APOD: Night Sky Reflected (2021 Sep 13)

Comments and questions about the APOD on the main view screen.
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johnnydeep
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Re: APOD: Night Sky Reflected (2021 Sep 13)

Post by johnnydeep » Tue Sep 14, 2021 12:44 pm

Chris Peterson wrote:
Mon Sep 13, 2021 9:28 pm
johnnydeep wrote:
Mon Sep 13, 2021 9:23 pm
Chris Peterson wrote:
Mon Sep 13, 2021 9:06 pm


We clearly see a very different view of the man's face in the two reflections! Look again.

Try drawing a little ray diagram from the side, and you'll quickly see that the light is following two different paths.
I'm saying the man's face in the mirror above the line appears to be the same as his face below the line. (He says, getting more confused by this picture by the post :( )
I disagree completely. In the mirror, we're looking up at his chin from below it. In the water, we're looking almost directly into his face. I'd say there's at least a 30° difference in the viewing angles there.
Ok, I can now see you are correct (as usual). I didn't look closely enough at the two faces. Still confused as heaven (not hell!) about the reflections though. The post by neufer didn't help :?
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neufer
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Re: APOD: Night Sky Reflected (2021 Sep 13)

Post by neufer » Tue Sep 14, 2021 2:30 pm

Ann wrote:
Tue Sep 14, 2021 4:47 am
neufer wrote:
Mon Sep 13, 2021 10:40 pm

Both the mirror and its reflection are picking up a vertical axis parallel to & slightly to the left of the left edge of the APOD (& "almost" perpendicular to the SMC/LMC axis). This axis (lies a little further left of the SMC than the SMC lies to left of the LMC and) passes past zenith through The Pipe Nebula. The mirror image is of an upside down Pipe Nebula. The reflected mirror image is of an upright asterism of comparable size but somewhat further past zenith through the same vertical axis.
Let me see if I got this straight. Should we imagine a vertical line through the Pipe Nebula, a line that is almost perpendicular to the axis between the LMC and the SMC? And what we see in the doubly reflected mirror image should lie somewhere along this perpendicular axis through the Pipe Nebula?
  • You did 't quite get it right ...but then neither did I :oops:

    Try, try, try again:
:arrow: The nearly vertical southern end of the Milky Way lies clearly to the right of the man. If the man looks back at the camera he will see the nearly vertical northern end of the Milky Way to the right of the camera. By angling the mirror to the right the man reflects that northern end of the Milky Way into the camera.

By angling the mirror up the man reflects the near zenith Pipe Nebula just above the man's head. Note that both the man and The Pipe Nebula have their northern ends at the bottom of the mirror image and thus appear upside down from normal.

The water reflection produces a more glancing blow on the mirror that centers on the man's head among the (as yet unlocated) southern end of the Milky Way. Both the man and the southern end of the Milky Way (including the man's Milky Way "halo" (that you noticed) have their northern ends at the top of the mirror image and thus appear right side up in the reflection. See if you can locate the man's Milky Way "halo" to the right of the Pipe Nebula in the provided image.
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alter-ego
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Re: APOD: Night Sky Reflected (2021 Sep 13)

Post by alter-ego » Wed Sep 15, 2021 6:10 am

I located the doubly-reflected image. Indeed it's toward the southern end the MW, but not very far away from the Pipe Nebula - only about 21.5° away. The photographer's head in both reflected images is ~15° from his zenith. When I can, I will follow up with the selected Stellarium FoV and convincing star and asterism correlations. Despite the distortion and irregular variations in relative star brightness, I could identify roughly 20 stars in the doubly-reflected image.
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Ann
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Re: APOD: Night Sky Reflected (2021 Sep 13)

Post by Ann » Wed Sep 15, 2021 8:57 am

alter-ego wrote:
Wed Sep 15, 2021 6:10 am
I located the doubly-reflected image. Indeed it's toward the southern end the MW, but not very far away from the Pipe Nebula - only about 21.5° away. The photographer's head in both reflected images is ~15° from his zenith. When I can, I will follow up with the selected Stellarium FoV and convincing star and asterism correlations. Despite the distortion and irregular variations in relative star brightness, I could identify roughly 20 stars in the doubly-reflected image.
I'm so curious!

I've been trying and failing to figure out where the doubly reflected skyscape is located. But like you, I have concluded that the most likely location is indeed near the Pipe Nebula. That is because the doubly reflected image shows both dark dust clouds and at least one patch of clear starry sky, as well as a number of at least relatively bright stars. There aren't too many places in the southern Milky Way near Scorpius, Ophiuchus, Ara, Centaurus, Lupus, Crux and Carina where you find that combination in a way that doesn't give itself away as a well-known asterism.

I'm very much looking forward to your disclosure!

