Lenticular_Murrieta_31325262633_3b5b64dce5_o (1)

Photographer: Mark Ritter

Summary Authors: Mark Ritter; Jim Foster

Featured above are a formation of eye-catching lenticular clouds (Altocumulus lenticularis) seen near sunset, not far from Murrieta, California. Strong airflow over mountain crests, in this case, the Santa Ana Mountains (just off the left edge of the photo), prompted these mid-level, orographic wave clouds to form on the lee side of the range. Since sufficient moisture was available to form clouds, and since the airflow aloft was quite strong, layers of clouds at the wave crest stacked one upon the other. Photo taken on January 5, 2017.

Photo Details:  Camera Model: Canon EOS 5D Mark III; Lens: EF24-105mm f/4L IS USM; Focal Length: 55mm; Aperture: ƒ/7.1; Exposure Time: 0.0063 s (1/160); ISO equiv: 1250; Software: Adobe Photoshop Lightroom 6.8 (Macintosh).


Each Sunday we present a notable item from our archives. This EPOD was originally published April 22, 2003.

Provided by: Teena Della, Terry Fox Secondary School

Summary author: Teena Della

The photo above shows a classic example of exfoliation. The U-shaped Coquihalla valley in British Columbia, Canada was carved by glaciers tens of thousands of years ago. As the overlying glacial material was removed, the rocks that had formed underneath the massive ice sheet rose up (isostasy) and tried to expand. Isostasy is also known as glacial rebound. Rocks, of course, aren’t very flexible so instead of expanding, their outer layers are peeling off like onion skins -- the process of exfoliation.

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EPOD_EncoreDeathValleylake bed110502-80lre

Today, and every Saturday Earth Science Picture of the Day invites you to rediscover favorites from the past. Saturday posts feature an EPOD that was chosen by viewers like you in our monthly Viewers' Choice polls. Join us as we look back at these intriguing and captivating images.


Photographer: Marli Bryant Miller

Summary Author: Marli Bryant Miller

November 2011 Earth Science Picture of the Day Viewer's ChoiceThe Mesquite Flat dune field, part of which is shown above, is the largest and most accessible of five dune fields in Death Valley National Park. Like all dune fields, it requires three conditions to form: 1) a steady supply of sand, which here is supplied by nearby alluvial fans, 2) plenty of wind to move the sand, and 3) a natural windbreak so the wind will actually deposit the sand. Most of the dune fields of Death Valley lie in windbreaks afforded by irregularities in the adjacent mountain front. The fine-grained, mud-cracked deposits in the foreground underlie many of the interdune areas of the dune field. They're sediments of a former lake, which covered the area when the climate was wetter. The mountains in the background, the Grapevine Mountains, were uplifted relative to the valley floor along an active fault zone. They consist mostly of Paleozoic limestone, dolomite, and sandstone. Photo taken on May 2, 2011.

Photo Details: Camera Model: Canon EOS 5D Mark II; Lens: EF17-40mm f/4L USM; Focal Length: 19.0mm; Aperture: f/10.0; Exposure Time: 0.020 s (1/50); ISO equiv: 100; Software: Adobe Photoshop Lightroom.

([syndicated profile] epod_feed Apr. 21st, 2017 03:01 am)

Constellation Leo and the chinese guardian lions (1)

Photographer: Jeff Dai

Summary Author: Jeff Dai

The constellation Leo the Lion is shown here rising above guardian lions in the Inner Mongolia region of China. Lions aren't native to China. But with increased trade during the Han dynasty and cultural exchanges through the Silk Road, lions were introduced into China from the ancient states of Central Asia and India. The Buddhist version of the lion was originally introduced to China as the protector of dharma. These lions have been depicted in religious art as early as 208 BC. Gradually, they were incorporated as guardians of the Chinese Imperial dharma. Apparently, lions seemed appropriately regal beasts to guard the gates and have been used as such ever since.

