SMART-1’s First Image of the Moon

Image credit: ESA
ESA’s SMART-1 captured its first close-range images of the Moon this January, during a sequence of test lunar observations from an altitude between 1000 and 5000 kilometres above the lunar surface.

SMART-1 entered its first orbit around the Moon on 15 November 2004. It has spent the two months following spiralling down to the Moon and testing its array of instruments.

The first four days after being captured by the lunar gravity were very critical. There had been the risk, being in an ‘unstable’ trajectory, of escaping the Moon’s orbit or crashing onto the surface. Because of this, the electric propulsion system (or ‘ion engine’) started a thrust to stabilise the capture.

The ion engine was switched on until 29 December, allowing SMART-1 to make ever-decreasing loops around the Moon. The engine was switched off between 29 December and 3 January 2005 to allow scientists to start observations. At this point, the AMIE camera took the close-up lunar images. The engine was switched off again to optimise fuel consumption on 12 January, and SMART-1 will spend until 9 February making a medium resolution survey of the Moon, taking advantage of the favourable illumination conditions.

ESA’s SMART-1 Project Scientist Bernard Foing said “A sequence of test lunar observations was done in January at distances between 1000 and 5000 kilometres altitude, when the electric propulsion was paused. We are conducting more survey test observations until the electric propulsion resumes from 9 February to spiral down further towards the Moon. SMART-1 will arrive on 28 February at the initial orbit with altitudes between 300 and 3000 kilometres to perform the first phase of nominal science observations for five months.”

The first close-up image shows an area at lunar latitude 75? North with impact craters of different sizes. The largest crater shown here, in the middle left of the image, is Brianchon. The second largest, at the bottom of the image, is called Pascal.

At low illumination angles, the crater shadows allow scientists to derive the height of crater rims.

“This image was the first proof that the AMIE camera is still working well in lunar orbit,” says AMIE Principal Investigator Jean-Luc Josset of Space-X.

The composite images shown here were created to show larger-scale features. The first mosaic shows the complex impact crater Pythagoras and the strip of images (bottom) was produced from images taken consecutively along one orbit.

Starting with this mosaic, SMART-1 scientists expect to build up a global medium-resolution context map, where high-resolution images later observed from lower altitude can be integrated.

Original Source: ESA News Release

Experiments Chosen For Lunar Orbiter

NASA has selected six proposals to provide instrumentation and associated exploration/science measurement investigations for the Lunar Reconnaissance Orbiter (LRO), the first spacecraft to be built as part of the Vision for Space Exploration.

The LRO mission is scheduled to launch in the fall of 2008 as part of NASA’s Robotic Lunar Exploration Program. The mission will deliver a powerful orbiter to the vicinity of the moon to obtain measurements necessary to characterize future robotic and human landing sites. It also will identify potential lunar resources and document aspects of the lunar radiation environment relevant to human biological responses.

Proposals were submitted to NASA in response to an Announcement of Opportunity released in June 2004. Instrumentation provided by these selected measurement investigations will be the payload of the mission scheduled to launch in October 2008.

“The payload we have selected for LRO builds on our collective experience in remote sensing of the Earth and Mars,” said NASA’s Deputy Associate Administrator for the Science Mission Directorate, Dr. Ghassem Asrar. “The measurements obtained by these instruments will characterize in unprecedented ways the moon’s surface and environment for return of humans in the next decade,” he added.

“LRO will deliver measurements that will be critical to the key decisions we must make before the end of this decade,” said NASA’s Associate Administrator for the Exploration Systems Mission Directorate, Craig Steidle. “We are extremely excited by this innovative payload, and we are confident it will fulfill our expectations and support the Vision for Space Exploration,” Steidle added.

“The instruments selected for LRO represent an ideal example of a dual use payload in which exploration relevance and potential scientific impact are jointly maximized,” NASA’s Chief Scientist, Dr. Jim Garvin said. “I am confident LRO will discover a ‘new moon’ for us, and in doing so shape our human exploration agenda for our nearest planetary neighbor for decades to come,” he said.

The selected proposals will conduct Phase A/B studies to focus on how proposed hardware can best be accommodated, completed, and delivered on a schedule consistent with the mission timeline. An Instrument Preliminary Design Review and Confirmation for Phase C Review will be held at the completion of Phase B.

