Posted on September 1, 2019
It’s midnight and I’m right back where my day had started 21 hours earlier. Standing in the frigid dark beside Lake Wanaka, I feel equal parts energized and exhausted by the longest photography day of my life. And for the first time all day, I’m alone.
With the moon’s arrival still a couple of hours away, most of my attention is on aligning the Milky Way with the much photographed Wanaka willow tree. But photographing the Milky Way with the tree also put the glow of the Wanaka’s lights directly in my field of view. As someone who always strives to photograph the natural world untouched by humans, this would have been a deal-breaker for the old me. But what the heck—the reflection is crisp, the light’s amber glow illuminating the fog is kind of pretty, and since I’m already out here….
Once I embrace the moment, I’m free to click and enjoy. For most of this night the fog ebbed and flowed in the distance, adding character to the scene without subtracting too many stars. I’m having a blast, city lights or not. But eventually the fog starts to take over, slowly expanding upward until it completely swallows most of the Milky Way. Bedtime….
But just as I decide to pack it in, the fog pulls back and the stars briefly rally. Much of the Milky Way is still obscured, but the sky in the west has opened and I quickly reposition, pointing my camera away from the fog, city, and Milky Way, and toward the dark, pristine sky. As my exposure begins, long, undulating ripples stir the lake surface that had been still all night, and I’m concerned that I’ll loose my reflection. Instead, the long exposure smooths the ripples and stretches the brightest stars into oblong balls of light.
With pretty much any mirrorless or DSLR camera, a sturdy tripod, fast lens, and just little knowledge, you can now capture landscapes beneath more stars than you ever imagined possible. A camera’s ability to accumulate light allows it to reveal stars far fainter than the naked eye sees; rapidly advancing digital SLR technology now enables usable (low noise) images at the extreme ISOs necessary for star-freezing shutter speeds in very low light.
I’m starting with the assumption that you have a relatively new mirrorless camera or digital SLR, one that allows you to capture fairly clean (low noise) images at 3200 ISO or higher. You’ll need to be fairly comfortable with managing the controls in the dark, and know how to get it into manual and bulb modes. For star trails a locking remote release is essential (one that allows you to lock down the shutter rather than forcing you to hold it down for the duration of the exposure).
And of course don’t even think about trying any of this without a rock-solid tripod (you don’t need to spend tons of money, but neither can you assume any tripod will work). A wide (28mm or wider on full frame is best), fast (at least f/2.8, but the faster the better) lens is best. Oh yeah, and take off your polarizer.
Moonlight photography is great for photographing landscapes beneath a few bright stars, but a sky filled with stars (and maybe even the Milky Way) can only happen when there’s no moon and city light washing out the faint stars.
When I go out on a moonless night, whether my goal is pinpoint stars, star trails, or both, I start with a test frame to determine the amount of light my planned image requires. The test frame also allows me to check my exposure, focus, level, and composition in light that’s nearly opaque to my eyes.
My initial test frame is usually no more than a 30-second, high ISO (the goal isn’t a usable image, it’s solely to determine exposure, focus, and composition) and my lens’s widest aperture. After each click I check my composition and focus, adjust, and reshoot. The first frame is mostly to gauge the light; subsequent frames refine both the exposure and composition. I’m usually ready to go after two or three test frames.
Once I have an exposure that works (the desired combination of stars and foreground light), I just need to decide which shutter speed will give me the star effect I want—short for pinpoint stars, long for star trails. With that, finding the ISO and/or f-stop that adds or subtracts the light subtracted or added by my chosen shutter speed is just simple math.
For example, let’s say my test exposure was perfect at ISO 12,800, f/2.8, and 30 seconds. A 30-minute star trail image will gather a lot more light (than my 30-second test exposure), so I start by figuring out how many stops 30 minutes adds to 15 seconds. Since I have to double ¼ minute (15 seconds) seven times to get to 32 minutes, I know going from 15 seconds to 32 minutes adds 7 stops of light. (2×1/4=1/2 minute -> 2×1/2=1 -> 2×1=2 -> 2×2=4 -> 2×4=8 -> 2×8=16 -> 2×16=32.)
