Great Salt Lake, Utah
You see some pretty strange things from 250 miles above the Earth’s surface. This enormous half-purple, half-green body of water is a fine example.
This orbital view of Utah’s Great Salt Lake reveals a dramatic color change along an oddly precise dividing line. What the high-altitude perspective does NOT reveal is the railroad causeway that cuts the lake in half, effectively turning it into two lakes, each with its own ecosystem.
Great Salt Lake has no natural outlet, meaning the only escape for its water is through evaporation. Most of the rivers that feed fresh water into the lake enter south of the causeway (right side of image), where salinity fluctuates between 6 and 27 percent. That’s already much saltier than the ocean, but bland compared to the northern section of the lake. Here water evaporates faster than it can be replaced, concentrating the minerals and producing an average salinity of around 30 percent.
Why purple? The briny conditions are just too harsh for most bacteria. Certain salt-tolerant species with naturally rosy complexions don’t seem to mind, however.
Previous Image of the Week resources
March 16-23, 2018
A Marvelous Night for a Moondance
This simple image of a waning crescent moon reminds us that we do not go alone in our annual journey around the Sun.
The Earth and Moon are partners in a very slow dance in which one partner circles the other, while both circle the Sun together. Throughout the dance both partners are half illuminated by the light of the Sun, but as the performance unfolds their view of each other continues to change. One partner sees all, then progressively less, then none, then progressively more of the illuminated half of the other, until the dance reprises again, and again.
For the other partner this experience is reversed. When Earthdancer faces her partner with the Sun at her back, she sees Moondancer fully illuminated. In the same moment, Moondancer must face toward the Sun to see her partner, only to find Earthdancer shrouded in the darkness of her own shadow.
Nature is the ultimate choreographer, and the Moondance is much more nuanced than this fairytale suggests. To see just how elegant nature really is, take a few minutes to explore how the phasing of the Moon produces breathtaking total solar eclipses and blood-red lunar eclipses.
March 9- 16, 2018
What do Mars and Hawaii Have in Common?
Peeking through the scattered clouds over the North Pacific Ocean on September 19, 2014 are the eight major islands that comprise the archipelago of the Hawaiian Islands.
The Pacific Plate is shifting northward above a volcanic hotspot in the Earth’s mantle at the whiplash-inducing rate of 32 miles every million years. This hotspot currently lies beneath the southernmost of the Hawaiian Islands, known as Hawai’i, or the Big Island. Erosion has taken its toll on the older islands to the north, which are all significantly smaller than the Big Island.
If the magma produced by a volcano is highly fluid it will spread out as it cools to form a shape not unlike a warrior’s shield. Mauna Loa is the largest such shield volcano on Earth, and fills up more than half of the Big Island of Hawai’i.
The largest volcano in the solar system is also of the shield variety. Unlike Mauna Loa however, Olympus Mons formed long after any tectonic activity on Mars had ceased. Rather than producing a series of smaller shields, the hotspot beneath Olympus Mons created one ridiculously large shield. It’s about as a wide as the entire Hawaiian chain, and at 15.5 miles high it dwarfs Mauna Loa, which peaks out at 5.7 miles above the ocean floor.
March 2- 9, 2018
Doha, the capital city of Qatar, was little more than a backwater pearl diving village on the shores of the Persian Gulf until its British Protectorate status ended in 1971. Thanks to tremendous wealth generated by vast natural gas and oil reserves Qatar now has the highest per capita income in the world.
The paisley-shaped configuration of artificial islands seen in this image is called the Pearl, a massive man-made complex of luxury hotels and apartment towers, marinas, and high-end shopping and dining. It was built atop one of the rich oyster beds that sustained the region’s economy prior to the oil boom.
Earlier practitioners of land reclamation, of which the Pearl and similar projects in Dubai and Abu Dhabi are just recent examples, include the Ancient Egyptians, prehistoric inhabitants of Scotland and Ireland, and the Aztecs.
