THE ULTIMATE GUIDE TO MASTER ASTROPHOTOGRAPHY.
The Ultimate Guide to Master Astrophotography is the ultimate manual for anyone looking to create spectacular landscape astrophotography images.
By explaining the science of landscape astrophotography in clear and straightforward language, it provides insights into phenomena such as the appearance or absence of the Milky Way, the moon, and constellations.
This unique approach, which combines the underlying scientific principles of astronomy with those of photography, will help deepen your understanding and give you the tools you need to fulfill your artistic vision.
Why astrophotography?
The night sky is an essential part of nature and not just an astronomer’s laboratory. However, for many people who live in urban light dominated areas, this part of nature is completely lost.
Astrophotography in any form and level, either by only a photo camera and tripod or a complete set of telescopic equipment, helps to reclaim the forgotten beauty of the night sky. There are few other scenes in nature that astound me so deeply in the way that the rise of the Milky Way does.
People have photographed such fiction-like starry scenes from bizarre locations of the planet; from the boundless darkness of the African Sahara when the summer Milky Way was arching above giant sandstones, to the shimmering beauty of the Grand Canyon under moonlight, and crystal sharp sky of Himalayas when the bright winter stars were rising above the roof of the world Mt. Everest. Astrophotography is not only about recording a part of the outer space. It leads you to a life of adventures and enjoyment which are not experienced by most of the people on this planet.
The age of digital imaging has revolutionized astrophotography. The possibility of creating inspiring images of the night sky with today’s off-the-shelf digital cameras, which was once only possible with highly sophisticated equipment, made a considerable amount of public interest to amateur astronomy and astrophotography, specially to nightscape (night sky landscape) imaging which is also often referred to as landscape astrophotography.
Landscape astrophotography combines compelling landscape subjects with carefully choreographed night sky objects. This guide explains the science behind the art of landscape astrophotography in clear and easy to understand language. The goal is to help you learn how to successfully plan and create your own nightscapes of the Milky Way, star trails, the Aurora Borealis, and much, much more.
The unique approach of this guide is its coupling of the underlying principles of astronomy and photography through practical, step-by-step methods to provide you with all the tools you need to fulfill your artistic vision. Without this knowledge, an inefficient, time-consuming and often frustrating ad hoc, trial and error approach is the only alternative to gaining expertise and proficiency in landscape astrophotography.
The theme of this guide is preparation. Understanding the basics of astronomy will give you deep insights into the “why” of the appearance or absence of the Milky Way, the moon, specific constellations, and more. Learning the relevant fundamentals of photography will enable you to adjust your camera’s settings for perfect exposures of the night skies.
Thorough planning and preparation will guide you to the right place at the right time and with the right equipment and experience. Far more than a cookbook of recipes, this guide delves deeply into the causes for the effects that you observe. This is accomplished through copious examples, detailed explanations and case studies. By mastering this knowledge, you will be able to predict with certainty, months and even years in advance, what you need to do; and when and where you need to go to create almost any new nightscape image you can imagine.
Finally, our hope in writing this guide is to convey our love of nature, photography, and especially the night skies. Through it, we hope that you, too, may gain a deeper appreciation of our incredible universe each time you step into the night.
A brief history of landscape astrophotography.
Landscape astrophotography has been around for decades. Prior to the advent of modern digital cameras, however, only the most dedicated possessed the patience to persist in their pursuit of quality images. Success was elusive owing to the large number of obstacles and the steep learning curve, difficulties exacerbated by the major delay in image review resulting from the need to develop at least the negatives of the film. Nonetheless, the lure of the night sky was irresistible to many who carefully and meticulously perfected their art.
All this changed with the incredible improvements in affordable digital photography for the consumer market during the 1990s and 2000s. Suddenly, not only were digital single-lens reflex (DSLR) cameras available that were capable of producing images of comparable quality to those based on film, digital cameras provided instant feedback. This latter point was a true game-changer; the photographer could now determine, on the spot, if the focus was off; if the exposure was wrong; if the composition needed to be tweaked, and so on.
You will find yourself constantly reviewing your images in the field, and you will improve your success rate enormously if you develop the habit of doing so. You will detect and be able to correct minor flaws that, if left undiscovered until you return home, could otherwise ruin an entire evening of shooting.
Today, landscape astrophotography, also known as nightscape photography, has exploded into our everyday lives—through science news, advertising, and social media. New apps and online resources designed especially for landscape astrophotography, especially those integrating augmented reality, are constantly being developed and improved. Camera and lens systems continue to be refined to be available at ever-lower costs. A host of online communities can be found to share and learn about the most obscure of landscape astrophotography topics. Clearly, this is a golden era!
A quick guide to get you started tonight.
Here is a straightforward recipe to get you outside tonight and embarked upon your landscape astrophotography journey. Fingers crossed for clear skies!
Description:
The starry skies have fascinated us for millennia. Here, you will want a clear view of the sky, and you will want to use a wide-angle lens, one with a focal length of approximately 24 mm or less for a camera with a full-frame sensor, or 18 mm or less for a camera with a crop sensor. Needless to say, you will want to mount your camera on a sturdy tripod!
What you’ll achieve:
One to two dozen (or more) images of starry skies.
What you need:
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Manual shutter release or self-timer .
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Manual exposure mode ISO 800–3200.