A moonless night doesn’t have enough light to see the controls on your camera, the contents of your bag, and the tripod leg you’re about to kick. Needless to say, there’s not enough light to focus either, at least in the traditional ways.
Because we’re usually wide, and very rarely concerned about close detail, all of our night subjects are probably at least 25 feet away with an infinity focus point. Unfortunately, that old prime lens habit of twisting the focus ring to the end for infinity focus doesn’t work on a zoom lens—every focal length has a different focus point (I’ve found this to be true even for lenses labeled parfocal). While I’ve simplified my night photography by usually going with my Sony 24mm f/ 1.4 GM lens, when I do use a zoom (usually my Sony 16-35 f/2.8 GM), I almost always use it at its widest focal length. Not only does a wide lens maximize the amount of sky in my frame, the extra depth of field increases my range of focus tolerance. And sticking with a single focal length reduces the times I need to mess with focus—once I get it sharp, I’m done with the focus hassle.
Despite the hardships, there are a number of methods for focusing at infinity in the dark. Here they are in my order of preference:
1. Autofocus on a bright planet or star. Some camera/lens combinations have excellent autofocus (the faster the lens, the better). I always start by picking out the brightest planet/star. Venus is great, but it won’t be up during the darkest hours of the night. Jupiter, Saturn, and Mars can work, as can Sirius and maybe a few other bright stars. Regardless, you don’t need to know what you’re pointing at—find something bright in the sky, center it in your viewfinder, and try to autofocus. (Any bright, distant object will do—headlights, a plane overhead, whatever.) Don’t forget to take your lens out of autofocus as soon as it’s focused.
2. Live-view focus on a bright planet or star. With my camera on my tripod I center the brightest object in the sky in my viewfinder and lock it in place. I go into live-view mode, center the star/planet in the LV magnification square, then magnify the view to the maximum (it’s 10x on my Canon), and manually focus. Since switching to Sony mirrorless, this is my preferred focus technique and I rarely try 1 or 3.
3. Autofocus on a nearby flashlight. When all else fails, I have somebody stand 50 feet or so away with a flashlight and autofocus on that. If I’m by myself, I rest the flashlight on a rock (or whatever) and walk (stumble?, grope?) 50 feet away. Believe it or not, if I focus my 24mm f/1.4 lens (for example), on a point 50 feet away, I’ll be sharp from about 25 feet to infinity, so you should be fine too unless your lens is significantly longer (which I don’t recommend for night photography) or faster (lucky you). Don’t forget to take your lens out of autofocus as soon as it’s focused.
Don’t forget!: Because there’s no fixed infinity on a zoom lens, if you change your focal length, you must refocus. And no matter what method you choose to focus, you must check the sharpness on the LCD before assuming it’s sharp (once you’ve verified sharpness, you don’t need to refocus or check sharpness again until you change your focal length).
Because I love stars, and it’s the stars that really set a night image apart, most of my night images are at least 2/3 sky. The foreground is usually more of a placeholder, an excuse to dazzle you with the celestial ceiling. But that does not mean the foreground doesn’t matter. Quite the contrary, because the sky is a relative constant, the foreground is the difference between another pretty picture and something that pulls people to a print from across the room.
It’s not necessary, but when possible I always try to include something recognizable, such as the Milky Way (my favorite), or a recognizable constellation like the Big Dipper, Orion, or Cassiopeia. This is especially nice in pinpoint star images. If you don’t know the night sky, spend a little time familiarizing yourself with the major constellations—there are many, many smartphone apps to help with this.
Most people’s vision subconsciously runs along the long edge of an image. Since the primary feature or a night image is the sky, most of my night images are oriented vertically. Regardless of my orientation preference for a particular night shoot, I always make sure I have at least one vertical and horizontally oriented image.
I’m constantly on the lookout for a striking foreground to feature beneath a starry sky. Bold objects without a lot of intricate detail work well, such as a prominent or mountain. Reflective subjects, like water, granite, and sand, work well too.
