Sky and Telescope - September 2017 - 53

Fifty miles from Wilkins' observatory in Kent, his close collaborator Patrick Moore, host of the BBC's popular
television program The Sky at Night,
kept a vigil with a 12½-inch reﬂector.
In a seemingly striking corroboration of
Wilkins' observation, Moore reported
seeing a "minute pinpoint of light" at
21:02:23 UT. "It appeared suddenly and
faded out within half a second . . . in
the Hyginus area, close to Schneckenberg." Moore cautioned that "the phenomenon was so uncertain and so close
to the limit of visibility that it seemed
unwise to trust it."
Meanwhile, at Konkoly Observatory
in Budapest, a young assistant observer
named Miklós Lovas turned a 7-inch
refractor on the Moon. Recounting the
events of that night a half century later,
he recalled:

KONKOLY OBSERVATORY / WOLBACH LIBR A RY

The Soviets had only provided the time, so
I had to ﬁt an eyepiece that allowed one to
see the whole face of the Moon. I think they
didn't even know where it would hit . . .
All of a sudden, a dark speck appeared.
The phenomenon lasted twenty minutes.
It expanded and faded slowly. At ﬁrst it
was quite dark, but it turned to gray and
was much fainter toward the end . . . The
ﬁrst detection of the speck (21h 02m 30s)
agreed well with the termination of the
radio signal of the probe (21h 02m 24s).

Lovas' slowly fading dusky cloud was
located in Palus Putredinus, on the
southeastern edge of the Mare Imbrium,
not far from the outer ramparts of the
crater Archimedes but hundreds of kilometers from the bright ﬂashes reported
by Wilkins and Moore.
Damningly, a series of photographs
taken that night through the 24-inch
refractor at Pic du Midi Observatory in
France failed to record anything out of
the ordinary. In time, Patrick Moore
would recant:
Eleven months later, when I was
in Moscow, I discussed the optical
observations with authorities at the
U.S.S.R. Academy of Sciences and studied
the other reports. They were, to put it
mildly, in violent disagreement with my

According to Hungarian observer Miklós Lovas, Luna 2's impact created a dark cloud of debris
that enlarged and dimmed for about 20 minutes. Modern impact simulations suggest such an
obvious splash would not have occurred.

observation and with each other; there
were ﬂashes, luminous glows, and dark
expanding spots dotted over a huge area
of the Moon! This conﬁrmed a view that
none of us had in fact seen the true impact.
When straining to catch a glimpse of an
excessively faint phenomenon, without
even knowing its position in advance, it is
only too easy to be deceived.

Modern-day consensus, based on
the observations of the impacts of other
spacecraft on the Moon, holds that the
crash of Luna 2 would not have been
visible against a sunlit background. The
sightings of Moore and his contemporaries are classic cases of the phenomenon that psychologists call expectation
bias, the proclivity of observers or experimenters to allow their expectations to
affect the outcome - and the tendency
to distort recalled events to make them
ﬁt expectations.
It's worth noting that the impact
sites reported by Wilkins, Moore, and
Lovas are all consistent with the rocket's initial ballistic trajectory, Jodrell
Bank's determination of its acceleration, and radio interferometry measurements of its course by Soviet tracking
stations. Although impact specialists
have grave doubts about Lovas' observation, Palus Putredinis is nonetheless
listed as the impact site of Luna 2 in
most databases.
Painstaking examination of Lunar
Reconnaissance Orbiter images has
turned up traces of 32 spacecraft or
components that have crashed into or
landed on the Moon - but the tiny
crater and ejecta blanket created by the

impact of Luna 2 remain an elusive
needle in a vast haystack.
More recently, telescopic observers
have indeed witnessed chunks of interplanetary debris crashing into the Moon.
But those impacts are much faster, and
the observed strikes have all occurred at
locations darkened by lunar night.
In three months you'll have a golden
opportunity to watch for impacts on the
unilluminated portion of the crescent Moon. In the predawn hours of
December 14th, Earth and Moon will
sweep through the stream of particles
shed by the near-Earth asteroid 3200
Phaethon during the annual Geminid
meteor shower. Cosmic shrapnel will
strike the lunar surface at roughly 36
km (22 miles) per second, an order of
magnitude faster than Luna 2 did. At
such speeds, a meteoroid with a mass
of only 5 kg can excavate a crater more
than 9 meters across and hurl 75 metric
tons of lunar soil and rock on ballistic
trajectories above the lunar surface.
The Moon will be a narrow waning
crescent only 14% illuminated. Keep a
vigil on the dim, earthlit portion of the
lunar disk, where Geminid impacts will
appear as ﬂashes of light as bright as
6th to 9th magnitude.
The Meteoroid Environment Ofﬁce
at NASA's Marshall Space Flight Center
monitors meteoroid impacts on the
Moon in collaboration with the Association of Lunar and Planetary Observers. Their websites are noted below.
¢ Contributing Editor TOM DOBBINS
has observed most reported phenomena
on the planets, both real and illusory.

* Learn more at https://is.gd/NASA_lunar_impacts & https://is.gd/ALPO_lunar_impacts.
s k y a n d t e l e s c o p e .c o m

* SEPTEMBER 2017

https://www.is.gd/NASA_lunar_impacts https://www.is.gd/ALPO_lunar_impacts http://www.skyandtelescope.com

Sky and Telescope - September 2017

Table of Contents for the Digital Edition of Sky and Telescope - September 2017