Understanding the Light

In a landscape photograph, particularly a black & white landscape, composition is the essence of the image; but it is usually the photographer’s use of light that brings the drama.

Emitted Light, Incident Light, and Reflected Light

The direct light from a light source, be it the sun, a lighthouse beacon, a campfire, is emitted light.

Emitted light that falls on the surface of a subject becomes that subject’s incident light.

When we look at a subject, what we see is its incident light reflected, i.e., its reflected light.

A spot meter or the light meter in a camera is a reflected light meter. It measures from a distance the light reflected by the subject. A mirror finish can reflect more than 95% of a subject’s incident light. An area in deep shade, or covered by a black, heavy weave fabric might reflect less than 5% of its incident light.

Alternatively, some photographers (e.g., portrait photographers) often hold an incident light meter next to the subject to measure the light falling on the subject (as opposed to the light reflected by the subject).

Sometimes, light that falls on a subject is indirect incident light. It is not coming directly from the sun or other light source. It is sunlight or other light that first falls as incident light on the molecules of moisture, smoke and dust in the atmosphere from which it is reflected and then falls on the subject. Especially on a cloudy or hazy day, a lot of the light falling on a subject is probably indirect incident light. As Ansel Adams pointed out in his seminal book, The Negative: “The clearer the air, the more intense the light from the sun and the less intense the light from the sky and therefore the greater the difference between sunlit and shadow areas.” 

The Law of Reflection

A surface in a subject reflects its incident light at an angle equal to the angle at which the light strikes it. That is, the surface reflects the light away at an angle equal to the light’s incoming angle. In physics, this is known as the Law of Reflection: the angle of incidence is equal to the angle of reflection.

Ambushing the Light

It is often to the landscape photographer’s advantage to predict the light on his or her intended subject to determine when to be there to snap the shutter. Ansel Adams used to call this “ambushing the light.” With the use of one of the powerful “apps” that are available for smart phones (see "Apps Make Ambushing the Light Easy", below), predicting the light today is much easier and much more accurate than in Ansel’s day.

In any case, to ambush the light, the photographer must be in place, set up and ready to press the shutter release at the moment when he or she thinks the light is optimal.

Planning an ambush can be rudimentary, based only on an awareness of approximately what time sunset will occur and what its approximate position on the horizon will be relative to the approximate alignment of the subject. For example, ambushing the light on a landscape subject that has a northwest/southeast axis can be as casual as picking a day when you know the sun will be setting as far south as it will all year, thus having its incoming rays as close to perpendicular as possible to the horizontal axis of the subject. To execute the ambush, then, just be at your pre-determined spot early enough to be set up and be ready to click the shutter as the sun approaches the horizon.

Planning an ambush also can be as precise as determining the day, the hour and the several minutes within that hour when the sun’s azimuth will be as congruent with the subject’s axis or as perpendicular to it – depending on the photographer’s artistic vision – as the sun’s seasonal transit will allow.

Many great images are captured without laying an ambush at all. Driving by an old country church in Hernandez, New Mexico, Ansel Adams serendipitously captured one of his most famous images: Moonrise. He noticed the moon was rising over snow-capped mountains in the east behind the church just as the setting sun’s rays struck the metal cross on the church’s roof so as to seemingly set it ablaze. He slammed on the brakes and raced to set up his 8x10 camera. He couldn’t find his light meter and so he set the aperture and shutter speed based on the one luminance value in the scene that he happened to know. the moon. He pressed the shutter and then hastened to reverse the film holder to make a second exposure. In the few seconds that took, clouds partially obscured the sunlight and the light on the cross dimmed before he could get to the shutter release.

However meticulous one wants to be in planning an ambush of the light, the essentials are knowing beforehand the precise spot on the ground on which the camera will be set up, and where the light (the sun or the moon) will be relative to that spot.

Where Will the Sun Be?