In Yosemite I like Half Dome for the way it stands out against the sky. For years I struggled getting enough light into the dark hole of the Grand Canyon at night, but today’s digital sensors and fast lenses have changed that. had better luck with Grand Canyon my star trail images because the long shutter time allows enough light at a very clean ISO. My current favorite location for night photography is New Zealand, which I always visit in June (winter). The skies are dark and clear, the nights are long (the Milky Way is up all night in June), and the foregrounds are off the charts
Successful star photography is all about managing star motion—either minimizing their motion or maximizing it. Unfortunately there’s an inverse relationship between the number of stars you capture and your ability to freeze their motion—for any given ISO and f-stop, the longer your shutter is open, the more stars you’ll expose, but the more they’ll move during your exposure.
Pinpoint star images require (relatively) fast shutter speeds to (more or less) freeze the stars’ motion; star trail images us long shutter speeds (either in one frame, or a series of blended frames), the longer the better, to maximize star motion. (Of course it’s not the stars’ motion we’re capturing, it’s Earth’s rotation against a fixed backdrop of stars, but you already knew that.)
Some nights I shoot both pinpoint stars and star trails; other nights I only photograph pinpoint stars. Because a pinpoint star exposure is usually only 15 to 30 seconds, even after I’ve completed my test exposures, they’re the best way to make sure I have everything right before moving on to the quite lengthy star trail exposures.
I’ve seen a formula floating around that’s supposed to ensure pinpoint stars. It’s called the “Rule of 600” (or 500) and says: “Divide 600 by your focal length to ensure a shutter speed that will freeze the stars.” My concern with solutions like this is that they sound far more precise than they are, and they create a false sense of security, often leading to longer or shorter exposures than the scene calls for.
The problem is, the amount of motion is a function of (among other things) a star’s distance from the axis of rotation. For example the North Star, which is less than a degree from Earth’s north axis, will show very little motion in exposures of many minutes or even hours; Betelgeuse, on the other hand, because it’s near the celestial equator will show a significant amount of motion in just a few minutes. For pinpoint stars I think it’s more important to find an exposure that delivers enough light with the least amount of noise.
My biggest problem with exposure speed rules like this is that they can create a worse problem than they correct. Night photography is all about compromise—less than ideal aperture, ISO, and shutter speeds. To me the most unrecoverable compromise, the thing that will render an image unusable more than anything, is too much noise. I generally will forgive the slight amount of star motion of a 30-second exposure (that’s not usually even visible at standard viewing distance) if it saves me from a too dark foreground or unsatisfactory ISO. I find that I’m satisfied with my results if I keep my shutter speeds to 30-seconds and below—the faster the lens, the more likely I am to drop my shutter speed into the 10-20 second range.
I currently (as of September 2019) shoot with a Sony a7SII and Sony 24mm f/1.4 GM lens. I know I can get usable images that clean up nicely with noise reduction software (DxO Prime and/or Topaz DeNoise is my choice) at 12800 ISO, which allows me to stop down to f/2.0 and/or use a 10-second shutter speed. ISO 12800 is higher than I’d use with most cameras, but it seems today’s full frame (and even some APS-C) sensors do fine at ISO 3200, which might require a 30-second shutter speed to get enough light for the foreground.
The Milky Way may just be the single most beautiful everyday feature of Earth’s night sky. Sadly, increased light pollution has made it all but unknown to the vast majority of us. Once upon a time observing the Milky Way’s glowing band stretching across the sky was for most people a matter of walking out and looking up on a dark, clear night; seeing it now usually requires planning and travel.
As most know, the Milky Way is the galaxy of which our Solar System is a very insignificant piece (the Sun is one star in nearly a half trillion). When you see the Milky Way, you’re looking toward our galaxy’s center and seeing the accumulated light of billions of stars. The dark areas you see aren’t areas without stars, they’re regions of interstellar dust so dense that it obscures all starlight (the occasional pinpoint of starlight in these dark regions are nearby stars between us and the galactic center).
Earth’s position in one of the Milky Way’s spiral arms is kind of like being in the distant suburbs of a large city. While all the discrete stars we view and imagine into constellations are the porch lights of our neighbors (technically they’re part of the Milky Way too, just as some cities have city limits that extend all the way out to the suburbs), when we view the Milky Way we’re looking beyond our neighborhood toward our galaxy’s distant, much more densely populated, urban skyline. Due to our Solar System’s skewed orientation (we don’t orbit the Sun on the same plane on which the Milky Way is laid out), parts of the Milky Way are visible regardless of the side of the Sun Earth is on.