Selected investigations and principal investigators:

“Lunar Orbiter Laser Altimeter (LOLA) Measurement Investigation” – principal investigator Dr. David E. Smith, NASA Goddard Space Flight Center (GSFC), Greenbelt, Md. LOLA will determine the global topography of the lunar surface at high resolution, measure landing site slopes and search for polar ices in shadowed regions.

“Lunar Reconnaissance Orbiter Camera” (LROC) – principal investigator Dr. Mark Robinson, Northwestern University, Evanston, Ill. LROC will acquire targeted images of the lunar surface capable of resolving small-scale features that could be landing site hazards, as well as wide-angle images at multiple wavelengths of the lunar poles to document changing illumination conditions and potential resources.

“Lunar Exploration Neutron Detector” (LEND) – principal investigator Dr. Igor Mitrofanov, Institute for Space Research, and Federal Space Agency, Moscow. LEND will map the flux of neutrons from the lunar surface to search for evidence of water ice and provide measurements of the space radiation environment which can be useful for future human exploration.

“Diviner Lunar Radiometer Experiment” – principal investigator Prof. David Paige, UCLA, Los Angeles. Diviner will map the temperature of the entire lunar surface at 300 meter horizontal scales to identify cold-traps and potential ice deposits.

“Lyman-Alpha Mapping Project” (LAMP) – principal investigator Dr. Alan Stern, Southwest Research Institute, Boulder, Colo. LAMP will observe the entire lunar surface in the far ultraviolet. LAMP will search for surface ices and frosts in the polar regions and provide images of permanently shadowed regions illuminated only by starlight.

“Cosmic Ray Telescope for the Effects of Radiation” (CRaTER) – principal investigator Prof. Harlan Spence, Boston University, Mass. CRaTER will investigate the effect of galactic cosmic rays on tissue-equivalent plastics as a constraint on models of biological response to background space radiation.

The LRO project is managed by GSFC. Goddard will acquire the launch system and spacecraft, provide payload accommodations, mission systems engineering, assurance, and management. For information about NASA and agency programs on the Internet, visit:

http://www.nasa.gov

Original Source: NASA News Release

SMART-1 Goes Into Lunar Orbit

Image credit: ESA
ESA?s SMART-1 is successfully making its first orbit of the Moon, a significant milestone for the first of Europe’s Small Missions for Advanced Research in Technology (SMART) spacecraft.

A complex package of tests on new technologies was successfully performed during the cruise to the Moon, while the spacecraft was getting ready for the scientific investigations which will come next. These technologies pave the way for future planetary missions.

SMART-1 reached its closest point to the lunar surface so far – its first ?perilune? ? at an altitude of about 5000 kilometres at 18:48 Central European Time (CET) on 15 November.

Just hours before that, at 06:24 CET, SMART-1?s solar-electric propulsion system (or ?ion engine?) was started up and is now being fired for the delicate manoeuvre that will stabilise the spacecraft in lunar orbit.

During this crucial phase, the engine will run almost continuously for the next four days, and then for a series of shorter burns, allowing SMART-1 to reach its final operational orbit by making ever-decreasing loops around the Moon. By about mid-January, SMART-1 will be orbiting the Moon at altitudes between 300 kilometres (over the lunar south pole) and 3000 kilometres (over the lunar north pole), beginning its scientific observations.

The main purpose of the first part of the SMART-1 mission, concluding with the arrival at the Moon, was to demonstrate new spacecraft technologies. In particular, the solar-electric propulsion system was tested over a long spiralling trip to the Moon of more than 84 million kilometres. This is a distance comparable to an interplanetary cruise.

For the first time ever, gravity-assist manoeuvres, which use the gravitational pull of the approaching Moon, were performed by an electrically propelled spacecraft. The success of this test is important to the prospects for future interplanetary missions using ion engines.

SMART-1 has demonstrated new techniques for eventually achieving autonomous spacecraft navigation. The OBAN experiment tested navigation software on ground computers to determine the exact position and velocity of the spacecraft using images of celestial objects taken by the AMIE camera on SMART-1 as references. Once used on board future spacecraft, the technique demonstrated by OBAN will allow spacecraft to know where they are in space and how fast they are moving, limiting the need for intervention by ground control teams.

