Sky & Telescope - August 2020 - 25

X CELESTIAL TWISTERS This Hubble image probes the Hourglass
region in the Lagoon. One "interstellar tornado" bisects the Hourglass at
its waist, and the other constitutes its southern border. The author saw
only the central tornado. Note how nebulosity heavily obscures Her 36. A
Bok globule peeks out from the lower left corner.

ﬂowing north then curving west. The southern extension is
somewhat more chaotic in appearance but generally proceeds
south then west. This all comes together in a faint loop surrounding the dark nebula that's trying to hide Her 36.
Two "interstellar twisters," one forming the Hourglass's
southern edge and the other pinching it at the waist, are
veritable cosmic tornadoes. They appear to be physically
twisting due to temperature differences between their cores
and surfaces. That's insanely awesome and seeing even one of
them has me all ﬁred up - knowing the incredible nature of
an obscure object like this makes observing deeply gratifying.
I had every expectation the Hourglass was a bipolar
nebula. Nope, not even close - it's merely a random shape
created by several overlapping layers of dark nebulae as seen
from our vantage point. These cosmic tornadoes even play a
role in creating the deceptively regular contours.
This interplay between bright and dark nebulosity in and
around the Hourglass is hypnotic: subtle shading, gentle contours, almost imperceptibly morphing edges are everywhere.
A few big and bright stars join dozens of fainter suns.
No matter their brightness, these points of brilliance
highlight the soft glow of surrounding nebulosity and are a
reminder of the slow but staggering process of star creation.
Shock waves and gravitation ever so gradually compress
extraordinarily rariﬁed wisps of interstellar gas and dust to
the point of nuclear fusion, resulting in monster stellar furnaces like Her 36 and 9 Sgr that ionize 54 by 36 light-years of
atomic hydrogen, and making it ﬂuoresce brightly enough that
we can see it without a telescope from 4,000 light-years away.

Twister

Herschel 36

Twister

Bok globule

Absolutely stupendous, and you don't even need a telescope to start swimmin'.

Contributing Editor HOWARD BANICH could be going for a
dip right now and can be reached upon his return at hbanich@
gmail.com.
FURTHER MATERIAL: Go to https://is.gd/3Dhourglass to see
a remarkable 3D flythrough showing how the landscape of the
Hourglass is arrayed.

Gems in the Lagoon
Object

Mag(v)

Size/Sep

Dec.

Messier 8

Em. nebula / H II region

6.0

45′ × 30′

Hourglass

H II region

30″

18h 03.7m

-24° 23′

4.6

15′

18h

04.4m

-24° 23′

04.6m

-24° 07′
-24° 22′

NGC 6530

N ASA / ESA / J. TR AUG ER

Type

Open cluster

18h

03.8m

-24° 23′

Barnard 88

Dark nebula

2.0′ × 0.5′

18h

Barnard 89

Dark nebula

0.5′ × 0.5′

18h 05.0m

Barnard 296

Dark nebula

6′ × 1′

18h 04.1m

-24° 32′

9 Sagittarii

Double star

6.3, 6.8

0.02″

18h 03.9m

-24° 22′

Herschel 36

Multiple star

7.6, 7.7, 10.3

0.0″, 3.5″

18h 03.7m

-24° 23′

HD 165052

Double star

6.9

0.0″

18h

05.2m

G5.97-1.17

H II region

0.4″

18h 03.7m

-24° 24′
-24° 23′

Angular sizes and separations are from recent catalogs. Visually, an object's size is often smaller than the cataloged value and varies according to the aperture
and magnification of the viewing instrument. Right ascension and declination are for equinox 2000.0.

sk yandtelescope.org * AUGUST 2 02 0

https://www.is.gd/3Dhourglass http://www.skyandtelescope.org

Sky & Telescope - August 2020

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