APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by Ann » Fri Mar 02, 2018 1:13 pm

Case wrote:
Fri Mar 02, 2018 12:21 pm
Ann wrote:
Fri Mar 02, 2018 8:00 am
But what can I see in the upper right quadrant? There is an extremely white and bright line there. Is that the Hyades?
I think it is. :D Note the bright line is shorter than the others, which I interpret as partially overlapping lines, like one would get with a cluster.
Ann wrote:
Fri Mar 02, 2018 8:00 am
There are also a lot of blue lines in the upper right corner. Could they possibly, possibly belong to the Pleiades? (Sort of correct position, wrong "cluster effect".)
I think the Pleiades are just outside the image area. I think the three not-so-blue streaks top-right are 94 Tau, 65 Tau, and 37 Tau (4.35). The real Pleiades are 4° further out and brighter (27 Tau: 3.60). So the two very blue streaks then must be 32 Tau (5.60) and 33 Tau (6.00), halfway between 37 Tau and the brighter stars of the Pleiades.

On a different note, the mountains are lit from the West, so I guess that part of the composition is the setting Sun, as the Moon should be in the East at the EXIF time.
Thanks, Case! :D

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Re: APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by dbooksta » Fri Mar 02, 2018 2:22 pm

What accounts for the marked coloration? Was this false-colorized or otherwise manipulated in post? Because we've seen plenty of star-trail photos and I've never seen such variation captured in the visible spectrum.

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Re: APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by Ann » Fri Mar 02, 2018 3:26 pm

dbooksta wrote:
Fri Mar 02, 2018 2:22 pm
What accounts for the marked coloration? Was this false-colorized or otherwise manipulated in post? Because we've seen plenty of star-trail photos and I've never seen such variation captured in the visible spectrum.

The Winter pentagon.
Photo: Jeff Dai.
I'd say that the colors have been enhanced, but not terribly enhanced. The colors of the star trails are more saturated than the stars appear to be when observed with the naked eye. But many RGB images (pictures taken through red, green and blue filters) show colorful starfields.

Take a look at the picture at left. That one may be an RGBHα image, where the hydrogen alpha filter has been used to bring out the red nebulosity of Barnard's Arc, the Lambda Orionis nebula and a few other emission nebulas.

As you can see, the stars are relatively colorful in Jeff Dai's image. The stars won't look like that to the naked eye, partly because the stars in the night sky are generally too faint to stimulate the color-sensitive cones in the human retina very much. The human eye is pretty good at spotting the difference between yellow and white objects when the general illumination is dim, which is one reason why people can see that Betelgeuse is a different color than the other bright stars in Orion. Also the color of cool stars is more saturated than the color of hot stars.

All in all though, the colors of the stars in today's APOD are enhanced but mostly "true".

Ann
Last edited by Ann on Fri Mar 02, 2018 7:48 pm, edited 1 time in total.
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Re: APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by Ann » Fri Mar 02, 2018 3:45 pm

I did a quick googling of star trails, though, and I must agree with you - almost all star trail pictures either show "all white stars" or truly weirdly colored stars. Star trails rarely show true RGB color.

At left you can see a picture where the camera is gradually getting more and more defocused, so that the light of the stars is spread out over a larger area. This also brings out their true color.


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Re: APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by MarkBour » Fri Mar 02, 2018 5:21 pm

rstevenson wrote:
Fri Mar 02, 2018 1:01 pm
... Eventually English will descend into an international version, understood by all and, except for us old curmudgeons, spelled the same way by all. Alas, by then it will likely consist of only about 600 words.
Rob
That's an interesting conjecture about language change.
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Re: APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by rstevenson » Sat Mar 03, 2018 1:28 am

MarkBour wrote:
Fri Mar 02, 2018 5:21 pm
rstevenson wrote:
Fri Mar 02, 2018 1:01 pm
... Eventually English will descend into an international version, understood by all and, except for us old curmudgeons, spelled the same way by all. Alas, by then it will likely consist of only about 600 words.
Rob
That's an interesting conjecture about language change.
I recall reading a popularized article summarizing current thinking (about 3 years ago) in [some portion of] the lexicographical community regarding the future of English as a lingua franca. They speculated that the subset of English used by ESL speakers would need to be about that size. I assume those of us born to the language would continue to have a much larger vocabulary, and will continue to insult each others spelling and pronunciation, if only because it's so much fun to do that.

There are, of course, competing possibilities. One article I read recently suggested that "the future for English is one of multiple Englishes."

