It’s nearly summer solstice for us in the Northern Hemisphere. This solstice occurs at the instant the sun reaches its most northerly point on the celestial sphere, the imaginary sphere of stars surrounding Earth. If you stood inside the Stonehenge monument on the day of the northern summer solstice, facing north-east through the entrance towards a rough hewn stone outside the circle – known as the Heel Stone – you would see the sun rise above the Heel Stone, as illustrated in the image below.

In 2013, summer solstice for the Northern Hemisphere (winter solstice for the Southern Hemisphere) will take place on June 21, 2013, 5:04 UTC (12:04 a.m. CDT in the United States)

Everything you need to know: June solstice 2013

View of the Heel Stone at summer solstice sunrise, as seen from inside the Stonehenge monument. Image Credit: Stonehenge: Hele and Station Stones

In the northern hemisphere at this time of year, the sun is shining on us most directly at midday. Except at high northerly latitudes, above the Arctic Circle – where daylight is continuous for many months – the day on which the summer solstice occurs is the day of the year with the longest period of daylight. Meanwhile, it is the shortest day for Earth’s Southern Hemisphere.

At the northern summer solstice – always around June 20 – the sun’s path stops moving northward in the sky. For us in the northern hemisphere, it’s the day on which the days stop growing longer and will soon begin to shorten again. For this reason, in festivals and celebrations across this hemisphere of Earth, the summer solstice is a time of celebration.

Stonehenge is tied to the winter solstice, too. At Stonehenge in England on the day of the northern winter solstice (always around December 20), people watch as the sun sets in the midst of three great stones – known as the Trilithon – consisting of two large vertical stones supporting a third, horizontal stone across the top.

In the case of Stonehenge, this great Trilithon faces outwards from the center of the monument, with its smooth flat face turned toward the midwinter sun. In fact, the primary axes of Stonehenge seems to have been carefully aligned on a sight-line pointing to the winter solstice sunset.

This Stonehenge monument – built in 3,000 to 2,000 BC – shows how carefully our ancestors watched the sun. Astronomical observations such as these surely controlled human activities such as the mating of animals, the sowing of crops and the metering of winter reserves between harvests. Stonehenge is perhaps the most famous of of the ancient astronomical monuments found around the world.

When Stonehenge was first opened to the public it was possible to walk among the stones – even climb on them.

The stones were roped off in 1977 as a result of serious erosion. Today, visitors to the monument are not permitted to touch the stones, but, if you go, you will be able to walk around the monument from a short distance away. Visitors can also make special bookings to access the stones throughout the year.

EarthSky Facebook friend Buddy Puckhaber of South Carolina took this photo of Stonehenge in the early morning, while visiting. He said, “My wife and I were among the first visitors of the day.” Thank you, Buddy! Used with permission.

Another beautiful shot of Stonehenge from our friend Buddy Puckhaber. Used with permission. Thank you, Buddy.

Bottom line: If you stood inside the Stonehenge monument on the day of the northern summer solstice, facing north-east through the entrance towards a rough hewn stone outside the circle – known as the Heel Stone – you would see the sun rise above the Heel Stone, as illustrated in the image below. This year’s June solstice comes on June 21, 2013, 5:04 UTC (12:04 a.m. CDT in the United States). That means that if you live in western North America or Hawaii, the exact time of this solstice falls on the evening of June 20, for you.

The winter solstice as seen from Stonehenge

This is a reduced version of panorama from NASA’s Mars rover Curiosity with 1.3 billion pixels in the full-resolution version. It shows Curiosity at the “Rocknest” site where the rover scooped up samples of windblown dust and sand. Curiosity used three cameras to take the component images on several different days between Oct. 5 and Nov. 16, 2012. Click here to explore this image with pan and zoom controls.. Image credit: NASA/JPL-Caltech/MSSS

The first NASA-produced view from the surface of Mars larger than one billion pixels stitches together nearly 900 exposures taken by cameras onboard Curiosity and shows details of the landscape along the rover’s route.

The 1.3-billion-pixel image is available for perusal with pan and zoom tools by clicking here.