The constellations the Milky Way “passes through” (from our perspective—in reality we’re looking through these constellations to the Milky Way center beyond) include Perseus, Cassiopeia, Lacerta, Cygnus, Aquila, Sagittarius, Ophiuchus and Scorpius, Norma, Circinus, Crux, and Carina. If you want to see it, simply pick one of these constellations, figure out when and where it will be visible (an star chart or app will do), pick a clear, moonless night, and position yourself a location
far from city lights. For example, in the Northern Hemisphere Cassiopeia is visible year-round more or less opposite the Big Dipper with Polaris (the North Star) in the center—you might be able to go out tonight to see it (assuming there’s no moon and you can get away from city lights).
But the Milky Way isn’t particularly bright in Cassiopeia—for most photographers (or anyone else who appreciates beauty) it’s the Milky Way center we’re looking for. For that Northern Hemisphere viewers need to look to the southern sky, toward Sagittarius, the constellation that aligns most closely with the Milky Way’s dense (most brilliant) center. And since the Sun is in or near Sagittarius (when we look in the direction of Sagittarius, we’re also looking toward the sun) in winter, we need to wait until Earth has circled around to the other side of the sun—summer.
In other words, viewing (and photographing) the Milky Way’s bright center is a summer (-ish—late spring and early fall will work too) activity. Get out your star chart/app and find a summer night when the moon is below the horizon while Sagittarius is above it (the closer to a new moon, the better your odds). Then get yourself as far from city lights as you can (mountains or desert are great), look to the south, and prepare to be awestruck. Stand there and appreciate the view for a while—when you’re ready to photograph, follow the instructions for pinpoint stars above.
Many people enjoy great success photographing star trails by combining many consecutive, relatively short exposures. In general this approach reduces noise and results in a cleaner image. But since all my images are captured in a single frame (I’m a film shooter with a digital camera), you’ll need to look elsewhere for guidance on that method.
My star trail images are usually 20-30 minute exposures, which I find to be more than adequate to achieve the motion effect I’m looking for. Start with pinpoint star frames and stick with those shots until you’re happy with your composition, exposure, and focus. When you’re ready for star trails, without changing your composition, focal length, or focus:
Before I start, let me just say that there are just about as many processing approaches as there are photographers. And there are far fewer absolute right/wrong ways to do things than you might read/hear/see. So what I’ll tell you here is the way I process a night image, rather than the way to process night image. If you already have a workflow you like, or if somebody else tells you a way you like better mine, go for it.
I wouldn’t even consider photographing night scenes in anything but raw. Not only do jpeg captures reduce your margin for error, a jpeg capture makes processing decisions that are difficult to impossible to reverse.
Posted on July 7, 2019
After one of the most exhausting, exhilarating, and just plain productive photography days of my life, our van rolled into Wanaka a little before midnight and everyone’s thoughts, including my own, were on sleep. But the stars were out and the moon was not (yet), and I knew it would be at least a year before I’d get another chance like this. With a warm bed and blissful sleep beckoning, was I really going to go back out to the lake in the frigid dark for the second time that day? You betcha.
Just what could inspire such craziness? Driven by more than a nice photo opportunity, I’d been infused with the infectious energy of a dozen young, Sony-sponsored social media influencers: the Sony Alpha Imaging Collective (AIC). (It would be doing them a disservice to label them mere photographers.) After spending months arranging this trip on Sony’s behalf, my ostensible role for its execution was as a guide and mentor. But the aggressive creativity of these visual artists was an inspiration to this conventional photographer’s vintage muse, and I can’t imagine that I was able to offer them nearly as much as they gave me.
So, with the Health app on my iPhone reporting that I’d already logged 9 miles and climbed the equivalent of 58 flights of stairs, I found myself standing alone, in icy lake water, photographing something I’d vowed I’d never photograph. So how did I get here?