Assuming clear skies, one can predict sunlight conditions on a given subject on the day and at the time one wants to photograph that subject. It is a matter of forecasting the sun’s position in the sky (and having a clear sky between the sun and the subject).

At any moment on any day, the sun’s position in the sky can be described in terms of its altitude above the horizon and its azimuth on the horizon.

Altitude

The sun’s altitude is the angle of the sun above the horizon, as shown in the diagram to the right. The sun’s altitude is the angle (i.e., the angle of incidence) that its rays fall on any part of a subject that has a vertical or partially vertical aspect. The lower the sun’s angle, i.e., the closer it is to the horizon, the more perpendicular are its rays to a perfectly vertical surface in the subject. The sun’s altitude changes continuously throughout the day, rising to its zenith near mid-day.

On April 15, 2020, at 9:11 AM, the sun’s altitude was 30°, as seen from Sausalito, California, and as illustrated in the diagram to the right. At 6:36 AM (three minutes after sunrise) it had been 0.1°, or virtually perpendicular to a vertical surface in the subject. Thus, at 9:11 AM, at an altitude of 30°, relative to a perfectly vertical surface, the angle of incidence was 30°. Of course, not all vertical surfaces are perfectly vertical, i.e., 90°, so the angle of incidence on some surfaces might have been more, or less, than 30°.

The sun’s altitude is different at the same time of day (e.g., 8:00 AM) on each day between the Summer Solstice (June 21st) and the Winter Solstice (December 21st). That is because the higher the latitude above the Equator on which the photographer is standing, or the lower it is below the Equator, the shorter and lower the sun’s arc across the sky appears day by day between the Summer Solstice (June 21st) and the Winter Solstice (December 21st). Correspondingly, the sun’s arc appears progressively longer and appears higher in the sky each day between the Winter Solstice and the Summer Solstice.

Azimuth

The sun’s azimuth is the compass bearing from the photographer’s location to the point on the horizon directly below the sun.

The sun’s azimuth on any given day changes literally minute by minute as the sun moves across the sky.

As the dark blue line segments show on the azimuth diagram below, in 2020 on the Winter Solstice, the sun rose on an approximate azimuth of 106° as seen from in Sausalito, California (center of circle). It set on an azimuth of 227°.

On the day of the Summer Solstice, as the red line segments show in the diagram, the sun rose on an azimuth of approximately 45° and it set at 287°.

On both the Equinoxes, March 21st and September 21st, as the lavender line segments show, the sun rose on an azimuth of at approximately 75° and set at approximately 257°. The Equinox sunrises and sunsets are halfway between the Solstice sunrises and sunsets.

The azimuth diagram also implies that the sun’s arc across the sky, relative to Sausalito, California, is the farthest north on the Summer Solstice (the longest day of the year), and the farthest south on the Winter Solstice (the shortest day of the year). See the first two Sun Surveyor screens below.

Indeed, on the Summer Solstice in Sausalito in 2020, there were 14 hours and 47 minutes that the sun was visible above the horizon. On the Winter Solstice, the sun was visible for 8 hours and 22 minutes.  On both Equinoxes it was visible for 12 hours and 10 minutes.

It is the sun’s azimuth that determines the angle of incidence on the horizontally aligned surfaces(s) of the subject.

The diagram to the left illustrates a 90° vertical surface in a subject that is horizontally (across the camera’s viewfinder) due north and south. It shows the sun’s rays’ angle of incidence on that surface of 240° which would have occurred at 4:35 PM on April 15, 2020 as seen from Sausalito, California.

The sunset azimuth on that day was due west: 270°. Given the 360°/180° alignment of the subject’s surface, the sun’s rays were exactly perpendicular (i.e., the most direct light) to that surface at sunset.

The sunrise and sunset azimuths decrease each day between the Summer Solstice and the Winter Solstice, and they increase each day over the following six months between the Winter Solstice and the Summer Solstice (see "Seasonal Sunrise and Sunset Azimuths" diagram above).