SMART-1 also carried out deep-space communication tests, with the KaTE and RSIS experiments, consisting of testing radio transmissions at very high frequencies compared to traditional radio frequencies. Such transmissions will allow the transfer of ever-increasing volumes of scientific data from future spacecraft. With the Laser Link experiment, SMART-1 tested the feasibility of pointing a laser beam from Earth at a spacecraft moving at deep-space distances for future communication purposes.

During the cruise, to prepare for the lunar science phase, SMART-1 made preliminary tests on four miniaturised instruments, which are being used for the first time in space: the AMIE camera, which has already imaged Earth, the Moon and two total lunar eclipses from space, the D-CIXS and XSM X-ray instruments, and the SIR infrared spectrometer.

In all, SMART-1 clocked up 332 orbits around Earth. It fired its engine 289 times during the cruise phase, operating for a total of about 3700 hours. Only 59 kilograms of xenon propellant were used (out of 82 kilograms). Overall, the engine performed extremely well, enabling the spacecraft to reach the Moon two months earlier than expected.

The extra fuel available also allowed the mission designers to significantly reduce the altitude of the final orbit around the Moon. This closer approach to the surface will be even more favourable for the science observations that start in January. The extra fuel will also be used to boost the spacecraft back into a stable orbit, after six months of operations around the Moon, in June, if the scientific mission is extended.

Original Source: ESA News Release

SMART-1 Nearly Captured By the Moon

Image credit: ESA
From 10 to 14 October the ion engine of ESA?s SMART-1 carried out a continuous thrust manoeuvre in a last major push that will get the spacecraft to the Moon capture point on 13 November.

SMART-1, on its way to the Moon, has now covered more than 80 million kilometres. Its journey started on 27 September 2003, when the spacecraft was launched on board an Ariane 5 rocket from Europe?s spaceport in Kourou, French Guiana. Since then, it has been spiralling in progressively larger orbits around Earth, to eventually be captured by the lunar gravity and enter into orbit around the Moon in November this year.

The SMART-1 mission was designed to pursue two main objectives. The first is purely technological: to demonstrate and test a number of space techniques to be applied to future interplanetary exploration missions. The second goal is scientific, mainly dedicated to lunar science. It is the technology demonstration goal, in particular the first European flight test of a solar-powered ion engine as a spacecraft?s main propulsion system, that gave shape to the peculiar route and duration (13 months) of the SMART-1 journey to the Moon.

The long spiralling orbit around Earth, which is bringing the spacecraft closer and closer to the Moon, is needed for the ion engine to function and be tested over a distance comparable to that a spacecraft would travel during a possible interplanetary trip. The SMART-1 mission is also testing the response of a spacecraft propelled by such an engine during gravity-assisted manoeuvres. These are techniques currently used on interplanetary journeys, which make use of the gravitational pull of celestial objects (e.g. planets) for the spacecraft to gain acceleration and reach its final target while saving fuel.

In SMART-1?s case, the Moon?s gravitational pull has been exploited in three ‘lunar resonance’ manoeuvres. The first two successfully took place in August and September 2004. The last resonance manoeuvre was on 12 October, during the last major ion engine thrust, which lasted nearly five days, from 10 to 14 October. Thanks to this final thrust, SMART-1 will make two more orbits around Earth without any further need to switch on the engine, apart from minor trajectory correction if needed. The same thrust will allow the spacecraft to progressively fall into the natural sphere of attraction of the Moon and start orbiting around it from 13 November, when it is 60 000 kilometres from the lunar surface.

SMART-1 will reach its first perilune (initial closest distance from the lunar surface) on 15 November, while the ion engine is performing its first and major thrust in orbit around the Moon. After that it will continue orbiting around the Moon in smaller loops until it reaches its final operational orbit (spanning between 3000 and 300 kilometres over the Moon?s poles) in mid-January 2005. From then, for six months Smart-1 will start the first comprehensive survey of key chemical elements on the lunar surface and will investigate the theory of how the Moon was formed.

Original Source: ESA News Release

Blue Moon on July 31

When you hear someone say “Once in a Blue Moon?” you know what they mean: Rare. Seldom. Maybe even absurd. After all, when was the last time you saw the moon turn blue?

On July 31st, you should look, because there’s going to be a Blue Moon.

According to modern folklore, a Blue Moon is the second full moon in a calendar month. Usually months have only one full moon, but occasionally a second one sneaks in. Full moons are separated by 29 days, while most months are 30 or 31 days long; so it is possible to fit two full moons in a single month. This happens every two and a half years, on average.

