Recent Submissions: 2010 August 28-29

[owlice]

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Please click on each image for best viewing; please click on the link below the
image title for more information about the image. Thank you!
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<- Previous submissions


NGC 281 in Cassiopeia
http://hwilson.zenfolio.com/img/s9/v15/p479455895-6.jpg
Copyright: Hunter Wilson

Click to view full size image

Dust Cirrus in Octans
Copyright: José Joaquín Pérez
[attachment=1]Octans_dust_2.jpg[/attachment][/i]

IC 5070: Pelican Nebula Bi-color
http://www.stern-fan.de/Seiten/galerie_ ... color.html
Copyright: Rolf Geissinger
[attachment=2]IC5070-Pelikan-Bicolor-1600.jpg[/attachment][/i]

M8 (Lagoon Nebula), M20 (Trifid Nebula), M21, IC 4685, IC 1274, LBN 105-6, vdB 115 in Sagittarius
http://starrysite.com/pliki/galeria/duz ... rysite.jpg
Copyright: Bogdan Jarzyna
[attachment=0]Sagittarius.jpg[/attachment][/i]

NGC 7217
http://www.caelumobservatory.com/gallery/n7217.shtml
Copyright: Adam Block

Click to view full size image

IC5076 Reflection Nebula
http://www.starkeeper.it/IC5076.htm
Copyright: Leonardo Orazi

Click to view full size image

Sun Crossing the Meridian Line in Rome
http://www.aquila-asso.org
Copyright: Jean-François Consigli

[attachment=3]Meridian.jpg[/attachment][/i]

The Basilica di Santa Maria degli Angeli e dei Martiri is a section of the remaining structure of the Baths of Diocletian (Thermae Diocletiani, built about AD 300) on the Quirinal Hill of Rome, nowadays the Piazza della Repubblica.

At the beginning of the eighteenth century, Pope Clement XI (1649-1721) commissioned Francesco Bianchini (1662-1729) to build a meridian line within the basilica to check the accuracy of the Gregorian reformation of the calendar (1582).

The sun shines through a small hole in the southern wall to cast its light on the meridian line each day (aperture gnomon).
Text source


<- Previous submissions

[owlice]

The Iris Nebula in Clouds of Dust
http://www.pbase.com/boren
Copyright: Harel Boren
[attachment=0]NGC7023-vdB139-C12-The-Iris-Nebula-in-Cepheus-1300-pixels---Brighter-Version.jpg[/attachment][/i]

[Ann]

The picture of NGC 7217 is nice. This galaxy is ever so slightly reminiscent of Hoag's Object (see http://antwrp.gsfc.nasa.gov/apod/ap100822.html), but NGC 7217 is not a true ring galaxy, because the starforming outer ring of NGC 7217 is not detached from the yellow disk and bulge.

Ann

[Ann]

The Pelican Nebula is nice enough, but as the resident Color Commentator I must point out that the overall color balance is too red, which affects the apparent brightness of the stars in the picture. The star which is brightest in visual light as seen from the Earth in this part of the Pelican Nebula is HD 199081, a hot blue star of spectral class B5V and a solid blue color index of between -0.14 and -0.16. Its visual magnitude is around 4.77. But this star, which is located near one "eye" of the pelican, looks decidedly fainter than another star near the center of the image. This other star is HD 198639, an A4V star with a color index of around +0.20, not nearly as blue. The visual magnitude of the A4 star is around 5.05, fainter than HD199081.

A third star, far to the left at a position of about ten o'clock, looks about equally bright as the A4 star. But this third star is visually fainter than the A4 star and considerably fainter than the hot blue B5 star. The third star is a red giant of spectral class K0II with a color index of about +1.1. Its visual magnitude is about 5.46, which really makes it about half as bright in visual light as the hot blue B5 star. And yet, in this image, the yellow K0 star looks brighter than the blue star! Why is that? Well, clearly this image discriminates against blue stars and makes them look fainter than they would look to the eye, and instead the image favors the redder stars by making them look brighter than they would to the eye.


This is another image of the Pelican Nebula. Note HD 199081, the blue B5 star near the top of the image. Below it is HD 198639, the A4 star which looks paler blue in this image. The B5 and the A4 star look about equally bright here.