February 23 - March 2, 2018
The Atlas Mountains – Natures Water Bandits
The winds that blow into Africa from the Atlantic Ocean are full of evaporated moisture. So why is the Sahara desert so dry?
No single phenomenon has yet been credited with the region’s dramatic, 10,000 year transition from lush savanna to arid wasteland, but several factors are thought to have contributed to the process. Reasons for the Sahara’s perennial water shortage may include a semi-permanent high pressure system over northern Africa introduced by the precession of Earth’s axis of rotation, overgrazing by domesticated animals, and the phenomenon pictured here.
This image shows the process of orographic lifting. As the moist Atlantic winds encounter the Atlas Mountains near the Strait of Gibraltar, the air is forced up the mountain slope. As the air cools with altitude, its dew point is reached – clouds form, and heavy rains develop. By the time the air mass makes it all the way up and over to the opposite side of the mountain range, most of its moisture has been squeezed out.
February 16-23, 2018
Record Wildfire Season in Washington State
According to the Washington State Department of Natural Resources, the 2015 wildfire season was the worst in the state’s history. By August 19, four days after this image was taken, a thinly stretched team of professional firefighters, National Guard troops, and civilian volunteers were battling 22 large fires across the state, burning through over a million acres.
Not coincidentally, Washington also experienced their warmest summer on record in 2015. Many consecutive years of drought conditions, combined with a diminishing snowpack in the Cascade Mountains, had left the forests sick and dangerously vulnerable to fire. Lightning strikes triggered a number of the conflagrations, but too many were needlessly set off by the irresponsible behavior of humans.
Climate change affects different parts of our planet in different ways. In US states like Washington and California, that means millions of acres of hot, tinder-dry forest defenseless against the vast destructive potential of a single spark.
February 9-16, 2018
Sky High DIY
Do you find working on the roof of your home challenging? Well, at least you know there’s a killer view of the neighborhood waiting for you once you gather up the nerve to climb the ladder, right?
Always ready to lend a helping hand, astronauts Randy Bresnik and Mark Vande Hei were about 250 miles above the ground when they replaced the grappling end of the International Space Station’s Canadarm 2 robotic arm during a seven-hour spacewalk on October 5, 2017. Then they got bored, so they started working ahead on tasks slated for future spacewalks. And the view? Just the entire planet!
A handle on astronaut Joe Acaba’s nitrogen-powered emergency jetpack popped open during a subsequent spacewalk to replace the Canadarms faulty camera, limiting his ability to fly back to the ISS should his safety tether fail. Joe kept right on working.
Not that cleaning out the gutters doesn’t ALSO require a laser focus and nerves of steel.
February 2 - 9, 2018
Night Time is the Light Time
While the natural beauty and rich geographic diversity of our planet may best be viewed during daylight hours, nothing beats the glamour and glitz of Earth after dark.
Bejeweled as if for an evening of urbane merriment, the western Mediterranean Sea glows with the diamonds and pearls of human society. Hot white flashes of lightning off the coast of Algiers contrast the golden tone of city lights, seen in the lower right corner of this image from September of 2017. The Spanish cities of Cartagena, Valencia, and Barcelona adorn the opposite coastline, while the resort island of Mallorca smolders beneath the cloud cover just right of center. Finally, the elegant look is made complete by a curved emerald band offset from the horizon, highlighting the upper limit of Earth’s most enchanting feature – its life-sustaining atmosphere.
Is there a dark side to all of this wonderful light? Indeed there is. City-dwelling stargazers know it all too well, and its name is Light Pollution.
January 26 - February 2, 2018
Peering into the Soul of a Storm
If the eye is the window to the soul, then this is one deeply troubled cloud.
The atmospheric disturbance that would ultimately evolve into tropical storm Saola began taking shape in the Pacific ocean, south of Guam, in late September of 2017. It was still continuing to build in strength at the time this image was captured on October 21. Saola achieved typhoon status seven days later, bringing 84 mph winds, torrential rains, churned up seas, and flooding to parts of Japan that had only recently been battered and saturated by the much more severe Typhoon Lan.