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Aperture—f/4, f/2.8 or similar.
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Shutter speed of say 5 seconds to start.
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Headlamp preferably with red light, or red plastic taped over a white light.
Directions:
During the day, focus your camera on the most distant object you can see—the horizon, distant mountaintops, or distant city buildings. After finding a good focus, set your camera lens and/or camera body to manual focus and leave it there. Many people will temporarily tape the focus ring of their lens in this position to keep this focus for the duration of the night.
Next, before heading out, look up the time of sunset/sunrise. The skies generally become fully dark around 1½ to 2 hours after the sun has set. Plan on arriving on location at least an hour prior to this time to give yourself enough time to unpack, find a good location, and set up your camera system properly.
Set up your camera/tripod with a clear view of the sky; perhaps with an interesting foreground subject—a line of trees, mountaintops, or beach. If your camera doesn’t have a viewfinder, don’t worry. Just aim it so that it is generally pointing at the sky—and be sure to keep the manual focus setting in place! With your camera pre-focused as described above, expose your first image and review it and its histogram on the back of the camera.
If needed, increase or decrease the shutter speed—speeds of 20–30 seconds are very common. If the image is too dark at exposure times of say 20 seconds, bump up the ISO; just try to keep the ISO below 6400. If no clouds are present, you should be able to make at least a dozen or so high quality images. And if this doesn’t yet make sense to you, it will; read on! We also have a great article we have written about Cameras and Imaging in Astrophotography. You can find it here.
The night sky and its movement.
The night sky is rich with objects to observe and include in your nightscapes. There is the moon, meteors, the planets, comets, the Milky Way, and Iridium flares.
There are dazzling atmospheric phenomena you may wish to pursue: the kaleidoscopic colors of sunsets and sunrises, deep twilights, the zodiacal light, sky glow, ice haloes, noctilucent clouds, moonbows, and the hypnotic Aurora Borealis/Australis. Your understanding of the origins and characteristics of the objects and phenomena of the night sky; and how they move during each night, between one day and the next, and from month-to-month, will be the basis for your landscape astrophotography journey.
This section provides you with the astronomical foundations necessary for successful landscape astrophotography. First, we will briefly review the structure of the universe and how it relates to the most common night sky objects you will see.
Next, we will learn how the earth’s motion—both its daily rotation about its axis, and its annual revolution, or orbit, around the sun causes these objects to move across the sky. We will see why this motion depends on the compass direction you’re facing, or from which of the earth’s hemispheres you’re observing.
You will learn about two simple tools you will want to learn how to use to understand the constantly moving night sky and predict the constellations that will be visible for any time or date. Finally, we will conclude with a brief review of the cause and effects of the seasons.
Overview of night sky objects.
As the sun slips below the horizon and night descends, its light slowly recedes from the sky. The glowing blue gases in the earth’s atmosphere become transparent, allowing us to peer into the realms beyond. What a universe awaits us! Moving beyond the earth, we first encounter our moon, along with our neighboring planets—Venus, Mercury, Mars, Jupiter, Saturn, Uranus, and Neptune.
Our solar neighborhood includes comets, which are frozen masses of gas, ice, and rock, as well as the debris they leave in their path that gives birth to annual meteor showers. Moving beyond the solar system into the encompassing Milky Way Galaxy, we find a rich variety of stars, gas nebulae, and star clusters. Finally, venturing beyond the Milky Way into deep space and the rest of the visible universe, we find ourselves in the realm of other galaxies and galaxy clusters.
All of these night sky objects can be put into one of two main categories for our purposes. The first category includes objects whose position relative to each other never changes —for example, the stars, the Milky Way, constellations, nebula, and star clusters. Once you’ve learned their arrangements, they will be your familiar night sky friends for the rest of your life. The second category includes objects whose position constantly changes relative to the background positions of the stars.
This category includes the planets, whose name originates from Greek for wandering star, the moon, comets/meteors, satellites, and Iridium flares. This section focuses on the first category of objects, specifically, stars, and constellations. Subsequent sections cover the night sky objects whose positions constantly change.
Stars and constellations.
We begin with those objects whose position remains constant relative to one another: the glittering stars and the constellations they form. You may be surprised to learn that all the individual stars distinguishable with your naked eyes are only located within a relatively small portion of the Milky Way.
Our eyes are only able to resolve galaxies in the vast space beyond the edges of the Milky Way in just a few instances. Einstein incorrectly considered the universe to be made up of a uniform “soup” of stars and occasional galaxies distributed within it. It was Hubble who first discovered that this wasn’t the case; rather, the universe was comprised of discrete galaxies with essentially no stars or much else 3 in between.
In fact, nearly all the night sky objects you can see with your naked eye are relatively nearby stars, planets or other objects contained within our own Milky Way Galaxy, including our solar system. The illusion of a universe filled with a moreor-less uniform distribution of stars is created simply by the necessity of viewing the night sky from our position embedded within the Milky Way Galaxy. Our view of the Andromeda Galaxy, M31, thus includes all the Milky Way stars that reside within our line-of-sight.
If we were to view M31 from a position outside the Milky Way, none of the stars would be present; we would simply see M31 floating alone in empty space.