The higher the latitude above the equator, and the lower the latitude below the equator, the greater the average daily azimuth differential. At the Equator, latitude 0.0°, the average daily azimuth change is about a quarter of a degree, i.e., a range between the Solstices of 47° over each six-month period. In Sausalito, California, latitude 37.86°, the inter-Solstice average daily azimuth change is about a third of a degree, a range of about 60° as shown on the "Seasonal Sunrise and Sunset Azimuth" diagram above. In Pelican, Alaska, latitude 57.96°, the average daily change is just over a half-degree each day, a range of 97°. 

In reversing its six-month transit on the day of each Solstice (north to south on the Summer Solstice and south to north on the Winter Solstice) the sun rises on the same azimuth twice a year: once southbound and once northbound. On the day that is the same number of days past the Winter Solstice that a given day was that number of days before the Winter Solstice, the sunrise azimuth is the same (within about a half-degree). The same is true for the sunset azimuth.

Thus, if the sunrise azimuth is optimal for the photographer’s vision of a particular subject on May 5th (135 days past the Winter Solstice), it will be on that same azimuth again on August 8th (135 days before the Winter Solstice).

Apps Make Ambushing the Light Easy

Today there are several “apps” for smart phones that, for any location on any day and for any time of day, give the photographer analog details and graphic plots of the sun’s and moon’s altitude and azimuth. As shown at the end of this article, they also provide ephemeris for the sun, the moon and the milky way. Among the best of these “apps” are:

• Sun Surveyor; and
• The Photographer’s Ephemeris (or “TPE”); and
• The Photographer’s Assistant.

Shown below are two screens from Sun Surveyor’s phone “app.” On the left is the screen for December 21, 2021, the Winter Solstice. On the right is the screen for June 21, 2021, the Summer Solstice. These plots are relative to Sausalito, California.

The dark orange straight-line segment from the edge of the compass (just before 6am) to the center (Sausalito, California) depicts the sunrise azimuth. The red straight-line segment from the edge of the compass (just past 8pm) depicts the sunset azimuth. The blue line segments depict the rising and setting moon azimuths. The light orange arc depicts the sun’s path across the sky. The sun’s path on the Winter Solstice is shorter than on the Summer Solstice because the sun is lower in the sky on the Winter Solstice.

While the data provided in these “apps” are astronomically precise, few landscape photographers will find much need for such fine precision. Distilling the data on the screen for precise timing (in terms of both day of the year and hour – even minute – of that day) at a chosen subject’s location, however, will be invaluable if the photographer wants to precisely “ambush” the light. The photograph and corresponding Sun Surveyor plot below illustrate the point.

A Precise Ambush

I captured this image at 4:45 on July 24, 2016 from the corner of Stockton and California Streets in San Francisco looking east down lower California Street. Months before, I had determined that the south side of this intersection would give me a classic San Francisco perspective, especially if I could catch a cable car in the right place.

Lower California Street in San Francisco’s financial district is lined with tall office buildings. They form a canyon which, much of the time, shades the street and the old Southern Pacific Building at the foot of the street. 

I wanted to click the shutter when sunlight filled the street and illuminated the Southern Pacific Building. That would be when the sun’s azimuth was aligned with the street.

So, several months before I took the picture, I scrolled through the coming days on the Sun Surveyor app and found that at 4:45 on the afternoon of July 24th the sun’s azimuth would be exactly congruent with the east-west alignment of California Street and that at that moment its altitude would be 41.5°, high enough to fill the canyon with light, provided the afternoon fog did not obscure the afternoon sun. 

So, several months before I took the picture, I scrolled through the coming days on the Sun Surveyor app and found that the afternoon of July 24th would be a good day, provided the afternoon fog did not obscure the afternoon sun. Mid-afternoon on the appointed day, I went to my preselected site and waited for 4:45 PM, the moment when the sun would pass through the desired azimuth. The fog did come, but not before I snapped the shutter. This image (previous page), "California Street", is the result.

