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!
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
[quote=alter-ego post_id=316763 time=1631934962 user_id=125299]
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
[float=left][img2]https://asterisk.apod.com/download/file.php?id=41595&t=1[/img2][/float]
Most stars in the Stellarium solution FoV ID the APOD image FoV very well.
[float=right][img2]https://asterisk.apod.com/download/file.php?id=41596&t=1[/img2][/float]
• The cyan-colored circle & ellipse show the first features I identified: The star cloud first, and the dipper-like asterism second
[/quote]
I'm so impressed! :D :clap:
Let me just say something about my own pitiful attempts at identification, and point out something I said:
[float=left][img2]https://asterisk.apod.com/download/file.php?id=41528&mode=view[/img2][/float][float=right][img2]https://asterisk.apod.com/download/file.php?id=41596&mode=view[/img2][/float]
[clear][/clear]
I said:
[quote][b][color=#0040FF]1[/color][/b]: 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 [b][i]some[/i][/b] 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.[/quote]
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 [b][i]is[/i][/b] 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