The full-circle scene surrounds the site where Curiosity collected its first scoops of dusty sand at a windblown patch called “Rocknest,” and extends to Mount Sharp on the horizon.

“It gives a sense of place and really shows off the cameras’ capabilities,” said Bob Deen of the Multi-Mission Image Processing Laboratory at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “You can see the context and also zoom in to see very fine details.”

Deen assembled the product using 850 frames from the telephoto camera of Curiosity’s Mast Camera instrument, supplemented with 21 frames from the Mastcam’s wider-angle camera and 25 black-and-white frames — mostly of the rover itself — from the Navigation Camera. The images were taken on several different Mars days between Oct. 5 and Nov. 16, 2012. Raw single-frame images received from Curiosity are promptly posted on a public website. Mars fans worldwide have used those images to assemble mosaic views, including at least one gigapixel scene.

The new mosaic from NASA shows illumination effects from variations in the time of day for pieces of the mosaic. It also shows variations in the clarity of the atmosphere due to variable dustiness during the month while the images were acquired.

NASA’s Mars Science Laboratory project is using Curiosity and the rover’s 10 science instruments to investigate the environmental history within Gale Crater, a location where the project has found that conditions were long ago favorable for microbial life.

Malin Space Science Systems, San Diego, built and operates Curiosity’s Mastcam. JPL, a division of the California Institute of Technology in Pasadena, manages the project for NASA’s Science Mission Directorate in Washington and built the Navigation Camera and the rover.

Via NASA/JPL

Spring floods across the Midwest are expected to contribute to a very large and potentially record-setting 2013 Gulf of Mexico “dead zone,” according to a University of Michigan ecologist and colleagues who released their annual forecast today, along with one for the Chesapeake Bay.

The Gulf forecast, one of two announced by the National Oceanic and Atmospheric Administration, calls for an oxygen-depleted, or hypoxic, region of between 7,286 and 8,561 square miles, which would place it among the 10 largest on record.

The low end of the forecast range is well above the long-term average and would be roughly equivalent to the size of Connecticut, Rhode Island and the District of Columbia combined. The upper end would exceed the largest ever reported (8,481 square miles in 2002) and would be comparable in size to New Jersey.

An oxygen-starved hypoxic zone, commonly called a dead zone and shown in red, forms each summer in the Gulf of Mexico. Fish and shellfish either leave the oxygen-depleted waters or die, resulting in losses to commercial and sports fisheries. Credit: NOAA

Farmland runoff containing fertilizers and livestock waste, some of it from as far away as the Corn Belt, is the main source of the nitrogen and phosphorus that cause the annual Gulf of Mexico hypoxic zone. In its 2001 and 2008 action plans, the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force, a coalition of federal, state and tribal agencies, set the goal of reducing the five-year running average areal extent of the Gulf hypoxic zone to 5,000 square kilometers (1,950 square miles) by 2015.

Little progress has been made toward that goal. Since 1995, the Gulf dead zone has averaged 5,960 square miles, an area roughly the size of Connecticut.

“The size of the Gulf dead zone goes up and down depending on that particular year’s weather patterns. But the bottom line is that we will never reach the action plan’s goal of 1,950 square miles until more serious actions are taken to reduce the loss of Midwest fertilizers to the Mississippi River system, regardless of the weather,” said U-M aquatic ecologist Donald Scavia, director of the Graham Sustainability Institute, who contributes to both the Gulf and Chesapeake Bay forecasts.

This year’s Chesapeake Bay forecast calls for a smaller-than-average dead zone in the nation’s biggest estuary. The forecast from Scavia and University of Maryland researchers has three parts: a prediction for the mid-summer volume of the low-oxygen hypoxic zone, one for the mid-summer oxygen-free anoxic zone, and a third that is an average value for the entire summer season.

The forecast calls for a mid-summer hypoxic zone of 1.46 cubic miles, a mid-summer anoxic zone of 0.26 to 0.38 cubic miles, and a summer average hypoxia of 1.108 cubic miles, all at the low end of previously recorded dead zones. Last year, the mid-summer hypoxic zone was 1.45 cubic miles. Because of the shallow nature of large parts of the estuary, the forecast focuses on water volume expressed in cubic miles instead of surface area in square miles.

