NASA Studies of the ultraviolet sun

Four of the telescopes on the Solar Dynamics Observatory observe extreme ultraviolet light activity on the sun that is invisible to the naked eye. 

Credit: NASA/SDO

You cannot look at the sun without special filters, and the naked eye cannot perceive certain wavelengths of sunlight.

Solar physicists must consequently rely on spacecraft that can observe this invisible light before the atmosphere absorbs it.

"Certain wavelengths either do not make it through Earth's atmosphere or cannot be seen by our eyes, so we cannot use normal optical telescopes to look at the spectrum," said Dean Pesnell, the project scientist for the Solar Dynamics Observatory (SDO), at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

Several spacecraft can observe these invisible light wavelengths. SDO for example has four telescopes that image the sun in the ultraviolet spectrum.

As beams of ultraviolet light pass into the telescope, a mirror with special coatings filters and amplifies the ultraviolet light's otherwise poor reflection.

The incoming photons are then recorded as pixels and converted into electrical signals, similar to how your cell phone camera sees visible light.

"It's exactly the same process, whether it's ultraviolet light, infrared light, visible light, or radio," said Joseph Gurman, project scientist for both the Solar and Heliospheric Observatory (SOHO) and the Solar Terrestrial Relations Observatory (STEREO) at Goddard.

"In this case we're trying to understand how the sun changes and how those changes affect life here on Earth."

Ultraviolet light causes molecular radiation damage to our skin, seen as sunburns that can lead to cancer.

Its cousin, extreme ultraviolet radiation, and the associated solar storms have the potential to disrupt communications and spacecraft navigation.

"These are very damaging, energetic photons, and we want to understand what chain of events produces these photons," Pesnell said.

The Solar Dynamics Observatory (SDO) observed a solar flare (upper left) and a coronal mass ejection (right) erupting from the sun’s limb in extreme ultraviolet light on August 6, 2010. 

Credit: NASA/SDO

Thankfully our planet's atmosphere absorbs much of this solar radiation, making life on Earth possible.

However, this means that to study extreme ultraviolet light, instruments must do it from the vacuum of space.

"Ultraviolet light from the sun can show us the origins of solar storms that can lead to power outages, cell phone disruptions, and delays in shipping packages due to the rerouting of planes from over the pole," Gurman said.

By understanding what occurs in the sun's atmosphere, scientists hope to predict when powerful solar events such as coronal mass ejections and solar flares may occur.

Spacecraft record solar activity as a binary code, 1s and 0s, which computer programs can translate into black and white. 

Scientists coloroured the images for realism, and then zoom in on areas of interest. 

Credit: NASA/Karen Fox

"You really want to know what's happening on the sun as soon as you can," said Jack Ireland, a solar visualization specialist at Goddard.

"We can then use computer models to estimate how solar events will affect Earth's space environment."

The information can then be used by NOAA's Space Weather Prediction Center, in Boulder, Co. to alert power companies and airlines to take the necessary precautions, thus avoiding power outages and keeping airplane passengers safe.

ESA Venus Express spies rainbow-like 'glories' in Venus atmosphere

False colour composite of a ‘glory’ seen on Venus on 24 July 2011. 

The image is composed of three images at ultraviolet, visible, and near-infrared wavelengths from the Venus Monitoring Camera (VMC). 

The images were taken 10 seconds apart and, due to the motion of the spacecraft, do not overlap perfectly. 

The glory is 1200 km across, as seen from the spacecraft, 6000 km away. 

Credit: ESA /MPS /DLR /IDA

INTERACTIVE 3D MODEL OF THE VENUS EXPRESS

A rainbow-like feature known as a 'glory' has been seen by ESA's Venus Express orbiter in the atmosphere of our nearest neighbour – the first time one has been fully imaged on another planet.

Rainbows and glories occur when sunlight shines on cloud droplets – water particles in the case of Earth.

While rainbows arch across wide swathes of the sky, glories are typically much smaller and comprise a series of coloured concentric rings centred on a bright core.

Glories are only seen when the observer is situated directly between the Sun and the cloud particles that are reflecting sunlight.

On Earth, they are often seen from aeroplanes, surrounding the shadow of the aircraft on the clouds below, or around the shadow of climbers atop misty mountain peaks.

A glory requires two characteristics: the cloud particles are spherical, and therefore most likely liquid droplets, and they are all of a similar size.

The atmosphere of Venus is thought to contain droplets rich in sulphuric acid.

By imaging the clouds with the Sun directly behind the Venus Express spacecraft, scientists hoped to spot a glory in order to determine important characteristics of the cloud droplets.

