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Klaus Seiersen
Works at Scienceblog.dk
Attended University of Aarhus
Lives in Skødstrup
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Klaus Seiersen

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Brian Koberlein originally shared to Our Universe:
 
Two Worlds, One Sun

There’s an image going around of a blue sunset on Mars. Yes, it’s a real image, and yes, the colors are reasonably true to life. It was taken by the Curiosity rover in April. Given that sunsets on Earth are typically red, how does Mars get a blue sunset? It all has to do with the way light scatters in the atmospheres of Earth and Mars.

Earth has a relatively thick atmosphere, so most of the atmospheric scattering occurs when light strikes a molecule of air, known as Rayleigh scattering. Rayleigh scattering occurs when the object a photon scatters off (the air molecule) is much smaller than the wavelength of the photon. The closer the wavelength is to the size of the molecule, the more likely it is to scatter. This means that red wavelengths (which are the longer wavelengths of visible light) don’t scatter with air molecules much, while blue wavelengths (which are shorter) tend to scatter a lot. In fact blue light is almost 10 times more likely to scatter against air molecules than red light. This is why the sky appears blue, since so much of the blue light is scattered.

When the Sun is low in the sky, it’s light has to travel a long path through the atmosphere to reach you. As the light travels through the atmosphere some of the photons are scattered off the air molecules. When the photons scatter off air molecules, they scatter randomly in all directions, so usually when a photon scatters, it scatters away from your line of sight. Since blue photons scatter much more often than red ones, much of the blue light is scattered away. This leaves red photons to reach your eye. Hence the Sun looks red when low in the sky. When the Sun is overhead, the path it takes to reach you is much shorter, so only a bit of the blue light is scattered. So the Sun looks yellow.

Mars has a much thinner atmosphere, so the amount of Rayleigh scattering is much less. But Mars also has a dry, dusty surface, and a weaker surface gravity, so the atmosphere of Mars is often filled with fine dust particles. These particles are more comparable in size to the wavelengths of visible light, so most of the light is scattered by Mie scattering. One of the main differences between Rayleigh and Mie scattering is that Rayleigh scattering tends to occur in all directions, but Mie scattering varies with scattering angle. What this means is that longer wavelengths (reds) tend to scatter more uniformly, while shorter wavelengths (blues) tend to scatter at slight angles. This means that blue light tends to be deflected less than red light. This means Mars can have a dusty red daytime sky, and a blue sunset.

Mie scattering does occur on Earth as well, but since Mie scattering is less efficient than Rayleigh scattering it’s never strong enough to give us a blue sunset. It can (rarely) produce a blue moon. The most widespread incidence of modern history occurred after the eruption of Krakatoa in 1883, which sent so much ash into the atmosphere it produced brilliantly red sunsets and visibly blue moons all across the globe for nearly two years. As a result, the phrase “once in a blue moon” came to mean a rare occurrence.
While Earth can have lovely red sunsets, Mars can have a sunset that is truly blue.
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The Sky from Mauna Kea
Image Credit & Copyright: Shane Black Photography; Rollover Annotation: Judy Schmidt
http://apod.nasa.gov/apod/ap150511.html

What if you could stand at the top of a volcano and peer out across the universe? It the timing is right, you might see an amazing panorama like the one featured here. In this case, the volcano is the Hawaii's Mauna Kea, and the time was a clear night last summer In the foreground of this south-facing panorama lies a rugged landscape dotted with rocks and hardy plants. Slightly above and further out, a white blanket of clouds spreads horizontally to the horizon, seemingly dividing heaven and Earth. City lights illuminate the clouds and sky on the far left, while orange lava in the volcanic caldera of Kilauea lights up the clouds just left of center. The summit of an even more distant Hawaiian volcano, Mauna Loa, is visible in dark silhouette near the central horizon. Green airglow is visible above the clouds, caused by air molecules excited by the Sun during the day. The Moon is the bright orb on the right. A diffuse band of light-colored zodiacal light extends up from the far right. Most distant, the dramatic central band of our Milky Way Galaxy appears to rise vertically from Mauna Loa. The person who witnessed and captured this breathtaking panorama stands before you in the image center.
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Aurora over Icelandic Glacier
Image Credit & Copyright: James Boardman Woodend (Images Inspired by Nature)
http://apod.nasa.gov/apod/ap150310.html

Several key conditions came together to create this award-winning shot. These included a dark night, few clouds, an epic auroral display, and a body of water that was both calm enough and unfrozen enough to show reflected stars. The featured skyscape of activity and serenity appeared over Iceland's Vatnajökull Glacier a year ago January, with the Jökulsárlón Iceberg Lagoon captured in the foreground. Aurora filled skies continue to be common near Earth's poles as our Sun, near Solar Maximum, continues to expel energetic clouds of plasma into the Solar System.
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Astronomers using NASA’s Hubble Space Telescope have spotted for the first time a distant supernova split into four images. The multiple images of the exploding star are caused by the powerful gravity of a foreground elliptical galaxy embedded in a massive cluster of galaxies. This unique observation will help astronomers refine their estimates of the mass of dark matter in the lensing galaxy and cluster. Dark matter is an invisible form of matter that makes up most of the mass of the universe.