Farmland runoff containing fertilizers and livestock waste, some of it from as far away as the Corn Belt, is the main source of the nitrogen and phosphorus that cause the annual Gulf of Mexico “dead zone.” Image credit: Donald Scavia

The annual Gulf forecast is prepared by researchers at U-M, Louisiana State University and the Louisiana Universities Marine Consortium. The Bay forecast is provided by U-M and the University of Maryland’s Center for Environmental Science. Both studies are funded by NOAA.

The forecasts are based on nutrient runoff and river-and-stream data from the U.S. Geological Survey, which are then fed into computer models developed with funding from NOAA’s National Centers for Coastal Ocean Science.

“Monitoring the health and vitality of our nation’s oceans, waterways and watersheds is critical as we work to preserve and protect coastal ecosystems,” said Kathryn Sullivan, acting undersecretary of commerce for oceans and atmosphere and acting NOAA administrator. “These ecological forecasts are good examples of the critical environmental intelligence products and tools that help shape a healthier coast, one that is so inextricably linked to the vitality of our communities and our livelihoods.”

Floods inundated much of the Midwest this spring. Several states, including Minnesota, Wisconsin, Illinois and Iowa, had spring seasons that ranked among the 10 wettest on record. Iowa had its wettest spring on record, with 17.61 inches of precipitation, according to the National Climatic Data Center.

Nutrient-rich runoff from those farming states ends up in the Mississippi River and eventually makes its way to the Gulf. The amount of nitrogen entering the Gulf of Mexico each spring has increased by about 300 percent since the 1960s, mainly due to increased agricultural runoff.

According to U.S. Geological Survey estimates, 153,000 metric tons of nutrients flowed down the Mississippi and Atchafalaya rivers to the northern Gulf in May 2013, an increase of 94,900 metric tons over last year’s drought-reduced 58,100 metric tons. The 2013 input is 16 percent higher than the average nutrient load estimated over the past 34 years.

In the Gulf and the Bay, the nutrient-rich waters fuel explosive algae blooms. When the algae die and sink, bottom-dwelling bacteria decompose the organic matter, consuming oxygen in the process. The result is a low-oxygen (hypoxic) or oxygen-free (anoxic) region in the bottom and near-bottom waters: the dead zone.

Fish and shellfish either leave the oxygen-depleted waters or die, resulting in losses to commercial and sports fisheries. In the Gulf, the dockside value of commercial fisheries was $629 million in 2009, and nearly 3 million recreational anglers contributed more than $1 billion to the region’s economy.

Chesapeake Bay dead zones, which have been highly variable in recent years, threaten a multi-
year effort to restore the bay’s water quality and to enhance its production of crabs, oysters and other fisheries. The Geological Survey estimates that 36,600 metric tons of nitrogen entered the estuary from the Susquehanna and Potomac rivers from January through May, which is 30 percent below the average loads estimated between 1990 and 2013.

The final Chesapeake Bay measurement will be released in October following surveys by the Maryland Department of Natural Resources and the Virginia Department of Environmental Quality.

The 2013 Gulf estimate is based on the assumption of no significant tropical storms in the two weeks preceding or during the official measurement survey cruise scheduled from July 25 to Aug. 3. If a storm does occur, the size estimate could drop to a low of 5,344 square miles, slightly smaller than Connecticut.

Last year’s Gulf dead zone was the fourth-smallest on record, due to drought conditions, and covered about 2,889 square miles, an area slightly larger than Delaware.

Via University of Michigan

Earth is the ocean planet, and 75% of our world is a relatively unchanging ocean of blue. But the remaining 25% of Earth’s surface is a dynamic green. Data from the NASA/NOAA Suomi NPP satellite is able to detect these subtle differences in greenness. Satellite data from April 2012 to April 2013 was used to generate these animations and images.

The resources on this page highlight our ever-changing planet, using highly detailed vegetation index data from the satellite, developed by scientists at NOAA. The darkest green areas are the lushest in vegetation, while the pale colors are sparse in vegetation cover either due to snow, drought, rock, or urban areas.

By Avi Roy. Re-posted with permission from The Conversation.