They were successful. The glory in the images here was seen at the Venus cloud tops, 70 km above the planet's surface, on 24 July 2011.

It is 1200 km wide as seen from the spacecraft, 6000 km away.

From these observations, the cloud particles are estimated to be 1.2 micrometres across, roughly a fiftieth of the width of a human hair.

The fact that the glory is 1200 km wide means that the particles at the cloud tops are uniform on this scale at least.

The variations of brightness of the rings of the observed glory is different than that expected from clouds of only sulphuric acid mixed with water, suggesting that other chemistry may be at play.

Simulated views of the glory phenomena on Venus (left) and Earth (right), without considering any effects of haze or background cloud brightness.

Glories occur when sunlight shines on cloud droplets – water particles in the case of Earth, sulphuric acid particles for Venus.

The main difference between the appearance of the glory on Venus and on Earth is not because of composition, but rather the particle size.

Cloud droplets on Earth are typically between 10 and 40 thousandths of a millimetre in diameter, but on Venus the droplets found at the cloud tops are much smaller, typically no more than 2 thousandths of a millimetre across. 

Because of this, the coloured fringes are further apart than they would appear on Earth. 

Credit: C. Wilson/P. Laven

One idea is that the cause is the "UV-absorber", an unknown atmospheric component responsible for mysterious dark markings seen in the cloud tops of Venus at ultraviolet wavelengths. More investigation is needed to draw a firm conclusion.

More information: "Glory on Venus Cloud Tops and the Unknown UV Absorber," by W.J. Markiewicz et al, is accepted for publication in Icarus. dx.doi.org/10.1016/j.icarus.2014.01.030

Lunar Reconnaissance Orbiter spectrometer detects helium in Moon's atmosphere

The Lyman Alpha Mapping Project (LAMP) aboard LRO (shown here in a pre-flight photo) uses a novel method to peer into the perpetual darkness of the moon's so-called permanently shadowed regions.

LAMP "sees" the lunar surface using the ultraviolet light from nearby space and stars, which bathes all bodies in space in a soft glow of ultraviolet light. (Credit: NASA Goddard/Debbie McCallum)

Geophysical Research Letters, Vol. 39, doi:10.1029/2012GL051797 , 2012.

Scientists using the Lyman Alpha Mapping Project (LAMP) aboard NASA's Lunar Reconnaissance Orbiter have made the first spectroscopic observations of the noble gas helium in the tenuous atmosphere surrounding the Moon.

These remote-sensing observations complement in-situ measurements taken in 1972 by the Lunar Atmosphere Composition Experiment (LACE) deployed by Apollo 17.

Although LAMP was designed to map the lunar surface, the team expanded its science investigation to examine the far ultraviolet emissions visible in the tenuous atmosphere above the lunar surface, detecting helium over a campaign spanning more than 50 orbits.

Because helium also resides in the interplanetary background, several techniques were applied to remove signal contributions from the background helium and determine the amount of helium native to the Moon.

Geophysical Research Letters published a paper on this research in 2012. "The question now becomes, does the helium originate from inside the Moon, for example, due to radioactive decay in rocks, or from an exterior source, such as the solar wind?" says Dr. Alan Stern, LAMP principal investigator and associate vice president of the Space Science and Engineering Division at Southwest Research Institute.

With support from LRO's suite of instruments, LAMP has previously determined that hydrogen, mercury and other volatile substances are present in the permanently shaded regions (PSRs) of the moon.

It has also observed PSRs are darker at far-ultraviolet wavelengths and redder than nearby surfaces that receive sunlight.

These darker regions indicate "fluffy" soils, while the reddening is consistent with the presence of water frost.

In a related study led by Dr. Paul Feldman of Johns Hopkins University and published in Icarus, observations showed day-to-day variations in helium abundances, possibly varying with the solar wind, and also significantly decreasing when the Moon passed behind Earth out of sight from the solar wind.

"If we find the solar wind is responsible, that will teach us a lot about how the same process works in other airless bodies," says Stern.

 If spacecraft observations show no such correlation, radioactive decay or other internal lunar processes could be producing helium that diffuses from the interior or that releases during lunar quakes.

Aberdeen Scientists Find Link Between Light Deficiency and Multiple Sclerosis

Aberdeen scientists have found that artificial sunlight can have a “striking effect” in helping treat sufferers of diseases such as multiple sclerosis.

Researchers from Aberdeen University studied patients in the north of Scotland – which has the highest rate of MS in the UK - who were being treated during winter with artificial UV (ultraviolet)-B light therapy for skin diseases caused by their immune systems acting inappropriately.