July has already had one full moon on July 2nd. The next, on July 31st, is by definition a Blue Moon.

But will it really be blue? Probably not. The date of a full moon, all by itself, doesn’t affect the moon’s color. The moon on July 31st will be pearly-gray, as usual. Unless….

There was a time, not long ago, when people saw blue moons almost every night. Full moons, half moons, crescent moons–they were all blue, except some nights when they were green.

The time was 1883, the year an Indonesian volcano named Krakatoa exploded. Scientists liken the blast to a 100-megaton nuclear bomb. Fully 600 km away, people heard the noise as loud as a cannon shot. Plumes of ash rose to the very top of Earth’s atmosphere. And the moon turned blue.

Krakatoa’s ash is the reason. Some of the ash-clouds were filled with particles about 1 micron (one millionth of a meter) wide–the right size to strongly scatter red light, while allowing other colors to pass. White moonbeams shining through the clouds emerged blue, and sometimes green.

Blue moons persisted for years after the eruption. People also saw lavender suns and, for the first time, noctilucent clouds. The ash caused “such vivid red sunsets that fire engines were called out in New York, Poughkeepsie, and New Haven to quench the apparent conflagration,” according to volcanologist Scott Rowland at the University of Hawaii.

Other less potent volcanos have turned the moon blue, too. People saw blue moons in 1983, for instance, after the eruption of the El Chichon volcano in Mexico. And there are reports of blue moons caused by Mt. St. Helens in 1980 and Mount Pinatubo in 1991.

The key to a blue moon is having in the air lots of particles slightly wider than the wavelength of red light (0.7 micron)–and no other sizes present. This is rare, but volcanoes sometimes spit out such clouds, as do forest fires:

“On September 23, 1950, several muskeg fires that had been quietly smoldering for several years in Alberta suddenly blew up into major–and very smoky–fires,” writes physics professor Sue Ann Bowling of the University of Alaska. “Winds carried the smoke eastward and southward with unusual speed, and the conditions of the fire produced large quantities of oily droplets of just the right size (about 1 micron in diameter) to scatter red and yellow light. Wherever the smoke cleared enough so that the sun was visible, it was lavender or blue. Ontario and much of the east coast of the U.S. were affected by the following day, but the smoke kept going. Two days later, observers in England reported an indigo sun in smoke-dimmed skies, followed by an equally blue moon that evening.”

In the western U.S., there will be wildfires burning on July 31st. If any of those fires produce ash or oily-smoke containing lots of 1-micron particles, the Blue Moon there could be blue.

More likely, it’ll be red. Ash and dust clouds thrown into the atmosphere by fires and storms usually contain a mixture of particles with a wide range of sizes. Most are smaller than 1 micron, and they tend to scatter blue light. This kind of cloud makes the Moon turn red; indeed, red Blue Moons are far more common than blue Blue Moons.

Absurd? Yes, but that’s what a Blue Moon is all about. Step outside at sunset on July 31st, look east, and see for yourself.

Original Source: NASA Science Article

Decreasing Earthshine Could Be Tied to Global Warming

Image credit: BBSO
Scientists who monitor Earth’s reflectance by measuring the moon’s “earthshine” have observed unexpectedly large climate fluctuations during the past two decades. By combining eight years of earthshine data with nearly twenty years of partially overlapping satellite cloud data, they have found a gradual decline in Earth’s reflectance that became sharper in the last part of the 1990s, perhaps associated with the accelerated global warming in recent years. Surprisingly, the declining reflectance reversed completely in the past three years. Such changes, which are not understood, seem to be a natural variability of Earth’s clouds.

The May 28, 2004, issue of the journal Science examines the phenomenon in an article, “Changes in Earth’s Reflectance Over the Past Two Decades,” written by Enric Palle, Philip R. Goode, Pilar Montaes Rodriguez, and Steven E. Koonin. Goode is distinguished professor of physics at the New Jersey Institute of Technology (NJIT), Palle and Monta=F1es Rodr=EDguez are postdoctoral associates at that institution, and Koonin is professor of theoretical physics at the California Institute of Technology. The observations were conducted at the Big Bear Solar Observatory (BBSO) in California, which NJIT has operated since 1997 with Goode as its director. The National Aeronautics Space Administration funded these observations.

