Exploring the Earth and Sky of the West

Posts tagged “photography

Halos, arcs, and bows…oh my!

Double rainbow near Gunnison, Colorado

The term “landscape photography” is a misnomer in some ways. After all, many of the most interesting and unique landscape shots are those in which something unique or interesting is happening in the sky: a vibrant sunset bathing the land in a golden glow, an ominous storm looming on the horizon, or a terrestrial scene backed by a sky awash in stars. A colorful sky, interesting clouds, or a stray meteor can single-handedly liven up otherwise passé landscapes. As a longtime astronomy educator, I have a habit of looking up…a habit that often pays photographic dividends. I had an astronomy professor in college who would often remark that “most people just don’t look up”, a sad but true (save for perhaps an occasional glace at the clouds on a stormy day) acknowledgement of just how little attention most of us pay to the sky above us. 

One of the things that we miss by not looking up is a myriad of features that result from the interaction of sunlight with water droplets or ice crystals in our atmosphere. These features lack a catchy collective name, but scientifically are often referred to as atmospheric optical phenomena. Perhaps the most frequently observed example is the humble rainbow: 

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Rainbow over the Wenatchee National Forest in central Washington. This photo was taken in the early afternoon, with the Sun still relatively high in the sky, thus the arc of the rainbow appears quite close to the ground and only a small portion is visible. 

The colorful band of light in a rainbow results from a process known as dispersion. When sunlight passes through water droplets in the Earth’s atmosphere, different colors of light are refracted (or “bent”) by different amounts as they pass through the droplet, thus spreading out the colors that make up “white” sunlight into a rainbow. The water droplets don’t have to be rain; sea spray or the mist of a waterfall can do the trick as well. The geometry of dispersion is such that the center of a rainbow’s curvature will always be directly opposite the Sun. Consequently, the largest and grandest rainbows are seen near sunrise or sunset (see photo below) when our star is low on the horizon. In contrast, when the Sun is higher in the sky, only a small portion of the arc will be visible (see photo above). 

Double rainbow near Gunnison, Colorado. This rainbow appeared not long before sunset, when the Sun was low in the sky, thus nearly an entire semi-circle is visible.

The light source for a rainbow need not be the Sun either. Light from the Moon can also be dispersed through water droplets, with a similar result. The caveat? Even a bright full moon is about 400,000 fainter than the Sun, so the resultant moonbow is much fainter than a rainbow and the colors not bright enough to trigger the color-seeing cones in our eyes. Thus, a moonbow appears monochromatic. I’ve only ever witnessed this eerie phenomenon once: on a damp and muggy evening on the north coast of New Zealand’s South Island, and unfortunately did not have the wherewithal to capture a photo at the time. 

Moving beyond water droplets, the possibilities when sunlight interacts with tiny ice crystals in our atmosphere (such as those that comprise high altitude clouds like cirrus and cirrostratus) are myriad. Depending on the shape, size, and orientation of said crystals, the height of the clouds, and the location of the Sun, a wide range of atmospheric phenomena can result when we see the Sun through these high-altitude icy clouds.  

One of the most common is the 22° halo, a ring of light that encircles the Sun (or the Moon) at a radius of (you guessed it) 22 degrees:

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22 degree halo, Lake Crescent, Olympic National Park, Washington. Blocking out the Sun (with a stick in this case) is often necessary to get a decent photo of these halos.

These halos can be a little difficult to spot (and photograph…) due to the Sun’s glare, but in most locations they are, statistically speaking, much more common than rainbows. Like rainbows, these halos are caused by dispersion as sunlight passes through tiny ice crystals in the atmosphere. If you look VERY carefully (such as in the photo above), you can see that the inner edge of the halo is reddish while the outer edge is bluish.

The name “22° halo” suggests that halos can appear at other distances from the Sun as well, which is indeed the case. Another member of the halo family is the circumhorizontal arc, a halo that takes the form of a brightly colored band circling the horizon at a radius of 46° from the Sun. Unlike 22° halos, circumhorizontal arcs are rarely visible in their entirety. Instead, you’ll usually only see one or two small fragments in areas of the sky where the background consists of the correct type and height of cloud. These fragments look like pieces of a rainbow oriented parallel to the horizon: 

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A portion of a circumhorizontal arc over the Angels Window arch on the North Rim of the Grand Canyon, Arizona

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Portion of a circumhorizontal arc over Ouray, Colorado

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Small fragment of a circumhorizontal arc (upper left) visible over Mt. Rainier, Washington

In order to see a circumhorizontal arc, the Sun needs to be at least 58° above the horizon. This means that, at least for us here in the mid-Northern latitudes, they are only visible in summertime. The rest of the year the Sun simply doesn’t get high enough in the sky to allow them to be seen, even when the right types of ice crystals are present. (Further north, close to the poles, they can’t be seen at all!) Indeed, a quick review of my photo archives shows that all the photos I have of this phenomenon were taken in late June or July. 