The research - published in the Journal of Allergy and Clinical Immunology – shows how UV-B light boosts vitamin D, as well as cells in our body that are responsible for regulating or balancing the immune system. Vitamin D is made in our bodies by UV-B light from the sun.

Some studies have suggested a link between vitamin D deficiency and autoimmune diseases such as MS.

This possible link might also explain the increasing prevalence of autoimmune disease among those living far from the equator, where there are lower levels of winter sun.

Autoimmune diseases - like MS and type 1 diabetes - are diseases where the immune system mistakenly attacks the body’s own tissues or harmless substances that enter the body.

Dr Anthony Ormerod, clinical reader in dermatology at the university, said: “Our study shows that UV-B light, which mimics sunshine, can have a striking effect on the immune system of patients.

“We found that UV-B light boosted the production of vitamin D, and of regulatory T cells, which play an important role keeping our immune systems in check.

“Our findings have important implications for future interventions including the recommendations for healthy lifestyle and a possible role for phototherapy and/or vitamin D supplementation in the prevention or treatment of autoimmune and inflammatory diseases.

“While too much exposure to sunlight is harmful and increases skin cancer risk, these results suggest that subjects in our study would have some benefits from small amounts equivalent to summer exposure in the winter but more work needs to determine the role of sunlight and the role of supplementing the diet with vitamin D.”

Dr Helen Macdonald, senior lecturer in nutrition and translational musculoskeletal research at the university and chair of the National Osteoporosis Society Nutrition and Lifestyle forum, said: “There are risks associated with high levels of both therapies, so it is important that we get the balance right.

“We would also want to stress that we are not advocating sun bed use since this is not the same type of radiation produced by sun beds which already have well-documented health risks.

“The average dose of UV light that the volunteers received was the equivalent to sunlight exposure in Aberdeen over spring and summer and further work is required to determine if lower doses are effective.”

Professor Mark Vickers, chair in applied medicine at the university, added: “Ours is the first study to demonstrate in patients a cause and effect between UV light, vitamin D and systemic immune function in people.”

NASA’s Galaxy Evolution Explorer: UV image of the Cygnus Loop Nebula

Wispy tendrils of hot dust and gas glow in this ultraviolet image of the Cygnus Loop Nebula, taken by NASA’s Galaxy Evolution Explorer.

The nebula lies about 1,500 light-years away, and is a supernova remnant, left over from a massive stellar explosion that occurred 5,000-8,000 years ago.

Picture: NASA/JPL-CALTECH/AFP/Getty

Glowing Nebula: Ultra-Violet Radiation

The Wide Field Imager on the MPG/ESO 2.2-meter telescope at the La Silla Observatory has imaged a region of star formation called NGC 3324. The intense radiation from several of NGC 3324's massive, blue-white stars has carved out a cavity in the surrounding gas and dust.
CREDIT: ESO

The Heart Of Cygnus Fermi: A Cosmic-ray Cocoon

Cygnus X hosts many young stellar groupings, including the OB2 and OB9 associations and the cluster NGC 6910. 

The combined outflows and ultraviolet radiation from the region's numerous massive stars have heated and pushed gas away from the clusters, producing cavities of hot, lower-density gas.

In this 8-micron infrared image, ridges of denser gas mark the boundaries of the cavities. Bright spots within these ridges show where stars are forming today. Credit: NASA/IPAC/MSX.

The constellation Cygnus, now visible in the western sky as twilight deepens after sunset, hosts one of our galaxy's richest-known stellar construction zones.

Astronomers viewing the region at visible wavelengths see only hints of this spectacular activity thanks to a veil of nearby dust clouds forming the Great Rift, a dark lane that splits the Milky Way, a faint band of light marking our galaxy's central plane.

Located in the vicinity of the second-magnitude star Gamma Cygni, the star-forming region was named Cygnus X when it was discovered as a diffuse radio source by surveys in the 1950s.

Now, a study using data from NASA's Fermi Gamma-ray Space Telescope finds that the tumult of star birth and death in Cygnus X has managed to corral fast-moving particles called cosmic rays.

Cosmic rays are subatomic particles - mainly protons - that move through space at nearly the speed of light. In their journey across the galaxy, the particles are deflected by magnetic fields, which scramble their paths and make it impossible to backtrack the particles to their sources.

Yet when cosmic rays collide with interstellar gas, they produce gamma rays - the most energetic and penetrating form of light - that travel to us straight from the source.

By tracing gamma-ray signals throughout the galaxy, Fermi's Large Area Telescope (LAT) is helping astronomers understand the sources of cosmic rays and how they're accelerated to such high speeds. In fact, this is one of the mission's key goals.

