Sky & Telescope - May 2021 - 26

One-hit Wonders

Far Out

13h 00m

12h 30m

12h 00m

Star magnitudes

Our next target
M64
is the tiny 16thCOMA
+20°
BERENICES
magnitude galaxy
LEO
M85
Kiso 5639,
which lies in the
M100
M88
M98
far southeastern
M99 HD 107170 β
corner of Ursa
ε
Major. In fact,
M87
3
it's so small that
+10°
4
ο
it was only ﬁrst
M49
5
detected in a sur6
VIRGO
ν
vey for emission7
M61
line galaxies in
the early 1980s.
To locate Kiso 5639, start at the rearmost leg of the Great
Bear and its naked-eye paw stars Nu (ν) and Xi (ξ) Ursae
Majoris. From there slide 5° east to 6th-magnitude 62 UMa.
At 73×, my nearly 1° ﬁeld can encompass this star, the
interacting galaxy pair NGC 3786 and NGC 3788 (Arp 294)
only 26′ to its west-northwest, and the location of Kiso 5639
just 41′ to its north. Even at 153×, however, all I can ﬁnd at
Kiso 5639's location is a 3′-wide, nearly equilateral triangle
of magnitude 10.1, 12.2, and 12.5 stars. Only after I increase
the magniﬁcation to 322× can I intermittently detect a stellar
spot 1′ east-northeast of the magnitude-12.2 star.
Kiso 5639 is also classiﬁed as a tadpole galaxy, and it isn't
hard to see why in the HST image on page 25. There it displays
a thick but faint streak 22″ long running east to west with
a high surface brightness H II/SFR on its eastern end. So it
turns out I'm not seeing the tadpole's " body " at all. Instead,
I'm glimpsing the massive H II region forming its " head "
- an astounding fact given that the galaxy lies 80 million
light-years away!
Our next target is one of the brightest spirals in the Virgo
Cluster and probably the most frequently observed galaxy
on our tour. That doesn't necessarily mean, however, that
you've noticed the star-forming region that it harbors! To ﬁnd
Messier 99, start at 2nd-magnitude Denebola in the tail of
Leo and slide 6.5° east to the 5.1-magnitude star 6 Comae Berenices. You'll ﬁnd the galaxy lies just 50′ southeast of 6 Comae
and in the same ﬁeld as the 6.5-magnitude star HD 107170.
At 73× in my 10-inch, the galaxy is a soft, 4′-wide glow
with a bright, offset center that gradually brightens to a
starlike core. With averted vision I can detect two of its
three strongest spiral arms at this magniﬁcation. At 153×,
after moving HD 107170 out of the ﬁeld, I can trace its
asymmetrical southern arm until it starts curving north. I
can also see a 13.5-magnitude star 2′ to the galaxy's southeast and a 14.1-magnitude star to its northeast. Upping the
magniﬁcation to 264×, the spiral arms become very tenuous,
but a nonstellar spot is now noticeable with averted vision
1.8′ east of the core.
Cataloged HK 1 in a 1983 paper by astronomers Paul
Hodge and Robert Kennicutt, this is a remarkable H II/SFR
26

M AY 2 0 2 1 * S K Y & T E L E S C O P E

SX M99 (Top) The only Messier object in our collection, M99 is a grand
design spiral, displaying long and clearly defined spiral arms, akin to
our own Milky Way. You'll find this galaxy in Coma Berenices, in the
northwestern corner of the Virgo Cluster. (Above) Using his 25-inch f/4
reflector, French amateur Bertrand Laville was able to easily see M99's
three largest arms and HK 1, shown also in the HST image at right.

Deep South
To ﬁnd our next galaxy, we need to travel far below the celestial equator into northern Centaurus. NGC 5398 lies about
6° southeast of the bright galaxy M83, but it's best found by
star-hopping north 3.5° from 2nd-magnitude Theta (θ) Centauri. Be forewarned, though: I found this to be the hardest
galaxy on our tour because of its low altitude, lack of nearby
bright stars, and low surface brightness.
With a nearly 1° ﬁeld at 73× in my 10-inch, I'm able to
ﬁnd the correct location with the aid of a ½°-wide Digitized
Sky Survey image (like the one on page 28), but the galaxy
remains invisible. By using a little more magniﬁcation (91×)

M 9 9: A DA M BLOCK / M OUN T LEM M ON SK YCEN TER /
UNIV ERSIT Y OF A RIZON A / SK E TCH: BERTR A ND L AVILLE

simply because it appears nonstellar despite being at a distance of nearly 50 million light-years. In fact, I was surprised
by how easy it was to see on my ﬁrst attempt and have since
estimated its magnitude at 15.2. Mysteriously, Lord Rosse
only drew HK 1 as a star on a drawing he made after turning
his 72-inch reﬂector to the galaxy in 1846.

Sky & Telescope - May 2021

Table of Contents for the Digital Edition of Sky & Telescope - May 2021