The stars that make up the Milky Way, including our sun, are enormously varied in their color and brightness. Just look at the variety of stars in the constellations of Ursa Major and Scorpius. Some stars are brighter than others, depending on their size and proximity. Bear in mind that nearby, dim stars can have the same brightness as massive, dazzlingly intense stars that are much further away.
Second, all stars have a characteristic color, ranging from deep red to vivid blue. The color of each star depends entirely on its mass and age—young, hot stars give off a noticeably bluer light than the deeper reddish light of older, cooler stars. The fact that hotter stars are blue while cooler stars are red may be opposite what you might think! Yet, owing to the peculiarities of human night vision, we perceive most stars as points of white light, with a few notable exceptions, such as the distinctly red gas giants Betelgeuse, Antares, and Aldebaran in Orion, Scorpius, and Taurus, respectively.
Your camera, however, has the capacity to record the true colors of all the stars—and its images will likely astound you! People have identified legendary figures, animals, and mythical creatures in the patterns of the stars across cultures for thousands of years. These groupings are called constellations, and some are most likely familiar to you.
The International Astronomical Union established eighty-eight constellations with internationally agreed upon boundaries nearly a century ago. These constellations provide a useful structure for night sky navigation, in addition to their human interest.
For example, we might say that Mars can be found in the constellation Leo on a given night, thus narrowing the region of the sky to examine. Each star within a constellation is ranked in terms of its brightness. The brightest star is generally designated by the Greek symbol α, the second brightest star by the symbol β, and so on. Thus, for example, the star Sirius, which is not only the brightest star in the constellation Canis Major but also in the entire sky, is designated Canis Majoris.
This information can be very helpful in pinpointing hard to see objects like comets, star clusters, and nebulae. For example, it greatly helps finding the North American nebula knowing it is near Cygni, or the second brightest star in the constellation Cygnus. There are many widely recognized sub-groupings of stars within constellations known as asterisms. Probably the most familiar asterism in the Northern Hemisphere is the Big Dipper, which is part of the constellation Ursa Major.
Other familiar Northern Hemisphere asterisms include Orion’s Belt, the Teapot within Sagittarius, the Summer Triangle, the Winter Cross, and the Fishhook in Scorpius. Familiar Southern Hemisphere asterisms include the Southern Cross, the Southern Pointers and the Diamond Cross.
The brightest stars in the sky.
As we will see later in this guide, achieving proper focus on the stars can be extremely challenging. Part of the difficulty lies in the scarcity of visible, sufficiently bright stars to use as targets. Knowing where to find them throughout the year can help. Searching for the brightest stars is worthwhile, since they are your best option for achieving a sharp focus on the night sky. Although they may be hidden behind a foreground object, such as a tree limb or building, knowing their presence and simply moving a short distance away can often bring them into view. This process allows you to achieve correct focus and then return to your composition of interest.
Earth’s annual orbit—How objects move during the course of the year.
So far, our discussion of the movements of the stars in the night skies has been confined to those that occur during a single night. What happens to our night sky view over the course of a year? This is easily answered by studying the changes that occur in our viewing direction as the earth orbits the sun. These changes affect what we see, just like the slow rotation of a revolving restaurant changes the view from its windows.
For example, in September, the constellation Aquarius is directly overhead at midnight, whereas in January, the earth has changed position so now the constellation Gemini is directly overhead at midnight. The night sky objects that are visible during different times of year change simply as the result of the earth’s motion along its orbit.
Now imagine that we were somehow able to discern the stars during the daytime. The constellations that become visible lie on the opposite side of the solar system from the sun. The sun would lie in the constellation that otherwise would only be visible at night, six months hence. For example, in January, the sun is positioned within the constellation Sagittarius which we see at night during July, six months later. In May, it is positioned within the constellation Aries, seen at night during November. The narrow band of the sky that includes the path of the sun’s orbit, or the ecliptic, is known as the zodiac.
The twelve constellations found within the zodiac are known as signs of the zodiac, or sun signs, since the sun is positioned within each constellation during the different months of the year. Knowledge of the changing nighttime view throughout the year results in predictable seasonal events. Many are highly relevant to landscape astrophotography. For example, the brightest, central part of the Milky Way, or its core, lies beyond Sagittarius and Scorpius, thus becoming visible between March and September. It is fruitless to attempt to photograph or even observe it during the rest of the year since it is obscured by the intervening sun and blue skies.
Meteor showers only occur on specific dates and constellations are only visible during certain months, as we have seen. Consequently, it is extremely helpful to be able to forecast the appearance of the night sky for different dates throughout the year.
Seasons.
Seasonal effects are important for landscape astrophotography. Sunrise and sunset positions change throughout the year, as do daylight, twilight, and darkness durations. The 23.5° angle between the axis of rotation of the earth and normal to the plane of its orbit cause the seasons, not changes in proximity between the earth and the sun.
The earth is actually physically closer to the sun during the Northern Hemisphere’s winter than in the summer! Because of this tilt, as the earth moves around its orbit throughout the year, observers at different latitudes on Earth will experience more direct sunlight during some months than others. During the summer, those in the Northern Hemisphere receive the highest, most direct intensity sunlight since the sun is higher in the sky; and For the greatest number of hours each day.
Conversely, in the winter, they receive much less direct sunlight and for fewer hours each day. An important outcome of the seasons is the changing position of sunrise and sunset on successive days during the year. This phenomenon can present a challenge to the landscape astrophotographer who wishes to capture the sun rising over a specific foreground object.
