Aug 6, 1999

Peering through a Hole in the Sky





NASA/Marshall scientists will probe an unlikely 50-year old mystery during the August 11, 1999 total solar eclipse


Aug 6, 1999: UPDATE - Decrypting the Eclipse: A Solar Eclipse, Global Measurements, and a Mystery: On August 11, scientists around the world will attempt to solve a 45 year mystery: Does a solar eclipse somehow affect the Foucault pendulum? Read the follow-on story, at

"Despite its omnipresence, gravity remains the least well tested of all the fundamental forces."
                Task Group On Gravity Probe B, National Research Council, Washington, D.C. 1995

solar eclipse
June 17, 1999: On August 11, 1999, millions of people in the Northern Hemisphere will have one last chance in this millennium to marvel at a total solar eclipse. The 50 mile wide path of totality will extend from the western Atlantic ocean, through Europe and Turkey, all the way across India into the Indian Ocean. At the instant of totality viewers situated along this narrow path can glimpse some of Nature's rarest wonders -- "Bailey's Beads," diffraction bands, and, of course, the Sun's ephemeral corona.

"No matter how many total eclipses you see," says one veteran eclipse watcher, "every single one is mind-blowing."

Above: The February 16, 1999 annular solar eclipse as viewed from Western Australia. Based on images captured by Oliver Staiger. See also Links to more eclipse images.

But for at least two NASA researchers, it's not the visual fireworks that might make August 11 memorable, instead, it's the prospect of probing a 50 year old mystery. David Noever and Ron Koczor of the Marshall Space Flight Center have recently been tasked with checking some hard-to-believe measurements reported 50 years ago by Nobel laureate Maurice Allais.


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In 1959, at the enthusiastic urging of rocket pioneer Werner von Braun, a peculiar set of physics experiments first appeared in English as a four-part series in the journal Aero/Space Engineering. The author, Maurice Allais, was a skilled physicist with an interest in the behavior of Foucault's Pendulum. From 1954 to 1960 he made careful observations of the motion of glass and metallic pendulums with the hope he would discover some connection between gravity and magnetism. Despite years of careful work, he never succeeded in finding a link between those disparate forces, but he did observe something extraordinary. During the total eclipses of June 30, 1954, and October 22, 1959, he detected "anomalies in the movement of the ... pendulum" during the time when the Earth, the Moon, and the Sun were aligned.

"A remarkable disturbance has been observed at the time of the total solar eclipse--June 30, 1954. ..[which] cannot be considered as due to the disturbances of an aleatory order [chance]. "Neither can it be considered as produced by an indirect influence of known factors (temperature, pressure, magnetism, etc.). Finally, it cannot be identified with periodic lunisolar effects resulting from the actual theory of gravitation."
        Maurice Allais, 1959, from the abstract of his articles in Aero/Space Engineering

When Allais won the Nobel Prize in 1988 he revisited his experiments in his acceptance speech and again noted that the phenomena he observed was "quite inexplicable within the framework of currently accepted theories" of gravity.

click for a larger image, credit Fred Espenak
Indeed, Allais’ unsettling measurements have received little credence, despite the fact that he is a Nobel laureate. That may be because his 1988 Nobel prize is in economics, not physics! Nevertheless, he was well-known to be a skilled physicist. For his careful experiments in gravitation he won the 1959 Galabert Prize of the French Astronautical Society and the 1959 annual award from the United States Gravity Research Foundation.

Left: The August 11, 1999 solar eclipse will be visible throughout much of Europe, Pakistan, India, northeast North America and parts of Asia in the Northern Hemisphere. The path of totality is indicated by the yellow and blue line. Credit: F. Espenak, GSFC/ NASA

Allais’ solar eclipse results are hard to understand, but he was undoubtedly a meticulous scientist. His experiments were well-conceived and he repeated his measurements during two solar eclipses.



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"If something strange is happening to Foucault pendulums during solar eclipses, then it's a real mystery," says Noever. "Is it some gravitational effect, a peculiar manifestation of tides, or something else entirely? The idea that some unexplained aspect of gravity is at work seems nonsensical when you consider that it would seem to imply planets spinning out of their orbits over very long time scales (among other things). Also, why would the effect show up only during a solar eclipse? The Sun, the Moon, and the Earth are nearly aligned about once a month near the time of the new moon. A solar eclipse takes place when they are precisely aligned. If something is happening to gravity once a month, wouldn't we have noticed by now?"

