ASTRO: Palomar 8

Palomar 8 is a dim globular in Sagittarius almost 42,000 light years
distant and 18,000 light-years from the center of the galaxy. That
means we have to look clear across the disk of our galaxy to see it
through all the dust that blocks our view. Fortunately, in this
particular direction the dust isn't too thick and we can see it in
ordinary light though greatly dimmed. It's diameter is stated to be
about 13.5 minutes of arc across but I can see only the center 5 minutes
of that in my image. Beyond that the stars are lost in the dense star
field of the Milky Way. The cluster was discovered in 1952 by George Abell.

This one is well below my 15 degree south limit. Seeing rarely allows
me to go this low, especially in 2012 but one night it did -- but not
for long and in a twilight sky. It was about to vanish into my Meridian
Tree so I had only a very short window. I grabbed 2 luminance frames
and one for each color hoping to get more luminance but the tree won.
It isn't getting taller very fast but is getting wider. I'm not sure
which is worse. Thanks to twilight the background was 10 times normal
limiting how deep I could go but considering how many stars I did
capture maybe that wasn't such a bad thing.

When I first looked at the data I was going to give up and try again
this year but usable seeing this low is very rare and my window very
small thanks to the Meridian Tree blocking much of the best seeing and
least atmospheric extinction. So I gave it a try. To get enough data I
combined all 5 frames into a pseudo luminance image. With only 10
minutes of color and with blue very poor in signal to noise ratio due to
being so low in the sky the color is rather questionable. I tried to
compensate for reddening both from looking so low in the sky and for all
the galactic dust we look through to see this cluster but blue was so
weak this didn't work very well. So I had to compromise and sort of
compensate for the reddening. This weak data required about every trick
I have in my bag of tricks and one new one I developed on the fly. The
new one was how to deal with the elongation of the stars in the
luminance image due to color dispersion this low in the sky. Pure RGB
would avoid this issue but requires far more time than I had available.
I surprised myself on how good it turned out. This would have been
spectacular if much higher in the sky and under a dark sky rather than
twilight.

This is the last of the Palomar globulars for me. 6, 9 and 12 are even
further south than 8. Too far for the walls of the observatory as well
as trees even if seeing would cooperate. At least I got a dozen of the 15.

14" LX200R @ f/10, Pseudo L=2Lx10'+1 each x 10' RGB, RGB=1x10',
STL-11000XM, Paramount ME

Rick
--
Prefix is correct. Domain is arvig dot net

Rick,

even though it is obscured your image clearly shows that this is a globular
and not an open cluster.
Nice one.

Stefan

"Rick Johnson" schrieb im Newsbeitrag
...

Palomar 8 is a dim globular in Sagittarius almost 42,000 light years
distant and 18,000 light-years from the center of the galaxy. That
means we have to look clear across the disk of our galaxy to see it
through all the dust that blocks our view. Fortunately, in this
particular direction the dust isn't too thick and we can see it in
ordinary light though greatly dimmed. It's diameter is stated to be
about 13.5 minutes of arc across but I can see only the center 5 minutes
of that in my image. Beyond that the stars are lost in the dense star
field of the Milky Way. The cluster was discovered in 1952 by George Abell.

This one is well below my 15 degree south limit. Seeing rarely allows
me to go this low, especially in 2012 but one night it did -- but not
for long and in a twilight sky. It was about to vanish into my Meridian
Tree so I had only a very short window. I grabbed 2 luminance frames
and one for each color hoping to get more luminance but the tree won.
It isn't getting taller very fast but is getting wider. I'm not sure
which is worse. Thanks to twilight the background was 10 times normal
limiting how deep I could go but considering how many stars I did
capture maybe that wasn't such a bad thing.

When I first looked at the data I was going to give up and try again
this year but usable seeing this low is very rare and my window very
small thanks to the Meridian Tree blocking much of the best seeing and
least atmospheric extinction. So I gave it a try. To get enough data I
combined all 5 frames into a pseudo luminance image. With only 10
minutes of color and with blue very poor in signal to noise ratio due to
being so low in the sky the color is rather questionable. I tried to
compensate for reddening both from looking so low in the sky and for all
the galactic dust we look through to see this cluster but blue was so
weak this didn't work very well. So I had to compromise and sort of
compensate for the reddening. This weak data required about every trick
I have in my bag of tricks and one new one I developed on the fly. The
new one was how to deal with the elongation of the stars in the
luminance image due to color dispersion this low in the sky. Pure RGB
would avoid this issue but requires far more time than I had available.
I surprised myself on how good it turned out. This would have been
spectacular if much higher in the sky and under a dark sky rather than
twilight.

This is the last of the Palomar globulars for me. 6, 9 and 12 are even
further south than 8. Too far for the walls of the observatory as well
as trees even if seeing would cooperate. At least I got a dozen of the 15.

14" LX200R @ f/10, Pseudo L=2Lx10'+1 each x 10' RGB, RGB=1x10',
STL-11000XM, Paramount ME

Rick
--
Prefix is correct. Domain is arvig dot net