Solstices and Equinoxes.
There are four days during the year of special seasonal and cultural significance that can also provide unique landscape astrophotography opportunities with great popular interest. The summer and winter solstices are the longest and shortest days of the year, respectively. The spring and autumnal equinoxes, on the other hand, are the days with equal lengths of day and night.
These important dates have been noted throughout human history, especially as they relate to the cultivation of crops. Stonehenge in England, the pyramids of Egypt and monuments throughout the southwestern deserts of the United States are just a few examples of the efforts of our predecessors to mark these dates.
One example of past civilizations marking the summer solstice is illustrated through a set of three, spiral rock petroglyphs inscribed in a rock boulder within an ancient Ancestral Puebloan village in southeastern Utah. The spirals are inscribed on an east-facing rock panel underneath an adjacent rock overhang. In turn, the rock panel is positioned a few feet to the west of a larger boulder which casts a shadow on the petroglyphs during sunrise.
This unique rock geometry results in the formation of two “light daggers” that appear on either side of the eastern boulder’s shadow, during sunrise on the summer solstice. The positions of the three spiral petroglyphs were carefully chosen so that on the summer solstice, as the sun ascends and the light daggers lengthen and eventually intersect, they do so directly through the three spiral petroglyphs. This happens since the sunlight is able to pass over the front boulder and illuminate the rock panel.
The different positions of the sun during the rest of the year preclude this sequence of events; the day when light daggers intersect the three spirals during sunrise confirms the summer solstice. Witnessing events such as these immediately forges a timeless bond between the observer, those in the past who created them, and the reliable cycles of astronomy.
Sunrises and sunsets.
Undeniable feelings of renewal and hope accompany the sunrise; and comfort and peace with the sunset. It is no surprise that so much prize-winning landscape photography is created during these special times. This section explains the science behind the phenomena of sunrises and sunsets, and why they appear the way they do. Consider Earth’s appearance from space. The half of the earth facing the sun is brightly illuminated and experiences daylight, whereas the half of the earth facing away from the sun is in the earth’s shadow, and experiences night. Sunset or sunrise occurs in the day-to-night transition zones.
Clouds permitting, bright blue skies will cover the regions experiencing day owing to preferential Rayleigh scattering of the blue wavelengths of sunlight by the oxygen and nitrogen gas molecules in the earth’s atmosphere. Dark, clear skies will cover the regions experiencing night as the result of the intrinsic transparency of our atmospheric gases coupled with the complete absence of sunlight-induced Rayleigh scattering. During the day, the entire sky dome becomes a diffuse source of bright, blue light in addition to the predominantly yellow light of direct sunlight.
When we’re outdoors on a clear, sunny day, it’s like we’re in a giant amphitheater with a glowing blue ceiling! The diffuse nature of the blue light from the sky allows it to illuminate observers who are shaded and thus not directly in line with the sun.
To observe this phenomenon, carefully examine a white sheet of paper outdoors in the shade of a tree or a building on a sunny afternoon. It will exhibit a distinctly bluish tint. If our sky had no atmosphere, shadows would be completely black, as they are on the moon, except for any light reflecting off nearby objects. So if the daytime sky is blue and the nighttime sky is clear, what is the source of the vivid oranges and reds of sunsets and sunrises? These colors appear because the light from the sun and adjacent sky that reaches observers during sunset and sunrise has traveled through a much greater distance of the earth’s atmosphere than during the day.
As light travels through this greater portion of the earth’s atmosphere during sunset and sunrise, most of its blue light gets scattered away and lost, thousands of miles away, before it reaches the observer. All that’s left by the time the sunlight reaches the observer is predominantly red and orange light, with scarcely any blue light remaining. The greater the distance of travel, the more of its blue light is scattered and lost, leading to an increasingly red sun and sky as the sun approaches the horizon during sunset and sunrise. These fiery, final red rays of sunset and first rays of sunrise that strike high altitude mountains, and clouds are the source of the gorgeous phenomenon of alpenglow.
These beautiful orange, pink, and red colors only last for a few minutes before the sun slips too far out of position for these intensely colored rays to reach terrestrial and atmospheric objects. Nonetheless, these elusive colors are well worth pursuing—you won’t be disappointed! The distinctly warm colors of direct sunlight during the hour or so immediately before sunset and immediately after sunrise lead to these periods being known to photographers as the “golden hour.” They create wonderful opportunities for award-winning images.
You can see this effect by comparing the two photographs; both created at the same location, but one during the harsh light of midday and the other during the warm light of the golden hour. Conversely, the approximately hour-long twilight periods just after sunset and just before sunrise are known as the “blue hour”. The distinctly blue light from the sky during this period is the source of this name, since there is a total lack of any direct light from the sun. The blue hour provides many opportunities to create images with a very serene and calm mood.
Azimuth Effects of Sky Color.
The observer’s azimuth, or compass direction, strongly affects the colors of the sky during the different periods of twilight. This phenomenon provides endless opportunities for nightscape astrophotography images. You can choreograph nearly any sky color combination you wish simply by selecting the appropriate period of twilight and azimuth!
Aurora Borealis / Australis.
