One of the great things about living in Washington is the occasional opportunity to see the aurora borealis (northern lights). While we rarely get the all-sky displays that are common in Alaska, Canada, or Scandinavia, there are typically at least a few nights per year where they are bright enough to see dancing on the northern horizon with the naked eye. This has been especially true this past year, as the Sun inches toward the next solar maximum in 2025. (Aurora are the result of interactions between our atmosphere, magnetic field, and charged particles spit out by the Sun. More solar activity generally means more opportunities to see aurorae.)
This past week, I witnessed a stellar (by Washington standards at least) auroral show. In a stroke of luck, I was already scheduled to lead a public stargazing event on the evening that Earth was hit by a large coronal mass ejection (CME), a burst of charged particles from the Sun that can trigger aurorae upon arrival at Earth. It was quite a treat for everyone, given that “see the northern lights” was not part of our event advertising. Instead, it was a nice bonus for everyone that braved the still-rather-chilly-and-windy spring weather.
This was my fourth time seeing the northern lights: three times from Washington, and once, oddly, from southern Utah. One big takeaway is that the show is a little different each time. This was the first time I had seen or photographed a red aurora. What’s more, the red color was easily visible to the naked eye. Seeing the sky glowing red was quite a strange sight; it felt like something was wrong with my eyes. In the photos, the aurora has an almost pink or magenta color, something that seems to be relatively uncommon. The display was brief: after less than 30 minutes, the lights dissipated.
Comparing these photos to one from my last sighting in October 2021, it’s almost hard to believe they are the same phenomenon. In October, the lights hugged the horizon and the green color was not nearly as apparent to the naked eye. (I find this odd given that the human eye is much more sensitive to green light than red light, especially at night…would expect it to be the other way around.)
These tantalizing glimpses of the aurora borealis the last few months are making me want to plan a winter trip to Alaska in the next few years while the Sun remains active. Fingers crossed we can make it happen!
Capturing stunning images of the night sky has become much easier in recent years. The low-light performance of modern cameras (and even my six-year old Nikon D750) far outpaces the capabilities of cameras made even a decade ago. Recently, I was flipping through some old astronomy magazines from the early 2000s and was shocked not only by the (low) quality of the wide-field astrophotography of the day, but also by the incredibly expensive gear used to produce those images at the time. 20 years ago, it was extremely difficult to capture a detailed image of the Milky Way without a high-end camera and an expensive tracking mount.
Today, even some phone cameras can capture passable images of the Milky Way. Stunning panoramas of our galaxy stretching from horizon to horizon are now a dime a dozen on social media. Given the advanced abilities of today’s cameras, it is natural to wonder: “Does the Milky Way really look like that?” Do the spectacular Milky Way images we see plastered across the internet accurately represent what the human eye can see? Or is this incredibly rich detail only visible to a high-tech camera sensor? Or, more nefariously, could these images simply be the result of some Photoshop trickery? The answer, perhaps not surprisingly, is a combination of all three!
Let’s begin by discussing one way in which most Milky Way images are not representative of what the human eye would see: color. The Milky Way will always look monochromatic to the naked eye. However, the reason why has to do more with the physiology of the human eye than any deception on the part of the photographer. Let me explain.
Some photographers do like to crank up the saturation of their Milky Way images beyond belief. Night sky photos with vibrant blues, purples, oranges, and pinks are the tell tale signs of digital embellishment. Rather than point fingers, I’ve created my own version below to illustrate:
To be clear, these colors aren’t real. This is Photoshop trickery, pure and simple. Here’s what the same image looks like without the saturation increase:
Much more subdued, certainly, but look closely and you’ll see that there is still some color there! Here’s the good news: those colors ARE real! Notice the pale green sky behind Mt. Adams. That’s airglow, a phenomenon caused by gas molecules in our atmosphere re-emitting energy they absorbed during the day in the form of ultraviolet radiation from the Sun. If you open the photo full screen and look really closely, you can also see some small pink-ish blotches along the plane of the Milky Way. These are hydrogen gas clouds—stellar nurseries if you will—glowing with the characteristic ruddy hue of ionized hydrogen.
Now for the bad news: while these subtle colors are “real”, you’ll never actually see them with the naked eye. Why not? To sum it up, our eyes suck at seeing colors at night. We see using two different sets of cells in our retinas: rods and cones. The cones are what allow us to see color. Unfortunately, the cones only work when there is lots of light entering our eyes, like during the day. Our rods are mostly responsible for our night vision and they are, sadly, colorblind. This is why the night sky (and low light scenes in general), always appear in shades of gray. Only a few of the brightest stars and planets emit enough light to trigger our color-seeing cones. The diffuse glow of the Milky Way does not.
Cameras on the other hand don’t have rods and cones. They are much better at picking up color in low light, so they naturally produce images that are more vibrant than what we actually experience…no editing necessary!
With this in mind, let’s remove the color entirely from our Milky Way image:
With the color out of the picture, is this now what the Milky Way actually looks like to the naked eye? Yes…under certain circumstances.