Ann
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Hskelter1975
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Re: APOD: Night Sky Reflected (2021 Sep 13)

Post by Hskelter1975 » Fri Sep 17, 2021 4:20 pm

johnnydeep wrote:
Mon Sep 13, 2021 2:08 pm
DeepintheHeartofTexas wrote:
Mon Sep 13, 2021 1:48 pm
Is anyone else bothered/confused by the mirror's impossible reflection in the lake?
Yeah, now that you mention it :) Also, clearly, the guy can't be standing IN the lake, so now I don't understand what I'm looking at all! The links don't seem to provide any more info about how this image was created.

EDIT: oh wait - is the lake actually frozen? I see the guy is wearing a hat, and now also the snow in the background. D'oh! But I still don't understand the mirror's reflection in the ice (or water).

EDIT #2: on the other hand, this pic was taken from Mostardas, south Brazil. Does it ever get cold enough there for snow or frozen lakes?
This Photo was taken during the winter (nearly 2⁰C) in southern Brazil in a region of dunes that can be seen on the horizon, the sky's reflection is in a pool of water accumulated in a rainy season in a special condition without winds. Not cold enough for frozen lakes but cold enough for a Brazilian.

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Re: APOD: Night Sky Reflected (2021 Sep 13)

Post by alter-ego » Sat Sep 18, 2021 3:16 am

The Stellarium view shows the locations of both single (Pipe Nebula) and double-reflection images on the Mostardus sky. Based on Jupiter's position, the Stellarium time is within a day or so. The white trapezoids represent the two mirror surfaces. They are well sized, shaped, oriented and positioned to show the APOD mirrored fields of view. I couldn't correct for distortions within the mirrored images, but the overall shape geometries and FoV agreement are very good.
• The separation between the mirrored FoV centers ≈ 23°, and
• The center of the double-reflection FoV (bottom trapezoid) is in the constellation Ara
• The photographer's azimuthal grid is also visible, and zenith labeled
 
Image Locations on Sky_2.jpg
 
Most stars in the Stellarium solution FoV ID the APOD image FoV very well.
 
Reflection & Stellarium FoV Comparsion.jpg
 
 
• The cyan-colored circle & ellipse show the first features I identified: The star cloud first, and the dipper-like asterism second
 
 
Mirrored Reflections.jpg
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neufer
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Re: APOD: Night Sky Reflected (2021 Sep 13)

Post by neufer » Sat Sep 18, 2021 2:26 pm

alter-ego wrote:
Sat Sep 18, 2021 3:16 am

• The separation between the mirrored FoV centers ≈ 23°, and
• The center of the double-reflection FoV (bottom trapezoid) is in the constellation Ara
• The photographer's azimuthal grid is also visible, and zenith labeled
:roll: I'm impressed :!:

So the double reflected image is really of the photographer's Altar ego :?:
Art Neuendorffer

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johnnydeep
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Re: APOD: Night Sky Reflected (2021 Sep 13)

Post by johnnydeep » Sat Sep 18, 2021 2:35 pm

neufer wrote:
Sat Sep 18, 2021 2:26 pm
alter-ego wrote:
Sat Sep 18, 2021 3:16 am

• The separation between the mirrored FoV centers ≈ 23°, and
• The center of the double-reflection FoV (bottom trapezoid) is in the constellation Ara
• The photographer's azimuthal grid is also visible, and zenith labeled
:roll: I'm impressed :!:

So the double reflected image is really of the photographer's Altar ego :?:
Indeed. But "altar"? As in:
Noun
A table or flat-topped block used as the focus for a religious ritual, especially for making sacrifices or offerings to a deity.
ORIGIN
Old English altar, alter, based on late Latin altar, altarium, from Latin altus ‘high’.
If that's what you meant, I guess I can see it. Sorta.
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Re: APOD: Night Sky Reflected (2021 Sep 13)

Post by neufer » Sat Sep 18, 2021 3:02 pm

johnnydeep wrote:
Sat Sep 18, 2021 2:35 pm
neufer wrote:
Sat Sep 18, 2021 2:26 pm
alter-ego wrote:
Sat Sep 18, 2021 3:16 am

• The separation between the mirrored FoV centers ≈ 23°, and
• The center of the double-reflection FoV (bottom trapezoid) is in the constellation Ara
• The photographer's azimuthal grid is also visible, and zenith labeled
:roll: I'm impressed :!:

So the double reflected image is really of the photographer's Altar ego :?:
Indeed. But "altar"? If that's what you meant, I guess I can see it. Sorta.
https://en.wikipedia.org/wiki/Ara_(constellation) wrote: <<Ara (Latin: "the Altar"), the southern constellation between Scorpius, Telescopium, Triangulum Australe and Norma, was (as Βωμός (Bōmǒs)) one of the Greek bulk (namely 48) described by the 2nd-century astronomer Ptolemy. In illustrations, Ara is usually depicted as compact classical altar with its smoke 'rising' southward. However, depictions often vary. In the early days of printing, a 1482 woodcut of Gaius Julius Hyginus's classic Poeticon Astronomicon depicts the altar as surrounded by demons. Hyginus depicted the same though his featured devils on either side of the flames. Willem Blaeu, a Dutch uranographer of the 16th and 17th centuries, drew Ara as an altar for sacrifices, with a burning animal offering unusually whose smoke rises northward, represented by Alpha Arae.>>
  • One way for a frozen Brazilian to stay warm, perhaps.
Hskelter1975 wrote:
Fri Sep 17, 2021 4:20 pm

This Photo was taken during the winter (nearly 2⁰C) in southern Brazil in a region of dunes that can be seen on the horizon, the sky's reflection is in a pool of water accumulated in a rainy season in a special condition without winds. Not cold enough for frozen lakes but cold enough for a Brazilian.
Art Neuendorffer

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johnnydeep
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Re: APOD: Night Sky Reflected (2021 Sep 13)

Post by johnnydeep » Sat Sep 18, 2021 3:38 pm

neufer wrote:
Sat Sep 18, 2021 3:02 pm
johnnydeep wrote:
Sat Sep 18, 2021 2:35 pm
neufer wrote:
Sat Sep 18, 2021 2:26 pm
:roll: I'm impressed :!:

So the double reflected image is really of the photographer's Altar ego :?:
Indeed. But "altar"? If that's what you meant, I guess I can see it. Sorta.
https://en.wikipedia.org/wiki/Ara_(constellation) wrote:
<<Ara (Latin: "the Altar"), the southern constellation between Scorpius, Telescopium, Triangulum Australe and Norma, was (as Βωμός (Bōmǒs)) one of the Greek bulk (namely 48) described by the 2nd-century astronomer Ptolemy. In illustrations, Ara is usually depicted as compact classical altar with its smoke 'rising' southward. However, depictions often vary. In the early days of printing, a 1482 woodcut of Gaius Julius Hyginus's classic Poeticon Astronomicon depicts the altar as surrounded by demons. Hyginus depicted the same though his featured devils on either side of the flames. Willem Blaeu, a Dutch uranographer of the 16th and 17th centuries, drew Ara as an altar for sacrifices, with a burning animal offering unusually whose smoke rises northward, represented by Alpha Arae.>>
Wow, I missed that one entirely.
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Ann
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Re: APOD: Night Sky Reflected (2021 Sep 13)

Post by Ann » Sat Sep 18, 2021 3:54 pm

alter-ego wrote:
Sat Sep 18, 2021 3:16 am
The Stellarium view shows the locations of both single (Pipe Nebula) and double-reflection images on the Mostardus sky. Based on Jupiter's position, the Stellarium time is within a day or so. The white trapezoids represent the two mirror surfaces. They are well sized, shaped, oriented and positioned to show the APOD mirrored fields of view. I couldn't correct for distortions within the mirrored images, but the overall shape geometries and FoV agreement are very good.
• The separation between the mirrored FoV centers ≈ 23°, and
• The center of the double-reflection FoV (bottom trapezoid) is in the constellation Ara
• The photographer's azimuthal grid is also visible, and zenith labeled
 
 
Most stars in the Stellarium solution FoV ID the APOD image FoV very well.
   
 
• The cyan-colored circle & ellipse show the first features I identified: The star cloud first, and the dipper-like asterism second
 
I'm so impressed! :D :clap:


Let me just say something about my own pitiful attempts at identification, and point out something I said:


I said:

1: A very blue star. Note that almost all the stars in the doubly reflected image looks more or less bluish, but this one stands out. I'd say that the light that reaches us from this star is at least as blue as Vega's and probably bluer.

2) This star looks almost completely non-blue. Since we definitely expect to see some yellow or orange stars in a patch of sky as big as the doubly reflected image appears to be, I'd say that this is a yellow or orange star, most likely of spectral class K. But other spectral classes are also possible.

It turns out that the star I called #1 in my annotated image is SAO 227972. It is a star of spectral class B8, and the light that reaches us from this star has a B-V index of -0.058. So it is bluer than Vega, both intrinsically and in the light that reaches us from it.

However, I wasn't correct that this star is the bluest in the doubly reflected image. A rather bright star at far right, almost touching the man's shoulder, is Epsilon Norma, a star of spectral class B4, with a (reddened) B-V index of -0.070. So this star is both intrinsically and "apparently" bluer than SAO 227972.

But the star I pointed out as non-blue, #2 in my annotated image, really is non-blue. It is in fact an orange dwarf star of spectral class G9V, SAO 227816.

Ann
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