"The bottom line," said Noever, "is this: It's unlikely, but Allais could have stumbled on to something important. So, rather than debate a set of 50 year old measurements we're going to roll up our sleeves and try to detect Allais’ signal directly."
The NASA/Marshall team plans to observe the August 11, 1999, solar eclipse in an unusual way, with a high precision gravitometer located at the Marshall Space Flight Center in Huntsville, AL. The gravitometer is a state-of-the-art gravity sensor tested as part of a Marshall project entitled "Ultra-high precision gravity measurements". Noever and Koczor are using this extraordinary device to carry out sensitive experiments in gravity physics at the Marshall Space Flight Center. They are also exploring the history of peer-reviewed gravity research and repeating or recasting experiments that would benefit from the high precision afforded by the gravitometer. Allais’ work falls in this group.

Above: Cutaway view of gravitometer, with magnetic, thermal and pressure shielding. The instrument reports very small changes in the gravitational force acting on a mechanical spring-mass. Gravitational changes are expressed as the electrical force (measured as voltage) required to maintain the spring-mass system at a predetermined position (the null point). The modified LaCoste-Romberg gravitometer (Edcon, Inc. Denver, CO) measures relative gravity until calibrated against a reference. The instrument is routinely calibrated along the 10-station Rocky Mountain Calibration range established by NOAA, Edcon and the Colorado School of Mines. The calibration is validated by comparing the measure of absolute gravity in Huntsville Alabama with reference values from the USAF gravity disk.

"If Allais’ disturbance is real, and if it has something to do with gravity, then we will be able to measure it to 10 significant digits," says Noever.

Routinely, Noever and Koczor have recorded the gravitational disturbance of relatively small masses moving in a terrestrial laboratory--akin to a variation of one part in a billion in the local gravity field in response to the movements of a nearby automobile. These sensitivities in mass detection are traditionally considered appropriate subjects only for studying the kinds of enormous mass flows found in stars, not the subject for thoughtful laboratory research. If Allais’ pendulum experiments prove correct, then the Marshall experiments may reveal a disturbance as high as one-thousand on their measurement scale for the instrument--a relative siren amidst the otherwise quiet background of solar and lunar influence on Earth.




Above: A typical gravitometer calibration curve showing the minute variation in relative gravity measured at two different heights, both separated by less distance than the average 1 m from floor to table top (or the equivalent altitude variation in gravity approximately 300 parts per billion in background gravity per meter of height). Reprinted from Noever, et al. Physica C, 1997.

"What we will do is what we do most weekdays," explains Noever, "that is, we'll measure the gravitational field in our lab with a precision of about 1 part in 10 billion. Our eclipse observations will be coordinated with a another research team in Denver - separated by 1500 miles and 8,000 feet in altitude. Afterwards we'll compare records and see if we detected anything unusual."

Noever and his colleagues also hope to enlist the aid of other scientists around the world with access to Foucault pendulums, to exactly reproduce Allais’ experiments on August 11. There are more than 60 Foucault pendulums located in museums and entrance halls, and thousands of amateur versions around the globe. Near the path of totality there are major Foucault pendulums at the Hall of Justice in Brussels, St Isaac's Cathedral in Leningrad, the Pantheon in Paris, and the UN Building in NY. Each one represents an opportunity to check Allais’ results.

Above: The pushpin symbols show some of the major museum and educational locations having large, publicly viewable Foucault pendulum on display in the United States.

"The most likely result of our work on August 11 is that nothing extraordinary will happen," says Noever, "but you never know. Von Braun himself and certainly Allais would have smiled to see us revisiting this mystery after 50 years."

As the famous physicist Max Planck once said, "For a theoretician really worthy of the name, it may be said in passing that nothing could be more interesting than a fact which runs counter to a theory .... for him [or her], the real work begins at that point."

Gravitometer research at the Marshall Space Flight Center is funded by the Marshall Center Director's Discretionary Fund.