The team has revived and modernized an old method of determining Earth’s reflectance, or albedo, by observing earthshine, sunlight reflected by the Earth that can be seen as a ghostly glow of the moon’s “dark side”-or the portion of the lunar disk not lit by the sun. As Koonin realized some 14 years ago, such observations can be a powerful tool for long-term climate monitoring. “The cloudier the Earth, the brighter the earthshine, and changing cloud cover is an important element of changing climate,” he said.

Precision earthshine observations to determine global reflectivity have been under way at BBSO since 1994, with regular observations commencing in late 1997.

“Using a phenomenon first explained by Leonardo DaVinci, we can precisely measure global climate change and find a surprising story of clouds. Our method has the advantage of being very precise because the bright lunar crescent serves as a standard against which to monitor earthshine, and light reflected by large portions of Earth can be observed simultaneously,” said Goode. “It is also inexpensive, requiring only a small telescope and a relatively simple electronic detector.”

By using a combination of earthshine observations and satellite data on cloud cover, the earthshine team has determined the following:

Earth’s average albedo is not constant from one year to the next; it also changes over decadal timescales. The computer models currently used to study the climate system do not show such large decadal-scale variability of the albedo.

The annual average albedo declined very gradually from 1985 to 1995, and then declined sharply in 1995 and 1996. These observed declines are broadly consistent with previously known satellite measures of cloud amount.

The low albedo during 1997-2001 increased solar heating of the globe at a rate more than twice that expected from a doubling of atmospheric carbon dioxide. This “dimming” of Earth, as it would be seen from space, is perhaps connected with the recent accelerated increase in mean global surface temperatures.

2001-2003 saw a reversal of the albedo to pre-1995 values; this “brightening” of the Earth is most likely attributable to the effect of increased cloud cover and thickness.

These large variations, which are comparable to those in the earth’s infrared (heat) radiation observed in the tropics by satellites, comprise a large influence on Earth’s radiation budget.

“Our results are only part of the story, since the Earth’s surface temperature is determined by a balance between sunlight that warms the planet and heat radiated back into space, which cools the planet,” said Palle. “This depends upon many factors in addition to albedo, such as the amount of greenhouse gases (water vapor, carbon dioxide, methane) present in the atmosphere. But these new data emphasize that clouds must be properly accounted for and illustrate that we still lack the detailed understanding of our climate system necessary to model future changes with confidence.”

Goode says the earthshine observations will continue for the next decade. “These will be important for monitoring ongoing changes in Earth’s climate system. It will also be essential to correlate our results with satellite data as they become available, particularly for the most recent years, to form a consistent description of the changing albedo. Earthshine observations through an 11-year solar cycle will also be important to assessing hypothesized influences of solar activity on climate.”

Monta=F1es Rodr=EDguez says that to carry out future observations, the team is working to establish a global network of observing stations. “These would allow continuous monitoring of the albedo during much of each lunar month and would also compensate for local weather conditions that sometimes prevent observations from a given site.”

BBSO observations are currently being supplemented with others from the Crimea in the Ukraine, and there will soon be observations from Yunnan in China, as well. A further improvement will be to fully automate the current manual observations. A prototype robotic telescope is being constructed and the team is seeking funds to construct, calibrate, and deploy a network of eight around the globe.

“Even as the scientific community acknowledges the likelihood of human impacts on climate, it must better document and understand climate changes,” said Koonin. “Our ongoing earthshine measurements will be an important part of that process.”

Original Source: Caltech News Release

Smart 1 Reaches its 250th Orbit

Image credit: ESA
ESA’s SMART-1 spacecraft has just made its 250th orbit, in good health and with all functions performing nominally.

Starting on 24 February 2004, operation of the electric propulsion system (‘ion engine’) was resumed. The engine is being turned on at the lowest point of every orbit for about 1.5 hours.

The spacecraft then entered a ‘season’ of long eclipses, due to the alignment of the Sun and Earth.

This was not necessarily a problem except that, due to a combination of factors (the position of the shadow of Earth, the inclination of spacecraft orbit and its orbital velocity), the spacecraft travelled at its slowest through a relatively large full shadow (umbra) region.

When the spacecraft is in the umbra it cannot receive light on its solar panels to produce power.

The eclipse season is now over, with the last eclipse on 21 March. The longest period of darkness was on 13 March, lasting for 2 hours and 15 minutes. This tested the power system and, in particular the batteries, to the limit but the spacecraft performed excellently.