The typical structure of a tropical cyclone eye is well defined in this photograph. The relative calm of the eye’s interior permits a view clear down to the sea below, which contrasts sharply with the intensely destructive forces generated by the thunderstorms lining the eye wall.
January 19-26, 2018
Dyeing To Be Noticed
It’s pretty hard not to notice a potash evaporation pond against the natural earth tones of the Utah desert, even from an altitude of 250 miles.
In the past, the production of potassium-based fertilizers has involved dangerous underground mining operations. These days the minerals are extracted from the ground via simple chemistry and solar energy.
At this site in Moab, Utah, water from the Colorado River is heated and injected into old shaft mines to dissolve the potash deposits. This solution is pumped into evaporation ponds, where the sun goes to work concentrating the solution through evaporation. An agent is added that attaches itself to the suspended potassium chloride and causes it to float to the surface, where it is skimmed off and packaged for use as plant fertilizer. A dye is added to accelerate the evaporation process, producing the somewhat shocking hue of electric blue.
January 12-19, 2018
Curtains of Unearthly Light
To mid-latitude dwellers in both the northern and southern hemispheres, the aurora may seem strange, even supernatural. A rare sight in the lower forty-eight, these dazzling displays nonetheless send a powerful message to the people of Earth by way of our northern brothers and sisters – that there’s more to our relationship with the sun than a nice afternoon at the beach. Much more.
By zooming in on the diffuse, drape-like quality of the Aurora Borealis from an altitude 250 miles above British Columbia in Western Canada, the camera challenges our sense of reality. Charged particles from the Sun interact with Earth’s atmosphere and magnetosphere to improvise a multicolored festival of light, as if to remind us that we must never take nature for granted.
Compare this shot with the ISS Image of the Week from November 11, 2017 (see archive below), a wide-angle shot that highlights the aurora’s overall circumpolar ring shape.
January 5 -12, 2018
Canal, Canali, Cannoli – Close Enough?
The late nineteenth century was all about canal building. The Suez Canal (pictured here) was completed in 1869, and reduced the travel distance between the North Atlantic and northern Indian Oceans by 4,300 miles by creating a shortcut from the Mediterranean to the Red Sea, through Egypt. The Panama Canal went online a mere eleven years later.
Telescopes were getting bigger and better at this time as well, and astronomers were spending long hours staring at neighboring planets (astrophotography wasn’t a thing yet) and mapping any discernible surface features their optics would resolve. In 1877 Italian astronomer Giovanni Schiaparelli observed a number of what he believed to be naturally occuring “canali”, an Italian word meaning “channels”, on the Martian surface. The word’s similarity to the English word “canal”, which refers specifically to an artificial waterway, led to years of bad astronomy in the person of well-to-do American astronomer Percival Lowell. Lowell devoted much of his later career to advancing his theory that the canals had been constructed by intelligent beings in order to redirect badly-needed water from the Martian poles to population centers nearer the planet’s equator.
Although most of Lowell’s contemporaries dismissed his ideas, it wasn’t until the Mars Mariner missions in the 1960s that remote sensing data could definitively prove him wrong.
December 30, 2017 - January 5, 2018
Just a few miles from Bora Bora among the Leeward Islands of French Polynesia lie Taha’a and Ra’iātea. The lush, inhabited tropical islands in the middle are remnants of eroded volcanos, while the keyhole-shaped network of turquois fringe encircling them are separate kingdoms altogether –living, evolving coral reef.
Communities of coral animals thrive in the warm, shallow waters around tropical volcanic islands. Even as the elements erode away the exposed volcanic land mass above the water, countless generations of coral go about their business building vast underwater cities of astounding biodiversity beneath the surface. Islands in tropical waters may erode away entirely, leaving behind only the surrounding reef – an atoll – to mark its former location.