Circumhorizontal arcs bear some resemblance to another phenomenon known as cloud iridescence. Unlike the features we’ve discussed so far, cloud iridescence is the result of diffraction (as opposed to refraction and dispersion), which is when light waves are bent around objects. Iridescence occurs at the edges of very thin clouds that are made of very similar sized water droplets or ice crystals. If the cloud layer is thin and uniform enough, light waves bent around these particles interfere with each other, producing a spectrum of colors. Without getting into the nitty gritty details, the colors that you see in an iridescent cloud are more akin to the colors that you sometimes see in soap bubbles or a pool of oil. 

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Close up of cloud iridescence over Walla Walla, Washington

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Cloud iridescence, Whitman Mission National Historic Site, Washington

Despite their similar appearance, cloud iridescence and circumhorizontal arcs are relatively easy to distinguish from one another. Fragments of circumhorizontal arcs always appear (you guessed it) horizontal relative to the horizon and will always have a bright red band on top. In contrast, cloud iridescence can appear in all sorts of shapes and patterns, and you’ll often see the spectrum of colors repeating themselves multiple times as well, as seen in the photos above. 

Like rainbows, many other atmospheric phenomena occur only when the Sun is close to the horizon, just before sunset or just after sunrise. Sun pillars, like those in the photos below, are the result of sunlight being reflected off the surface of flat, hexagonal-shaped, ice crystals and redirected back to the observer: 

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Sun pillar, Grand Canyon National Park, Arizona

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Sun pillar, Yakima, Washington

Once in a great while, conditions will be just right and you’ll get a whole truckload of these phenomena all at once, such as on the evening I took the photo below on a recent neighborhood walk as the Sun set over the Cascade range: 

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Atmospheric phenomena galore! Here, the Sun is surrounded by a 22° halo complete with a tangent arc (the triangular wedge of light at the top of the halo). A sun pillar extends vertically above the Sun, while a sundog (the bright patch on the halo to the right of Sun) is visible at right.  

Sundogs and tangent arcs will have to wait until another day. Until then, keep your eyes on the sky. Chances are you’ll spot a nalo, arc, or bow before too long! 


More Spring Wildflowers (this time with spines!)

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A clump of hedgehog cacti (Pediocactus nigrispinus) blooming in the deserts of central Washington

One of our favorite times of year when living in southern Utah was late spring, when the desert would come alive with a wide variety of vibrantly colored cactus blossoms (which were soon followed by delicious fruits that made superb sauces, beer, and margaritas!) Central Washington is a bit lacking in the cacti-department, but we do actually have a few species that can put on a springtime show if you know where to look. 

The most widespread species is the Columbia Prickly Pear (Opuntia columbiana), however I’ve yet to see any flowers. I am beginning to suspect that this species blooms only in certain years with the proper moisture conditions, though I haven’t been able to confirm this. 

Another species, a variety of hedgehog cactus (Pediocactus nigrispinus), is harder to find, but quite reminiscent of the stout barrel cacti of Utah, Arizona, and Nevada. Once more common in central Washington, Pediocactus nigrispinus has sadly been the target of illegal collecting and poaching, reducing its numbers to the point that it is now a threatened species here in Washington. We’ve run across patches of this cactus on two recent hikes, and the second time we were delighted to find many of the buds in bloom. This little cactus, robust but generally no more than a few inches high, has electric-pink flowers that really stand out, even when surrounded by tons of other spring flowers on the sagebrush steppe.  

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A hedgehog cactus (Pediocactus nigrispinus) blooming in the deserts of central Washington

And for good measure, a few other flowers from recent excursions:

Large yellow flowers in the sunshine

Balsamroot (Balsamorhiza sp.) flowers in the Yakima River Canyon of central Washington. 

 

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Low-growing lupine (Lupinus sp.) in the Yakima River Canyon of central Washington. 

 

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Balsamroot (Balsamorhiza sp.) flowers at Steamboat Rock State Park in central Washington. 

