Salutations celestial sight seers!
I'm David Fuller, welcome to Eyes on the Sky; what's up this week?
NGC stands for “New General Catalog” - a “new” compilation of deep sky objects
collected oh-so-recently IN... 1888.
I know, that doesn't exactly make it “new” does it?
The Danish-Irish astronomer John Dreyer amassed 5,840 objects into his new catalog that, in
all fairness, was updating John Herschel's General Catalog.
Dreyer published two subsequent updates followed, first with 1,520 objects in 1895 and the next
with an additional 3,866 obects in 1908; these were published as the “Index Catalog”
or IC list of objects.
Let's look at two this week from the NGC and IC catalogs.
Start at Altair in Aquila, and follow the “spine” of the eagle in the direction
of Scutum and Sagittarius to locate 3.4 magnitude Delta Aquilae.
From there, look west towards Cebelrai in Ophiuchus that we observed a few weeks ago,
though we won't actually be going that far.
It happens to be the next fairly bright star that direction, and as you can see, the sky
looks somewhat blank here, yet there's actually three constellations – Aquila, Serpens and
Ophiuchus.
But the fifth magnitude double star of Theta Serpentis is along the way, and being that
dim, some observers will need help getting there.
So use binoculars or a moderate to large finderscope, center Delta Aquilae, and find this pattern
of 6-th and 7-th magnitude stars nearby.
Using the closest ones to Delta – these two – draw a line from them, through Delta,
and move your telescope in that direction.
You'll move a FULL field of view away, slightly more than 7 degrees, to get to Theta Serpentis.
And while you're there, stop and take a look through your telescope at these stars that
are separated by about 22 arc seconds.
A nice double star!
I'll have more information Theta Serpentis at Eyes on the Sky dot com, and more after
this.
Dark Sky Fact: Be nice to your neighbors!
IF you do need to use light at night, aim it down, and most importantly - shield it!
Parshields are an effective and inexpensive way to ensure floodlight illumination is directed
only where it's needed.
Back at the finderscope, locate a right angle shape created by Theta, these two sixth magnitude
stars – one of which is 64 Serpentis - and this sixth magnitude star, that lies somewhat
along the line of our original direction.
Generally move that way, though slightly north of the line made by Theta and that single
star.
Go less than a full finder's field of view – just about 5 degrees – and locate four
stars of 6-th magnitude that are in a slightly curved line.
Split the difference between the middle two, and center your telescope outside the radius
of the curve that they make, slightly north.
This is IC 4756, a lovely, and HUGE open cluster.
Rich field, short focal length telescopes with the widest possible telescopic field
of view are best here, as the stars seem to go beyond it's designated 52 arc minutes of
diameter, which is nearly a full degree.
But if you can't get a 1.5 to 2 degree field with your scope and eyepieces that's ok, slowly
sweep your telescope back and forth; you'll see the wonderful density of stars inside,
as well as edges of the starfield, and be able to take in most of the 80 to 100 stars
visible in a telescope.
This cluster contains about twice that many stars, but seeing half of them is pretty good.
Our next stop takes us to a smaller cluster, but is perhaps even prettier to view.
Continue with your finder in the same general direction, and look for this 5.7 magnitude
star 3 degrees from IC 4756.
Right next to this star in the same telescopic field of view is NGC 6633, a cluster that
spans 27 arc minutes, or about half the size of IC 4756.
However, this cluster is a bit brighter, and somewhat more compact, so while not containing
as many stars, it seems brighter and is easier to frame at the eyepiece.
It's also easier to see in a finderscope.
Look for more information on these clusters and finding them at eyes on the sky dot com.
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Keep your eyes on the sky and your outdoor lights aimed down, so we can all see, what's
up.
I'm David Fuller, wishing you clear and dark skies.