The gravity from both the elliptical galaxy and its galaxy cluster distorts and magnifies the light from the supernova behind it in an effect called gravitational lensing. First predicted by Albert Einstein, this effect is similar to a glass lens bending light to magnify and distort the image of an object behind it. The multiple images are arranged around the elliptical galaxy in a cross-shaped pattern, also known an Einstein Cross.

The elliptical galaxy and its galaxy cluster, MACS J1149.6+2223, are 5 billion light-years away from Earth. The supernova behind it is 9.3 billion light-years away.

The image shows the galaxy's location within a hefty cluster of galaxies called MACS J1149.6+2223. Arrows (inset) point to the multiple copies of Supernova Refsdal. The four images were spotted on Nov. 11, 2014.

Image Credit: NASA/ESA/STScI/UCLA
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Two to Tonga
Photograph by Fabrice Guerin,
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Milky Way over Monument Valley Navajo Tribal Park
[BML] http://asterisk.apod.com/viewtopic.php?f=29&t=34055&start=125
Copyright: César Cantú
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China’s Lunar Test Spacecraft Takes Incredible Picture of Earth and Moon Together

The Chinese lunar test mission Chang’e 5T1 has sent back some amazing and unique views of the Moon’s far side, with the Earth joining in for a cameo in the image above. According to the crew at UnmannedSpaceflight.com the images were taken with the spacecraft’s solar array monitoring camera.

http://www.universetoday.com/115750/chinas-lunar-test-spacecraft-takes-incredible-picture-of-earth-and-moon-together/
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Landmannalaugar
Landmannalaugar is a volcanic hotspot in the country’s southern highlands. Landmannalaugar is famous for the multi-coloured mountains caused by the interaction of rhyolite rock and geothermal gasses. It is tough to drive there, the road is tough for a car, but a jeep copes with the rough road much better.

#iceland #icelandphotography #volcanic #enjoyyourtime
http://icelandaurora.com/tours/landmannalaugar/
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Simplemente maravillosa toma!
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Northern Equinox Eclipse
Image Credit & Copyright: Stan Honda
http://apod.nasa.gov/apod/ap150321.html

Snowy and cold is weather you might expect at the start of spring for Longyearbyen on the Arctic archipelago of Svalbard, Norway. But that turned out to be good weather for watching the Moon's umbral shadow race across northern planet Earth. The region was plunged into darkness for 3 minutes during the March 20 total solar eclipse while insulated eclipse chasers witnessed the dark Sun in the cold clear sky. In this well-timed snapshot captured near the end of totality, the Moon's shadow sweeps away from the horizon and the solar corona fades as the lunar disk just begins to uncover the Sun. Streaming past the Moon's edge, direct rays of sunlight create the fleeting appearance of a glistening diamond ring.
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Volcano of Fire Erupts Under the Stars
Image Credit & Copyright: Diego Rizzo
http://apod.nasa.gov/apod/ap150311.html

First, there was an unusual smell. Then there was a loud bang. But what appeared to the eye was the most amazing of all. While waiting near midnight to see a possible eruption of Volcán de Fuego (Volcano of Fire) in Guatemala last month, a ready camera captured this extraordinary image. Lava is seen running down the side of the volcano, while ash rises up, and glowing magma bubbles explode out of the caldera. Lights near the town of Escuintla can be seen in the background, one of several nearby towns that have witnessed several spectacular eruptions previously. High above, seemingly tranquil by comparison, are familiar stars from the night sky. Although the Volcán de Fuego usually undergoes low-level activity, when the next spectacular eruption will occur is unknown.
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A Night at Poker Flat
Image Credit: +NASA / Jamie Adkins
http://apod.nasa.gov/apod/ap150130.html

Four NASA suborbital sounding rockets leapt into the night on January 26, from the University of Alaska's Poker Flat Research Range. This time lapse composite image follows all four launches of the small, multi-stage rockets to explore winter's mesmerizing, aurora-filled skies. During the exposures, stars trailed around the North Celestial Pole, high above the horizon at the site 30 miles north of Fairbanks, Alaska. Lidar, beams of pulsed green lasers, also left traces through the scene. Operating successfully, the payloads lofted were two Mesosphere-Lower Thermosphere Turbulence Experiments (M-TeX) and two Mesospheric Inversion-layer Stratified Turbulence (MIST) experiments, creating vapor trails at high altitudes to be tracked by ground-based observations.
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Aurora Borealis, Northern Lights, Troms region, Norway

Photo by : Gavin Hellier
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Medical physicist and science communicator
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  • Scienceblog.dk
    Owner, community builder, 2006 - present
  • Aarhus University Hospital
    Medical physicist, 2006 - present
  • Nyhedsmagasinet Ingeniøren
    Science blogger, 2006 - 2014
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Skødstrup
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Højbjerg - Århus
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Medical physicist, blogger and science communicator.
Introduction
PhD in atomic and molecular physics from the University of Aarhus.

Working as a medical physicist at Aarhus University Hospital.

Science blogger for the Danish technical magazine Ingeniøren.

Founder of the Danish Physics Show, and the website Fysikbasen.dk.
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I've seen af wild kiwi (the bird, not the New Zealander!)
Education
  • University of Aarhus
    PhD atomic and molecular physics, 1995 - 2003
  • Marselisborg Gymnasium
    1992 - 1995
  • Aarhus University Hospital
    Medical physicist, 2006 - 2009
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