Evidence suggests that like lions the 12 zodiacal constellations were introduced to China from India. The ancient Chinese had their own independent astronomy, but the zodiacal constellations are still widely noted in art and literature. For example, numerous ancient Chinese books mention the names of the zodiacal constellations. Photo taken on December 27, 2016.

([syndicated profile] epod_feed Apr. 20th, 2017 03:01 am)

Optics in My Home Garden copy

Photographer: Menashe Davidson

Summary Author: Menashe Davidson

One advantage of keeping a garden is the opportunity to understand nature better. As Albert Einstein said, "Look deep into nature, and then you will understand everything better."

After it rains, I always check its effect on the plants of my terrace garden in Rishon LeZion, Israel. The above photos were taken after a recent rain and demonstrate the optical phenomena of a mirror and a lens nicely. On the top photo (taken on December 17, 2016) notice the rain that had accumulated in the little metal basin holding the Cyclamen flower pot, in the foreground. Like a flat mirror, the light rays were reflected (specular reflection) resulting in the upside-down image of the tall building adjacent to my apartment. On the second photo, water drops are adhering to Adenium (Desert Rose) flower tubes. These drops functioned as a lens, refracting light through the drops to produce the inverted image of the same tall building that appears in the top photo.

Photo Details: Top - Camera Model: NIKON D7100; Focal Length: 22mm (35mm equivalent: 33mm); Aperture: ƒ/22.0; Exposure Time: 0.0063 s (1/160); ISO equiv: 2000; Software: Windows Photo Editor 10.0.10011.16384. Bottom - same except:  Lens: 18.0-200.0 mm f/3.5-5.6; Focal Length: 200mm (35mm equivalent: 300mm); Aperture: ƒ/16.0; Exposure Time: 0.0020 s (1/500); ISO equiv: 500; Software: Adobe Photoshop CS5 Windows.

([syndicated profile] epod_feed Apr. 19th, 2017 03:01 am)

BuffaloFalls (2)

Photographer: Rod Benson

Summary Author: Rod Benson

A big part of the history of humanity is the story of cultures figuring out how to make a living using what nature has given them. Buffalo Falls, located 25 mi (40 km) west of Great Falls, Montana, provides an interesting example of this. Volcanic activity during the late Cretaceous period, several miles southwest of here, caused several dikes, laccoliths and sills to form. Note that Buffalo Falls is the edge of a sill, and Birdtail Butte (in the background) is a laccolith. Since igneous rock is more durable than the sandstone that it intruded, the edge of the sill was exposed as a cliff.

Centuries before the arrival of horses, Native Americans in the area took advantage of this resource, using it as a bison kill site. Two rows of evenly spaced rock cairns about two mi (3.2 km) long formed a V that funneled the stampeding bison to the cliff where they fell to their death. Those not killed by the fall were finished off by hunters positioned below. Evidence such as arrowheads indicates that Shoshone, Salish and Blackfeet peoples probably all used the site during different time periods. Several tipi rings located in the narrow valley just below the cliff show where the groups camped as the meat and other materials were harvested and processed.

According to the Office of Historic Preservation (Montana), archeologists have identified over 300 bison kill sites in Montana, and there are likely more that haven't been found or reported. We know them as buffalo jumps, however, most are not cliffs, but rather places where bison were driven into natural or artificial enclosures, or into bogs or snow-banks and then finished off with weapons. No two are the same, but they often contain a wealth of evidence, including bison bones, arrowheads, tools, roasting pits, and fire-cracked rock. The use of buffalo jumps started to decline in the 1700s with the arrival of the horse - an animal that brought many big changes to the Indian way of life. Photo taken on June 13, 2015.

Photo Details: Camera Maker: Panasonic; Camera Model: DMC-LX7; Focal Length: 4.7mm (35mm equivalent: 24mm); Aperture: ƒ/2.8; Exposure Time: 0.0008 s (1/1300); ISO equiv: 80; Software: QuickTime 7.6.6.