The shimmering, dancing lights of the Aurora Borealis and the Aurora Australis are certainly one of the most mystical and unforgettable phenomena of the night sky. The experience of witnessing cascading sheets of auroral light pouring over the dome of the sky has left many a night sky observer, including myself, speechless and in awe. Including an auroral display in a nightscape image is surely on the bucket list of most landscape astrophotographers.
Fortunately, aurorae are technically quite straightforward to photograph owing to their relative brightness compared to most of the other subjects described in this guide. In many cases, even a smartphone will suffice! It can be challenging to view the aurora, however, since they are restricted to specific regions of the earth, often necessitate significant travel and occur only sporadically. It can also be tempting to over-process aurora nightscape images with results that are unnaturally over-saturated and over-contrasted.
Popular locations for viewing the aurora with international air access include Fairbanks, Alaska; Yellowknife, Canada; Reykjavík, Iceland; Tromsø, Norway; and Kiruna, Sweden. Here, we will review the origins of the aurorae and the role of the earth’s magnetic field so that we may predict when and where they are likely to occur.
Origins of the Aurora.
The sun is constantly hurling incomprehensible quantities of electrons, protons, and a host of other subatomic particles into space at immense speeds. While most of these emissions occur more or less uniformly over its surface, local disturbances, such as sunspots and flares, can cause locally concentrated outbursts of particles and energy, and a temporary increase in auroral activity on Earth. The prevalence of notable auroral displays in a given year is thus strongly correlated with the manifestation of sunspots. In turn, the number of sunspots fluctuates in a cycle with a period of approximately eleven years.
The most recent maximum occurred around 2013; the next maximum is expected approximately in 2024. Of course, aurorae occur even without sunspots; there is simply a higher chance of a strong display when sunspots appear. Occasionally, the sun will “burp” and discharge a relatively large quantity of matter during an event called a coronal mass ejection (CME). CMEs can be responsible for spectacular displays of the aurora.
This is because of their particularly high density of high-energy particles. When the massive quantities of high-energy particles ejected from a CME reach the earth, their interactions with the gases in the earth’s atmosphere are so extensive the result is called a geomagnetic storm. Another source of energy into the earth’s atmosphere are solar wind streams from open coronal holes in the sun, although they tend to be less strong than CMEs.
In either case, communications and electrical power distribution systems can be adversely affected and even disrupted during a geomagnetic storm.
Predicting the Aurora.
The near-term likelihood of an auroral display can be predicted by monitoring the surface activity of the sun, along with measurements of the magnetic fields of the earth and the sun. Vigilant aurora watchers monitor sunspot and other solar activity closely for any signs of an impending CME or other significant solar event. If an eruption occurs, scientists and amateurs alike carefully calculate the trajectory of the outgoing stream of particles to assess whether or not it is likely to significantly interact with the earth’s magnetic field.
Since aurora-causing particles have mass, they travel towards the earth at a fraction of the speed of light, and can take up to several days to arrive. In contrast, the light and heat emitted from the sun only takes a little over 8 minutes to travel from the sun to the earth. Consequently, aurora-causing geomagnetic storms can often be predicted up to several days in advance owing to the time required for CME particles to travel from the sun to the earth compared to the much shorter time required to visually detect the onset of a CME. There are several space weather measurements constantly being made and analyzed to determine the likelihood of a near-term aurora display.
Both the raw data and the results of the analyses are continuously generated from the U.S. Space Weather Center as well as the National Oceanic and Atmospheric Agency (NOAA), and are made freely available to the public in a variety of useful formats. You may wish to become familiar with how to access and interpret these rich sources of information. While none by themselves may be enough to predict a visible display with certainty, simultaneously favorable levels of two or more of the key indices can nearly guarantee a visible display.
Viewing Tips and Alerts.
Displays of the aurora occur every day of the year, day or night. However, most displays are insignificant and only visible at extremely high latitudes. Spectacular displays can also occur any day of the year and any time of night, although they are most commonly viewed after midnight owing to the dark skies, and around the spring and fall equinoxes. Dates around the new moon each month also result in the darkest possible skies and allow the most vivid colors to be seen at a given location. A crescent or quarter moon may cast enough light to illuminate the foreground without overexposing the sky.
Nights of the full or nearly full moon tend to wash out the aurora owing to the relatively bright skies. Stunning images are often captured of the aurora over a large, calm body of water that produces gorgeous reflections. There are several free and subscription services that allow you to automatically receive alerts of impending auroral displays.
These alerts can be very helpful when a display unexpectedly develops in the middle of the night and you happen to be asleep. Several online communities also exist to help alert their members to ongoing displays. For example, one very active and popular Facebook group is the Great Lakes Aurora Hunters (GLAH) group, whose over thirteen thousand members actively report and generously share up-to-the-minute information and viewing tips.
These are related to ongoing and imminent auroral displays across continental North America and Alaska, Canada, and Scandinavia. Finally, there is the time honored “telephone tree” in which friends simply call one another to drag them out of bed during an active display!
We also have written an in depth article about Common Astrophotography Obstacles & How to Solve Them. You can find the article here.
The Moon.