3:00 a.m.: Note to self
When my alarm went off at 3 a.m. that morning, I’d staggered from bed without high expectations. This wasn’t the first time I’d tried rising photograph the Milky Way above the lone willow in Lake Wanaka, but I’d always been thwarted by fog. This morning, instead of another foggy reprieve and a few more hours of welcome sleep, the stars were out.
Despite a 48% waning gibbous moon, the Milky Way was clearly visible and I photographed for about an hour with three or four others from the AIC group. Having never photographed the Milky Way here, I made mental notes for how it could be better the next time. First, the galactic center was a little left of the tree and quite high. And the moon, while adding light to the foreground, washed out the sky a little too much.
Note to self: Next time, come earlier and make sure the moon isn’t up.
11:00 a.m.: Stop the van!
The three hour drive from Wanaka to Aoraki / Mt. Cook National Park had been slowed by a detour, a couple of unplanned stops, and now dense fog. With at least an hour’s drive and a full photography schedule ahead head of us, we couldn’t really afford to stop. But… Oh. My. God. Look at those trees, glazed with hoarfrost and shrouded with fog… The visibility was so limited, by the time the scene popped out of the fog we were past them, but when a simultaneous command issued from every seat, “Stop the van!”, stop we did. (It didn’t hurt that our driver was a photographer too.)
Doubling back, we poked along the shoulder until we found a narrow, unpaved road on which to park, then sprinted toward the trees—which turned out to line a small lake. Wow. The next hour was some of the most magical photography I’ve ever experienced. When the fog started to thin, the sun broke through, framing the trees with a shimmering fogbow that I just had time to capture.
5:30 p.m.: I can’t believe I’ve never been here
After a beautiful hike to Kea Point (where I opened my bag and realized I’d left my camera in the van—oops, don’t tell anyone), we wrapped our daylight hours with a sunset shoot at Tasman Lake. Normally I scale the 335 steps to the vista overlooking the lake, but it didn’t take much urging to get me to join the group who took the longer but less steep hike to the foot of the lake, where I’d never been.
Getting to the lake from the end of the trail was a short boulder-hopping scramble down a steep hillside, but once I made it down I couldn’t believe I’d never been here. Icebergs, large and small, mingled with the reflection of snowcapped peaks in the clear, turquoise water. We didn’t have clouds to provide an electric sunset, but New Zealand’s impossibly pristine air delivered something I found even more beautiful, the deep magenta of the Belt of Venus.
7:00 p.m.: You’re gonna need a bigger lens
From the very first time my eyes feasted on it, I marveled at what a spectacular spot the vista above Tasman Lake would be for Milky Way photography. I was especially pleased to be guiding an entire group of photographers who were as excited about photographing the Milky Way as I was, so this shoot was the plan since before the workshop started. But as the sky darkened, I was still down at the foot of the lake (just off the screen on the far right) where I’d photographed sunset. Most of the group wanted to stay there for the Milky Way shoot, and while I had to admit that spot would be no less spectacular, I just had to check the higher view off my list. Plus, I knew the Milky Way would align better with the peaks up here. So I scrambled back up the boulders and made the roughly two kilometer walk up here in virtual darkness to make it happen.
I thought a couple others in the group would already be up here, but I arrived to find the view empty. While I was happy to eventually be joined by a couple of others, the solitude I enjoyed for the first 30 minutes I was up here was downright spiritual. Going with my dedicated night camera, the Sony a7SII, I started with my default night lens, the amazing Sony 24mm f/1.4. But the scene was so expansive that I soon switched to my Sony 16-35 f/2.8 GM for a wider view. That did the job for a while, but when I found myself wanting an even bigger view, I reached for my Sony 12-24 f/4 G lens. F/4 is a little slow for night photography, but the a7SII can handle 10,000 ISO without any problem, and at 12mm the star motion of a 30-second exposure isn’t too bad. It didn’t hurt that the best parts of the scene, the snow and water, were highly reflective, and the dark rock wasn’t really essential to the scene.
12:00 Midnight: Completing the Circle
I’d spent the week sharing my favorite New Zealand South Island sights with the Sony AIC crew. With lots of night photography and driving, each day had been long, but this one took the record. I’d started 21 hours earlier and had been a non-stop blur of driving to the beat of music I’d never heard (Bubble Butt?), hiking to and through breathtaking scenery both old and new, and taking pictures, lots and lots of pictures.
