Sentinel point in Yosemite National Park. One of my first digital startrail images comprises four exposures of 15 minutes each. Image composited and noise reduced in Photoshop. 27 April 2006 Canon EOS 20Da, EF-S 10-22m at 10mm 4 x 15 min at f/4, ISO800

I had learned that there was a famous feature of the Colorado River called Horseshoe Bend near Page Arizona, but it was not particularly obvious to travelers passing through that town. Sure enough, marked by an inconspicuous sign, I found a parking area at the trailhead of a half-mile hike that ends abruptly at the rim of the canyon. Thousands of feet below, the river makes a dramatic winding around this peninsula from the far side plateau. It is a huge view; this wide angle shot attempts to fit it all in. A nearly full moon is out, illuminating the scene. This is a composite of individual frames, each of 5 minute duration taken over a two hour period. During that time, clouds of various types drifted past, sometimes obscuring most of the sky. This image shows the first 30 minutes and the last 40 minute periods of the total time, revealing the brightest stars trailing across a lunar-lit sky.

This is an early experiment in taking star trail photos with a digital camera. Ninety exposures of 1-minute each were composited with the "lighten" blending mode in Photoshop. During this elapsed time, the moon entered the frame. It has been dodged out except for its position in the final exposure. I had traveled to Boulder Colorado frequently, where this section of the Rocky Mountain's front range offers protection and beauty to the CU campus. In all of my prior trips, the days were sunny and clear, but when the sun set, the mountains pulled a blanket of clouds over themselves. Not so on this day, the day I had come to see my son graduate. A few wisps of moisture drifted across the peaks, but the sky stayed open, and the full moon illuminated the slabs of the flatirons with its distinctive diffuse light. In the high resolution copy of this image, the individual exposures are discerned. Each was actually 55 seconds long, separated from the next by 5 seconds. This is too long a delay, the gaps between the star trail segments is visible. At lower resolution, the segments merge together to form the classic pattern of stars apparently streaming across the sky. 12 May 2006 EOS 20Da, EF-S 10-22mm at 22mm 55sec, f/5.6, ISO 200

The Watchman is the peak that dominates the campground at the south end of Zion National Park. This is a view up the valley of the Virgin River over an hour and a half period, at the end of which the moon rose and illuminated the canyon walls. Trees and camping vehicles were occasionally lit by the headlights of a late-to-bed car finding the way to its campsite. 6 May 2007 Canon EOS 20Da, EF-S 10-22mm at 10mm 12 x 8min at f/5.6 ISO 800

Gouldings Resort is a historical island of lodging within the island of the Navajo nation within the state of Arizona. It borders the sacred area of Monument Valley whose iconic mitten shapes are seen silhouetted on the horizon. The resort itself is in the lower foreground, casting its bright lights onto the eroded red walls of the ancient mesa. This is a composite of 14 exposures representing an elapsed time of almost two hours. Evening travelers through the reservation are seen on the distant road. Some are workers preparing for an upcoming weekend airshow event that will feature the monuments as a backdrop. Hollywood westerns were once the source of this activity, but the only signs of of those movies now are nostalgic photos and posters found in museums, and hotel lobbies. 8 May 2007 EOS 20Da, EFS 17-55mm at 35mm 8 min, f/8, ISO 400

Overlooking the Grand Canyon from the South Rim on a moonless night. Wispy clouds travel through, creating a staccato effect on the startrail arcs. Grand Canyon National Park 12 May 2007 Canon EOS 20Da, 17-55mm (17mm), f/2.8, ISO 800 2-hour elapsed from 8 15-minute exposures

Natural Bridges National Monument is in Utah and is the first International Dark Sky Park. It is so remote, and the air so dry, that one can see stars all the way to the horizon! And nowhere on that horizon is any hint of city light dome. The park itself is powered by a solar array; the residents are misers in conserving their battery power. The bridges are not to be confused with "arches" (found in a national park elsewhere in the state), as they are formed by different geologic processes. There are three popular bridges here, accessible by short hikes. This one suited my purposes best, lying on an east-west axis and in a valley allowing a view at the celestial pole. Across a dry riverbed, I found the position to capture this low angle composition. I set up my cameras (I was also shooting film) and started the exposure sequence. The moon was in the process of setting and it illuminated the texture of the rocks, and also helped me find my way back to the trail head where I had a telescope and mount. I enjoyed some deep sky observing, but then needed to get back to tend my cameras. The 15-minute hike was now in complete darkness. A flashlight was needed to avoid wandering off into the desert at a missed trail marker, and the last of it was the climb under the bridge and down into the riverbed. The route I took is apparent. 15 Nov 2007 EOS 20Da, EF-S 10-22mm at 10mm 18x5min, f/6.7, ISO 800

