Let's Photograph Comet 46P Wirtanen

On Tuesday, December 18, 2018 at 7:43:04 PM UTC-8, Davoud wrote:
Chris L Peterson:
http://cloudbait.com/gallery/comet/20181217_46P_800.jpg

Shot early this morning after the Moon went down, 2-minute exposure
with a Canon 7D on a 4" refractor (Stellarvue 102A). Image is 1° on a
side.

Davoud:
Very nice!

I made this stack of five exposures with a Canon 5D Mk IV on the 11th
https://www.flickr.com/photos/primeval/31330206277. I also used a 4"
refractor, a Tak FSQ-106. I have been clouded out since that night.
Tonight will be clear and it is likely my last shot at the comet as
holiday social obligations and more cloudy weather intrude on my time.
With a bright moon, I'm not expecting anything great tonight, but we
gotta try, right?

Chris L Peterson:
You bet. I'm lucky with very dry air and a high altitude that the
impact of the Moon is somewhat reduced. The image I linked I took
after the Moon set (about 2 am), but I was doing test shots before
that and the results were quite good. Getting tougher, though. The
Moon is now just 45° from the comet, and getting pretty big.

OK, the sky was remarkably clear for the Mid-Atlantic. It was dry, and
when I was checking focus with 5X and 10X magnification the stars in
the DSLR Live View they were dancing around like a water droplet on a
hot griddle. My fix for that is to ignore it, and do what I can with
what I have. The effect of the Moon, I think, was to reduce the
contrast of the coma a bit. Maybe I could doctor it a bit in Photoshop.

Tonight's result with details is at
https://www.flickr.com/photos/primeval/32503667868.

High altitude? What do you know about high altitude? I'm at 30 meters‹I
could get a nosebleed!

--
I agree with almost everything that you have said and almost everything that
you will say in your entire life.

usenet *at* davidillig dawt cawm

Well, I'm impressed!

\Paul A

On Dec 18, 2018, Davoud wrote
(in article ):

Chris L Peterson:
http://cloudbait.com/gallery/comet/20181217_46P_800.jpg

Shot early this morning after the Moon went down, 2-minute exposure
with a Canon 7D on a 4" refractor (Stellarvue 102A). Image is 1° on a
side.

Davoud:
Very nice!

I made this stack of five exposures with a Canon 5D Mk IV on the 11th
https://www.flickr.com/photos/primeval/31330206277. I also used a 4"
refractor, a Tak FSQ-106. I have been clouded out since that night.
Tonight will be clear and it is likely my last shot at the comet as
holiday social obligations and more cloudy weather intrude on my time.
With a bright moon, I'm not expecting anything great tonight, but we
gotta try, right?

Chris L Peterson:
You bet. I'm lucky with very dry air and a high altitude that the
impact of the Moon is somewhat reduced. The image I linked I took
after the Moon set (about 2 am), but I was doing test shots before
that and the results were quite good. Getting tougher, though. The
Moon is now just 45° from the comet, and getting pretty big.

OK, the sky was remarkably clear for the Mid-Atlantic. It was dry, and
when I was checking focus with 5X and 10X magnification the stars in
the DSLR Live View they were dancing around like a water droplet on a
hot griddle. My fix for that is to ignore it, and do what I can with
what I have. The effect of the Moon, I think, was to reduce the
contrast of the coma a bit. Maybe I could doctor it a bit in Photoshop.

Tonight's result with details is at
https://www.flickr.com/photos/primeval/32503667868.

High altitude? What do you know about high altitude? I'm at 30 meters‹I
could get a nosebleed!

That is very nice. Is it that green in reality, or as close to reality as we
normally get?

I haven’t had a chance to see it yet, though the weather service says that
the skies are clear, Clear Sky Chart shows no transparency and lousy seeing.
I am getting really tired of this. (N.E. Kansas)

--
Harry F. Leopold

The Prints of Darkness (remove gene to email)

On Wed, 19 Dec 2018 02:13:09 -0600, hleopold
wrote:

That is very nice. Is it that green in reality, or as close to reality as we
normally get?

Well, "reality" is that this isn't bright enough to stimulate color
vision, so the "real" color is gray.