Despite all this, no one got tired. It would have been easy to attribute this group’s boundless energy to youth, but the more I watched them work this week, the more I realized their carpe diem passion for experiencing and expressing our world was the driving real force. While I lack some of the non-photography technical skills they employ so effortlessly (specifically video and the computer as an artistic tool), as soon as followed their lead and I allowed myself to stretch my own personal boundaries in other ways, I had no problem keeping up with the pace. (Though I did draw the line at the all-night processing parties.)
As I’d expected when I returned to the lake late that night, the sky was moonless and the Milky Way better aligned with the Wanaka Willow that anchors the scene. But photographing the Milky Way with the tree also put the glow of the Wanaka sky directly in my field of view. As someone who always strives to photograph the natural world untouched by humans, this would have been a deal-breaker for the old me. But what the heck—those lights are kind of pretty, and I’m already out here….
Once I embraced the moment, I was free to click and enjoy. And enjoy I did. For the entire time I was out here, I was completely alone (though a couple of others in the group did come out to shoot shortly after I left). The fog was barely visible in the distance when I arrived, but while I was there I got to watch it ebb and flow like the tide, dropping down to lake level, expanding upward until at times it nearly obscured the sky completely. Benefiting from the extra light my camera could capture (beyond what I saw), what appeared to my eyes as a faint amber hue in the clouds registered on my LCD as a vivid gold even more brilliant than what you see in this image (I toned it down slightly simply for credibility).
And when the bank of fog receded at one point to expose most of the southern hemisphere stars, I pointed my camera away from city lights, toward the darkest sky. Just as my new composition and exposure were ready, a rogue patch of fog wafted up, providing the ideal background for the tree. As if in collaboration with the fog, the lake chose that instant to smooth its ripples and dial up the reflection.
After this night I can’t say that cityscapes are going to become a regular part of my repertoire, but for one night it was liberating discard my shackles and roll with the scene—and I’ll be much less hesitant to do it the next time. But more than the images, it was simply a joy being out there to watch the fog dance with the stars.
Posted on July 24, 2018
We’ve all heard it: “That’s so fake,” or “You Photoshopped that,” or some other derisive barb implying that an image is trying to be something it isn’t. But before you say that about this image, let me say that I processed it five times, each time dialing down the saturation, attempting to create something that would appear credible to the dubious masses. And with each pass, the color looked a little less like what we saw this unforgettable New Zealand morning. So finally I just said, enough is enough—you’ll just have trust me when I tell you that for the sake of credibility, you’re already being cheated of that morning’s full spectacle.
Don Smith and I got our New Zealand winter workshop group up early to photograph sunrise at the famous Wanaka willow tree. The tree was just a short walk from our hotel, and even though we still had 45 minutes until sunrise, it was apparent the second we stepped outside that something special was in store. Though it was still dark enough to require flashlights, already the entire sky radiated a rich ruby red. Since we’d shown the group the tree the prior afternoon, a few rushed ahead, but Don and I held back with the stragglers. Nevertheless, even the stragglers pace quickened as the red deepened, and by the time we reached the tree we were pretty much jogging.
Turns out we needn’t have rushed. For the next 30 minutes the red intensified until everything in sight seemed to buzz with color. I’ve experienced color like this a few times in my life, and the best way to describe is that it feels like the light possesses a physical component that penetrates my skin and everything else it touches. And with the sky throbbing in all directions, I felt like I might get dizzy whirling about to avoid missing something. Soon we all just started laughing at how unbelievable the show was, knowing that every picture we shared would be met with the obligatory “That’s so fake” skepticism.
All this got me thinking again about what causes color in the sky, so I dusted off a post I wrote a few years ago, tweaked a few things, and…
A sunset myth
If your goal is a colorful sunset/sunrise and you have to choose between pristine or polluted air, which would you choose? If you said clean air, you’re in the minority. You’re also right. But despite some pretty obvious evidence to the contrary, it seems that the myth that a colorful sunset requires lots of particles in the air persists. If particles in the air were necessary for sunset color, Los Angeles would be known for its incredible sunsets and Hawaii would only be known for its beaches.
