Horizon to Horizon (APOD 21 Dec 2007)

[auroradude]

This is a very creative and outstanding image. Well Done!

That being said, can anyone tell me why the stars are rendered pinkish in so many digital images? (I remember a time when blue stars still ruled the sky!)

Thank you for any light on this.

[BMAONE23]

If blue stars are new stars and yellow stars are older stars, perhaps it is testament to the aging universe

In reality though, I have no fractile idea.

[rollovermikey]

Very original photography concept. I've never seen such a panoramic image before. I've visited APOD everyday for years. I have never inspected any other image longer than I have this one. Well, maybe the Hubble Deep Field. Where I live, light pollution only allows us to see the major stars of any constellation on any given night. From a horizon to horizon perspective, this puts everything in place/proximity much better than, say a "fish eye" photograph which distorts the actual image that is percieved. You know, like "OBJECTS IN MIRROR MAY BE CLOSER THAN THEY APPEAR." I found Comet Holmes no problem, but I can't see the stars in Perseus that I can usually easily identify because there are so many in the field of the photo. Anyhow, outstanding photograph. Nice little sliver of French beach! Nice pic!

[rollovermikey]

Just a guess, but my first impulse was to think atmospheric and light pollution. Especially those pesky mercury vapor streetlights. They may help keep the neighborhood secure, but they sure can mess up an observing session, photos too. Check out the International Dark-Sky Association http://www.nextrionet.com/mc/page.do?orgId=idsa for more information. There are some really nice, affordable filters on the market today which dramatically cut down on the back-scattering of mercury vapor streetlights for your telescope. Try Orion Telescopes and Binoculars or Lumicon for a Broadband Light-Pollution Filter. They dramatically increase contrast for better views. But overall I think the answer to your question is probably today's increased light and atmospheric pollution. Although the reply "If blue stars are new stars.." provokes much thought!

[auroradude]

Yea, the blue stars are younger and hotter but they also tend to be more luminous so as you get further into space with longer exposures, showing more and more stars, the blue ones tend to dominate images since the yellower stars are dimmer and less visible except maybe in the center of the galaxy where older stars are more prevelent.
Light pollution is a definate factor in the overall appearance if an image but I have seen this "pinking effect" on many digital images taken from dark skies without light pollution as well.

This image seems to exibit the effect.

http://antwrp.gsfc.nasa.gov/apod/ap070930.html

Here is another good example:

http://www.spacew.com/gallery/image005233.html

So is it the nature of the camera's sensor? Does it occur with off-the-shelf digitals or maybe just the ones that have the infrared filter removed for astronomical purposes? Is it correctable?

[geonuc]

Not sure about the pink star phenomenon.

What struck me about this APOD is that I had to look several times to make out Orion, which perhaps more than any other northern constellation stands out like a sore thumb. Betegeuse and Rigel are not prominent at all in this image. Funny the way photography often doesn't depict things quite as they really are.

[auroradude]

I think in part the lack of differentation of bright stars verses fainter stars it could be a testament to good optics. Since the stars are all point sources of light, they only saturate a few pixels of the sensor, in the case of digital, and only a few grains are affected on film so that fainter stars will saturate just as many pixels and appear just as bright.
If the light were spread out more then the brighter stars would be more apparent. This could occur when an optic has more aberations such as coma - the inability of a lens to bring all light rays to a single focus. A diffusion filter can actually be used during the exposure or part of the exposure to spread ot the light. This will affect the brighter point sources more so that they will appear larger or brighter.
The atmospheric transparency or seeing can affect the image size as well. Turbulance, ice crystals or water droplets in the air (or on the lens), dust and smoke can all contribute to diffusing the stellar image. This is not as noticable with wide-angle lenses as the stars are still rendered small but as higher power is used, atmospheric conditions become much more important.

[John Sheppard]

I was impressed with the interesting picture as a strip across the sky but I was mildly surprised at how just the objects being pointed out were seemingly enhanced in the picture, so much so that it took me aback. The stars of Orion are hardly identifiable whereas comet holmes jumps off the screen. Surely Sirius is brighter than Rigel but not that much.
Well the concept is really neat!

--john

[auroradude]

Yes, Holmes and other diffuse objects ,such as the many star clusters and Orion's nebula, would saturate more pixels than the point sources of the stars so they might appear brighter.

[iamlucky13]

This is a very creative and outstanding image. Well Done!

That being said, can anyone tell me why the stars are rendered pinkish in so many digital images? (I remember a time when blue stars still ruled the sky!)

Thank you for any light on this.

I'm not sure, and I personally hadn't noticed this, but it may have to do with more common use of digital cameras now. Film cameras do not filter the light coming into them unless you added a filter. Instead, the film responded mainly to the visible spectrum (plus a little bit of UV and infrared).

Digital cameras are slightly different. Each pixel consists of a photocell and a colored filter, either red, green, or blue. The UV especially is filtered out. While this provides a nearly correct rendition of the colors we see, it actually does slightly change what is recorded compared to using film.

Great picture!