What it would look like if it were brighter, or our eyes more
sensitive, isn't a simple question. The gamut of the sensor in the
camera is quite different from that of our eyes. The color is coming
from several fairly narrow emission lines produced by CN and C2. Those
lines lie in violet, blue, cyan, and green parts of the spectrum.
Because they are emission lines and not a continuum, the color that
gets rendered by any camera is very sensitive to the bandpass of the
RGB filters in that camera, and their crossover points. So different
images of the comet will show a range of colors, typically from the
blue side of cyan to the green side.

Davoud:
Tonight's result with details is at
https://www.flickr.com/photos/primeval/32503667868.

palsing:
Well, I'm impressed!

\Paul A

Your kind words about my shabby little photograph are greatly
appreciated. :-)

--
I agree with almost everything that you have said and almost everything that
you will say in your entire life.

usenet *at* davidillig dawt cawm

Davoud on 18 December:
Tonight's result with details is at
https://www.flickr.com/photos/primeval/32503667868.

hleopold:
That is very nice. Is it that green in reality, or as close to reality as we
normally get?

Thank you. Good question! I did not purposely manipulate the color in
Photoshop, but it is possible that it changed slightly in stacking or
in the course of brightness and contrast adjustments (curves tool).
Most of the descriptions I have read describe the coma as being green.
But a photo that I made on 11 December looks more aqua blue than green
to my eyes: https://www.flickr.com/photos/primeval/31330206277. Take
your pick!

I haven’t had a chance to see it yet, though the weather service says that
the skies are clear, Clear Sky Chart shows no transparency and lousy seeing.
I am getting really tired of this. (N.E. Kansas)

Good luck with the waxing moon. Full moon on 22 December.

--
I agree with almost everything that you have said and almost everything that
you will say in your entire life.

usenet *at* davidillig dawt cawm

hleopold:
That is very nice. Is it that green in reality, or as close to reality as we
normally get?

Chris L Peterson:
Well, "reality" is that this isn't bright enough to stimulate color
vision, so the "real" color is gray.

What it would look like if it were brighter, or our eyes more
sensitive, isn't a simple question. The gamut of the sensor in the
camera is quite different from that of our eyes. The color is coming
from several fairly narrow emission lines produced by CN and C2. Those
lines lie in violet, blue, cyan, and green parts of the spectrum.
Because they are emission lines and not a continuum, the color that
gets rendered by any camera is very sensitive to the bandpass of the
RGB filters in that camera, and their crossover points. So different
images of the comet will show a range of colors, typically from the
blue side of cyan to the green side.

As I said! Aqua blue in one pic, green in the next. Take your pick,
flip a coin.

--
I agree with almost everything that you have said and almost everything that
you will say in your entire life.

usenet *at* davidillig dawt cawm

On Dec 19, 2018, Chris L Peterson wrote
(in ):

On Wed, 19 Dec 2018 02:13:09 -0600,
wrote:

That is very nice. Is it that green in reality, or as close to reality as we
normally get?

Well, "reality" is that this isn't bright enough to stimulate color
vision, so the "real" color is gray.

What it would look like if it were brighter, or our eyes more
sensitive, isn't a simple question. The gamut of the sensor in the
camera is quite different from that of our eyes. The color is coming
from several fairly narrow emission lines produced by CN and C2. Those
lines lie in violet, blue, cyan, and green parts of the spectrum.
Because they are emission lines and not a continuum, the color that
gets rendered by any camera is very sensitive to the bandpass of the
RGB filters in that camera, and their crossover points. So different
images of the comet will show a range of colors, typically from the
blue side of cyan to the green side.

Ah, yes, I understood most of that before I asked, but had not yet put it all
together. But that really is a beautiful green color. I know that even if I
get to see it my little 5� is never going to show much, if any, color. But
it really has to clear up someday, I hope.

--
Harry F. Leopold
The Prints of Darkness (remove gene to email)

Of course I am a Marxist, I love Groucho, Chico and Harpo! Zeppo is ok, I
guess.

On Dec 19, 2018, Davoud wrote
(in article ):

Davoud on 18 December:
Tonight's result with details is at
https://www.flickr.com/photos/primeval/32503667868.

hleopold:
That is very nice. Is it that green in reality, or as close to reality as we
normally get?