Next to the timing of sunrise and sunset, the phase of the moon is the single most important factor for you to consider in creating your nightscape images. Especially if you’re new to landscape astrophotography, the effects of moonlight on nightscapes can be surprising. One reason for this is that both camera sensors and film accurately record moonlit nightscapes in full color, in contrast to human night vision, which perceives them primarily in black and white. The results can be pleasantly disorienting—otherworldly nightscapes that appear to be illuminated by sunlight, yet with skies clearly containing a multitude of stars!
Whether the moon is present or absent in the night sky when you make your nightscapes directly affects two of their most important aspects. First, when the moon is visible, it acts like a dim version of the sun, causing the gases in the earth’s atmosphere to glow with a bluish tinge.
However, this glow tends to drown out the dimmer night sky objects, resulting in fewer observable stars and other phenomena. In contrast, when the moon is absent, the earth’s atmosphere remains as transparent as window glass, allowing us to see all the way through to the inky blackness of space. Such conditions are best for viewing the largest number of dim night sky objects, especially the Milky Way.
Second, when the moon is present, its light richly illuminates the objects on the ground, compared to the much darker, nearly featureless foregrounds during moonless nights. Clearly, it is crucial for you to know how to predict whether or not the moon will be visible on any given night.
Moonrise and Moonset.
A special consequence of the timing of moonrise and moonset relates to the outstanding opportunity to capture the nearly full moon rising the day before or setting on the day of the full moon. At these moments, the moon can appear magically suspended in the earth’s shadow, or floating between the earth’s shadow and the Belt of Venus.
Especially for the case of a Supermoon, or Harvest Moon, these photo opportunities can be real prizewinners! A special note of hard-learned practicality however—the actual timing of the moment of moonrise relative to that of sunset/sunrise on these days can differ by 20–30 minutes from month to month, which can significantly impact the moon’s position relative to the earth’s shadow.
In fact, the specific moonrise/set when the moon rises in a position exactly straddling the boundary between the earth’s shadow and the Belt of Venus may only occur once per year! So carefully consult your planning tools to pinpoint that one day when your shot may present itself. Oh, and keep your fingers crossed for good weather!
Supermoon, Blood Moon, and Harvest Moon.
You have probably heard of the “Supermoon,” or “Blood Moon,” and asked yourself what’s the big deal? The answers are more societal than scientific. Along with other astronomical phenomena, the full moon has always played a prominent role in human culture, and notable annual events like these have given us a reassuring sense of the regular cycles of nature.
Each has its origin in a combination of astronomy and popular culture. As one example, let’s consider the “Supermoon” designation, which in addition to appearing slightly larger than normal, has been credited with triggering natural disasters! Supermoons are full moon that occurs during the part of the moon’s orbit when the moon is in the closest physical proximity to Earth, or at its perigee.
What’s that? The orbit of the moon around the Earth isn’t perfectly circular, but is actually an oval, or an ellipse. As a natural consequence, there is one point when the moon is closest to (perigee) and one point when it is farthest away from (apogee) the earth. The difference in moon-Earth distance between these two points is about 50,000 km, which although not inconsiderable, only leads to a difference in apparent diameter of about 14 percent as well as a difference in apparent brightness of about 30 percent.
This brightness difference isn’t especially significant. Nevertheless, each full moon can provide you with an opportunity to link the beauty of astrophotography with increasingly publicized popular culture.
The Moon Illusion.
Finally, no discussion of moon astrophotography would be complete without explaining the phenomenon known as the “Moon Illusion.” The moon illusion refers to the purely psychological perception that the moon appears larger when it is nearer the horizon than when it has ascended high into the sky.
When we see the moon next to objects on Earth that decrease in size as they increase in distance from us, we interpret the moon as being enormous! This happens simply owing to the decreasing size of terrestrial objects through parallax. Once the moon has risen into the sky with no reference points, its size appears to shrink. You can use an index card with calibrated markings to “measure” the moon’s diameter the next time it is full in order to test this phenomenon for yourself.
Be sure to hold the card at arm’s length in order to get a consistent measurement. Now, during this or the next full moon, measure the size of the full moon when it is both next to the horizon and when it is overhead. When you compare measurements, you will see they are the same!
An interesting outcome of this exercise is the ability to develop a handy field guide to estimating the size of the moon relative to possible foreground candidates that might be good subjects to juxtapose with the full moon. If you repeat the exercise above but simply with, say, the fingernail of one of your outstretched hands at arm’s length, you will be able to develop an estimate of the size in of the full moon in comparison to the width of the fingernail.
For example, in my personal experience, the full moon is approximately half the width of the fingernail on the little finger of either hand when held outstretched at arm’s length. This knowledge has proved invaluable during day scouting trips in preparation for a rising full moon nightscape image. I simply hold up my hand at arm’s length, and compare the size of half the width of my fingernail to the size of the foreground object. If they are roughly the same, then I know that the rising full moon will appear to be of equivalent size.
One last point that should be made concerns the ability to photograph the details of the craters on the surface of the moon. These craters and mountain ranges are generally not possible to resolve even with common 100–300 mm lenses. Much higher focal length lenses, and even a telescope may be necessary.
Also, exposure bracketing is often required to simultaneously record images with sufficient surface detail of the full, or nearly full moon but that are badly underexposed for the foreground, and images correctly exposed for the foreground, or stars, but that show the moon as an overexposed, featureless disc.
Solar System.