([syndicated profile] epod_feed Apr. 18th, 2017 03:01 am)

Bayside-sea slippers and barnacles

Photographer: Rob Sheridan

Summary Author: Rob Sheridan

A number of invasive invertebrates have disrupted New England’s intertidal ecosystems in recent decades, but three old stalwart natives remain common. All three form amazing but different marine adhesives. The Blue Mussel (Mytilus edulis), shown in my hand, is a bivalve mollusk that adheres to rocks and to each other with strong slightly elastic byssal threads. These fine filaments are secreted by byssal glands along the foot of the mussel, forming as soon as the final planktonic stage finds a resting place and anchoring the maturing mussel for life.

The Atlantic Slipper Limpet (Crepidula fornicata) is a gastropod mollusk that has evolved a mucous based glue that prevents vertical removal (by predators) while permitting lateral motion, allowing the mobile animal to graze on algae. They're the whitish, rounded objects on the of the mussel's shell. Interestingly, the New England native Atlantic Slipper Limpet has become a difficult invasive in European waters, interfering with oyster production.

The Northern Rock Barnacle (Balanus balanoides), the objects with holes at the center of their shells, is a crustacean, like lobsters and crabs, rather than a mollusk. It's oriented with its head glued down by cement, excreted by glands at the base of its first antennae. After this cementing process, the barnacle then forms a calcium carbonate enclosure. It's the only crustacean that remains fixed in one spot for life. When covered with water, barnacles open their enclosure and extend feathery modified leg appendages (cirri) that filter nutritional organic matter from the water and function as gills.

All three species share a somewhat similar reproductive strategy. They adhere to hard substrates, including boat hulls and larger animals and to each other. Having female and male animals in proximity promotes reproduction; timing release of their gametes to facilitate commingling in the water. Fertilized eggs in all three species are initially planktonic before fixing on a stable surface for life, with their amazing adhesives. Scientists are actively pursuing these adhesives for a variety of medical uses. Photo taken on September 22, 2008.

Photo Details: Camera Model: Canon PowerShot SD1000; Focal Length: 5.8mm; Aperture: ƒ/2.8; Exposure Time: 0.0031 s (1/320); ISO equiv: 80. 

Mila_Mirage_sunset (2)

Photographer: Mila Zinkova

Summary Author: Mila Zinkova

Most everyone has seen a sunset where the round disk of the Sun slowly sets and eventually disperses below the horizon. As seen from San Francisco, the setting Sun is rarely round, as shown above, and sometimes it's rising instead of setting! Click here to see a video of one such rare and amazing sunset.

On this video, at first the Sun isn't really going down but is rather getting flatter. Then at around the 1:02 mark you'll see a thin red line at the sea's horizon. At this point, the real Sun is already below the horizon. What you're seeing is a mirage of the Sun. You'll notice that multiple images of the miraged Sun start appearing above each other. After a few more seconds, the Sun looks more like a nuclear explosion than our home star. Continue watching the video and you'll observe that the lower images of the Sun are connected to each other and take on a rectangular shape. At the 4:16 mark the lowermost images of the Sun begin to show the Novaya Zemlya effect, first commented on by polar explorers.

The miraged Sun isn't really setting; rather it's melting into the sky. Yet it's reluctant to disappear. Notice how some of the images of the Sun that seemed to have disappeared actually reappear again a split second later. For example, at 5:58 it seems that only the uppermost image of the Sun is still present, but at 5:59, the image of the Sun below it is reappearing and in addition is getting brighter. Also, note the weird clouds at upper right (they're much better seen after the 4:16 mark). They look odd because they're miraged as well -- a fata morgana in the clouds. This mesmerizing sunset was delayed by more than 6 minutes based on the ephemeris time for sunset in San Francisco.

So what's going on here? As with all mirages, temperature gradients are involved. However, in this case, a complex temperature profile over the sea, including a thermal inversion, wildly distorted the shape of the Sun as it set.

([syndicated profile] epod_feed Apr. 16th, 2017 03:01 am)


Each Sunday we present a notable item from our archives. This EPOD was originally published April 25, 2003.