In rich countries, more than 80% of the population today will survive past the age of 70. About 150 years ago, only 20% did. In all this while, though, only one person lived beyond the age of 120*. This has led experts to believe that there may be a limit to how long humans can live.

Animals display an astounding variety of maximum lifespan ranging from mayflies and gastrotrichs, which live for 2 to 3 days, to giant tortoises and bowhead whales, which can live to 200 years. The record for the longest living animal belongs to the quahog clam, which can live for more than 400 years.

If we look beyond the animal kingdom, among plants the giant sequoia lives past 3,000 years, and bristlecone pines reach 5,000 years. The record for the longest living plant belongs to the Mediterranean tapeweed, which has been found in a flourishing colony estimated at 100,000 years old.

Some animals like the hydra and a species of jellyfish may have found ways to cheat death, but further research is needed to validate this.

The natural laws of physics may dictate that most things must die. But that does not mean we cannot use nature’s templates to extend healthy human lifespan beyond 120 years.

“110 and still going strong.” Image by Nuno Cruz.

Hayflick limit and telomeres: Putting the lid on the can

Gerontologist Leonard Hayflick at the University of California thinks that humans have a definite expiry date. In 1961, he showed that human skin cells grown under laboratory conditions tend to divide approximately 50 times before becoming senescent, which means no longer able to divide. This phenomenon that any cell can multiply only a limited number of times is called the Hayflick limit.

Since then, Hayflick and others have successfully documented the Hayflick limits of cells from animals with varied life spans, including the long-lived Galapagos turtle (200 years) and the relatively short-lived laboratory mouse (3 years). The cells of a Galapagos turtle divide approximately 110 times before senescing, whereas mice cells become senescent within 15 divisions.

The Hayflick limit gained more support when Elizabeth Blackburn and colleagues discovered the ticking clock of the cell in the form of telomeres. Telomeres are repetitive DNA sequence at the end of chromosomes which protects the chromosomes from degrading. With every cell division, it seemed these telomeres get shorter. The result of each shortening was that these cells were more likely to become senescent.

Other scientists used census data and complex modelling methods to come to the same conclusion: that maximum human lifespan may be around 120 years. But no one has yet determined whether we can change the human Hayflick limit to become more like long-lived organisms such as the bowhead whales or the giant tortoise.

What gives more hope is that no one has actually proved that the Hayflick limit actually limits the lifespan of an organism. Correlation is not causation. For instance, despite having a very small Hayflick limit, mouse cells typically divide indefinitely when grown in standard laboratory conditions. They behave as if they have no Hayflick limit at all when grown in the concentration of oxygen that they experience in the living animal (3-5% versus 20%). They make enough telomerase, an enzyme that replaces degraded telomeres with new ones. So it might be that currently the Hayflick “limit” is more the Hayflick “clock”, giving readout of the age of the cell rather than driving the cell to death.

The trouble with limits

The Hayflick limit may represent an organism’s maximal lifespan, but what is it that actually kills us in the end? To test the Hayflick limit’s ability to predict our mortality we can take cell samples from young and old people and grow them in the lab. If the Hayflick limit is the culprit, a 60-year-old person’s cells should divide far fewer times than a 20-year-old’s cells.

But this experiment fails time after time. The 60-year-old’s skin cells still divide approximately 50 times – just as many as the young person’s cells. But what about the telomeres: aren’t they the inbuilt biological clock? Well, it’s complicated.

When cells are grown in a lab their telomeres do indeed shorten with every cell division and can be used to find the cell’s “expiry date.” Unfortunately, this does not seem to relate to actual health of the cells.

It is true that as we get older our telomeres shorten, but only for certain cells and only during certain time. Most importantly, trusty lab mice have telomeres that are five times longer than ours but their lives are 40 times shorter. That is why the relationship between telomere length and lifespan is unclear.

Apparently using the Hayflick limit and telomere length to judge maximum human lifespan is akin to understanding the demise of the Roman empire by studying the material properties of the Colosseum. Rome did not fall because the Colosseum degraded; quite the opposite in fact, the Colosseum degraded because the Roman Empire fell.