But what is the secret to a great sunrise or sunset? Granted, a cool breeze, warm surf, and a Mai Tai are a great start, but I’m thinking more photographically than recreationally (sorry). I look for a mix of sky (to pass the sunlight) and clouds (to catch the color), with a particular emphasis on a clear horizon in the direction of the sun. But even with a nice mix of clouds and sky, sometimes the color fizzles. Often the missing ingredient, contrary to common belief, is clean air, the cleaner the better. And like most things, it all makes sense when you understand what’s going on.
Light and color
Understanding sunset color starts with understanding how sunlight and the atmosphere interact to make the sky blue. As you probably know, visible light reaches our eyes in waves of varying length, with each wavelength perceived as a different color. Starting with the shortest wavelengths and moving toward the longest, visible light goes from violet, indigo, blue, green, yellow, orange, and red. (These color names are arbitrary labels we’ve assigned to the colors we perceive at various points along the visible portion of the electromagnetic spectrum—there are an infinite number of colors in between each of these colors.) When a beam of light passes through a vacuum (such as space), it moves in a straight line, without interference, so all its wavelengths reach our eyes simultaneously and we perceive the light as white.
Why is the sky blue?
When light interacts with a foreign object—for example, when a beam of sunlight enters our atmosphere—different wavelengths respond differently depending on the size of the molecules they encounter. If sunlight encounters molecules that are larger than its wavelengths, such as atmospheric impurities like dust or smoke, all of the wavelengths bounce off (reflect). Because these large molecules are of varying sizes, a variety of wavelengths (colors) get blended into a murky sky with a gray or brown cast. If all the wavelengths get bounced equally, the sky will appear white(ish).
When a beam of sunlight hits the much smaller molecules of the gases that comprise our atmosphere (such as nitrogen and oxygen), some of its wavelengths are absorbed while others are reflected and scattered in all directions. Because the shorter wavelengths (violet and blue) scatter most easily; the longer wavelengths (orange and red) continue on to color the sky of someone farther away. The more direct the sunlight’s path to our eyes, the less atmosphere it passes through and the more we see the first (blue) wavelengths to scatter. When the sun is high in our sky, its light takes the most direct path through the atmosphere and our sky is most blue (assuming no pollutants have altered the scattering). In the mountains, sunlight has passed through even less atmosphere and the sky appears even more blue than it does at sea level.
When the sun is on the horizon, the light that reaches us has traveled through so much atmosphere that at the very least it has been stripped of its blueness because the blue wavelengths are the first to scatter (those wavelengths are coloring the sky of someone whose sun is high overhead). And if that sunrise/sunset light hasn’t encountered larger dust and smoke molecules on its journey, only the red wavelengths will have survived unscathed, and everyone enjoys the show.
The cleaner the air, the more vivid the sunrise/sunset color. To understand the mixing effect that happens when a variety of wavelengths are bounced around by large airborne particles, think about blending a smoothie consisting of a variety of brightly colored ingredients (such as strawberries, blueberries, and spinach—yum). Your smoothie’s color won’t be nearly as vivid as any of its ingredients, not even close. Instead you’ll end up with a brownish or grayish muck that might at best be slightly tinted with the color of the predominant ingredient. That’s what happens to the color when the light has to interact with large airborne particles like dust, smoke, and smog. Because these particles aren’t of uniform size, they each reflect a slightly different color rather than allowing one vivid color to dominate. In the middle of the day pollution means less blue; at sunrise/sunset, it’s less pink, red, and orange.
Clouds can enhance sunrise/sunset color by catching the red wavelengths and reflecting them back to our eyes, but only if there’s an opening on the horizon for the light pass through. Without clouds, the red wavelengths continue on to color the horizon opposite the sun—a “twilight wedge” when the color is in the sky, and “alpenglow” when mountains jut into the colored region of the sky and take on the color themselves.
So. To the skeptics who reflexively dismiss pictures like this, you might want to suggest that they spend more time out in nature. Whether it’s a tropical bird, a fluttering butterfly, a field of wildflowers, or a New Zealand sunrise, there really is nothing subtle about color in nature.