Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Source of ‘Moon Curse’ Revealed by Eclipse

12.02.2014
Strange events have long been linked to nights of a full moon, though careful scrutiny dispels any association.

So, when signals bounced off the lunar surface returned surprisingly faint echoes on full moon nights, scientists sought an explanation in reason rather than superstition. Still, the most compelling evidence arrived during another event that once evoked irrational fears—on a night when Earth's shadow eclipsed the full moon.


Lunar-ranging laser illuminates a spot of high thin clouds on its way to the surface of the eclipsed moon. Image credit, Jack Dembicky, Apache Point Observatory


A laser beam from the Apache Point Observatory heads toward the moon on a nearly clear night. Image credit, Jack Dembicky, Apache Point Observatory

Tom Murphy, a physicist at UC San Diego, is among the scientists who have aimed laser beams at suitcase-sized reflectors placed on the moon by Apollo astronauts and unmanned Soviet rovers. By precisely timing the light's return to Earth, Murphy can measure the distance from here to the moon with millimeter precision.

Lunar ranging, as this is called, has revealed that the moon is slowly spiraling away from us and suggested that it has a molten core. Murphy's group is using precise measurements of the changing shape of the lunar orbit to subject Einstein's theory of general relativity to the most stringent test yet.

Murphy Does the Math
When he's not testing one theory of science's best-known genius, Tom Murphy turns his analytical mind to a different set of problems: human use of energy and our propensity toward growth.
In his blog, Do the Math, Murphy uses quantitative estimations to bring clarity to complex issues. His posts delve into questions of energy balance from the personal to galactic scales and use mathematics and physics to evaluate choices to be made as individuals and as communities.

Q&A with Tom Murphy

Over time, signals returned by the reflectors, faint to begin with, have faded. The project Murphy leads at Apache Point Observatory in New Mexico sends laser pulses of 100 quadrillion photons, of which, on average, a single lonely photon returns – if any at all. Earth's atmosphere nudges some photons off target so that they hit the lunar soil, and the reflectors slightly diffract the returning beam so that most miss the telescope when they return.

Even after accounting for these losses, Murphy's team records ten times fewer photons than they expect. And on full moon nights it's even worse, dropping to just 1 percent of the predicted performance. Other observatories are unable to detect any returned signal on full moon nights.

The team jokingly dubbed this lousy performance "the full-moon curse," Murphy says. "For a while we thought we were just victims of bad luck, but the trend continued, month after month."

Murphy thinks accumulated moon dust could account for the diminished returns, which could spell bad news for plans to place telescopes up there. Although there's no wind on the moon, electrostatic forces and a constant bombardment by tiny meteorites could have kicked up some of the lunar dust to coat the surface of the clear glass prisms arrayed in each reflector.

Light must pass through the surface of each prism twice—on the way in and on the way back out. A dusting that covers 50 percent of the glass would be enough to account for the dimming of the return signal they observe on most nights, Murphy calculates.

But something else, something in addition to simple obscuration is needed to account for the dramatic drop on full moon nights. Murphy thinks it's heat.

The prisms are sunk a bit into cylinders so that the sun only fully illuminates them when it shines straight in. Because the arrays face Earth, that only happens on full moon nights. When it does, the dark dust of the lunar regolith would heat up, setting up a thermal gradient between the surface and the depths of the prisms. That would degrade their performance by altering the refractive index, turning the prism into an unintentional lens and diverging the returning light so that even fewer photons return to the telescope.

It's a beautiful idea because it generates a thing scientists probably love most: a testable prediction. If the poor performance on full moon nights resulted from heating of the surface of the cubes, turning off the light should boost the signal as soon as the surface cools so that the temperature throughout the cubes is uniform.

All you'd have to do is turn off the Sun. Or wait for the Earth to pass between the Sun and moon, as it does during a lunar eclipse. On the night of December 21, 2010, Murphy's team was fortunate to have decent observing conditions during a lunar eclipse. For five and half hours, they ranged lasers from the three Apollo reflector arrays and a fourth mounted on a Soviet rover (once thought lost for good) as the edge of Earth's shadow passed by each in turn and as they re-emerged one-by-one into full sunlight.

As predicted, they saw a tenfold spike in performance as the celestial light switch was thrown, restoring the signal to levels they see on other nights, the team recently reported in the scientific journal Icarus.

So why, skeptics might wonder, if moon dust is moving about, can the boot prints left by astronauts decades ago still be seen? Murphy has a calculation for that too: at the rate of deposition that must have occurred to obscure the reflectors, it would take tens of thousands of years.

Susan Brown | EurekAlert!
Further information:
http://www.ucsd.edu
http://ucsdnews.ucsd.edu/feature/source_of_moon_curse_revealed_by_eclipse

More articles from Physics and Astronomy:

nachricht Shape matters when light meets atom
05.12.2016 | Centre for Quantum Technologies at the National University of Singapore

nachricht Climate cycles may explain how running water carved Mars' surface features
02.12.2016 | Penn State

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

IHP presents the fastest silicon-based transistor in the world

05.12.2016 | Power and Electrical Engineering

InLight study: insights into chemical processes using light

05.12.2016 | Materials Sciences

High-precision magnetic field sensing

05.12.2016 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>