It seems incredible that only just over four hundred years ago, all humankind believed in the geocentric model, which places the earth at the center of the entire universe. It was only in 1609 that Galileo conclusively recorded the movement of Jupiter’s moons around Jupiter, not Earth, proving that the geocentric model was wrong. Of course, we now know that the sun is the center of our solar system, in what astronomers call the heliocentric model. In this section, we will briefly review the characteristics of our solar system to aid in our nightscape quests, including the differences between its eight planets.
You will also learn about several new and striking astronomical phenomena associated with the solar system: planetary conjunctions, the zodiacal light, and solar and lunar analemmas.
Zodiacal Light.
The zodiacal light is a relatively rare phenomenon that is beautiful to behold. It is only visible under completely dark skies for an hour or so around when astronomical twilight begins or ends. The zodiacal light is a cone of diffuse, white light emanating upwards from the horizon above where the sun has set or will rise. The zodiacal light, also known as the “false dawn,” originates from sunlight reflected from vast fields of dust that lie along the midplane of the solar system, or the ecliptic.
These dust fields are thought to be the remnants of comets that originate from far beyond the outskirts of the solar system, rather than leftover remnants of asteroids within the solar system. The zodiacal light is best seen during the spring equinox during early astronomical twilight in the evening, and during the autumnal equinox during late astronomical twilight in the morning. The zodiacal light is more prominent nearer the equator owing to the nearly perpendicular orientation of the ecliptic at tropical and lower latitudes. It is best photographed with a wide-angle or fisheye lens under extremely dark skies, far from city lights.
Solar and Lunar Analemmas.
A wonderful, but challenging, landscape astrophotography image is that of a solar analemma. Combining photographs of the sun taken at the same time on regularly spaced, clear days throughout an entire year allows you to create a solar analemma. They are the result of two completely independent features of the earth’s motion around the sun:
its 23 ½° tilt about its rotational axis; and
the ellipticity of its orbit.
The earth’s tilt results in the figure-eight shape of the analemma, while the ellipticity of its orbit causes the asymmetry in the figure eight. The similar tilt of the moon and ellipticity of its orbit allows the creation of a lunar analemma as well. The main difference between a solar and lunar analemma is that the lunar analemma must be created, on average, 51 minutes later each day during one lunation, or lunar month, to result in the moon arriving at equivalent positions, whereas a solar analemma must be created at precisely the same time of day. This is the result of the fact that the moon rises approximately 51 minutes later on successive days.
Light and the Human Eye.
The ability of the human eye to perceive light is truly one of the wonders of nature. Incredibly complex and delicate, the human eye is sensitive to a remarkable range of light levels and detail. In order to understand how we perceive light and color, let’s begin by considering light’s basic characteristics— where does it come from and how do we describe it. We will then explore the characteristics of the eye and human vision to better understand the components of compelling nightscape images.
Hue, Saturation and Scene Luminance, LV.
Photography is the collection and rendering of ambient light. Sources of ambient light are either direct sources, i.e. objects that emit light, or indirect sources, i.e. objects that redirect light produced from direct sources.
Examples of direct sources include the incandescent and luminescent sources described above. Indirect light source examples include light scatterers, like the sky and its atmospheric gases; light refractors, like atmospheric ice crystals and water droplets; and perhaps most commonly, light reflectors, such as the moon, satellites, planets, comets, people, mountains, lakes, and trees. Light reflectors can be further classified as diffuse reflectors, such as trees, mountains, and people, where the reflected light is sent in random directions, and specular reflectors, such as mirrors, where the incident light rays are simply redirected by reflection.
The light that enters our camera can be characterized by three main qualities: hue, saturation, and luminance/lightness/brightness/value/intensity. These, in turn, depend on the specific characteristics of the direct or indirect light sources within the camera’s field of view.
Hue is what we think of as the color of light–turquoise water or a red headlamp. Hue has an infinite range of possibilities, depending on the hues of the constituent sources. For example, outdoor subjects in full sunlight have two different hues of light illuminating them: the direct white light from the sun and the primarily blue, scattered light from the sky.
This combination is generally unflattering, which is why the best outdoor portraits are made under neutral, cloudy skies. The brightness of a direct or indirect light source is characterized by its luminance, also termed lightness, value, or intensity.
Luminance has nothing to do with color; two red and green objects can have exactly the same luminance. The luminance, Sx, is measured in units of lux, which simply indicates the amount of light available per unit area. All the direct and indirect sources of light within a scene contribute to its total, overall brightness.
The extraordinary sensitivity of the human vision system allows it to detect and interpret images with luminance levels ranging from less than 0.001 lux to well over 50,000 lux. However, this enormous range makes luminance a completely impractical parameter for photography. The currency equivalent would be to conduct all your purchases, from sticks of gum to groceries to cars to real estate, solely with individual pennies!
Instead, photographers have devised a way to convert the luminance into a much more useful parameter called the light value (LV), which only ranges from −12 to +12 or so. A LV of −12 corresponds to near total darkness; a LV of +12 to blazingly intense light.
The LV is obtained from luminance simply by taking its logarithm: LV = log2 ( ) = 1.44 Ln ( )
where C is a calibration coefficient for the light-meter used to measure the scene luminance, safely assumed to be approximately equal to the number one. Following the example of currency, the LV would the equivalent of higher denomination coins and paper currency. The practical interpretation of the equation is straightforward—when the ambient brightness, or Sx, doubles, LV increases by one; when Sx quadruples, LV increases by two, and so on.
