My first Magazine Sky & Telescope - 04.2019 | Page 59

Going Deep by Mel Bartels
Shimmering
Clouds
Galactic cirrus is challenging
to observe, but follow
the author’s advice and
treat yourself to a special
experience.
t’s a funny position to be in, that
of observing a galaxy that I’ve seen
countless times and yet seeing it for the
fi rst time in a new light. With apologies
to Arthur Schopenhauer, I like to think
“the task is not to see what has never
been seen before, it’s instead to think
what nobody has yet thought about that
which everyone sees.”
After observing many extraordinarily
faint objects with my new 13-inch
f/3.0 high-etendue richest-fi eld tele-
scope, under the stars one gloriously
clear and transparent night I thought
to “go for broke” and try observing the
galactic cirrus near M81 and M82. To
my astonishment, upon centering the
galaxies, I could detect faint nebulosity
crisscrossing the fi eld of view. It was an
extraordinary moment — like stepping
through a door into a new universe of
observing possibilities. Shivering with
excitement, I began searching for other
signs of galactic cirrus.
Galactic cirrus lives far above and
below the galactic plane. Shining with
the refl ected light of countless millions
of stars, the cirrus forms ghostly shim-
mering arcs across the sky.
From Arndt Lattusek’s research (see
S&T: Apr. 2017, p. 30 for references), we
know the scant and forgotten history of
galactic cirrus observations. In the late
1700s William Herschel described 52
areas where he thought the sky “fl oor”
was brighter than the adjoining areas.
Austrian-born Father Johann Hagen,
fi rst Jesuit director of the Vatican
Observatory in the 1920s, observed
I
N
galactic cirrus but with many false-
positive sightings. The great French
astronomer and musician Marcel de
Kérolyr not only observed but also
photographed galactic cirrus in the
1930s. Baron Renaud de Terwangne,
an accomplished double star, lunar,
and planetary observer (his planetary
sketches are quite beautiful), began
observing extremely faint nebulous
regions in 1929. He later published a
map that illustrated his astonishing
observations showing that galactic cir-
rus forms streamers perpendicular to
the galactic plane.
p FIRST GLIMPSE It was the author’s initial
sight of galactic cirrus near M81 and M82 that
prompted his search for more. All sketches
are from the author’s logbook and feature his
handwritten notes as well as our labeling.
q WIDE FIELDS The author fi nds wide fi elds
of view particularly satisfying when viewing
galactic cirrus, as in this sketch of M101, the
Pinwheel Galaxy, in Ursa Major.
NGC 5422
NGC 5485
NGC 5473
Observing Notes
Serendipitously, the brightest galactic
cirrus shine at 24.5 mag/arcsec 2 accord-
ing to Allan Sandage (see his Astro-
nomical Journal paper from 1976), which
under very dark skies that glow at 21.5
mag/arcsec 2 yields a contrast of 5–6% to
the human eye (as calculated by [object
+ sky background] / object background).
I’ve discovered that I can observe as low
M101
NGC 5474
N
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