A Rudimentary Ambush

I wanted a signature image of the iconic Transamerica Building in San Francisco. Over the course of two years of reconnaissance forays looking for subjects in San Francisco, I took a a dozen “study” shots of the building from various perspectives. I finally found my spot: the tip of a traffic island on the north side of the intersection of Broadway and Columbus Avenue.

I can see San Francisco across the Golden Gate bridge from my home in Sausalito. On May 16, 2010, at about 6:15 PM, I happened to look out my window. I could see a mid-Spring rain shower approaching the City. It was a squall, not a wide front. I checked my tide table (Sun Surveyor was not available in 2010). Sunset was going to occur at 8:15 PM. I could already see the light softening on my subject just looking at it from Sausalito.

I thought that, if the clouds allowed a lot of sunlight to break through, there might be a wonderful combination of clearing storm and soft light on my subject.

I grabbed my camera bag, jumped in my car and drove as fast as I thought I could get away with to Columbus Avenue a couple of blocks north of Broadway. I found a parking place, put on my rain suit, and hurried down to my designated intersection at Broadway and Columbus. When I got there at a little after 7:00, it was still raining. I waited under the awning of a Chinese restaurant. The rain stopped. The clouds were now moving fast. I ran out to my carefully pre-selected traffic island and set up my tripod and camera, using a yellow filter. Two lanes of rush hour traffic were within two feet of me on either side of the island. A police cruiser drove by and the cop gave me a dirty look but drove on.

I spot-metered the long, external elevator shaft on the side of the building, put on my 150 mm lens and set the aperture on f/32 (to maximize depth of field) and the shutter speed on a 1/2 second (to admit enough light at the high aperture setting), thus placing the bright white on Zone 8. With the slow shutter speed, I had to wait for the traffic light controlling the on-coming traffic to turn yellow. I wanted that traffic to stop while the cross traffic was also stopped so there would not be blurred cars in the image due to my slow shutter speed. At 7:30 PM, in the split second that both flows of traffic were stopped, I snapped the shutter. The on-coming traffic had its headlights on because it was getting dark, the street was wet because the rain had just stopped, and the light was diffuse and soft on the sides of the buildings because it was just an hour before sunset, and the clouds had just passed out of the way of the sun (and were blowing away rapidly). The shadows were beginning to climb up the side of the TransAmerica building. Had I waited another few minutes the image would have been less dramatic.

My Most Successful Ambush

On a reconnaissance drive up the Sonoma and Mendocino coasts one June day in the early summer of 2010, looking for interesting subjects, I determined that the Point Arena Light would make a wonderful image. Looking at the angle of the little peninsula on which the light house sits, even without knowing the precise azimuth of the peninsula, I was enough of a Boy Scout to know that the sun would have to be at its southernmost point — the Winter Solstice — for the light to be nearly perpendicular to alignment of the cliffs. This was before the availability of “Sun Surveyor” and “The Photographer’s Ephemeris.”

On Christmas Day that year, the lovely lady who had invited me to Christmas dinner became ill and had to cancel the evening. What to do? I thought it too late to call other friends and invite myself to dinner.

It occurred to me that Christmas Day is only four days past the Winter Solstice. But it was pouring rain. On a hunch, I pulled up the NOAA weather buoy website and checked the data for Buoy 46014, nineteen nautical miles northwest of Point Arena. In several readings over the next couple of hours, it showed that the pressure was rising. If that continued, the weather on the horizon north and west Point Arena would start to clear.

What I envisioned was a band of clear sky right at the horizon so that at sunset the sun’s rays would shine through that band, under the east-moving clouds, and strike the vertical plane of the cliff and the lighthouse nearly perpendicularly. Also, on December 25th, I knew that the sun’s azimuth at sunset would be within four days of its furthest south point on the horizon. That would place the sun’s rays as close to perpendicular to the cliff’s horizontal plane as they could get. What might unfold here was what I define as “perfect light" (see below).

