Sky & Telescope - October 2021 - 39

(Cramer, Philosophical Transactions of the Royal Society,
1730, volume 36, pp. 279-282)
The abbreviation " N.S. " stands for " New Style " calendar,
that is, the same Gregorian calendar that Pezenas used.
An online search turned up numerous reports of this auroral
display. I found primary sources by first consulting compilations
of historical aurora observations in publications like
those by Anders Celsius (1733), Jean Jacques d'Ortous Mairan
(1733), Hermann Fritz (1873), and Alfred Angot (1897).
For the arc observed in the southern sky on February
15, 1730, most of these accounts described the color as red,
blood-red, scarlet, crimson, or russet, with some mentions of
purple and violet hues. Many observers described the shape as
" a form like that of the rainbow " or along similar lines.
Based on reports from locations throughout Europe and
Asia, the brightness of the light, and the intensely red color,
it's clear that Pezenas did not observe the gegenschein.
Indeed, his observation may represent an early sighting of
the atmospheric phenomenon now known as STEVE (Strong
Thermal Emission Velocity Enhancement), which can appear
as a red or magenta arc in the southern sky and accompany a
more normal green aurora in the northern sky.
If Pezenas didn't discover the gegenschein, the question
still remains: Who did? Many later writers accept that famed
German explorer Alexander von Humboldt observed this elusive
glow in 1803. Based on entries in his journal from March
that year, Humboldt wrote the following description in his
monumental compilation titled Cosmos:
. . . the zodiacal light. . . . An hour after sunset it suddenly
becomes visible in great brilliancy. . . . On the 16th of
March, when the phenomenon presented itself in the
greatest splendor, a faint counter glow [ " Gegenschein " in
the original German] was visible in the east.
(Humboldt, Kosmos, Erster Band, 1845, pp. 143-144;
translated from the German)
Another account by Humboldt gives more detail regarding
the sky on the evening of March 16, 1803:
. . . the Zodiacal Light. . . . The luminous pyramid
terminated between Aldebaran and the Pleiades . . . after
7h 15m [7:15 p.m.] the luminous spindle appeared at once
in all its beauty. . . . While the light was very bright in the
west, we constantly perceived in the east . . . a whitish
light, which was also of a pyramidal form . . . this double
light in the west and the east.
(Humboldt, Monthly Notices of the Royal Astronomical
Society, 1855, volume 16, p. 17)
It's not clear what Humboldt actually saw. He described
luminous pyramids near both the western horizon and the
COMET CATCHER Of the five comets Brorsen discovered, the one
most familiar to Sky & Telescope readers is Comet 1847 V, later known as
23P/Brorsen-Metcalf. This periodic comet returned in 1919 and again in
1989, when the photo above was captured.
eastern horizon during the early evening, not near midnight
when the oval of the gegenschein is high overhead. The
astronomer Robert Roosen, an expert on night-sky glows,
completely rejects Humboldt's account as describing the
discovery of the gegenschein. Roosen points out that some
scholars were:
. . . very impressed with Humboldt's claim, primarily
because Humboldt used the word " Gegenschein " in
describing his observation. However . . . his observation
was made shortly after sunset (when the Gegenschein is of
course impossible to see) . . . Humboldt neither observed
nor suggested the existence of 'the' Gegenschein.
(Roosen, The Gegenschein, PhD thesis, University of Texas
at Austin, 1969, pp. 2-3)
A Comet Hunter Extraordinaire
Many readers will likely be familiar with Danish astronomer
Theodor Johann Christian Ambders Brorsen (1819-1895)
from his comet discoveries. Brorsen was a philosophy student
at the University of Kiel, in northern Germany, when he
discovered his first comet on February 26, 1846. Initially designated
1846 III, this object - later classified as the periodic
comet 5D/Brorsen - was observed during returns in 1857,
1868, 1873, and 1879, after which it was lost. Brorsen discovered
his second comet, 1846 VII, at Kiel on May 1, 1846.
With a growing interest in astronomy, he relocated to
Altona Observatory near Hamburg, Germany, where he discovered
comet 1847 V on July 20, 1847. This periodic comet
became known as 23P/Brorsen-Metcalf and made returns in
1919 (when it was recovered by the American astronomer Joel
sk yand tele scope .o r g * OCTOBER 2021 39
BILL & SALLY FLETCHER
http://skyandtelescope.org
Sky & Telescope - October 2021

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