ESA’s flight control team and the power specialists watched the spacecraft behaviour carefully during this period, but the power and the thermal control systems were able to cope with ‘long night’ without problem. Now SMART-1 can restart its journey to the Moon.

Original Source: ESA News Release

There Might Not Be Ice at the Moon’s Pole

Image credit: Cornell University

At the South Pole of the Moon, there is a region that is always in the shadow of craters which scientists have long believed could have deposits of water ice. Despite the fact that ice was detected by two spacecraft that orbited the moon, a new survey of the area by the giant Arecibo radio observatory has failed to find any surface deposits of ice. This doesn’t mean that the ice isn’t there, but it might be trapped in a large area under the surface, like lunar permafrost. Arecibo is a good instrument for detecting ice because it gives a very specific echo signature in the radio spectrum.

Despite evidence from two space probes in the 1990s, radar astronomers say they can find no signs of thick ice at the moon’s poles. If there is water at the lunar poles, the researchers say, it is widely scattered and permanently frozen inside the dust layers, something akin to terrestrial permafrost.

Using the 70-centimeter (cm)-wavelength radar system at the National Science Foundation’s (NSF) Arecibo Observatory, Puerto Rico, the research group sent signals deeper into the lunar polar surface — more than five meters (about 5.5 yards) — than ever before at this spatial resolution. “If there is ice at the poles, the only way left to test it is to go there directly and melt a small volume around the dust and look for water with a mass spectrometer,” says Bruce Campbell of the Center for Earth and Planetary Studies at the Smithsonian Institution.

Campbell is the lead author of an article, “Long-Wavelength Radar Probing of the Lunar Poles,” in the Nov. 13, 2003, issue of the journal Nature . His collaborators on the latest radar probe of the moon were Donald Campbell, professor of astronomy at Cornell University; J.F. Chandler of Smithsonian Astrophysical Observatory; and Alice Hine, Mike Nolan and Phil Perillat of the Arecibo Observatory, which is managed by the National Astronomy and Ionosphere Center at Cornell for the NSF.

Suggestions of lunar ice first came in 1996 when radio data from the Clementine spacecraft gave some indications of the presence of ice on the wall of a crater at the moon’s south pole. Then, neutron spectrometer data from the Lunar Prospector spacecraft, launched in 1998, indicated the presence of hydrogen, and by inference, water, at a depth of about a meter at the lunar poles. But radar probes by the 12-cm-wavelength radar at Arecibo showed no evidence of thick ice at depths of up to a meter. “Lunar Prospector had found significant concentrations of hydrogen at the lunar poles equivalent to water ice at concentrations of a few percent of the lunar soil,” says Donald Campbell. “There have been suggestions that it may be in the form of thick deposits of ice at some depth, but this new data from Arecibo makes that unlikely.”

Says Bruce Campbell, “There are no places that we have looked at with any of these wavelengths where you see that kind of signature.”

The Nature paper notes that if ice does exist at the lunar poles it would be considerably different from “the thick, coherent layers of ice observed in shadowed craters on Mercury,” found in Arecibo radar imaging. “On Mercury what you see are quite thick deposits on the order of a meter or more buried by, at most, a shallow layer of dust. That’s the scenario we were trying to nail down for the moon,” says Bruce Campbell. The difference between Mercury and the moon, the researchers say, could be due to the lower average rate of comets striking the lunar surface, to recent comet impacts on Mercury or to a more rapid loss of ice on the moon.

What makes the lunar poles good cold traps for water is a temperature of minus 173 degrees Celsius (minus 280 degrees Fahrenheit). The limb of the sun rises only about two degrees above the horizon at the lunar poles so that sunlight never penetrates into deep craters, and a person standing on the crater floor would never see the sun. The Arecibo radar probed the floors of two craters in permanent shadow at the lunar south pole, Shoemaker and Faustini, and, at the north pole, the floors of Hermite and several small craters within the large crater Peary. In contrast, Clementine focused on the sloping walls of Shackleton crater, whose floor can’t be “seen” from Earth. “There is a debate on how to interpret data from a rough, tilted surface,” says Bruce Campbell.

The Arecibo radar probe is a particularly good detector of thick ice because it takes advantage of a phenomenon known as “coherent backscatter.” Radar waves can travel long distances without being absorbed in ice at temperatures well below freezing. Reflections from irregularities inside the ice produce a very strong radar echo. In contrast, lunar soil is much more absorptive and does not give as strong a radar echo.