Taha’a and Ra’iātea probably comprised a single, larger island before millennia of erosion split them apart.
December 16 - 29 2017
Betsiboka River Delta
Madagascar may well be the most unique place on earth. 90% of the wildlife found on Madagascar is exclusive to this small island country off of Africa’s eastern coast, including over 100 species and subspecies of lemur alone.
Unfortunately, human activity is taking its toll on this biodiversity hotspot. Erosion caused by the widespread destruction of forest habitats is silting the rivers, turning them brick red – the color of the soil. While visually striking, it is symptomatic of an ecosystem in distress.
December 9 - 15 2017
A gargantuan dust storm redistributes the sands of a North African desert in this image from August 8, 2014. This large-scale weather system included many cumulonimbus clouds, or thunderstorms, whose characteristic anvil-shaped tops can be seen protruding through the dust-choked base layer.
We share our atmosphere with all who inhabit this planet, and while the greatest and most immediate impact of African dust storms is on the local population, the impact, as it turns out, is not exclusively local. Evidence suggests these storms play a role in the development of tropical cyclones in the Atlantic, which in turn impact the multinational islands of the Caribbean, and the United States gulf coast and eastern seaboard.
African dust intrusions have even been observed in Houston, TX, where the superfluous airborne particles can contribute to respiratory problems, such as asthma.
December 2 - 8, 2017
Hey Everybody, Look at me!
If a volcano could post, the Twitter-verse might have recently exploded with this self-admiring cry for attention.
The pre-eruptive venting of eastern Bali’s Mount Agung, seen in this September 19, 2017, image from the ISS, foretells of the spectacular and purely natural performance which would take place just ten weeks later.
At 5:30 pm local time on Saturday, November 25, plumes of thick volcanic ash spewed from Agung’s central crater. By Sunday the cloud of smoke and ash reached 5.6 miles into the Indonesian skies, forcing thousands of island residents and tourists to evacuate, and air traffic to be either suspended or rerouted.
Agung appears to be on the verge of a more severe, magmatic eruption phase. A powerful eruption could launch ash particles and sulfur dioxide gas into the stratosphere, reflecting sunlight and measurably cooling the entire planet.
According to Balinese tradition, Mount Agung is a replica of Mount Meru, the sacred cosmological mountain at the center of all physical, metaphysical, and spiritual universes.
November 24- December 1, 2017
WHEN CHILE WAS EVEN CHILLIER
Whether you study it for evidence of climate change or hang it on your wall as art, this image of the Southern Patagonian Ice Field is extraordinary. The ice field fills all of Chile’s 8.7 million acre Bernardo O’Higgins National Park and then some. It is a remnant of the much larger ice sheet that covered all of southern Chile during the last glacial period. The terminus of O’Higgins Glacier can be seen protruding into O’Higgins Lake in the lower left of the photo.
In 2007 a glacial lake in the park vanished when pressure from accumulated melt water ultimately destroyed an ancient ice dam. Scientists have linked the accelerated melt rate to climate change.
November 16- November 23, 2017
Hey, Who Let the Air out of the Moon?!
You can thank atmospheric refraction for this droll little optical illusion.
In this image from August of 2016, sunlight reflected off of the Moon’s surface is bent as it passes through Earth’s atmosphere. By the time it arrives at the camera lens peering through the space station’s cupola window, something’s off.
Misshapen, yes. Permanent, no. Light travels fastest through a vacuum, slower through a medium – like air, for example. Where the atmosphere is denser its velocity is somewhat slower, and the light is bent, or refracted. Atmospheric refraction displaces stars from their expected location, and warps the shape of larger objects like the Sun and Moon. These ‘altered states’ are most noticeable just above the horizon, where the atmosphere is densest.
November 11- November 15, 2017
Best. Lightshow. Ever.