The galaxy's best candidate sites for cosmic-ray acceleration are the rapidly expanding shells of ionized gas and magnetic field associated with supernova explosions. For stars, mass is destiny, and the most massive ones - known as types O and B - live fast and die young.

They're also relatively rare because such extreme stars, with masses more than 40 times that of our sun and surface temperatures eight times hotter, exert tremendous influence on their surroundings.

With intense ultraviolet radiation and powerful outflows known as stellar winds, the most massive stars rapidly disperse their natal gas clouds, naturally limiting the number of massive stars in any given region.

Which brings us back to Cygnus X. Located about 4,500 light-years away, this star factory is believed to contain enough raw material to make two million stars like our sun.

Within it are many young star clusters and several sprawling groups of related O- and B-type stars, called OB associations.

One, called Cygnus OB2, contains 65 O stars - the most massive, luminous and hottest type - and nearly 500 B stars.

Astronomers estimate that the association's total stellar mass is 30,000 times that of our sun, making Cygnus OB2 the largest object of its type within 6,500 light-years. And with ages of less than 5 million years, few of its most massive stars have lived long enough to exhaust their fuel and explode as supernovae.

Intense light and outflows from the monster stars in Cygnus OB2 and from several other nearby associations and star clusters have excavated vast amounts of gas from their vicinities.

The stars reside within cavities filled with hot, thin gas surrounded by ridges of cool, dense gas where stars are now forming.

It's within the hollowed-out zones that Fermi's LAT detects intense gamma-ray emission, according to a paper describing the findings that was published in the journal Science.

Giant Space Blob Glows from Within: Lyman-alpha blob LAB-1

This image shows one of the largest known single objects in the Universe, the Lyman-alpha blob LAB-1.

This picture is a composite of two different images taken with the FORS instrument on the Very Large Telescope (VLT) - a wider image showing the surrounding galaxies and a much deeper observation of the blob itself at the centre made to detect its polarisation.

The intense Lyman-alpha ultraviolet radiation from the blob appears green after it has been stretched by the expansion of the Universe during its long journey to Earth.

These new observations show for the first time that the light from this object is polarised.

This means that the giant "blob" must be powered by galaxies embedded within the cloud.

Credit: ESO/M. Hayes.

The Germicidal and Sanitising effect of UV-C Light

UV-C light is the name for a certain spectrum of the (invisible) light. UV-C light is formed by the light in the range between 200 and 280 nm. This light is very much suitable for the so-called UV-C disinfection and is everything that is being done to terminate microorganisms with the help of UV-C energy.

UV-C lamps are especially produced for these purposes. Mostly we use mercury to generate the specific UV-C radiation. The lamps are coated specifically in order to burn a minimum of 8,000 hours and retain 80% of the initial UV-C energy. After 8,000 burning hours it is recommended to replace the lamps.

UV-C disinfection is applied to water, air and surfaces. Benefit of the UV-C application is that no chemicals need to be added to the air or water and the composition of the air or water does not alter. Moreover, the system is very economic compared with many other disinfecting methods. It goes without saying that UV-C disinfection is a very environmental-friendly and safe technique.

To read the whole paper from Hygienitech in PDF format Click here

NASA Ultraviolet Optical telescope: Image of M31

This mosaic of M31 merges 330 individual images taken by the Ultraviolet/Optical Telescope aboard NASA's Swift spacecraft.

It is the highest-resolution image of the galaxy ever recorded in the ultraviolet.

Also known as the Andromeda Galaxy, M31 is more than 220,000 light-years across and lies 2.5 million light-years away.

On a clear, dark night, the galaxy is faintly visible as a misty patch to the naked eye.

The irregular shape of the image results when the more than 300 images were assembled to make the final image.

Image Credit: NASA/Swift/Stefan Immler (GSFC) and Erin Grand (UMCP)

Venus in the ultraviolet

Venus in the ultraviolet

Venus Monitoring Camera image taken in the ultraviolet (0.365 micrometres), from a distance of about 30 000 km. It shows numerous high-contrast features, caused by an unknown chemical in the clouds that absorbs ultraviolet light, creating the bright and dark zones. With data from Venus Express, scientists have learnt that the equatorial areas on Venus that appear dark in ultraviolet light are regions of relatively high temperature, where intense convection brings up dark material from below. In contrast, the bright regions at mid-latitudes are areas where the temperature in the atmosphere decreases with depth. The temperature reaches a minimum at the cloud tops suppressing vertical mixing. This annulus of cold air, nicknamed the ‘cold collar’, appears as a bright band in the ultraviolet images. Credits: ESA/MPS/DLR/IDA

This artist’s concept of Venus, dated 2006, suggests the presence of lightning in the atmosphere.