Thank you. Good question! I did not purposely manipulate the color in
Photoshop, but it is possible that it changed slightly in stacking or
in the course of brightness and contrast adjustments (curves tool).
Most of the descriptions I have read describe the coma as being green.
But a photo that I made on 11 December looks more aqua blue than green
to my eyes:https://www.flickr.com/photos/primeval/31330206277. Take
your pick!

I haven’t had a chance to see it yet, though the weather service
says that
the skies are clear, Clear Sky Chart shows no transparency and lousy seeing.
I am getting really tired of this. (N.E. Kansas)

Good luck with the waxing moon. Full moon on 22 December.

This so much reminds me of that other “Christmas Comet� back 15? years
ago. I finally got to see it, it was stated as being a bright blue. When I
did get to see it it actually was a very nice blue, with a larger scope, and
darker skies I think I might have even called it an electric blue. Of course
this is a much small, and I think, more distant comet so of course color is
going to be much fainter. (Of course I won’t even mention that the eyes are
much older as well. Oh, sorry, I did mention it.)

Always a joy to see your photos, David, I look forward to more in the future.
I mostly read here, hardly ever comment. Not to mention I am jealous of your
set-up, though not of your location, as bad as our seeing is here you have it
worse.

--
Harry F. Leopold
aa #2076
AA/Vet #4
The Prints of Darkness (remove gene to email)

Campus Crusade for Cthulhu

On Thu, 20 Dec 2018 21:15:38 -0600, hleopold
wrote:

On Dec 19, 2018, Chris L Peterson wrote

What it would look like if it were brighter, or our eyes more
sensitive, isn't a simple question. The gamut of the sensor in the
camera is quite different from that of our eyes. The color is coming
from several fairly narrow emission lines produced by CN and C2. Those
lines lie in violet, blue, cyan, and green parts of the spectrum.
Because they are emission lines and not a continuum, the color that
gets rendered by any camera is very sensitive to the bandpass of the
RGB filters in that camera, and their crossover points. So different
images of the comet will show a range of colors, typically from the
blue side of cyan to the green side.

Ah, yes, I understood most of that before I asked, but had not yet put it all
together. But that really is a beautiful green color. I know that even if I
get to see it my little 5” is never going to show much, if any, color. But
it really has to clear up someday, I hope.

Indeed, aperture is irrelevant. No amount of aperture can ever
increase the surface brightness of an extended object beyond what we
can see with our unaided eye. Given the size of this comet, it is best
viewed at low magnifications, and therefore there's no advantage to
more than just a few inches of aperture. (But aperture is critical to
good imaging, as it allows for shorter exposures and therefore a
better capture of this fast moving body.)

On Dec 21, 2018, Chris L Peterson wrote
(in ):

On Thu, 20 Dec 2018 21:15:38 -0600,
wrote:

On Dec 19, 2018, Chris L Peterson wrote

What it would look like if it were brighter, or our eyes more
sensitive, isn't a simple question. The gamut of the sensor in the
camera is quite different from that of our eyes. The color is coming
from several fairly narrow emission lines produced by CN and C2. Those
lines lie in violet, blue, cyan, and green parts of the spectrum.
Because they are emission lines and not a continuum, the color that
gets rendered by any camera is very sensitive to the bandpass of the
RGB filters in that camera, and their crossover points. So different
images of the comet will show a range of colors, typically from the
blue side of cyan to the green side.

Ah, yes, I understood most of that before I asked, but had not yet put it
all
together. But that really is a beautiful green color. I know that even if I
get to see it my little 5� is never going to show much, if any, color. But
it really has to clear up someday, I hope.

Indeed, aperture is irrelevant. No amount of aperture can ever
increase the surface brightness of an extended object beyond what we
can see with our unaided eye. Given the size of this comet, it is best
viewed at low magnifications, and therefore there's no advantage to
more than just a few inches of aperture. (But aperture is critical to
good imaging, as it allows for shorter exposures and therefore a
better capture of this fast moving body.)

I agree. As for the speed of this comet, I had noticed that in David’s 4
shot stack where he pointed out that it was not a tail but movement between
the shots. I was really surprised to see that it had moved that far in, I
believe part of a night. I realize that when they are close comets are
normally moving quite quickly. Well depending on the geometry of course. But
so surprising to actually see it in the sky, where things seldom move fast.

--
Harry F. Leopold
The Prints of Darkness (remove gene to email)

“He's so dumb he moves his lips when someone ELSE is reading.“-Doc
Smartass