Any
seasoned observer knows that Spring is galaxy season. The skies are rich with bright galaxies, and armed with a 6”
telescope the best and brightest can be enjoyed. With our club’s 14” scope (RASC Windsor), most of the fainter NGC list can be
picked off, too. Uranometria 2000 lists
over 26,000 galaxies and/or galaxy clusters in its charts, a daunting task for
any one person to observe or photograph.
Until summer constellations begin to rise later in the night, there is
not much to see in the way of clusters.
In a future Spring post, I would like to discuss in greater detail some of the galaxy
wonders of Leo, and not just the one famous triplet, but a number of other
“triplets” as well.
This time, however, I am turning to a pair of globular clusters, one of them a
highlight of the entire flock.
Uranometria 2000 plots 170 globulars, including those inside the
Magellenic Clouds. I’m not certain how
many are observable from northern latitudes, but it seems reasonable to assume that
observing the entire viewable list is not too daunting a task. We all know that the summer sky is crowded
with globulars, though after seeing too many in short order they can tend to
look somewhat similar, at least in smaller scopes.
If you did not
catch the recent Hubble view of M5 published in APOD on April 25th,
you should stop reading now and go take a look ("Astronomy Picture of the Day). Hubble’s view of M5 is the perfect image of this object type, and
the image we are all seeking when we go to the eyepiece, whether with a 6”
mirror or a 36”. I am convinced that
globular clusters alone are responsible for most of us wanting bigger and
bigger mirrors at our disposal.
M5
is not well placed in early spring skies, but a worthy competitor is. M3 (gc 5272) is one of the finest globulars
in the sky, and makes a very refreshing sight after viewing so many
galaxies. Finding M3 is easy. Locate Arcturus, and then nearby Eta (just
south preceding it, mag. 2.5). Make
Arcturus and Eta the east-west baseline for a right-angle triangle, shooting
north twice the distance of that baseline (see map, below: note M53 is also
shown, but is not part of this discussion).
At a visual mag. of 6.3, even in binoculars M3 is impressive. It resolves nicely in a 6” mirror, and in my
12” at 170x I’m beginning to get that Hubble feeling. The main body spreads out over 18’, though outliers go well
beyond. The brightest star is mag.
12.7, so in a really dark sky smaller scopes will partially resolve this
cluster nicely.
By
comparison, the second globular is much harder to see and resolve. GC 5466 can be located 25’ following M3, and
looks impressive enough on paper. Its
combined visual mag. is 9.2. However,
it is spread out over 9’ and the brightest star is only mag. 13.8. In a great sky this one is barely visible in
a 6” scope, and I have swept past it with the 12”. Once located, it provides another wonderful lesson in
interstellar distances. In the larger
scope the centre shows a slow burn, rather than the hot intensity of M3. Resolution of stars is more ephemeral. Patience is needed to begin to see the
wonders of this large but very faint object.
Still, it is a gem and would be worth a trek to the club observatory’s
14” to see. In fact, it would be better
to begin with gc 5466, as our observatory scope will track right to it. After observing the fainter object for a
time with different eyepieces, moving to M3 will be guaranteed to give the
viewer a rush.
Amidst
a night of viewing Spring galaxies, I always enjoy stopping for a break and viewing
these two globulars. Even after dozens
of times I still enjoy the contrast and quiet spectacle they provide.
Mapman Mike
No comments:
Post a Comment