This is another image where the color balance is far too red. The B5 star does indeed look blue, but it looks decidedly fainter than the A4 star, which has taken on a shockingly yellow hue.

Ann

[dan rabin]

The Iris Nebula in Clouds of Dust
http://www.pbase.com/boren
Copyright: Harel Boren
[attachment=0]NGC7023-vdB139-C12-The-Iris-Nebula-in-Cepheus-1300-pixels---Brighter-Version.jpg[/attachment][/i]

[geissi]

Hi Ann,

thanks for color-checking my pelican-pic.
The image-data only consists of a deep and crisp H-alpha pic and a fairly weak OIII image.
Both b/w pics have been combined with the bi-color method by Steve Cannistra.
This method generates a synthetic green-channel.
The only goal was, to generate a colored image. I think it's not possible (not for me) to achieve
real looking star-colors with this method, if one channel is as weak as the used OIII-data.
So, it never was my intention to achieve true star colors.

Regards
Rolf

http://www.stern-fan.de

[Ann]

Hi Ann,

thanks for color-checking my pelican-pic.
The image-data only consists of a deep and crisp H-alpha pic and a fairly weak OIII image.
Both b/w pics have been combined with the bi-color method by Steve Cannistra.
This method generates a synthetic green-channel.
The only goal was, to generate a colored image. I think it's not possible (not for me) to achieve
real looking star-colors with this method, if one channel is as weak as the used OIII-data.
So, it never was my intention to achieve true star colors.

Regards
Rolf

http://www.stern-fan.de

Thanks for the clarification, Rolf! I can see how an HII + OIII image might produce the stellar colors and brightnesses that we can see in your image.

I must congratulate you on bringing out some really interesting details about the emission that is illuminating the nebula. The Pelican nebula is dominated by HII emission and is therefore mostly red, but it is interesting to see the "whiter" parts of the nebula where OIII emission becomes significant. In particular, there is a long, sharp dust lane seen in front of some bright HII + OIII ionization along the pelican's "lower beak". Little dark shapes are jutting out and seen in silhouette against the bright emission. This is actually slightly similar to the oh-so-well-known Horsehead region in Orion:



I also want to thank Dan Rabin for his link to more images by Harel Boren. Harel has produced an image of the Pelican Nebula where the color and brightness of the B5 and A4 stars in that nebula are perfect.

Ann

[owlice]

Moon over Trosky Castle
http://www.15sunrises.com/
Copyright: David Tschorn

Click to view full size image

[owlice]

NGC 6888: Crescent Nebula - Bicolor Ha/OIII
http://hwilson.zenfolio.com/f129011888
Copyright: Hunter Wilson

Click to view full size image

[Harel Boren]

Hi Ann,

thanks for color-checking my pelican-pic.
The image-data only consists of a deep and crisp H-alpha pic and a fairly weak OIII image.
Both b/w pics have been combined with the bi-color method by Steve Cannistra.
This method generates a synthetic green-channel.
The only goal was, to generate a colored image. I think it's not possible (not for me) to achieve
real looking star-colors with this method, if one channel is as weak as the used OIII-data.
So, it never was my intention to achieve true star colors.

Regards
Rolf

http://www.stern-fan.de

Thanks for the clarification, Rolf! I can see how an HII + OIII image might produce the stellar colors and brightnesses that we can see in your image.

I must congratulate you on bringing out some really interesting details about the emission that is illuminating the nebula. The Pelican nebula is dominated by HII emission and is therefore mostly red, but it is interesting to see the "whiter" parts of the nebula where OIII emission becomes significant. In particular, there is a long, sharp dust lane seen in front of some bright HII + OIII ionization along the pelican's "lower beak". Little dark shapes are jutting out and seen in silhouette against the bright emission. This is actually slightly similar to the oh-so-well-known Horsehead region in Orion:

I also want to thank Dan Rabin for his link to more images by Harel Boren. Harel has produced an image of the Pelican Nebula where the color and brightness of the B5 and A4 stars in that nebula are perfect.

Ann

Hi Following Rolf's excellent image - and Ann's note about how the stars came out in my RGB image - here's a link to it on my site: http://www.pbase.com/boren/image/126577957
I enjoy the images this week tremendously.
Cheers,
Harel