My first numbered picture (37)
Last night, January 19, I was able to
get back out under the stars for a little while. There was a
waxing,gibbous moon, so faint nebulae were out; too much light
pollution. So I decided to aim for star clusters. It's also much
quicker to photograph star clusters because the “open shutter”
time is much reduced. However, I didn't realize just how much shorter
the time needed to be, as we will see below. The two targets were M34
and NGC 2169, aka the 37 cluster.
First M34. M34 is an open cluster of
stars that are estimated to be around 250 million years old and about
1500 light years away in the constellation of Perseus.
NGC 2169 is also know as the “37
cluster”. From the image, I think you can see why. It's about 3600
light years away in the constellation of Orion.
On the technical side, both images
contain a problem know as “blooming”. It shows up as a streak of
light on the brighter stars, in my case, going to the right of the
star. NGC2169 has an obvious example in the bright blue star in the
flat, upper “bar” of the 3. There is a dimmer star just above the
streak. What's going on? The photons is a digital camera are
converted to elections that are read off the CCD chip and converted
to the image we see. When too many photons land on a pixel, which is
where the conversion to elections occurs, they spill over onto the
adjacent pixel. Think of several cups on a table with the rims
touching. You pour water into the center cup, but it gets too full
and spills over into the adjacent cup and starts filling it up.
Although you didn't pour water into the adjacent cup, water ends up
in it nevertheless. That's basically, what's happening only it's
elections, not water. The cure will be to limit the exposure time to
less than the 1 minute I used for these images.
For in interesting comparison, I would
direct you to the blog of a friend of mine, Michael Covingtion. He
has recently photographed NGC 2169, but with a much wider field of
view. See:
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