Provided and copyright by: Jean Chiasson

Summary authors & editors: Jean Chiasson; Jim Foster

The above photo of Meteor Crater was taken from a commercial jet over north central Arizona, at an altitude of 27,000 feet (8,230 m). Also known as Barringer Crater, Meteor Crater is easy to identify. It's nearly 0.8 miles (1.3 km) in width and was formed by the impact of a meteorite (about 150 ft or 46 m in diameter) approximately 50,000 years ago. Because of its relatively youthful age and arid location, it's one of the most well-preserved impact craters in the world. See also the Earth Science Picture of the Day for June 26, 2001.

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EPOD_EncoreGslset428_8july11 (2)

Today and every Saturday Earth Science Picture of the Day invites you to rediscover favorites from the past. Saturday posts feature an EPOD that was chosen by viewers like you in our monthly Viewers' Choice polls. Join us as we look back at these intriguing and captivating images.

Photographer: Ray Boren

Summary Author: Ray Boren

October 2011 Earth Science Picture of the Day Viewer's ChoiceThe photo above showing a veil of virga over the Great Salt Lake, was taken from Bountiful, Utah on July 8, 2011. Virga is precipitation that mostly evaporates before reaching the surface. The Sun on this early July day was setting beyond Great Salt Lake, coloring monsoon-generated clouds. In midsummer, but usually a bit later than when this photo was captured, a high-pressure zone sets up over the Four Corners area (New Mexico, Arizona, Colorado and Utah) pumping moisture northward. This is referred to as monsoon weather. Clouds tend to build during the heating of the day, fomenting weather that can range from very dangerous flashfloods to the less troubling virga wisps shown here. If the moisture-bearing clouds are hefty enough, however, rain can fall at any time of day or night, and post-midnight thunderstorms are not uncommon.

([syndicated profile] epod_feed Apr. 14th, 2017 03:01 am)

Slcgsl693c_24feb17 (1)

Photographer: Ray Boren

Summary Author: Ray Boren

It seems a good idea to ponder occasionally our place in the scheme of things, as this photo helps us do, in a way. This panoramic evening scene, captured just before sunset on a chilly, below-freezing winter's day, features the Wasatch Mountains, freshly blanketed with what Utah likes to promote, for its canyon ski resorts, as “The Greatest Snow on Earth.” Bolstered by a wet winter, the beautiful sky and peaks are reflecting in the shallow waters of the eastern bays of Great Salt Lake. The largest natural lake west of the Mississippi River, as well as the biggest saline lake in the Western Hemisphere, it's a terminal, or endorheic, lake (with no outlet to the sea), and as a result is much saltier than the Earth’s oceans. Due to a multi-year drought and the diversion of water for use upstream, the lake’s surface level is at near-record lows.

Have you noticed the tiny rectangles by the shore toward the left? They represent the skyline of downtown Salt Lake City — itself originally known as Great Salt Lake City when pioneers first established the community in the mid-19th century. Utah’s State Capitol is a domed structure on that rise just to the left of the teensy skyline. An illuminated late-afternoon squall behind the city’s skyscrapers is helping to define the seemingly little buildings.

The Wasatch Mountains, variously composed of igneous (granite) and sedimentary (mostly limestone) layers, were shaped by 20 million years of geologic faulting and Ice Age glaciation. The highest of them semi-visible here — Mount Olympus, Twin Peaks and Lone Peak — top out near or just above 11,000 ft (3,354 m) in elevation. Yet at this angle and from this vantage, along a causeway to Antelope Island, you might be hard-pressed to discern that a million people live right there, in the valley beyond Great Salt Lake’s southern shore. Photo taken on February 24, 2017.

Photo Details: Camera Model: NIKON D3200; Lens: AF-S VR Zoom-Nikkor 70-300mm f/4.5-5.6G IF-ED; Focal Length: 70mm (35mm equivalent: 105mm); Aperture: ƒ/5.6; Exposure Time: 0.0080 s (1/125); ISO equiv: 100.