Look closely at the Milky Way in the image above. Notice the detail. It’s complex. It’s interesting. Some parts are brighter, others fuzzier, with dark blotches and voids winding sinuously from upper left to lower right. The Milky Way is a complex place, and this manifests itself in our view of it from Earth. In this regard, this photo actually does a pretty good job of depicting what the Milky Way actually looks like. You CAN see this detail and complexity with your own eyes…provided that a few things are true:
#1: You have a dark sky. For most people, light pollution prevents the Milky Way from being seen in its full glory. If you want to see the kind of detail shown in a photo like this one, you need to be somewhere dark. Not “turn off the porch light” dark. Not “drive out to the edge of town” dark. Not even “drive an hour up into the mountains” dark. Light pollution is incredibly pervasive and the view of the Milky Way can be degraded for literally hundreds of miles from a major city. Even some of the most remote wilderness areas in the United States are still awash in the glow of artificial light. Places like eastern Oregon, central Idaho, northern Nevada, and southern Utah are among the few locales where you can still experience a pristine night sky. A view of the Milky Way from anywhere else simply doesn’t compare.
#2: Your eyes are dark adapted. Remember the rods from earlier? While our rods allow us to see fairly well in low light, they need at least 20-30 minutes of darkness in order to reach peak sensitivity. This period is known as “dark adaptation” and it is a key ingredient of a successful stargazing session. Gazing at the Milky Way before your rods have had time to fully dark adapt is like looking at a Van Gogh or Monet with dark sunglasses on; you miss many of the finest details. If you walk out of a brightly lit RV or tent and look skyward expecting to see the Milky Way like it appears in a photo, you’ll be quite disappointed. Even using a headlamp or checking the time on your phone while waiting for your eyes to dark adapt can inhibit the process. For this reason, astronomers typically use red lights at night because our rods are less sensitive to that color, making it easier to preserve night vision.
#3: You are in the right place at the right time. We live in the suburbs of the Milky Way galaxy. When we look toward the center of the Milky Way (downtown), it looks brighter, because we are looking at a greater concentration of stars, gas, and dust. When we look away from the center, it looks dimmer. Images like the one I’ve been using in this post are taken looking downtown…toward the galactic center. This portion of the Milky Way is only visible during certain times of year. In late fall, it’s behind the Sun, making it rather difficult to photograph or see. Late evening in the summer and early fall, or early morning in the Spring is the ideal time to catch it. At other times of year, when the galactic outskirts grace our sky, the Milky Way is much more ho-hum. You’ll also want to avoid the Moon, whose glow will mostly overwhelm the diffuse and relatively faint Milky Way.
If all three of these things are true, then yes, the black and white image above is a good representation of what the Milky Way looks like to the naked eye. Sadly, only about 20% of North Americans can even see the Milky Way from their homes, much less see it under ideal circumstances. Light pollution has masked the view of our home galaxy to the point that most of us no longer know what it should look like. Ecologists call this “shifting baseline syndrome”, a phenomenon in which each successive generation comes to regard the state of the environment around them as “normal”. In other words, as we degrade our environment, we gradually forget what things used to be like, or, in this case, look like.
While increasingly rare, such a view of the Milky Way is one of the most spectacular sights in the natural world. I vividly remember a backpacking trip I took over a decade in Aoraki/Mt. Cook National Park in New Zealand. The Milky Way appeared so bright that it cast shadows on the ground, and I was able to read a book (albeit barely…) by its light. Oddly enough, sometimes the “darkest” skies are actually the brightest because so many stars are visible.
Fortunately, light pollution is an easy problem to fix. Many outdoor light fixtures are poorly designed and allow light to escape upward into the night sky. While our modern lives certainly require light at night, that light is almost always needed on the ground, not up in the sky. Illuminating the sky or the crown of a tree makes no one safer or more secure from hazards real or imagined. Light fixtures that direct light downwards (known as “fully shielded” fixtures) eliminate much of the problem. Cities that use such lights, like Flagstaff, Arizona (where I grew up), produce substantially less light pollution than other cities of comparable population. You can see the summer Milky Way from downtown Flagstaff…a city of nearly 100,000 people. Simple actions can go a long ways toward preserving the view of the Milky Way for future generations. (For more on what you can do to combat light pollution, check out the great work being done by the fine folks over at the International Dark Sky Association.)
Comet C/2020 F3 (NEOWISE) continues to put on a stellar show for skywatchers in the northern hemisphere. Over the past week, the comet has moved into the evening sky, making a trip out to see it somewhat more palatable than it was when I first highlighted the comet 11 days ago. Last week, I had the pleasure of viewing the comet twice in one night while camping on the east flank of Mt. St. Helens. High clouds prevented a great view at sunset, but had mostly cleared just four hours later when the comet rose again in the northeast. Just below and to the left of the comet was the distant cone of Mt. Rainier. Low clouds in the river valleys below us made for a spectacular view:
Unfortunately, the comet has dimmed noticeably over the past few evenings. While we still have a few days until its closest approach to Earth, the comet has receded from the Sun enough that its activity is likely beginning to wane. The next few nights will likely provide the final chance to see this comet and its tail with the unaided eye (until it returns ~6,800 years from now that is!) The waxing moon will begin to interfere by later this week and by the time the moon leaves the evening sky a few weeks from now, the comet will likely have faded from naked eye visibility. To see it, look northwest 1-2 hours after sunset. The comet will appear a little below the bowl of the Big Dipper, and is far enough north now that viewing is significantly better from more northerly locations. More details on spotting the comet can be found here: https://earthsky.org/space/how-to-see-comet-c2020-f3-neowise