I said to myself, “Why not?” I loaded my camera bag and tripod in my car at about 1:30 PM and, in the pouring rain, set off for Point Arena, 125 miles north up the Pacific Coast Highway. Even in the rain, it is a beautiful drive.

By the time I got to Jenner, about 50 miles south of the lighthouse, it was still raining, but the western sky was lightening. By the time I got to Sea Ranch, about 25 miles south of the lighthouse, the western sky was even lighter. I arrived at the spot I had identified six months earlier about 4:20 PM. It was still raining. The western horizon was still obscured, but the sky just above the horizon was very bright. Sunset would be at 4:56.Still in the car, I put a 150 mm lens on my Hasselblad, with a yellow filter and a lens shade. I put my rain suit on, sheltered my camera under a large umbrella and walked over to my spot and set up my tripod and camera. Then I looked to western horizon. It was still raining lightly and the horizon was very bright, but still obscured. It was about 4:30. I waited. At about 4:45 or so, I concluded that the horizon was not going to clear in time. Deflated, I picked up my tripod and camera and walked back to my car. I put the tripod in the back seat and the camera in the front seat without breaking it down and putting it in its bag. Just as I was about to turn on the ignition, at about five minutes before sunset, I took one last look to the west. Lo, and behold! A thin band of clear sky had opened at the horizon! The sun was just breaking into the clear sky. 

It had stopped raining. I grabbed my camera and tripod, rushed over to my spot and set up for the shot. As the sun dropped emerged fully into the band of clear sky, I quickly focused my spot meter on the white waves and foam in front of me, and “placed” their luminance value on Zone 8 and set the shutter speed and aperture accordingly. 

I quickly framed the image in the viewfinder and pressed the shutter release cable. I wound the film, opened the aperture one stop and pressed the shutter release one more time. 

That was it. The bottom edge of the sun was now dropping below the horizon. The direct sunlight was diminished and then gone in less than a couple of minutes. I did not have the presence of mind to wait and expose a frame or two with Blue Hour light. Still, I got the image I set out that day to capture.

I did not have Sun Surveyor on Christmas Day, 2010. The Sun Surveyor screen capture to the right shows what I would have had as an ambush planning tool had it been available.

• Using the satellite view of Point Arena, I could have determined the alignment of the west-facing cliff under the lighthouse: 310°. This is done by dragging the sun back into the morning hours until its azimuth is congruent with the alignment off the cliff. That occurs at 9:47 AM at an azimuth of 130°.  
• I could have confirmed that sunset would be at 4:58 PM at an azimuth of 225.5, and at 4:45 PM, just before sunset (when I anticipated that the light would be optimal), the azimuth would have been 223.3°.
• Knowing that I wanted the sun’s rays coming into the cliff face as close to perpendicular as possible, adding the 90° to the 9:47 AM azimuth equals 220°: only 3° off the 4:45 PM azimuth, and thus only 3° from perpendicular to the 130° cliff face alignment.

The light, when I clicked the shutter that day, was as close to “perfect” as in any image I’ve ever captured.

Attacking the Light

Basic photography instruction invariably counsels shooting with the sun at your back. Most of my images I captured with the sunlight coming over my shoulder or shining from the side. A few however, I made in “violation” of that basic rule: doing what I call “attacking the light.”

Attacking the light, contrary to the technique outlined above in which the goal is to get the light as nearly perpendicular to the aesthetically critical surfaces in the image as possible, is bringing the light onto the subject at an angle that is nearly the reciprocal of the axis of the camera lens. In short, I point the camera into the sun or nearly so.

The surf image, above, left, “Clearing Storm at Rodeo Beach”, I took shooting directly into the setting sun. I did not use a neutral density filter (which is often useful in such situations) or any filter, for that matter. The heavy overcast acted as a filter.  Pursuant to Ansel Adams’ Zone System, my exposure was at f/5.6 at 1/125th of a second. This “placed” the foreground surf foam on Zone 8 and the sun and the reflections on the sand “fell” accordingly. The sun highlights were blown, but actually being pure white in the image, they gave the sun needed intensity.