([syndicated profile] epod_feed Apr. 13th, 2017 03:01 am)


: Ralph Winrich

Summary Authors: Ralph Winrich; Jim Foster

The photo above may look like an image from a flyby of Pluto, but instead is a strange diamond or cubic-shaped frost pattern on my car windshield, as observed at my home near Stoughton, Wisconsin, on the morning of February 27, 2017. It's a standard windshield, made of laminated glass like nearly all windshields today, and as far as I could tell, it wasn't pitted or defective in any way.

The temperature at the time the image was taken was 26 F (-3.2 C). The previous day's maximum at nearby Stoughton, was 41 F (5 C) and the minimum on the 27th was 21 F (-6 C). The sky was clear and the winds very light, from the south at less than 5 mph (8 km/h). A similar pattern was photographed on a windshield in Birch Bay, Washington (November 22, 2013), with temperature, wind and sky conditions nearly the same as for the Wisconsin case.

Frost crystals are affected by surface imperfections (scratches, cracks, concavity, etc.) as well as the temperature and cleanliness of the glass, the presence of moisture and even the presence of chemical residues on the glass surface. For instance, pollen or dust particles may act as nucleation points for crystalline formation. Ice crystals can grow quickly and take on bizarre patterns when both atmospheric and glass conditions are favorable. How these crystals formed as they did is hard to fathom, but perhaps the windshield being warmed in the previous afternoon's sunshine together with sufficient water vapor near the ground (during the overnight hours) and chemical residues on the glass surface all contributed to this strange pattern.

Photo Details: Nikon D 80 camera; lens 35 mm; ISO 800. Top - Close up of windshield showing strange frost pattern. Bottom - Full image showing entire windshield.

([syndicated profile] epod_feed Apr. 12th, 2017 03:01 am)


Photographer: Patti Weeks

Summary Author: Patti Weeks

Shown above is the bathtub ring that surrounds Lake Powell, Utah. It's the broad mineral-covered swath of white at the base of the cliff. This band is seen all along the lake and reveals the area that was covered by the lake when at its peak level—nearly 100 ft (30 m) higher than today.

Lake Powell reached capacity (at the 3,700 ft or 1,238 m level) in 1980. The statistic about the bathtub ring is updated continually and at the time of this writing is less than half capacity—at only at 47.79 percent. The steadily decreasing lake level is caused not only by evaporation in the windy, arid environment (exacerbated by the past 17-year drought in the Colorado River Basin) but also by the steady overuse of the Colorado River systems and the seeping of water back into the fissures at the bottom of Glen Canyon. The combined water loss from evaporation and seepage equals 280 billion gallons annually.

Note the fingers of land protruding into the lake. They were shaped by deep, stream channels that were cut prior to the formation of the Rainbow Bridge. Also noteworthy are the vertical streaks of desert varnish, visible on nearly all of the rock faces. Photos taken August 21, 2016.

Photo Details: Camera Maker: SONY; Camera Model: DSC-RX100M4; Lens: 8.8-25.7mm ƒ/1.8-2.8;

Focal Length: 19.29mm (35mm equivalent: 53mm); Aperture: ƒ/5.6; Exposure Time: 0.010 s (1/100); ISO equiv: 125.      

RedSprite_224127 (1 z 1) (1)

Photographer: Martin Popek

Summary Authors: Martin Popek; Jim Foster

Shown above are the first red sprites of the 2017 storm season, over Europe, as viewed from over 250 miles (400 km) away. My location was in the extreme eastern Czech Republic, the storm cells were along the border between Germany and the Czech Republic -- at left. Cold season thunderstorms over Europe tend to have low cloud heights, so being able to observe the red sprites, a high altitude form of lightning, was a surprise. Additionally, though it's thought that sprites form over the more active thunderstorms, those having a strong electric field, little conventional lightning activity (cloud-to-cloud, cloud-to-ground) was reported from the storm that produced these enigmatic flashes. The sprites featured here occurred approximately 35 mi (56 km) above the surface. It should be noted that even with excellent viewing conditions these quick flashes are hard to catch with the naked eye. Photo taken on March 9, 2017.