The view to the south at Owachomo Natural Bridge does not include the south celestial pole, but it clearly shows the stars revolving around it. At higher elevations, the stars transition across the celestial equator, and then arc the other way, following the rules for the northern hemisphere. 15 Nov 2007 EOS 20Da, EF-S 10-22mm at 10mm 18x5min, f/6.7, ISO 800

I return to this iconic overlook in Glacier Park and try again. Previously (2001), the weather compromised the view, tonight it is perfectly clear and the traffic over Logan Pass nonexistent. The pink smudge to the left is not a cloud, it is the core of the Milky Way, moving its way across the sky on a beautifully clear August night. 25 August 2009 Glacier Park, Montana Canon EOS 20Da, 10-22mm (10mm) at f/3.5, ISO 3200 Composited series of 8-second exposures over a duration of two hours

A safari in Tanzania takes one almost exactly to the Earth’s equator. A camera pointed east to make a startrail image will show those due-east stars taking paths perfectly perpendicular to the horizon. Stars to the north and south bend toward their respective centers of apparent motion. 14 June 2008 Serengeti National Park, Tanzania Canon EOS 30D, 10-22mm (10mm), ISO 400 composite of 3-minute exposures at f/6.7

I had been here before, in 2001, attempting to recreate a scene of the night sky reflected in a calm alpine lake. I didn’t succeed then, but here I was with another opportunity. I’m still not fully satisfied; I guess I will have to come back and try again! 25 July 2011 Beartooth Pass, Montana Canon EOS 20Da, 17-55mm (17mm), ISO 1600, f/2.8

A safari in Tanzania takes one just south of the Earth’s equator. Here there is no visible North Star; it resides just below the horizon, obscured by the acacia trees and grasses of the Serengeti plain. A startrail image reveals its implicit location; the arcs to the north are perfect semicircles. 14 June 2008 Serengeti National Park, Tanzania Canon EOS 30D, 10-22mm (10mm), ISO 400 composite of 3-minute exposures at f/8

We are guests on the river boat Omar El Kayan, named after an Arab poet, visiting the areas of Egypt where the reservoir Lake Nasser, formed by the Aswan dam has submerged the ancient temples along the banks of the Nile river. Abu Simbel was the most famous, but there were others, and we visited the sites where they had been carefully relocated. At the end of a hot day navigating the lake, the boat moored. The wind and water were calm and the sky was dark on this section of the Nile. Out of curiosity I made a series of exposures hoping to capture the feeling of stars above the famous river and the desert around me. But calm water does not mean motionless water, and the camera recorded the small wave motions rocking the boat on which I was a passenger for the night. Nile River near Kasr Ibrim 8 October 2016 Composite of 23 5-minute exposures (~2 hours)

The Earth moves under the North Star while the moon illuminates the red rock canyon wall of Ayers Natural Bridges Park. We were pleasantly surprised to discover this hidden gem in Wyoming, land donated from their ranch by the Ayres family. The park was entirely free, including campsites, but no pets are allowed. This is considered a benefit to some. 10 July 2019 Ayres Natural Bridge Park, Douglas Wyoming Canon 60Da with EOS EFS 10-22mm(@10mm) Composited 5-minute exposures at f/5.6, ISO 200, 2-1/2 hours elapsed