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Re: APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by Boomer12k » Sat Mar 03, 2018 1:44 am

Ooooh....colors....

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Re: APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by MarkBour » Sat Mar 03, 2018 2:06 am

rstevenson wrote:
Sat Mar 03, 2018 1:28 am
I recall reading a popularized article summarizing current thinking (about 3 years ago) in [some portion of] the lexicographical community regarding the future of English as a lingua franca. They speculated that the subset of English used by ESL speakers would need to be about that size. I assume those of us born to the language would continue to have a much larger vocabulary, and will continue to insult each others spelling and pronunciation, if only because it's so much fun to do that.

There are, of course, competing possibilities. One article I read recently suggested that "the future for English is one of multiple Englishes."

Rob
Nice, I love the sentiment in the next-to-last sentence (you wrote "others" as bait, right? :P ).

I have no data nor much expertise, but I'm thinking your last sentence is plausible, so English might become much like today's photograph -- a smear. That would lead to multiple dialects, and yet possibly an internationally-usable core. Of course the past is no guarantee at all, because technology is impacting this hugely, so past language mutation trends may be a poor guide to our future ... but it's fun to think about.
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Re: APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by MarkBour » Sat Mar 03, 2018 2:47 am

Ann wrote:
Fri Mar 02, 2018 8:00 am
Star trail pictures often make me sigh, because I feel that the astrosights are flashing by so fast that everything is smeared out into long rather meaningless lines. Imagine having to watch people that way. Talk about spaghettification! . . .
Ann
I think making a plug-in that re-squeezes all those trails to just dots would make a good project for some Photoshop or Gimp guru.

If the star trails are short (like I get by accident) there is a Photoshop technique, using the Darken filter, that can improve them, but a long lapse like this is too challenging for that technique, as far as I know.

On the other hand, I loved your progressively de-focused image!
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Re: APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by rstevenson » Sat Mar 03, 2018 3:19 pm

MarkBour wrote:
Sat Mar 03, 2018 2:06 am
rstevenson wrote:
Sat Mar 03, 2018 1:28 am
I recall reading a popularized article summarizing current thinking (about 3 years ago) in [some portion of] the lexicographical community regarding the future of English as a lingua franca. They speculated that the subset of English used by ESL speakers would need to be about that size. I assume those of us born to the language would continue to have a much larger vocabulary, and will continue to insult each others spelling and pronunciation, if only because it's so much fun to do that.

There are, of course, competing possibilities. One article I read recently suggested that "the future for English is one of multiple Englishes."

Rob
Nice, I love the sentiment in the next-to-last sentence (you wrote "others" as bait, right? :P ).
No, I just forgot the apostrophe! But the apostrophe is one of those bits of English usage that is changing rapidly, due as much to poor schooling as to laziness. And no great loss, say I.
MarkBour wrote:
Sat Mar 03, 2018 2:06 am
I have no data nor much expertise, but I'm thinking your last sentence is plausible, so English might become much like today's photograph -- a smear. That would lead to multiple dialects, and yet possibly an internationally-usable core. Of course the past is no guarantee at all, because technology is impacting this hugely, so past language mutation trends may be a poor guide to our future ... but it's fun to think about.
I agree, fun to think about. I don't get overwrought about language change. Sometimes a particular change is not good but inevitable, sometimes it's an improvement. For example, I've seen a lot of confusion in recent years between 'your' and 'you're', including in what should be professionally edited online publications. If the dust settles and we end up with just one, likely 'your', I won't be terribly upset, because I can't think of any instance where it isn't possible to grasp the meaning from context. (But we have to keep 'yore', though it's already archaic.)

Rob

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Re: APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by Chris Peterson » Sat Mar 03, 2018 9:29 pm

dbooksta wrote:
Fri Mar 02, 2018 2:22 pm
What accounts for the marked coloration? Was this false-colorized or otherwise manipulated in post? Because we've seen plenty of star-trail photos and I've never seen such variation captured in the visible spectrum.
Stars tend to show low color in many images because they are so easily overexposed. It doesn't matter what the star color actually is, if you saturate all three color channels it's going to look white. To get colored stars, you can make a short exposure (which is how this APOD was made), you can use low ISO, you can defocus the image to spread out the light and lower the intensity on any one pixel.

