AFOV vs Aperture Poll

c (Bill Ferris) wrote in message ...

The summer and winter
Milky Way are filled with many [large nebulous or pseudo-nebulous objects
and stellar associations] --not all of which have been catalogued or been
given cute common names--but all of which will be much more
detailed and interesting in the binoculars.

Having been so negative about the rest of your post, I must say that here
I agree 100%. It is precisely those objects -- many better even to the
naked eye than in binoculars -- that make me prefer 10x50 binoculars under
a dark sky to a 12-inch scope under full Moon. Oh yes, and don't forget
dark nebulae.

- Tony Flanders

On 28 Dec 2003 17:22:27 -0800, (Tony Flanders)
wrote:

Suppose you had to spend the rest of your life on a desert
island with one of the following sets of equipment, which
would you choose?

* An 8-inch scope with a full set of 80-degree-AFOV EPs.
* A 10-inch scope with a full set of 50-degree-AFOV EPs.

I missed the poll; but given the above choice my preference would go
one way with a manually driven alt-az and the other way for any
thoughtfully engineered equatorial. Mounts matter! I wouldn't care a
whole lot about the difference in aperture given a desert island that
presumedly has pristine skies.

OTOH, if you had included the option of a 9 inch scope with a full set
of 65 degree AFOV EPs I would go for it even without any knowledge of
the mount.

P.S. Congratulations on your new job!

Bill Greer

On 28 Dec 2003 17:22:27 -0800, (Tony Flanders)
wrote:

Suppose you had to spend the rest of your life on a desert
island with one of the following sets of equipment, which
would you choose?

* An 8-inch scope with a full set of 80-degree-AFOV EPs.
* A 10-inch scope with a full set of 50-degree-AFOV EPs.

I missed the poll; but given the above choice my preference would go
one way with a manually driven alt-az and the other way for any
thoughtfully engineered equatorial. Mounts matter! I wouldn't care a
whole lot about the difference in aperture given a desert island that
presumedly has pristine skies.

OTOH, if you had included the option of a 9 inch scope with a full set
of 65 degree AFOV EPs I would go for it even without any knowledge of
the mount.

P.S. Congratulations on your new job!

Bill Greer

On 28 Dec 2003 17:22:27 -0800, (Tony Flanders)
wrote:

Suppose you had to spend the rest of your life on a desert
island with one of the following sets of equipment, which
would you choose?

* An 8-inch scope with a full set of 80-degree-AFOV EPs.
* A 10-inch scope with a full set of 50-degree-AFOV EPs.

I missed the poll; but given the above choice my preference would go
one way with a manually driven alt-az and the other way for any
thoughtfully engineered equatorial. Mounts matter! I wouldn't care a
whole lot about the difference in aperture given a desert island that
presumedly has pristine skies.

OTOH, if you had included the option of a 9 inch scope with a full set
of 65 degree AFOV EPs I would go for it even without any knowledge of
the mount.

P.S. Congratulations on your new job!

Bill Greer

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

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

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

c (Bill Ferris) wrote in message ...

It's difficult to know how closely my idea of "suburban" and your idea of
"suburban" match

Indeed. "Suburb" is a terrible word; it has all kinds of subjective
connotations and covers a huge range of objective realities. Some
suburbs have skies considerably brighter than my own hometown of
Cambridge, and some have skies where the winter Milky Way is bright
and obvious on any clear night.

Batavia Illinois is probably typical of what I was calling a "mediocre
suburb". Note that Batavia has about 2,500 people per square mile,
whereas my favorite close-in suburban viewing spot in Boston is in
Lincoln, with 550 people per square miles -- but only 15 miles from
the center of Boston. One of the interesting results from my
current series of sky-brightness measurements is that a hefty
portion of the total sky brightness comes from sources within a
mile of the site, even inside a major urban light dome. Lincoln
throws pretty darned close to no light up into the atmosphere,
and indeed, the summer Milky Way is *very* obvious there.

The sky brightness at full Moon from Lowell Observatory's Mars
Hill site--west side of Flagstaff--is about 18.0 MPSA.

Do you have a date and time for that observation? The brightness
of the Moon varies significantly from one full Moon to another.
Even more important, my sky-brightness measurements show that
the zenith brightness is quite sensititive to the altitude of
the Moon. And even a touch of haze raises the skyglow immensely.
Add all the variations together, let the errors in someone else's
observations err in the opposite directions, and two people could
be off by a full magnitude -- a huge amount.

I wish that I could correlate the readings that I get with my
digital camera to an absolute scale of MPSA, but so far I have
not succeeded to my own satisfaction. In any case, I find that
the zenith in Cambridge is about one magnitude brighter than
the zenith at an otherwise dark sky at full Moon, give or take
a factor of two. That's how I derived my estimate of 17 MPSA,
based on your 18 MPSA for full Moon.

At this Cambridge site, I have succeeded in viewing all but one
of the Messier objects (M98) in my 7-inch scope. By contrast,
there are 6 Messier objects which I am not sure of in 10x50
binoculars under very good skies (M74, M76, M95, M105, M109,
M98). Intriguingly, all of the Messier objects are reasonably
easy in my 15x45 image-stabilized binoculars, indicating that
the handicap of the binoculars is due more to low magnification
than to small aperture. But any way you look at it, the handicap
of the binoculars is *enormous*. And I am talking about 17 MPSA
skies rather than 18 MPSA, and a 7-inch scope rather than 12-inch.

Why don't you try it yourself? You've got a fair-sized scope,
and full Moon happens once a month. Granted, it is a little
pig-headed to do deep-sky observing at full Moon, but it is
also instructive. I think you will be surprised just how
much you can see.