Original Source: Cornell News Release

Brightest Full Moon this Year


Image credit: NASA
The full moon on February 27 is going to be the brightest one of 2002. The moon’s orbit isn’t a perfect circle; over the course of its 28-day trip around the Earth, its distance varies from 406,700 km to 356,400. And today’s full moon happens to coincide with the closest point of that orbit, making it 20% brighter than an average full moon.

A pale ray of light shines through the bedroom window. In the distance, something howls. Eyes open. The clock ticks, it’s 2 a.m.. You’re wide awake — roused by a bright full Moon.

Don’t be surprised if this soon happens to you. The Moon will become full on Feb. 27th. It happens every 29.5 days, yet this full Moon is special: It’s the biggest and brightest of the year.

“Not all full Moons are alike,” says astronomy professor George Lebo. “Sometimes pollution or volcanic ash shades them with interesting colors. Sometimes haloes form around them — a result of ice crystals in the air.”

“This full Moon is unique in another way,” he says. “It will be closer to Earth than usual.”

Right: The apparent size of the Moon at perigee (top) and apogee (bottom).

“The moon’s orbit around our planet is not a perfect circle,” Lebo explains. “It’s an ellipse.” At one end of the ellipse (called apogee) the Moon lies 406,700 km from Earth. At the other end (called perigee) the Moon is only 356,400 km away — a difference of 50 thousand km!

When the Moon is full on Feb. 27th it will be near perigee — close to Earth. As a result the Moon will appear 9% wider than normal and shine 20% brighter.

The extra moonlight is caused, in part, by the Moon’s nearness to Earth. But that’s not all. The Sun is closer to Earth, too. Lebo explains: “Every year during northern winter, Earth is about 1.6% closer to the Sun than normal. (Like the Moon’s orbit around Earth, Earth’s orbit around the Sun is elliptical. Our closest approach to the Sun is called perihelion.) The Moon reflects sunlight, so the Moon is brighter during that time.”

This effect should not to be confused with the famous “Moon Illusion” — a trick of the eye that makes Moons rising near the horizon appear swollen. The nearby full Moon this week really will be bigger and brighter.

Below: The brightness of full Moons in 2002 relative to that of an average full Moon. In Feb., for example, the Moon will be 20% brighter than average; in Aug. it will be 12% dimmer. These values take into account the varying distances of the Moon from Earth and of the Earth from the Sun.

The first three full Moons of 2002 are all brighter-than-average. All three happen when the Moon is near perigee, and when Earth is relatively close to the Sun. Full Moons later this year will be smaller and dimmer by comparison. For example, August’s full Moon — an “apogee Moon” — will be about one-third dimmer than February’s.

But will anyone notice the difference?

“The human eye can easily discern a 20 or 30% difference in the brightness of two similar light sources,” says eye doctor Stuart Hiroyasu. By that reckoning, a sky watcher could tell the difference between a bright perigee Moon and a dimmer apogee Moon. But the two Moons would have to be side by side to effect the comparison — not likely except in a science fiction movie!

Below: Our Moon’s appearance changes nightly. This time-lapse sequence (Credit: Ant?nio Cidad?o) shows what our Moon looks like during a lunation, a complete lunar cycle. [more]

Even the dimmest full Moons are very bright, notes Lebo. They outshine Sirius, the brightest star in the sky, by twenty-five thousand times. They cast shadows, and provide enough light to read by. “There’s really no such thing as a faint full Moon. It’s all relative.”

Nevertheless, some sky watchers will sense that this Moon has something “extra” — particularly northerners. Many northern landscapes in February remain covered with snow. Snow reflects about two-thirds of the light that hits it, while bare ground reflects only about 15%. A snowy moonlit landscape always seems remarkably bright.

Perigee, perihelion, snowy terrain — they all add up to a big dose of Moonlight. Can you tell the difference? There’s only one way to find out: Go outside and look!

Original Source: NASA Science Story

Moon Could Still Have Molten Interior

Astronomers have calculated that the Moon, pulled by the gravity of the Earth and the Sun, may bulge as much as 10 centimetres over the course of its 27 day journey around our planet. The bulging could be caused by a molten slush surrounding the Moon’s core. The measurements were gathered by firing a laser pulse from the Earth to the Moon, and it measures the round-trip distance to an accuracy of 2 centimetres.