Tips on identifying specific balsamroot or lupine species are welcome! There seem to be dozens of different varieties out here, but I sure as heck can’t tell them apart…


Throwback Thursday: Glacier Peak

A tall mountain peak is just visible above clouds, with green meadows and forests belows.
A tall mountain peak is just visible above clouds, with green meadows and forests belows.

Glacier Peak…the top of it at least. This was about the most we saw of it on our three-day trip. 

While we wait for the snows to melt once again, time for another flashback to 2020. I realize that phrase likely strikes fear in the hearts of most, so feel free to pretend these photos are from some other year. While it was a rough year in many ways, the wilderness was just as spectacular as ever!

For a while last summer, our goal was to camp in the shadow of every active Cascade Range stratovolcano in Washington and Oregon. We ended up getting to 8/10, but late season plans for Mt. Baker and Mt. Jefferson ended up being derailed by fires, weather, or both. In total we camped 28 nights and hiked/backpacked over 250 miles in our COVID-safe exploration of the Cascades last summer. To minimize contact with others (and to save money), we eschewed developed campgrounds in favor of dispersed camping. Aside from backpacking permits, we paid for accommodations just once the entire summer, at a five-site Forest Service “campground” on the north side of Mt. Hood that we ended up having all to ourselves for the night.

One of our most memorable excursions was a quick two-night backpacking trip to the Glacier Peak and Henry Jackson Wilderness areas in north-central Washington.

Sunrise light illuminates rocks in an alpine lake basin.

Early morning light at a campsite along the Pacific Crest Trail in the Henry Jackson Wilderness Area of central Washington

Of all the active volcanoes in the Cascade Range, Glacier Peak is by far the most difficult to glimpse up close. Tucked away in the north Cascades, reaching the vicinity of the Glacier Peak edifice requires a hike of at least 10-12 miles, making a backpacking trip really the only way to truly experience the mountain. For us, it was a ~35 mile, 3-day, 2-night trip beginning from the valley of the Little Wenatchee River. While were able to get quite close to the mountain, this was (amazingly) the only trip of the summer where the weather didn’t really cooperate with our desire to see the mountain in whose shadow we were camping. We got a handful of summit glimpses through breaks in the clouds, but Glacier Peak was obscured for the majority of our trip.

The summit of a glacier clad peak is visible through a break in the clouds

Tantalizing glimpses of Glacier Peak through the low clouds. 

A tall mountain peak is just visible above clouds, with green meadows and forests belows.

A fleeting view of the glacier-clad (not surprisingly) summit of Glacier Peak. 

A variety of wildflowers on a ridge looking down into the valley of the Little Wenatchee River.

Looking down the Little Wenatchee River valley with some late season paintbrush providing a splash of color. 

A hiker stands atop a ridge looking out onto grassy meadows and mountains

The view from Kodak Peak in the Glacier Peak Wilderness. Glacier peak is behind those clouds somewhere! 

A marmot sits on a rock above a slope of rocks and wildflowers

A marmot enjoys the view from Kodak Peak.

Despite the lack of peak views, the rugged, high altitude terrain was stunning and while we were a little too late for peak wildflower season, there were still lots of blooms covering the slopes:

A trio of yellow flowers with brown spots against a blue sky

Tiger lilies (Lilium columbianum) in the Glacier Peak Wilderness, Washington

The most memorable elements of the trip came on Day 3. After a COLD morning and a close brush with hypothermia, we decided (based largely on consulting with other hikers) to take a slightly longer, but less steep, route back to the car. Our ascent two days earlier had been short, steep, and rocky, and we weren’t thrilled about the idea of descending the same trail with heavy packs. Plus an alternate trail back to the car would result in a loop and who doesn’t love a good loop? According to maps and other hikers, our descent would be about 8-9 miles, instead of the six miles we had come up. Despite the modest mileage, it ended up being quite the slog. I’ve done enough hiking and backpacking that I normally feel pretty confident estimating mileage, and that descent sure felt like a LOT more than 9 miles. The trail was in decent shape, save for crossing a series of avalanche chutes choked with head high brush. Someone had kindly taken a machete to some, but not others. By the time we got back to the car, I was spent to put it mildly. I honestly can’t ever remember being so totally wiped out after a hike in my life.

Thankfully there was a bag of Chex mix waiting for me at the car. A few moments after diving in, I realized that the container it had been in was filled with mice droppings…and we soon noticed that the rest of the car was as well. Yum!