- Tony Flanders

c (Bill Ferris) wrote in message ...

It's difficult to know how closely my idea of "suburban" and your idea of
"suburban" match

Indeed. "Suburb" is a terrible word; it has all kinds of subjective
connotations and covers a huge range of objective realities. Some
suburbs have skies considerably brighter than my own hometown of
Cambridge, and some have skies where the winter Milky Way is bright
and obvious on any clear night.

Batavia Illinois is probably typical of what I was calling a "mediocre
suburb". Note that Batavia has about 2,500 people per square mile,
whereas my favorite close-in suburban viewing spot in Boston is in
Lincoln, with 550 people per square miles -- but only 15 miles from
the center of Boston. One of the interesting results from my
current series of sky-brightness measurements is that a hefty
portion of the total sky brightness comes from sources within a
mile of the site, even inside a major urban light dome. Lincoln
throws pretty darned close to no light up into the atmosphere,
and indeed, the summer Milky Way is *very* obvious there.

The sky brightness at full Moon from Lowell Observatory's Mars
Hill site--west side of Flagstaff--is about 18.0 MPSA.

Do you have a date and time for that observation? The brightness
of the Moon varies significantly from one full Moon to another.
Even more important, my sky-brightness measurements show that
the zenith brightness is quite sensititive to the altitude of
the Moon. And even a touch of haze raises the skyglow immensely.
Add all the variations together, let the errors in someone else's
observations err in the opposite directions, and two people could
be off by a full magnitude -- a huge amount.

I wish that I could correlate the readings that I get with my
digital camera to an absolute scale of MPSA, but so far I have
not succeeded to my own satisfaction. In any case, I find that
the zenith in Cambridge is about one magnitude brighter than
the zenith at an otherwise dark sky at full Moon, give or take
a factor of two. That's how I derived my estimate of 17 MPSA,
based on your 18 MPSA for full Moon.

At this Cambridge site, I have succeeded in viewing all but one
of the Messier objects (M98) in my 7-inch scope. By contrast,
there are 6 Messier objects which I am not sure of in 10x50
binoculars under very good skies (M74, M76, M95, M105, M109,
M98). Intriguingly, all of the Messier objects are reasonably
easy in my 15x45 image-stabilized binoculars, indicating that
the handicap of the binoculars is due more to low magnification
than to small aperture. But any way you look at it, the handicap
of the binoculars is *enormous*. And I am talking about 17 MPSA
skies rather than 18 MPSA, and a 7-inch scope rather than 12-inch.

Why don't you try it yourself? You've got a fair-sized scope,
and full Moon happens once a month. Granted, it is a little
pig-headed to do deep-sky observing at full Moon, but it is
also instructive. I think you will be surprised just how
much you can see.

- Tony Flanders

c (Bill Ferris) wrote in message ...

It's difficult to know how closely my idea of "suburban" and your idea of
"suburban" match

Indeed. "Suburb" is a terrible word; it has all kinds of subjective
connotations and covers a huge range of objective realities. Some
suburbs have skies considerably brighter than my own hometown of
Cambridge, and some have skies where the winter Milky Way is bright
and obvious on any clear night.

Batavia Illinois is probably typical of what I was calling a "mediocre
suburb". Note that Batavia has about 2,500 people per square mile,
whereas my favorite close-in suburban viewing spot in Boston is in
Lincoln, with 550 people per square miles -- but only 15 miles from
the center of Boston. One of the interesting results from my
current series of sky-brightness measurements is that a hefty
portion of the total sky brightness comes from sources within a
mile of the site, even inside a major urban light dome. Lincoln
throws pretty darned close to no light up into the atmosphere,
and indeed, the summer Milky Way is *very* obvious there.

The sky brightness at full Moon from Lowell Observatory's Mars
Hill site--west side of Flagstaff--is about 18.0 MPSA.

Do you have a date and time for that observation? The brightness
of the Moon varies significantly from one full Moon to another.
Even more important, my sky-brightness measurements show that
the zenith brightness is quite sensititive to the altitude of
the Moon. And even a touch of haze raises the skyglow immensely.
Add all the variations together, let the errors in someone else's
observations err in the opposite directions, and two people could
be off by a full magnitude -- a huge amount.

I wish that I could correlate the readings that I get with my
digital camera to an absolute scale of MPSA, but so far I have
not succeeded to my own satisfaction. In any case, I find that
the zenith in Cambridge is about one magnitude brighter than
the zenith at an otherwise dark sky at full Moon, give or take
a factor of two. That's how I derived my estimate of 17 MPSA,
based on your 18 MPSA for full Moon.

At this Cambridge site, I have succeeded in viewing all but one
of the Messier objects (M98) in my 7-inch scope. By contrast,
there are 6 Messier objects which I am not sure of in 10x50
binoculars under very good skies (M74, M76, M95, M105, M109,
M98). Intriguingly, all of the Messier objects are reasonably
easy in my 15x45 image-stabilized binoculars, indicating that
the handicap of the binoculars is due more to low magnification
than to small aperture. But any way you look at it, the handicap
of the binoculars is *enormous*. And I am talking about 17 MPSA
skies rather than 18 MPSA, and a 7-inch scope rather than 12-inch.

Why don't you try it yourself? You've got a fair-sized scope,
and full Moon happens once a month. Granted, it is a little
pig-headed to do deep-sky observing at full Moon, but it is
also instructive. I think you will be surprised just how
much you can see.

- Tony Flanders