Sky & Telescope - November 2023 - 60

Face-on Splendor
only hints at all the delights that the galaxy
has to offer the observer.
When I observe M33, or any deepsky
object for that matter, as I get to
increasingly dark and transparent
skies I feel as if I'm peeling away
layers of atmosphere and light pollution.
I also envision ever larger
telescopes adding layers of detail.
Let's explore all this and more in
the next sections.
General Observing Tips
Due to its relative proximity, M33
has a large apparent diameter, yet it's a
delicate thing visually. Even under the best
observing conditions, don't expect to see much
at first. I suggest starting with your lowest magnification
and then linger. Let the subtleties
of the Triangulum Galaxy gradually
reveal themselves as you use both direct
and averted vision. If you can, sketch
what you see. Then increase the
magnification to your next most
powerful eyepiece. Add any new
details to your sketch - or memory
- and repeat this cycle with your
eyepieces until you can no longer
discern further nuances.
Next, go back to the eyepiece
that gave you the most pleasing overall
view and absorb the gentle glory of
this fascinating galaxy. This collection of
around 40 billion stars is part of the reason
M33 seems so ephemeral. Because it's so close
by and we view it mostly face-on, we can see many
of the elements that make up a typical spiral galaxy - but
we're also looking through its thinnest dimension. So, our
viewing angle, combined with the relative paucity of stars
in M33 (less than half and maybe as few as one-tenth the
Milky Way's number), gives it a low surface brightness.
Nonetheless, in a dark, transparent sky you can expect to
see wonderful things.
If you can detect 5.7-magnitude M33 naked-eye from your
observing site, you're in for a treat once you start using your
telescope. In my experience, seeing the Triangulum naked-eye
means the sky is not only dark but also very transparent. The
ease or difficulty in viewing it without optical aid is a good
way to gauge observing conditions.
On a few occasions, M33 has jumped out with direct
vision when I glanced up at its location in Triangulum, but I
usually need to use averted vision to detect it. Sometimes it's
invisible no matter how long I try to fish it out of what seems
like an excellent sky - that's a clue that atmospheric transparency
isn't as good as it might initially seem.
60 NOVEMBER 2023 * SKY & TELESCOPE
SHARED VIEWS Top: This drawing depicts the view
of M33 through my 80-mm finderscope - and is
probably quite similar to what Charles Messier
saw when he first sighted the galaxy. Neither
he nor I saw spiral structure, but the general
glow of M33 was a direct-vision sight.
DETAILS EMERGE Bottom: The sketch
shows how I saw M33 through my 8-inch
f/3.3 scope - holy cow, I'm amazed
at how much I could see! Compare this
drawing to the one made with the 30-inch
scope (on page 58), and although most of
the details in that sketch aren't visible here,
the overall spiral structure is spectacular.
Notice near the end of the northern spiral arm
how prominent the H II region NGC 604 is, even
if I didn't mention it in my observing notes.
Through the Finderscope
A few years ago, I added a zoom eyepiece (8-mm
to 24-mm) to my 80-mm finder. By modifying
the magnification I can use the 80-mm
finderscope as a regular telescope.
From my moderately light-polluted
backyard and with direct vision,
M33 through the 80-mm looks like
a rather large and subtle oval mist
with indistinct edges. There are a
few field stars scattered around it,
and the inner portion of the galaxy
is slightly brighter than the rest.
As it turns out, my view is similar
to what Charles Messier saw when he
logged M33 in 1764 with a 3-inch f/4
refractor, an instrument nearly identical
to my finder. Here are his notes:
The nebula is of a whitish light of almost even density [of
brightness], however a little brighter along two-third [sic] of its
diameter, & contains no star. One sees it with difficulty with an
ordinary telescope of 1-foot [FL].
In fact, it seems that Messier wasn't the first to view M33
in a telescope. It turns out that Giovanni Battista Hodierna
was probably the first to see it using a Galilean refractor at
20× sometime before 1654.
In my finderscope under a dark sky, Messier's " whitish
light " is bright and obvious, as I noted:
This is a fun view to sketch - M33 as seen through my 80-mm
finder! M33 looks like an oval smudge, slightly brighter in its
center, and with indefinite perimeter that fades imperceptibly
into the dark. I can't see any trace of the spiral arms, even with
the zoom eyepiece cranked up to full magnification (37.5×).
M33 is set in a lovely star field and (is within) a quadrangle of
stars that are the brightest in the FOV. Beautiful! 21.37 SQM.
https://www.nsf.gov/ https://www.nsf.gov/ https://www.nsf.gov/
Sky & Telescope - November 2023

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