I have long been fascinated by sunflowers. On my travels across the prairies of the Dakotas I loved to encounter sunflower fields with their collective bright yellow heads all aimed in the same direction. It is generally known that sunflowers track the sun across the sky, from east to west. I wondered what happens after sunset, when the flowers would all be facing west. With no phototropism to guide it, how would they get ready for the eastern sunrise? Would they be caught off-guard in the morning and suddenly swing their heads back at the risk of floral whiplash? Or is there a gradual re-setting of the neck-stalk fibers back to an easterly gaze? I thought I could answer this by capturing a nighttime movie of a sunflower field. I was pleased to learn that other people share my enjoyment of sunflowers and in fact there is a small family-farmer industry of growing sunflower fields for the purpose of providing a beautiful setting for photo shoots. Weddings and family photos are popular at such places, as well as individual portraits, making enticing promotional shots for whatever the personal business or interest. I encountered one such field in Otsego MN, planted as one of a dozen or so by Fish Sunflowers [https://www.fishsunflowers.com], an activity sponsored by Fish Realty. Each field is timed to reach its peak bloom over successive weeks in the late summer and is open to the public for their enjoyment as a way for Fish to express their appreciation to the community. On the night I was there, many families were enjoying the setting. Most had prepared by dressing up for the photo opportunity; some had brought professional photographers, who were striking photographic gold during the beauty light preceding sunset. My project was less flamboyant than the scenes created by families and artists at the props in the field: benches, tractors, antique cars, pianos, boats etc. I was able to find locations to place my cameras that did not intrude on those photo-shoot activities but captured a feeling of being in a rural setting while watching the beauty of the sky progress through its diurnal and nocturnal rhythms It turns out that sunflowers tracking the sun is ephemeral, it happens only during a particular growth phase, and when the blooms mature, they all face east; there is no more tracking. This field of sunflowers had reached that maturity. The mystery of what they do when they are left facing west at the end of a day of tracking, will have to wait for another day. 2 September 2020 Otsego MN Canon EOS Ra with EFS 10-22mm(@10mm) Blended 10 sec intervals at f/4, ISO 800, 1/2 hour elapsed

A beautiful state park along Montana’s Dinosaur Trail. 24 August 2015 Makoshika State Park, Montana Canon EOS 60Da, 10-22mm (10mm), ISO 400 Two hour composition of 5-minute exposures at f/5.6

I had another camera in the sunflower field. This one faced south and caught the arcs of stars and planets near the ecliptic. Eventually the full moon entered the scene. 2 September 2020 Otsego MN Canon EOS 6D with EF 17-40mm(@17mm) Blended 10 sec intervals at f/4, ISO 800, 1/2 hour elapsed

Forest fires have become common occurrences in our western states, a consequence of global warming, and our national parks are not immune. On this date we could enjoy the facilities of our campground at Two Medicine Lake, but other areas of the park were closed off, including those just north of the distinctive peak of Rising Wolf. The glow of the fire is reflected by the smoke in the sky in this startrail exposure. 13 August 2015 Glacier Park, Montana Canon EOS 60Da, 10-22mm (10mm), ISO 800, f/8 Composition of 4-minute exposures.

One of the active topics in modern photography involves the distinction between “blends” (combining multiple exposures from a single camera viewpoint), and “composites” (which combine unrelated images into a synthetic scene). Both are valid uses of photography, but I prefer to limit my efforts to the former, hoping to reveal some scientific beauty in the result. In this case the relative motion of the stars is “stacked” (added) from 2,335 10-second exposures. Each frame looks like a normal picture of the sky, but when accumulated, creates the star trail effect. The frames were selected from the period after “astronomical twilight” when the sun is more than 18-degrees below the horizon. On this date, official "night" lasted over six hours, and the star trails cover more than 1/4 of a full circle (and even Polaris shows that it is not exactly on the north celestial pole). Although it was night, it was not completely dark. The moon was up and illuminated the scene until it set around midnight. This allowed the foreground to show, including the “sailing stone” [https://en.wikipedia.org/wiki/Sailing_stones] with its path on the dry lakebed trailing behind it, a contrast of time scales against the motion of the sky. A final detail to explain: the streaks below and to the left are the result of two "trains" of Starlink satellites moving across the sky. Dozens of satellites follow each other into and out of the sunlight at their altitude, reflecting it down to our observing position on the playa and creating its own trail in the picture. A time-lapse created from these frames can be found at https://vimeo.com/564797859 For more of the backstory on making this image, see https://thorolson.com/.../06/22/a-night-on-the-playa-part-2/

“The Citadel” remains the focus for this startrail image. The moon dominates the scene, and this blend of exposures shows its path among the stars. The cloud persisted above the monument over the course of the exposure, growing and shrinking, but never moving away or evaporating. 15 May 2021 Wupatki National Monument Flagstaff AZ Canon EOS 6D with Sigma 14mm f/1.8 458 exposures, 8 sec @ f/2, ISO 3200 (76 minutes)