Sky & Telescope - August 2020 - 24

Celestial Pool

S THE HOURGLASS Seen here is the inverted version of the author's high-power finished drawing portraying the Hourglass region. This view shows
how much dark nebulosity attenuates the light of Her 36 - the relatively faint star immediately west of the Hourglass - as compared to 9 Sgr, left
of center. These two multiple stars supply most of the energy that ionizes the Lagoon Nebula. Both this and the low-power drawing started as pencil
sketches, and the author subsequently photographed and adjusted them in GIMP to more closely portray what he saw in the eyepiece.

AUGUST 2 02 0 * SK Y & TELESCOPE

ultraviolet output. O-stars such as these are the rarest of
main sequence stars, and their energetic stellar winds are the
engines that light up H II regions like the Lagoon.

Divin' into the Hourglass
Despite its brightness, the Hourglass is frequently overlooked
- fellow observers are often surprised at the amount of detail
here when I share the view of this wondrous area. Although
not as rich as the Huygens Region in M42, it's just as much
fun to explore. But as bright as this area is, I can barely detect
a warm hue in places. No deﬁnite reddish tint like in the
Triﬁd Nebula or M42.
The Hourglass is actually a window into the interior of an
ultra-compact H II region, cataloged as G5.97-1.17, where
the nearby star Her 36 is furiously ionizing atomic hydrogen.
It's also well-deﬁned, with its two narrow ends nearly touching. In fact, only in moments of steady seeing at 408× could
I tell they weren't in contact, but now that has me rarin' to
observe this area again. The bright north and south wings of
the Hourglass have fainter extensions, with the northern wing

HOWA RD BA NICH

the seemingly unremarkable star Herschel 36 resides. But
don't let looks deceive you: Her 36 is a triple star comprising
a spectroscopic binary with O9 and B0.5 components and a
more distant O7.5 companion. Although we see their combined glow shining only at magnitude 10.3, Her 36 is considerably reddened by nebulosity. Make no mistake, this young,
monster stellar system is pumping out blistering torrents of
ultraviolet light that ionize not only the nearby Hourglass,
but also the entire western portion of the Lagoon.
The other powerhouse in the nebula, 9 Sagittarii, looks
much brighter at magnitude 6.0 and is a spectroscopic double,
with an O3.5 primary star and an O5-5.5 secondary. This
energetic pair, located just northeast of the Hourglass and
Her 36, ﬂuoresces the eastern part of the Lagoon. A third star,
HD 165052, is also a massive binary, with O6.5 and O7.5
components, and it adds to the ionization of the eastern part
of the Lagoon. But its overall contribution is fairly minor compared to 9 Sgr and Her 36. There are other bright stars in and
near the Lagoon, but these three are the ones most responsible
for sculpting and ionizing the nebulosity with their intense

Sky & Telescope - August 2020

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