Within the human body, most cells do not simply senesce. They are repaired, cleaned or replaced by stem cells. Your skin degrades as you age because your body cannot carry out its normal functions of repair and regeneration.

Can we substantially increase our lifespans?

If we could maintain our body’s ability to repair and regenerate itself, could we substantially increase our lifespans? This question is, unfortunately, vastly under-researched for us to be able to answer confidently. Most institutes on aging promote research that delays onset of the diseases of aging and not research that targets human life extension.

Those that look at extension study how diets like calorie restriction affect human health or the health impacts of molecules like resveratrol derived from red wine. Other research tries to understand the mechanisms underlying the beneficial effects of certain diets and foods with hopes of synthesising drugs that do the same. The tacit understanding in the field of gerontology seems to be that, if we can keep a person healthy longer, we may be able to modestly improve lifespan.

Avi Roy is a PhD student at the University of Buckingham in the UK, researching aging, mitochondria, and regenerative medicine; he is also an Ultimate (frisbee) enthusiast.

Living long and having good health are not mutually exclusive. On the contrary, you cannot have a long life without good health. Currently most aging research is concentrated on improving “health”, not lifespan. If we are going to live substantially longer, we need to engineer our way out of the current 120-year-barrier.

*The longest confirmed human lifespan in history belonged to Jeanne Louise Calment, according to the Guinness Book of Records, 1999 edition. She lived from 1875 to 1997, dying at age of 122 years, 164 days. She lived in Arles, France for her entire life, outliving both her daughter and grandson by several decades. She entered the Guinness Book of records in 1999, but apparently, in the intervening years, no one beat her record.

Bottom line: Is there a limit to how long humans can live? The Hayflick limit and discovery of telomeres – added to census data – suggest the that maximum human lifespan may be around 120 years. However, this evidence is not entirely convincing, and some researchers believe it might be possible – via research on life extension and continued research on good health practices and the abolishment of certain diseases – to learn what would enable us humans to substantially increase our lifespans.

A weak tornado formed right outside the Denver International Airport yesterday (June 18, 2013) in the afternoon hours. As of now, no one was directly impacted by this tornado, and very little damage was reported. It formed near the airport, but never directly hit the airport. The tornado produced roughly 97 mile per hour winds right around 2:30 p.m. local time in Denver. All flights were canceled or rerouted due to the storms in the area, and everyone was able to take shelter inside. Check out the amazing footage and photos of this tornado!

Picture of the tornado near the Denver airport. Image Credit: Mike Sellers

Tornado near the Denver airport. Image Credit: Jen Milazzo

Bottom line: A tornado formed right near the Denver airport producing winds of nearly 100 mph. The airport had safety procedures in place, and everyone was able to take shelter, as all flights were canceled or delayed until the storm pushed through. In my opinion, it was one of the more “photogenic” tornado pictures and video I have seen in a long time. Plus, everyone was safe!

June 19, 1900. On this date, the subway system in Paris, France began operations on Line 1 after two years of construction that involved tearing up several streets of the famed city. The Paris Metro was the first subway system in France and was said to symbolize a country in the forefront technologically, worldwide. Today, this rapid transit system in Paris remains mostly underground and runs to 214 kilometers (133 mi) in length. With 303 stations, of which 62 facilitate transfer to another line, it’s said to be Europe’s second busiest metro system after Moscow.

A train at Bastille Station in Paris in 1908. Photo via Wikimedia Commons

Le Métro, as residents called it, was not without controversy when it was first constructed. The city had decided in 1898 to commence construction on the subway to connect sites for the 1900 Paris Exposition Universelle (World Fair). The effort involved serious disruption to Paris residents, as streets were dug up and torn up. A RATP Group, the state-owned operator of the subway, said on its website:

Complaints flooded in, and there was widespread opposition to the project.

However, the city persevered, and the Paris Metro became part of a building boom of subways worldwide: Boston, Chicago, Philadelphia, Berlin and Hamburg were just some of the subways built in the decade between 1900 and 1910.

This photo shows continued construction of the Paris Metro from 1902 to 1910. Description page on Wikimedia Commons.

