#1
|
|||
|
|||
Stupid Question
Hello All,
Not really an amateur - more like a casual observer with an interest - please forgive the intrusion. I've been watching the Cassini stuff, and something struck me that I've never really thought too much about before, so I'm hoping this isn't the proverbial stupid question! When I see these images of planets within our solar system, why do I never see stars in the backdrop (at least that I can remember?) I've seen images of Pluto at distance, shown as a smudge in a starfield, so that one's obvious. But when I see pictures of the moon, for instance, I can't remember ever really seeing stars adjacent. Do they just crop them out, is the light too great, do they just happen to choose photographs that have no stars in them for aesthetics, etc. Or, if I'm wrong, and just haven't seen the right pictures (I'm getting your National Geographic and Mars Rovers and Cassini type images - stuff from NASA and friends), could someone maybe direct me to a good site? TIA Steve |
#2
|
|||
|
|||
Stupid Question
Steve wrote:
When I see these images of planets within our solar system, why do I never see stars in the backdrop (at least that I can remember?) Generally speaking, the planet is too bright for an exposure long enough to capture any stars in addition. Brian Tung The Astronomy Corner at http://astro.isi.edu/ Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/ The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/ My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt |
#4
|
|||
|
|||
Stupid Question
You don't see the stars because even now CCD cameras don't have the dynamic
range of the eye. Being an avid imager of planets for almost the past year, I can tell you that recording stars and planets clearly in the same image is nearly impossible unless the star is of the nearly the same brightness as the planet. The only advantage CCDs have over the eye is to save light over longer periods of time, minutes instead of seconds, but this is not necessary for the planets due to their high brightness. -- Sincerely, --- Dave ---------------------------------------------------------------------- A man is a god in ruins. --- Duke Ellington ---------------------------------------------------------------------- "LSL" wrote in message m... Hello All, Not really an amateur - more like a casual observer with an interest - please forgive the intrusion. I've been watching the Cassini stuff, and something struck me that I've never really thought too much about before, so I'm hoping this isn't the proverbial stupid question! When I see these images of planets within our solar system, why do I never see stars in the backdrop (at least that I can remember?) I've seen images of Pluto at distance, shown as a smudge in a starfield, so that one's obvious. But when I see pictures of the moon, for instance, I can't remember ever really seeing stars adjacent. Do they just crop them out, is the light too great, do they just happen to choose photographs that have no stars in them for aesthetics, etc. Or, if I'm wrong, and just haven't seen the right pictures (I'm getting your National Geographic and Mars Rovers and Cassini type images - stuff from NASA and friends), could someone maybe direct me to a good site? TIA Steve |
#5
|
|||
|
|||
Stupid Question
On Tue, 08 Jun 2004 23:25:34 GMT, "David Nakamoto" wrote:
You don't see the stars because even now CCD cameras don't have the dynamic range of the eye. Being an avid imager of planets for almost the past year, I can tell you that recording stars and planets clearly in the same image is nearly impossible unless the star is of the nearly the same brightness as the planet. I don't entirely agree. Good CCD cameras have a dynamic range of 1:5000 to 1:10000, which is certainly enough to get a good planetary image showing stars. For instance, if you expose Jupiter with such a camera, just filling the wells with the brightest features, you will record stars to magnitude 10. With Saturn, which isn't as bright, you can go even deeper. What the many people, including the original poster, might fail to realize is just how small a field a planet sits in when imaged from Earth, and how few stars brighter then mag 10 are even in it (typically, none). This is pretty apparent when you view Jupiter at high magnification with a small scope- there may be no stars visible to the eye, or at least, very few. The only advantage CCDs have over the eye is to save light over longer periods of time, minutes instead of seconds, but this is not necessary for the planets due to their high brightness. I'd add the advantage of collecting data which can be manipulated. Thus, structures with contrast differences too small to be discerned by the eye are readily stretched into visibility in the digital realm. That's why CCD images of even bright planets show so much more detail than ever shows up visually. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
#6
|
|||
|
|||
Stupid Question
On 2004-06-08, LSL wrote:
Do they just crop them out, is the light too great, do they just happen to choose photographs that have no stars in them for aesthetics, etc. The moon is bright and stars are faint so with the correct exposure for the moon stars are underexposed. The photographs of planets you see are at high magnification so you can see details on the planet. The field of view is small so few stars would be in the picture. You can take a wide field picture showing a planet among the stars, but the planet looks like a bright star. |
#7
|
|||
|
|||
Stupid Question
While reading in the bathroom on Tue, 08 Jun 2004 21:46:32 -0500, I
saw that William Hamblen had written: On 2004-06-08, LSL wrote: Do they just crop them out, is the light too great, do they just happen to choose photographs that have no stars in them for aesthetics, etc. The moon is bright and stars are faint so with the correct exposure for the moon stars are underexposed. Liar! The moon is a fake, otherwise there would be stars. It's all really set up on a sound stage in the Arizona desert. -------------- Beady's Corollary to Occam's Razor: "The likeliest explanation of any phenomenon is almost always the most boring one imaginable." -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
#8
|
|||
|
|||
Stupid Question
In message , Brian Tung writes
Steve wrote: When I see these images of planets within our solar system, why do I never see stars in the backdrop (at least that I can remember?) Generally speaking, the planet is too bright for an exposure long enough to capture any stars in addition. Or you can burn out the planetary disk and see satellites (for Jupiter and outwards) and any bright field stars. Actually with modern astro-CCD imaging if you stretch the contrast on a decent image you can usually see the Jovian satellites and the belt detail on a single exposure. On the rare occasions when the moon passes between us and a planet you get to see the difference in brightness and size clearly. The last time Saturn passed behind a gibbous phase moon was very pretty indeed. It is quite rare to get a bright star and a planet in close proximity. Regards, -- Martin Brown |
#9
|
|||
|
|||
Stupid Question
On 8 Jun 2004 16:05:47 -0700, LSL wrote:
Hello All, Not really an amateur - more like a casual observer with an interest - please forgive the intrusion. I've been watching the Cassini stuff, and something struck me that I've never really thought too much about before, so I'm hoping this isn't the proverbial stupid question! When I see these images of planets within our solar system, why do I never see stars in the backdrop (at least that I can remember?) [snip] Exposure time. Stars take time to show up on film (and CCD). The light needs to accumulate. The exposures of planets and the like are pretty short, especially those of a full moon. There's not enough time for most stars to begin showing up. You can replicate it yourself by taking a picture outside on a clear night. Make sure the sky is visible in the frame, and use either bright floodlights or a flash. The exposure will be short, and you won't see many (or any) stars. I expect it now seems obvious. -- - Mike Remove 'spambegone.net' and reverse to send e-mail. |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Instead of the parachute and bouncing balls, engineer a capsule that withstands the damage | Archimedes Plutonium | Astronomy Misc | 31 | January 8th 04 12:13 AM |
Question about alignment & pointing north, level | Mike | Amateur Astronomy | 8 | September 7th 03 12:04 AM |
Rookie question. How dark is MY sky? | justbeats | Amateur Astronomy | 4 | August 3rd 03 12:08 PM |
MAN AS OLD AS COAL -- Catastrophic Evidence | Ed Conrad | Amateur Astronomy | 10 | July 10th 03 01:02 PM |