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AFOV vs Aperture Poll
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#52
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AFOV vs Aperture Poll
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#53
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AFOV vs Aperture Poll
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#54
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AFOV vs Aperture Poll
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#55
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AFOV vs Aperture Poll
Tony Flanders wrote:
Well, I suppose that it all depends what you count as an "object". Also, how heavy is heavy light pollution? If you are talking about broad daylight, I will agree with you. That is why I chose full Moon as a widely-available reference point; I find an otherwise dark sky at full Moon roughly equal to a mediocre suburban sky. And I will say again that by any *reasonable* definition of "object", a 12-inch scope at full Moon will show *far* more deep- sky objects than 10x50 binoculars under pristine skies. At a crude guess, ten times as many. It's difficult to know how closely my idea of "suburban" and your idea of "suburban" match. You live in the greater Boston area where a suburb has a population of 50,000--more or less--is bordered by several suburbs of similar population, and by Boston. The largest city I've lived in since taking up visual observing is Madison, Wisconsin, which has a population about twice that of Cambridge and is bordered by suburbs with populations of 15,000 or less. To put the discussion on common ground, let's look at some hard numbers. The sky brightness at full Moon from Lowell Observatory's Mars Hill site--west side of Flagstaff--is about 18.0 MPSA. Tom Droege of the TASS project has measured the sky brightness at his "suburban" Batavia, Illionois site at the same ~18.0 MPSA level. (http://www.astropix.com/HTML/L_STORY/SKYBRITE.HTM ) Mr. Droege has setup a clear sky clock for his observing site. Here's the URL: http://cleardarksky.com/c/TASSHILkey.html?1 If you click on the "Light Pollution" link (http://cleardarksky.com/lp/TASSHILlp.html ), you'll see that his site is at the very edge of the Chicago conurbation. This region is colored white with deep red regions bordering to the north, south and west. Downtown Chicago is about 30-miles due east. We're talking about a site that rates a Bortle 7 or 8, where the brightest portions of the Milky Way are barely detectable to the naked eye, if visible at all. Observing within 30- to 35-degrees of the horizon is a waste of time. Only the highest surface brightness nebulae will be visible in *any* aperture. Compare this with a Bortle class 1 or 2 site, which would describe a pristine sky. The sky brightness is 4 magnitudes fainter. You've seen sites this dark so you know that, even to the naked eye, the stellar assocations and nebulosity that can be seen is astounding. A simple pair of binoculars opens an entire universe for exploration. The key to deep-sky observing is contrast and the first reduction filter is sky brightness. Once you start making the sky noticeably brighter, you start losing objects for visual observation *that no increase in aperture can regain.* At the level of light pollution we're discussing for the bright site in your hypothetical, any aperture is significantly constrained. I stand by my statement that the 10x50 binoculars under a pristine sky will allow an observer to explore more deep-sky objects than will be visible in a 12-inch aperture under heavy light pollution. And expanding the observing list to include phenomena such as aurorae, meteor showers and comets further drives home that advantage. Regards, Bill Ferris "Cosmic Voyage: The Online Resource for Amateur Astronomers" URL: http://www.cosmic-voyage.net ============= Email: Remove "ic" from .comic above to respond |
#56
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AFOV vs Aperture Poll
Tony Flanders wrote:
Well, I suppose that it all depends what you count as an "object". Also, how heavy is heavy light pollution? If you are talking about broad daylight, I will agree with you. That is why I chose full Moon as a widely-available reference point; I find an otherwise dark sky at full Moon roughly equal to a mediocre suburban sky. And I will say again that by any *reasonable* definition of "object", a 12-inch scope at full Moon will show *far* more deep- sky objects than 10x50 binoculars under pristine skies. At a crude guess, ten times as many. It's difficult to know how closely my idea of "suburban" and your idea of "suburban" match. You live in the greater Boston area where a suburb has a population of 50,000--more or less--is bordered by several suburbs of similar population, and by Boston. The largest city I've lived in since taking up visual observing is Madison, Wisconsin, which has a population about twice that of Cambridge and is bordered by suburbs with populations of 15,000 or less. To put the discussion on common ground, let's look at some hard numbers. The sky brightness at full Moon from Lowell Observatory's Mars Hill site--west side of Flagstaff--is about 18.0 MPSA. Tom Droege of the TASS project has measured the sky brightness at his "suburban" Batavia, Illionois site at the same ~18.0 MPSA level. (http://www.astropix.com/HTML/L_STORY/SKYBRITE.HTM ) Mr. Droege has setup a clear sky clock for his observing site. Here's the URL: http://cleardarksky.com/c/TASSHILkey.html?1 If you click on the "Light Pollution" link (http://cleardarksky.com/lp/TASSHILlp.html ), you'll see that his site is at the very edge of the Chicago conurbation. This region is colored white with deep red regions bordering to the north, south and west. Downtown Chicago is about 30-miles due east. We're talking about a site that rates a Bortle 7 or 8, where the brightest portions of the Milky Way are barely detectable to the naked eye, if visible at all. Observing within 30- to 35-degrees of the horizon is a waste of time. Only the highest surface brightness nebulae will be visible in *any* aperture. Compare this with a Bortle class 1 or 2 site, which would describe a pristine sky. The sky brightness is 4 magnitudes fainter. You've seen sites this dark so you know that, even to the naked eye, the stellar assocations and nebulosity that can be seen is astounding. A simple pair of binoculars opens an entire universe for exploration. The key to deep-sky observing is contrast and the first reduction filter is sky brightness. Once you start making the sky noticeably brighter, you start losing objects for visual observation *that no increase in aperture can regain.* At the level of light pollution we're discussing for the bright site in your hypothetical, any aperture is significantly constrained. I stand by my statement that the 10x50 binoculars under a pristine sky will allow an observer to explore more deep-sky objects than will be visible in a 12-inch aperture under heavy light pollution. And expanding the observing list to include phenomena such as aurorae, meteor showers and comets further drives home that advantage. Regards, Bill Ferris "Cosmic Voyage: The Online Resource for Amateur Astronomers" URL: http://www.cosmic-voyage.net ============= Email: Remove "ic" from .comic above to respond |
#57
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AFOV vs Aperture Poll
Tony Flanders wrote:
Well, I suppose that it all depends what you count as an "object". Also, how heavy is heavy light pollution? If you are talking about broad daylight, I will agree with you. That is why I chose full Moon as a widely-available reference point; I find an otherwise dark sky at full Moon roughly equal to a mediocre suburban sky. And I will say again that by any *reasonable* definition of "object", a 12-inch scope at full Moon will show *far* more deep- sky objects than 10x50 binoculars under pristine skies. At a crude guess, ten times as many. It's difficult to know how closely my idea of "suburban" and your idea of "suburban" match. You live in the greater Boston area where a suburb has a population of 50,000--more or less--is bordered by several suburbs of similar population, and by Boston. The largest city I've lived in since taking up visual observing is Madison, Wisconsin, which has a population about twice that of Cambridge and is bordered by suburbs with populations of 15,000 or less. To put the discussion on common ground, let's look at some hard numbers. The sky brightness at full Moon from Lowell Observatory's Mars Hill site--west side of Flagstaff--is about 18.0 MPSA. Tom Droege of the TASS project has measured the sky brightness at his "suburban" Batavia, Illionois site at the same ~18.0 MPSA level. (http://www.astropix.com/HTML/L_STORY/SKYBRITE.HTM ) Mr. Droege has setup a clear sky clock for his observing site. Here's the URL: http://cleardarksky.com/c/TASSHILkey.html?1 If you click on the "Light Pollution" link (http://cleardarksky.com/lp/TASSHILlp.html ), you'll see that his site is at the very edge of the Chicago conurbation. This region is colored white with deep red regions bordering to the north, south and west. Downtown Chicago is about 30-miles due east. We're talking about a site that rates a Bortle 7 or 8, where the brightest portions of the Milky Way are barely detectable to the naked eye, if visible at all. Observing within 30- to 35-degrees of the horizon is a waste of time. Only the highest surface brightness nebulae will be visible in *any* aperture. Compare this with a Bortle class 1 or 2 site, which would describe a pristine sky. The sky brightness is 4 magnitudes fainter. You've seen sites this dark so you know that, even to the naked eye, the stellar assocations and nebulosity that can be seen is astounding. A simple pair of binoculars opens an entire universe for exploration. The key to deep-sky observing is contrast and the first reduction filter is sky brightness. Once you start making the sky noticeably brighter, you start losing objects for visual observation *that no increase in aperture can regain.* At the level of light pollution we're discussing for the bright site in your hypothetical, any aperture is significantly constrained. I stand by my statement that the 10x50 binoculars under a pristine sky will allow an observer to explore more deep-sky objects than will be visible in a 12-inch aperture under heavy light pollution. And expanding the observing list to include phenomena such as aurorae, meteor showers and comets further drives home that advantage. Regards, Bill Ferris "Cosmic Voyage: The Online Resource for Amateur Astronomers" URL: http://www.cosmic-voyage.net ============= Email: Remove "ic" from .comic above to respond |
#58
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AFOV vs Aperture Poll
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#59
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AFOV vs Aperture Poll
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#60
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AFOV vs Aperture Poll
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