Sky & Telescope - July 2020 - 64

Big, Bold, Bright, Beautiful

split in two by a dark lane, which is the "lagoon" in its name.
Stars are being formed here, so stick around a few dozen millennia - it will only become more impressive with time.
You can't look at the Lagoon without moving north 1.5° to
M20, the Triﬁd Nebula. Its listed magnitude of 6.3 is deceptive; this nebula is spread out enough to have a fairly low
surface brightness, but with a little aperture and/or a nebula
ﬁlter it stands right out. It, too, comes in two parts: the emission nebula with the three-vaned dark lane in front of it that
gives it its name, and a reﬂection nebula just to the north of

q M4 One of the closest and brightest globular clusters, in telescopes M4 has a distinctive string of stars running through it.
FOV=45′

that. In photographs the emission nebula is bright red while
the reﬂection nebula is pale blue, yet to the eye in a relatively
large-aperture telescope, it looks just the opposite.
Why is that? I have a theory: Because our eyes are much
more sensitive to blue-green than to red light, when we just
barely begin to perceive color we see it as green. The red
emission nebula is brighter than the blue reﬂection nebula,
so our brains interpret it as green, which makes the other
one red in comparison.
There's a bonus at the heart of the emission nebula: The
central star is a triple. Another reason to call it the Triﬁd!
Rather than continue straight up through the steam, let's
shift a little to the right to catch an underappreciated open
cluster, M23. With all the other spectacular sights around,
M23 is often overlooked, but in any other part of the sky it
would be the showcase object - and I believe it should be here,
too. M23 is a beautiful cluster, ﬁlled with streams of stars,
including one that leads to a 6.5-magnitude star at the northwest edge of the cluster. M23 is about the same size as the
Moon, so it's great in binoculars or in a telescope at low power.
But this cluster continues to reward every increase in magniﬁcation until it overﬁlls the ﬁeld of view. Spend some time here!

Celestial Creatures

16h 30m

Star magnitudes

17h 00m

16h 00m

χ
ν

2
3
4
5
6
7

OPHIUCHUS

M80

ρ
Antares

M19

-20°

-25°

τ
M62

SCORPIUS

ρ
-30°

LUPUS
χ
ε

J U LY 2 0 2 0 * S K Y & T E L E S C O P E

-35°

Diving back into the Teapot's steam we come to M24, the
Great Sagittarius Star Cloud. This is a huge patch of Milky
Way that stands out from behind the intervening dust and
gas much like Baade's Window. It's easy to spot with the
naked eye and is glorious in binoculars. In all but the widestﬁeld telescopes it extends beyond the ﬁeld of view, but that's
okay; it's great fun to drive around in this thick cloud of
stars. You'll ﬁnd two distinct dark nebulae, Barnard 92 and
Barnard 93, forming what I call the "coal miner's lungs,"
and a tiny cluster within the cluster of objects, NGC 6603.
You'll also ﬁnd an asterism that I call the Caribou. It's
made up of a couple of obvious arcs of stars that form the
rump and back and neck of the animal, with its head down
as if cropping grass, and another distinct arc of stars with
forward-facing spurs that looks for all the world like a rack
of antlers. This is one of those asterisms that you can't unsee
once you've seen it. It's not just a deer; it's a caribou!
As long as we're looking at celestial animals, let's move
on up the steam cloud to M17, the Swan Nebula. This is
a large, obvious swatch of brightness against a rich stellar
background, with a curved extension rising from its western
end. In the inverted ﬁeld of a Newtonian telescope it looks for
all the world like a duck ﬂoating on a pond. Wait . . . a duck?
Not a swan? Nope. The neck is too short to be a swan. It's a
duck. But we call it the Swan Nebula because . . . just because.
Put a nebula ﬁlter on this one and you'll see a lot more
nebulosity surrounding it. Now it's a duck in a fog bank.
Onward north and veering slightly west some 2° you'll
ﬁnd M16, the Eagle Nebula. This one looks sort of vaguely
eaglelike in photographs, but in a telescope you're just
going to see a patch of nebulosity at the northern end of an

Sky & Telescope - July 2020

Table of Contents for the Digital Edition of Sky & Telescope - July 2020