“Le Métro” became a vital method of transportation throughout Paris. In this 1914 photo, French soldiers guard a subway entrance at the beginning of World War I. Description page on Wikimedia Commons.

After the subway’s opening June 19, 1900 – delayed by several weeks due to a general strike – Line 1 quickly became popular enough to justify building more subway lines in the city.

As of 2010, Line 1 carries 225 million passengers annually through 25 stations that span 10.3 miles (16.6 km) of track. Line 1 also now includes driverless trains.

Bottom line: On June 19, 1900, the subway in Paris, France began operations on Line 1 after two years of construction. It was France’s first subway system and was said to symbolize a country in the forefront technologically, worldwide.

Photo credit: Mark Myers. Thank you Mark!

Here’s a telescopic view of a waxing gibbous moon from earlier this week. You might have seen this moon high in the east at sunset, appearing more than half-lighted, but less than full. A waxing gibbous moon rises during the hours between noon and sunset. It sets in the wee hours after midnight. This June 17, 2013 moon is waxing toward the next supermoon on June 22-23.

By the way, the word gibbous comes from a root word that means hump-backed. Any moon that appears more than half lighted but less than full is called a gibbous moon. You can see the hump-backed shape in the waxing gibbous moon.

EarthSky Facebook friend Mark Myers took this picture on June 17. Thank you Mark! We’ve been getting lots of great moon images, perhaps in anticipation of the supermoon coming up on Saturday night (June 22-23). Check them out on the EarthSky Facebook page!

Most “super” supermoon of 2013 on June 22-23

The moon and the planet Venus rank as the second-brightest and third-brightest celestial bodies to bedeck the heavens after the sun. As soon as dusk gives way to darkness, use dazzling Venus to find the planet Mercury, and then use the bright waxing gibbous moon to find the golden planet Saturn (plus the sparkling blue-white star Spica).

Look first for Venus and Mercury rather low over the west-northwest horizon some 45 to 60 minutes after sunset. That’s because these two worlds will follow the sun beneath the horizon before it gets good and dark. The moon and Saturn, on the other hand, will be out all evening long.

Venus and Mercury will only be about 2^o apart – about the width of your little finger at an arm length away. Venus shines about 100 times more brightly than Mercury does, so you may need binoculars to spot Mercury in Venus’s glare. If you live in the Northern Hemisphere, you may also see the nearby Gemini stars, Castor and Pollux.

Look westward some 45 to 60 minutes after sunset to spot Venus and Mercury near the horizon. You may – or may not – need binoculars to see Mercury

Both of these planets – Mercury and Venus – circle the sun inside of Earth’s orbit. Mercury is the innermost planet of the solar system whereas Venus is the second planet outward from the sun. Earth, the third planet outward, cirlces the sun sun inside of Mars’ orbit, the fourth planet outward. At present, Mars is extremely hard to see because it sits in the glare of morning dawn.

Bird’s-eye view of inner solar system on June 19, 2013

Bird’s-eye view of the inner solar system on 2013 June 19 as seen to the north of the solar system. In their order going outward, these planets are Mercury, Venus, Earth and Mars. From north of the ecliptic, the planets revolve around the sun in a counter-clockwise direction. Image credit: Solar System Live

From either the Northern or Southern Hemisphere, the moon and Saturn stay out till the wee hours of the morning. Saturn, the sixth planet outward from the sun, is the most distant world that you can easily see with the unaided eye. However, you can easily see this planet’s glorious rings through a modest, backyard telescope.

Photo of the moon, Saturn (left)) and Spica (right) taken by Carl Galloway of NW Indiana on June 18, 2013. Thank you Carl! See more photos on the EarthSky Facebook page.

This early evening, you can see three planets at the drop of the hat. Venus points out Mercury at evening dusk, and the moon points out the ringed planet Saturn at nightfall.

A sensor developed by scientists at SINTEF’s MiNaLab will help to make microphones hypersensitive:

“Think of traditional videoconference equipment. Several people are sitting around the table, but the microphone has been placed where its sound reception is less than optimal.

With technology of this sort, a microphone will be able to “see” where the sound comes from, pick up the voice of the person speaking, and filter out other sources of noise in the room,” explains ICT researcher Matthieu Lacolle, who emphasises that acoustics scientists at SINTEF have also contributed to this innovative solution.