The warehouse image, above, right, “Pier 17”, was taken along San Francisco’s Embarcadero, I used the same approach. While I did not shoot directly into the sun (although you can see its glare on the upper right edge of the image), I was only twenty degrees or so off.

My favorite "attack" is the image below: "Bay Bridge, Rain." The sun is rising directly behind the bridge, and although it is heavily obscured by the clouds, it is creating high contrast on the water and the wet street.

 

Help from the Clouds

Clouds can be a significant source of reflected light in an image. In many good black and white images, they are a primary evocation of emotional response.

In the image above, right, “City Clouds”, I did something I almost never do. I took my camera out of the bag at noon. The sun was at its zenith, hardly in obvious compliance with my rules for capturing perfect light. However, it was shining directly down on this massive cloud formation that was scudding along above San Francisco. The aesthetically critical planes in the image were the tops of the clouds. The sun’s rays were perpendicular to them at noon. That’s what creates the dramatic filtered light through the cloud formation. And the cloud formation shades the city skyline so that part of the image is a high contrast light show in the clouds and below you have a virtual silhouette of San Francisco.

A more conventional use of clouds is in “Coit Tower – The Conversation”, above, left. The meteorological consternation going on in the background lends a lot of drama. The vertical surfaces in the image, by the way, are almost perfectly perpendicular to the incoming rays from the soon-to-be setting sun.

Evanescent Light – The Golden Hour

The Golden Hour in astronomical terms is when the sun’s altitude is less than 6° above the horizon and less than 4° below the horizon. When the sun passes into this range of altitude, the blue wavelengths of its light are more scattered by the earth’s atmosphere.

To a landscape photographer, the Golden Hour is when the light becomes soft and warm and fragile and seems “likely to vanish like vapor.” It becomes evanescent. 

Visible sunlight has violet, indigo, blue, green, yellow, orange and red wave lengths. The further toward violet the shorter the wavelength and the higher the energy of the radiation (middle of the day). The further toward red the longer the wavelength and the lower the energy of the radiation (near sunrise and sunset).

The higher the energy of the radiation, the more efficiently it is absorbed by the component molecules of the atmosphere (mostly nitrogen and oxygen) and re-emitted, or “scattered.” The absorption of the blue end of the spectrum by the molecules of the atmosphere causes us to see the sky in the colors absorbed, i.e., mostly blue.

The lower the energy of the radiation, the more easily it is transmitted through the component molecules of the atmosphere and on to the ground, and the more of the red end of the spectrum we see reflected off our subject.The altitude of the sun determines the length of path of its rays through the atmosphere. As shown in the illustration to the left, when the sun is high overhead, the path is direct and short. When it is near the horizon, the path is oblique and long.

The longer the sun’s rays’ paths through the atmosphere, the more the blue end of the spectrum is absorbed, and the more the yellow, orange and red wavelengths predominate. That is why, near sunrise and sunset, the sunlight on the subject has a warm cast. It is when alpenglow occurs. It is the Golden Hour. The light is evanescent.

The various “apps’ that I reference above calculate times for the Golden Hour at sunrise and sunset. See the appropriate Sun Surveyor ephemeris phone screen at the end of this article.

Perfect Light

Perfect light is my own arbitrary standard. It is certainly not necessary for the capture of dramatic images.

I define the moment of perfect light for a landscape photograph to be that moment when the sun’s altitude is perpendicular to the aesthetically critical vertical surface in the subject, i.e., at sunrise or sunset; and when the sun’s setting azimuth (for an evening shot) or rising azimuth (for a morning shot) is simultaneously perpendicular to the critical surface’s horizontal alignment in the scene to be photographed. See "My Favorite Ambush", above.

