Sky & Telescope - November 2020 - 63

M AURY: LEIG H WILLIA MS / SCIENTIST OF THE SE A / LIBR ARY OF CONGRESS / WIKIMEDIA COMMONS / PUBLIC DOMAIN; SECCHI:
FR ATELLI D'ALESSANDRI / SMITHSONIAN INSTITUTION LIBR ARIES / WIKIMEDIA COMMONS / PUBLIC DOMAIN; MARSDEN: HOWA RD
DORWIN / CEN TER FOR ASTROPH YSICS / H A RVA RD & SMITHSONIA N; KOHOU TEK: N ASA

The Andromedids - A Checkered History
The saga of the Andromedid meteor
shower did not begin with the stupendous display of 1872.
Indeed, strong meteor showers, with
rates ranging from dozens to some 400
per hour, had been noted on December
5th, 1741; December 6th, 1798; December 7th, 1830; December 7th, 1838;
December 6th, 1847; and November
30th, 1867. Edward C. Herrick, of New
Haven, Connecticut, who was a witness to the 1838 display, was able to
cull additional observations from other
parts of Connecticut, New York, and
Georgia. He concluded that the meteors
appeared to emanate from a region of
the sky "not far from Cassiopeia; or
perhaps more nearly, from the vicinity of
the cluster in the sword of Perseus."
In 1867, Viennese astronomer
Edmund Weiss, quickly followed by
German astronomer Heinrich Louis
d'Arrest, proposed a connection
between the orbit of Biela's Comet
and these unusual late-autumn meteor
displays. But Weiss went even further,
noting in an 1868 paper published in
Astronomische Nachrichten (one of
the first international journals in the
field of astronomy) that meteor activity
produced by Biela's Comet was possible on November 28th in either 1872
or 1879.
Those who remembered his paper
were thus on high alert and carefully
monitoring the skies around the time of
the appointed night in 1872 and caught

Matthew Fontaine Maury
(1806-1873)

the magnificent meteor storm. But the
meteor show was far from over.
While nothing was seen in 1879,
several astronomers predicted a recurrence in 1885, and these predictions
were more than fulfilled. From Broughty
Ferry, Scotland, on November 27th,
James Smieton recorded a maximum
of 100 meteors per minute, most of
which "had brilliant phosphorescent
trains, which continued to glow for
several seconds after the meteors
themselves had vanished." William
F. Denning, observing from Bristol,
England, commented that observers
with especially clear skies experienced
rates of roughly 1 meteor per second,
or 3,600 per hour.
After 1885, the meteors from Biela's
Comet became much less numerous,
as the shower began to fade with the
returns of 1892 (300-700 per hour),
1899 (100 per hour), and 1904 (only 20
per hour).
Today, this once-intense shower,
which some sources refer to as the
Bielids after the parent comet, has become seemingly almost extinct. That's
primarily because the orbit of the main
stream of meteor particles was shifted
significantly after 1892 by planetary
perturbations so that it no longer crosses Earth's orbit, the gap eventually
having widened to a distance of about
0.04 a.u. As a consequence, these meteors are scarcely detectable and are
more or less widely scattered from the

Angelo Secchi
(1818-1878)

middle of November through the first
week of December, with no obvious
maximum. If any Andromedid meteors
are reported nowadays (one or two per
hour?), they might be caused by meteoroids that got separated from the main
stream. It is also quite possible that
the stream has dispersed over the last
150 years so that its density has been
significantly reduced.
Quite unexpectedly, however, on
the night of December 4, 2011, six
Canadian radar stations, which send
out pulses of radio waves that bounce
off meteor trails, detected a zenithal
hourly rate of about 50 meteors, which
marked a revival of the Andromedids,
according to astronomer Paul Wiegert
(University of Western Ontario). In modeling the 2011 shower, Wiegert traced
the meteors' origin to particles that
Biela's Comet shed in 1649, more than
a century before the comet itself was
seen. In a paper published in the March
2013 issue of the Astronomical Journal,
Wiegert and colleagues made forecasts
regarding other appearances of the
Bielid shower in the years 2000-2047
based on a numerical model. Notes Peter Brown, a coauthor of that paper: "A
shower in 2023 (Dec. 2) might yield as
many as 200 meteors an hour, surpassing the Perseids and Geminids; not a
storm, but a very strong outburst."
What more can we say? Mark your
calendars!
-Joe Rao

Brian Marsden
(1937-2010)

Luboš Kohoutek
(1935-)

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