Small but tightly packed

The microphone is packed full of microelectronics. What makes it really special, however, is an optical position sensor that is no more than a millimetre in diameter.

The technology that makes the microphone so sensitive is based on a combination of two optical phenomena; interference and diffraction. Credit: SINTEF

The reason for giving a position sensor such an important role is that a microphone is completely dependent on a membrane, which picks up the pressure waves produced by the sound.

“In principle, a microphone acts like a drum. You have a membrane that vibrates when it is impacted by a sound – which is just a series of pressure waves. And then you have a reference surface in the background. The distance between these two surfaces registers the sound. We do this by measuring light waves from a microscopically small laser, so we can say that the sensor in microphones actually sees the sound,” explains Lacolle.

The sensor can measure incredibly small movements, and thus also extremely quiet sounds. If we make the membrane light enough, and let it oscillate freely in the air, the microphone also becomes directionally sensitive. “That also tells us where the sound is coming from,” says Lacolle, adding that the membrane is only 100 nanometres thick, almost 1000 times thinner than a human hair.

Coloured by light

The technology that makes the microphone so sensitive is based on a combination of two optical phenomena; interference and diffraction, both of which are due to the wave character of light.
“If we hold up a CD to the light, we see the play of colours where it reflects the light. This happens because light consists of a spectrum of wavelengths that the naked eye perceives as colours, and these wavelengths are diffracted in different directions, explains Lacolle.

Another phenomenon that can be utilised to measure sound is interference, which occurs when a number of waves are superimposed on each other. You can observe this when you stand in a harbour where incoming waves are reflected by a pier and are superimposed on top of the waves that follow them into the harbour. Complex, apparently chaotic wave patterns can occur, but so do standing waves, which don’t appear to move at all,” says the SINTEF researcher.

What the SINTEF scientists did was to exploit optical diffraction and interference to measure membrane movements of less than the diameter of an atom by using the optimal sensor.

We have created very special grooved microstructures on the reference surface, which lies directly underneath the microphone membrane. When the laser illuminates these microstructures, we can read off the direction in which the light is reflected by means of photodetectors, which transform the light into electrical signals.”

Laboratory mass-production

The microphone thus consists of several elements: an ultrathin membrane, tiny grooved microstructures, a miniaturised laser and a number of photodetectors. Everything is integrated into a tiny circuit that is mass-produced on a silicon wafer on which all the structures are etched, using special equipment within a clean room.

Dust-free production

In MiNaLab’s clean room, production takes place in a highly controlled environment. The production process is extremely sensitive; even a tiny grain of dust can destroy a whole production series, because it can affect the tiny microstructures.

“That’s why our laboratory is equipped with vibration damping and air filters that take out particles as small as 100 nanometres,” explains Lacolle.

Noise monitoring

The Norwegian company Norsonic supplies various types of noise-measurement equipment, and intends to use the new microphone to measure both sound pressure and acoustic power.

“The microphone is the very heart of the equipment that we supply. What is unique about this technology is that it can give us an extremely sensitive microphone that is capable of registering sound waves far beyond the range that microphones in this price class can do today. This lets us compete in a market that is currently occupied by very expensive equipment. Our version is also much smaller, which is an advantage in itself, because the physical size of the microphone actually affects the sound field that it is measuring,” says senior scientist Ole Herman Bjor in Norsonic.

Fact box: How the microphone works

In simple terms, we can say that the new microphone operates as follows:
• First, sound pressure is transformed into movements of the membrane.
• These movements are read optically via the light-sensitive detector.
• The light intensity is measured by a sensor which in turn transforms it into an electronic signal that is capable of reproducing the sound.
Other potential applications for the sensor include:
• geophones for seismic shooting
• photoacoustic gas sensors
• accelerometers
• vibration sensors
• gyroscopes
• pressure sensors
• high-temperature versions of the above-mentioned sensors
• sensors for highly irradiated sites (nuclear power stations, x-ray equipment) or with electromagnetic radiation (sensors in motors or magnetic resonance equipment).

Via SINTEF