Sky & Telescope - April 2020 - 45

Under the Stars by Fred Schaaf

The Great
Comet of
1970
Fifty years ago this month a
feathery visitor adorned the
spring sky.

SK Y & TELESCOPE ARCHIVES

n each Under the Sky column this
spring, I'm featuring a different
celestial wonder that I witnessed 50
years ago. The initial marvel, which
happened on March 7th that year, was
my ﬁrst total eclipse of the Sun (discussed in last month's column). But
this month's featured wonder, at its allaround best in April 1970, is what may
have been the most beautiful comet of
the 20th century.
Enter Comet Bennett. I had
recently observed my ﬁrst comet, TagoSato-Kosaka. I found this modestly
bright object by myself with both naked
eye and telescope in January 1970, the
month after my 15th birthday. That was
an incredibly thrilling and rewarding
experience. But the March 1970 issue
of Sky & Telescope soon arrived with a
brief item announcing the approach of
"Bright Comet Bennett."
Discovered at the end of December
1969 by accomplished amateur astronomer John Caister Bennett of South
Africa, Comet Bennett (C/1969 Y1, or
1969i as it was then designated) was
solely visible in the Southern Hemisphere until it sped north in its highly
inclined orbit, passing the Sun and
emerging in bright morning twilight in
March 1970.
My ﬁrst sight of Comet Bennett
came after watching in stronger and
stronger morning twilight in the hope
the comet would somehow be bright
enough to be visible with the unaided
eye when it ﬁnally rose above my
treeline to the east. I was losing hope

p BEAUTIFUL STRANGER Comet Bennett graced the spring sky 50 years ago and proved to be
one of the finest comets of the 20th century. J. U. Gunter captured this photo on the morning of
March 28, 1970.

that morning and then it appeared - a
starlike object brighter than Altair,
with an awesome similarly bright short
spike of intense tail. I didn't record
which date in late March I made that
observation, but Bennett passed perihelion, 0.54 a.u. from the Sun, on March
20th and was closest to Earth, at a
distance of 0.69 a.u., on March 26th.
On March 23rd, one observer followed
Bennett naked eye until less than 5
minutes before sunrise, and on the
28th estimated the comet as magnitude
-0.3 with 10° of tail visible even in
bright moonlight.
April's angel or sword below
Cygnus. The rapidly northbound Comet
Bennett lofted magically higher and
higher out of morning twilight like an
angel. So, April 1970 was the month
it was most splendid. Bennett sported
both dust and gas tails. The gas tail was
prominently curved and underwent dramatic changes as a strong (solar maximum) solar wind buffeted it. In telescopes, Bennett also displayed an orange
pinwheel of jets from its nucleus and,
for master comet observer John Bortle,
as many as ﬁve jets at once. What was
most beautiful about Bennett in my
4¼-inch Edmund reﬂector that month
was the silky strands of streamers in the

ﬁrst star-sprinkled several degrees of the
tail - a phenomenon the like of which
I've still never seen in any other comet
with any telescope.
John Bortle and a few other observers traced Comet Bennett's tail out
to well over 20° long. But what was
amazing to me was that Bennett's tail
wasn't at its brightest for just a few
degrees of its length, like Hale-Bopp's
and Hyakutake's. As I recall, Bennett's
tail maintained similar great intensity out to roughly 10° or 12°. In my
book Comet of the Century, I had the
following to say: "It hung breathlessly
like some vast shining swan's feather
by the graceful constellation of Cygnus the Swan; it was a snowy sword
laid in peace (but power!) near one of
the brightest parts of the Milky Way's
stream; it ﬂoated into the north circumpolar regions of Cassiopeia the Queen
to spend ever more of the night aloft."
You can stay up late these nights of
April 2020 and watch the lovely constellations Cygnus and Cassiopeia wheel
into view in the northeast. But 50 Aprils
ago, they were accompanied by the oncein-a-lifetime beauty of Comet Bennett.
¢ FRED SCHAAF welcomes your letters
and comments at fschaaf@aol.com.
sk yandtelescope.org * APRIL 2 02 0

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Sky & Telescope - April 2020

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