That's not to say the saturation wasn't boosted a bit in post-processing to emphasize the color, but first you have to shoot the image so that the color information is there at all. (In telescopic images, it's common for all the stars to be white, but to see their approximate colors in the diffraction or scatter halos that surround them, which are much less bright.)
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Re: APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by alter-ego » Sun Mar 04, 2018 5:56 am

Case wrote:
Fri Mar 02, 2018 12:21 pm
I think the Pleiades are just outside the image area. I think the three not-so-blue streaks top-right are 94 Tau, 65 Tau, and 37 Tau (4.35). The real Pleiades are 4° further out and brighter (27 Tau: 3.60). So the two very blue streaks then must be 32 Tau (5.60) and 33 Tau (6.00), halfway between 37 Tau and the brighter stars of the Pleiades.
You identified the stars correctly. I think a vestige of a Pleiades member, 23 Tau, is barely visible at the edge of the APOD image. Even with the field distortion difference between the APOD and the Stellarium overlay image, the white dots (marking the left edge of star trails) correlate well enough to real stars that the Pleiades position can be located within < few tenths of a degree. The upper right corner of the APOD image is presented here, and if you look closely, there appears to be an obscured brighter star at the edge where the arrow is pointing. I believe that star is 23 Tau.
 
Click to view full size image 1 or image 2
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Re: APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by Ann » Sun Mar 04, 2018 6:53 am

alter-ego wrote:
Sun Mar 04, 2018 5:56 am
Case wrote:
Fri Mar 02, 2018 12:21 pm
I think the Pleiades are just outside the image area. I think the three not-so-blue streaks top-right are 94 Tau, 65 Tau, and 37 Tau (4.35). The real Pleiades are 4° further out and brighter (27 Tau: 3.60). So the two very blue streaks then must be 32 Tau (5.60) and 33 Tau (6.00), halfway between 37 Tau and the brighter stars of the Pleiades.
You identified the stars correctly. I think a vestige of a Pleiades member, 23 Tau, is barely visible at the edge of the APOD image. Even with the field distortion difference between the APOD and the Stellarium overlay image, the white dots (marking the left edge of star trails) correlate well enough to real stars that the Pleiades position can be located within < few tenths of a degree. The upper right corner of the APOD image is presented here, and if you look closely, there appears to be an obscured brighter star at the edge where the arrow is pointing. I believe that star is 23 Tau.
 
Click to view full size image 1 or image 2
Thanks a bunch, alter-ego!!! :D

The slow student that I am, I tried to make sense of your "image 2", where you had marked several stars that made some of the star trails. Since most of the bright star trails were made by stars that are bluer than the Sun, one very orange star trail stood out. Could that one have been made by HD 27639 (SAO 76571), an M0III star whose V magnitude is about 6.07?

There are a bunch of blue or bluish star trails in the upper right quadrant, north (and west, in other words right) of the Hyades. Could these trails have been made by stars like Upsilon Tau (69 Tau), Kappa 1 (65 Tau) and Kappa 2 Tau (67 Tau), HD 27309 (56 Tau), HD 27176 (51 Tau), HD 27295 (53 Tau), HD 27742 and Omega 2 Tau (50 Tau)? Maybe HD 26571 is part of the "blue star trail action" too?

All these stars are fourth, fifth och sixth magnitude, they belong to spectral classes A and B (except for one star that is spectral class F0), and they are in the correct position to make blue or bluish star trails to the upper right of the Hyades in the picture.

By the way, 23 Tau is the famous Merope! :D

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Re: APOD: Alborz Mountain Star Trails (2018 Mar 02)

Post by alter-ego » Mon Mar 05, 2018 4:39 am

Ann wrote:
Sun Mar 04, 2018 6:53 am
...

The slow student that I am, I tried to make sense of your "image 2", where you had marked several stars that made some of the star trails. Since most of the bright star trails were made by stars that are bluer than the Sun, one very orange star trail stood out. Could that one have been made by HD 27639 (SAO 76571), an M0III star whose V magnitude is about 6.07?
Yes.
There are a bunch of blue or bluish star trails in the upper right quadrant, north (and west, in other words right) of the Hyades. Could these trails have been made by stars like Upsilon Tau (69 Tau), Kappa 1 (65 Tau) and Kappa 2 Tau (67 Tau), HD 27309 (56 Tau), HD 27176 (51 Tau), HD 27295 (53 Tau), HD 27742 and Omega 2 Tau (50 Tau)? Maybe HD 26571 is part of the "blue star trail action" too?
Sorry, I didn't look as there are a lot of blue stars and I'm not sure which ones you're talking about.
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