Depending upon the latitude, perfect light is not achievable for all subjects. This is because, in Sausalito, California, for example, in the six months between the Solstices, sunrise occurs across only a 60° range of azimuths between the Summer and Winter Solstices. If the axis of the critical horizontal plane is not perpendicular to an azimuth within that 60° range, sunlight that falls on that plane will not have an angle of incidence that is perpendicular to that plane.

For the angle of incidence to be perpendicular to the horizontal alignment of the subject at sunrise in Sausalito, California, the axis of the subject’s horizontal alignment must be between 135° (90° from the sunrise azimuth on the Summer Solstice) and 196° (90° from the sunrise azimuth on the Winter Solstice). 

If, for example, the horizontal axis runs east (90°) to west (270°), its axis will lie north of both the Winter Solstice sunrise and sunset azimuths and south of both the Summer Solstice sunrise and sunset azimuths. See “Seasonal Sunrise and Sunset Azimuth….” diagram above. The dark blue line segments in that diagram depict the Winter Solstice azimuths and red line segments depict the Summer Solstice azimuths. As described, the subject’s horizontal axis running east and west would lie along the green East-West segment.

The Blue Hour

The period of twilight each morning (when the sun has not yet risen above the horizon) and evening (after the sun has fallen below the horizon) is referred to by astronomers as the Blue Hour. In astronomical terms, the Blue Hour is when the geometric center of the sun is between 4° and 6° below the horizon.

When the sun is just below the horizon, its light does not fall directly on the earth within our view. It passes above us through the atmosphere. As it encounters the atmosphere, the lower energy wavelengths, particularly the yellow, orange and red wavelengths, pass through the molecules in the atmosphere and on into space. If these longer wavelengths encounter clouds, we see them reflected in brilliant sunset cloud displays even though the surface of the earth within our horizon is turning dark. If they don’t encounter high clouds, the lower energy yellow, orange and red wavelengths are lost to us until the morrow’s dawn. For a brief time after sunset, the higher energy blue wavelengths, on the other hand, are absorbed by the molecules in the atmosphere and reflect down on the earth indirectly as blue light even though the sun is below the horizon.

I captured the image below, right, "Lower Manhattan Skyline" in 2012 with a Sony Cybershot RX100, truly a snap shooter’s camera. Indeed, the picture is a snapshot, not a laboriously crafted image. The mirror-finish of the glass curtain walls on the skyscrapers exaggerate the potential of making an image during the Blue Hour. I took the picture at 5:00 PM on November 18, 2012. Sunset that afternoon on the Hudson River was at 4:35 PM.

Everything in the picture has a blue cast, even the bronze-colored glass curtainwall of the “illuminated” building faces. Earlier, all this glass would reflect much warmer colors or show as close to white. Note that that older buildings with stone and concrete fascia do not reflect much light at all and are quickly fading into the darkness. The reflection of predominantly blue wavelengths off the atmosphere creates an almost ethereal contrast to the darkness falling all around the “illuminated” buildings.

Taken a few minutes later, the picture would have been of a gathering of fading dark gray shapes. Taken a couple of hours earlier, it would have been a routine post card shot.

The various “apps’ that I reference above calculate times for the Blue Hour at sunrise and sunset as shown below.

An Ephemeris

Each of the various “apps” I list above includes an ephemeris which calculates the sun’s, moon’s and Milky Way’s visible times from the photographer’s location for any time on day (or night). 

In the screen to the right, the "Sun" tab has been selected. For the date and time shown, the screen shows:

• the moment of sunrise, solar noon and sunset as well as the day length;
• the azimuth, altitude, and the shadow ratio;
• the start and end of the morning and evening Golden Hour and the Blue Hour.
• the three moments of dawn and dusk.

It also shows the moments of the Solstices and Equinoxes for the calendar year.

Clicking on the "Moon" or the "Milky Way" tab shows their relevant times and other data.

The "Photo Opportunity" tab lists over 300 dates and times when the moon or the Milky Way will offer light conditions suitable for photographing during the year.