Web Links


The Millennium's Last Solar Eclipse -- from Sky &Telescope

Fred Espenak's Solar Eclipse Home Page -- at the NASA/Goddard Space Flight Center

Autobiography of Maurice Allais -- Copyright ©1999 The Nobel Foundation

The Foucault Pendulum -- a excellent tutorial discussion by by Professor B. Nickel, Physics Department, University of Guelph. This web site also reviews some peculiarities in pendulum motion detected by experiments at the University of Guelph.


M. Allais, Aero/Space Engineering, Sept. 1959, p. 46-52; Aero/Space Engineering, Oct. 1959, p. 51-55; Aero/Space Engineering, Nov. 1959, p. 55; C.R.A.S. (Fr.), 247,1958, p. 1428; ibid, p. 2284; C.R.A.S. (Fr.), 248,1959, p. 764; ibid, p. 359

A partial list of gravity anomaly news and research references

Three Spacecraft Reveal Unexplained Motions -- from Newswise

The Apparent Anomalous, Weak, Long-Range Acceleration of Pioneer 10 and 11

Unexplained sunward deceleration -- Dr. John Anderson, a planetary scientist at NASA's Jet Propulsion Laboratory John D. Anderson, Philip A. Laing, Eunice L. Lau, Anthony S. Liu, Michael Martin Nieto, Slava G. Turyshev, Phys.Rev.Lett. 81 (1998) 2858-2861, reported acceleration residuals ~8(+3)x10-8 cm/s2 directed towards the Sun, or approximately 0.1 nano-g (where g=980 cm/s2 ).

Big Bang Acceleration -- Observations of supernova explosions halfway back to the Big Bang give plausible evidence that the expansion of the universe has been accelerating since that epoch, approximately 8 billion years ago and suggest that energy associated with the vacuum itself may be responsible for the acceleration. R.P. Kirshner, Harvard-Smithsonian Center for Astrophysics, Proc. Natl. Acad. Sci. 96, 4224-4227 (1999).

A possible explanation for the anomalous acceleration of Pioneer 10

More NASA Science News

The Foucault Pendulum


Right: The most famous Foucault pendulum, the original 1851 device, installed in 1995 at the Paris Pantheon.

Since its accidental discovery prior to the 1851 World’s Fair, the Foucault pendulum has become recognized as the first wholly non-astronomical demonstration of the Earth’s rotation. In brief, when a mass on a wire is set in motion over the course of hours, its azimuthal direction will rotate with the Earth’s axial spin. An especially clear demonstration would arrange a rim of sand or pegs along the periphery of the pendulum’s maximum swing--a sort of sand fortress surrounded by a moat of semi-permanent wooden soldiers. As the day progresses, each soldier gets knocked down in the path of one circular turn of the pendulum. Either at the North or South pole particularly, each mark on the full circumference would have been visited exactly once per day--a phenomenon called the Foucault effect. Amazingly, from a closed room with no outside view of any time passage, it is possible to observe the Earth’s rotation using this classical demonstration of the pendulum’s inertial interplay with the Earth’s rotation and gravity. Relative to the stars, the floor under the pendulum turns.


More on Foucault's Pendulum....
The link, above, will transport you to an excellent web site maintained by the Physics Department at the University of Guelph. It includes a historical and tutorial discussion of Foucault's pendulum and a review of some anomalies in pendulum motion measured at the University of Guelph.


Left: Starting the Foucault Pendulum in the building of the National Academy of Sciences and the National Research Council at Washington; this instrument demonstrates the rotation of the earth. (adapted from Science News and Letters, October 8, 1927 issue; Timeline Archives). In addition to showing the cumulative effects of what was then thought to be unmeasureably small Coriolis forces, Foucault’s experiments defined for the first time a terrestrial reference frame relative to the stars and thus strongly influenced the genesis of two landmark findings in physics-- Mach’s principle and Einstein’s general relativity. Whatever corrections that Allais may have observed, these cannot result from any direct consequence of general relativity--the effects of which would be an astonishingly small contribution to any pendulum acted on by lunar or solar action (100 million times too small for any influence on Allais’ observations).


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For more information, please contact:
Dr. John M. Horack , Director of Science Communications
Authors: Dr. David Noever,Dr. Tony Phillips
Curator: Linda Porter
NASA Official: Ron Koczor