Don’t book a room anywhere near Santa’s workshop if your goal is to observe the northern lights overhead. The aurora usually appear as a ring around the earth’s magnetic poles, called an auroral oval, with a diameter of about 2,500 miles. Consider a visit to Alaska, Denmark, or Iceland if it’s straight-up amazing light shows you’re looking for.
The crew of the International Space Station was passing over Mongolia, looking north toward Russia, when this image was taken. Notice the relative positions of the yellowish line that marks the edge of earth’s atmosphere, and the vivid green auroral display. What does this tell us about where in the atmosphere the aurora form?
November 4 - November 10, 2017
Mount Etna – It’s Alive!
Dual vents on Europe’s largest active volcano send plumes of steam in the direction of Riposto, a town along the eastern coast of Sicily. Mount Etna sits above a geologic hotspot, where the African plate subducts beneath the Eurasian plate. The active, 10,922-foot stratovolcano is about 500,000 years old. This image dates from August, 2014.
In 2013 Mount Etna was declared a UNESCO World Heritage site, largely for its “exceptional level of volcanic activity”. In spite of the hazards, about a quarter of the island’s population lives in the volcano’s immediate vicinity. And why wouldn’t they – thanks to Etna the soil is rich and fertile, vineyards and olive groves abound, and tourists spend money with considerable enthusiasm.
The moral of this story – if life gives you lava, make a Mediterranean paradise.
October 28 - November 3, 2017
“You’re old, dusty, gassy and warped. But beautiful. “
Scott Kelly’s words say a lot. He snapped this evocative image of our galactic hometown through the space station’s cupola window in September of 2015. Framed here by the humble forgings of mankind and the elegant arch of earth’s atmosphere, the sheer abundance of solar systems with which we share the neighborhood is breathtakingly apparent.
The fairly long exposure time required for this image – five seconds – accounts for the elongation of the stars, which would otherwise appear as sharp pinpoints of light. Temperature differences produce the wide range of colors seen here, from cooler red stars to hotter blue stars. Our yellowish sun is in the low to mid-range of this scale.
October 20 - 26, 2017
London After Dark
We love our electric lights. In fact, if you want to get a good sense of the population density of any first-world city, just wait for the sun to go down. 8.7 million people inhabit Greater London, and as this image from January of 2017 clearly illustrates, they all own at least one high-intensity light bulb.
Star gazing in these conditions can be frustrating or even impossible, thanks to a phenomenon known as skyglow. Light scattered by the atmosphere above our cities serves as a perpetual night light. Sleep deprivation induced by this relentless exposure has become a significant public health problem in many urban areas.
A grassroots effort known as the dark-sky movement works to raise awareness of, if not shed new light on, the impact of light pollution on people and wildlife.
October 13 - 19, 2017
Great American Eclipse
Our moon is 400-times smaller than our Sun, which the Earth and Moon orbit together. In a purely coincidental fact of celestial geometry, our moon is also 400-times CLOSER to the Earth than is the Sun. Every now and then the tilted orbital planes of the Earth and Moon intersect during a new moon, and the Moon’s elliptical orbit places it at just the right distance. Thus, from our perspective here on Earth, the Moon is centered in front of the Sun at a moment when their apparent sizes are the same. Thank you, 400.
October 6 - 12, 2017
Harvey Approaches the Coast of Texas
“Imagine being on a spaceship, watching this storm barreling down on your family. Fingers crossed for the Gulf Coast.”
Former ISS astronaut Chris Hadfield was referencing the fact that Johnson Space Center in Houston, TX is home to the astronaut corps, as well as their families, when he tweeted these words on August 24, 2017. This image was taken as the ISS flew over Hurricane Harvey prior to landfall on Friday, August 25 at 1:16 PM.
The massive storm came ashore just east of Corpus Christi, TX on Friday night as a Category 4 hurricane. It progressed very slowly once over land, meandering in the direction of San Antonio before heading back into the Gulf of Mexico, northeast to Houston, and eventually into Louisiana. The result was unrelenting rainfall for days, and widespread devastation due to flooding.