The fact that the quantity of light doubles or halves between individual LV levels has led to the designation of a one-LV difference in luminance as being one exposure stop, or one f-stop. In other words, when the LV changes by one exposure stop, the amount of light either increases or decreases by a factor of two. Since each scene contains of a unique set of direct and indirect light sources, each with their own characteristic luminance, each scene will have a unique LV.
For example, typical nightscapes will include both direct light sources, such as stars, and streetlights, and indirect light sources, such as the moon, planets, mountains, and other foreground objects that reflect light originating from the direct sources. A key advantage of using light values as a measure of brightness in determining exposure settings in photography is that scenes with comparable overall lighting will have roughly equivalent LV levels, regardless of minor differences in light levels within the scenes.
For example, perhaps we have a scene with relatively abundant ambient light, such as is the case during late evening before the sun has set. It is a safe and practical starting point to assume that this scene would likely have a LV of approximately six to eight, regardless of the details of what’s in the scene, or where in the world it’s located.
Or maybe we are attempting an image an hour after sunset during a waxing gibbous moon, where the foreground is dimly illuminated. In this case, our LV would be lower since there is less light, likely around −4 or so. Or possibly we are seeking an image of the relatively faint Milky Way during the middle of the night of the new moon, deep in the wilderness, far away from any city lights. Here, our light value would be even lower, likely around −6 to −5 or so.
This ability to characterize most landscape astrophotography scenes in terms of their approximate light value is extremely helpful to the next step of knowledgably setting your camera exposure settings in preparation for creating your nightscape image. The final parameter of interest used to characterize light is its saturation, which simply refers to the vividness of its hue. If two different subjects have the same hue and luminance, but different saturation levels, the one with the lower saturation appears more wan, or “washed-out,” than the other.
Human Eye.
The human eye has several characteristics worth appreciating from a photographic perspective, especially for night photography. Let’s start with its anatomy. In many ways, the human eye is roughly analogous to a camera with many of the same features. It has a lens, an aperture stop (the iris), and a sensor (the retina). Missing is the shutter; our eyelids are simply part of a protective and cleansing system. Instead, our vision acquisition system functions in much the same way as a video camera, which also lacks a mechanical shutter.
Images are extracted from our retinas approximately twenty times per second and sequenced together by our brains to create the perception of motion. This ability provides the basis for motion pictures and video.
By sequencing a series of still images at a faster rate than the retinal extraction rate of our brain, we are able to perceive the sequence of images as showing motion. If the sequence is animated at a rate slower than our brain’s retinal extraction rate, then we are able to discern the individual images, and we recognize the animation as a sequence of still images rather than fluid motion.
The lens of our eye is truly a miracle of nature. It contains both living cells and inert, structural protein molecules arranged in such a way as to be optically transparent and mechanically flexible.
There are relatively few blood capillaries within the lens, owing to the need for optical transparency, which makes its regeneration relatively slow when damaged. The curvature of the lens is what allows it to form an image on the retina. Since the lens always sits at the same distance away from the retina, its curvature must change to allow it to focus on objects that are at different distances away. This is accomplished through a series of small muscle groups connected between the lens and other regions of the eye.
When the muscles contract, the lens stretches and becomes more flat. When the muscles loosen, the lens relaxes and becomes more convex. This process constantly occurs as we focus on objects around us—even as you read these words! The iris of our eyes is the direct equivalent of the diaphragm in our camera.
Both are mechanical systems that open or close depending on the desired quantity of light. The hole in the center of the iris is called the pupil; the hole in the center of the camera’s diaphragm is called the aperture. The next time you look in the mirror, take a careful look at your pupil. Did you know that it is actually a transparent opening into your eye? Although obvious in retrospect, it is still amazing to think that with the right equipment you could actually look into your eyes in the mirror and see your retina!
The pigments in the cells that make up the iris are responsible for giving the iris its color. The pupil can range in size diameter from approximately 1.5 mm in bright conditions to 8 mm in dim conditions. It has a range of effective aperture from f/2 to f/11, with a focal length of approximately 35 mm. A 35 mm camera lens on a full-frame camera is often considered to produce images having equivalent dimensions as human vision.
The eye’s retina is the layer of photoreceptor cells coating its inner, rear surface that converts light into biochemical signals that can be interpreted by our brain. The retina contains two different types of cells: rods and cones. Both contain photopigments, proteins that change form when they absorb light.
There are three types of cones, each with peak sensitivity to blue, green, and red light, respectively. Consequently, cones are responsible for color vision, although they are not as sensitive as rods to low luminance scenes. Although rods are much more sensitive to low light levels, they only yield vision in black and white, and have a peak sensitivity to blue light. How different our vision would be if our retina only contained one of these four types of cells!
Both sets of cells are concentrated in the retina in an area near the center of the optical axis of the lens, known as the macula. Within the macula is the fovea—the region of the retina with the very highest concentration of cones. There is a critical difference in how the rods and cones are distributed within the macula that produces important differences between our vision during the day and at night. The very highest concentration of cones is found at the center of the fovea, which helps us see with the greatest clarity of color during the day.
The very highest concentration of rods, however, are found in a donut-shaped ring surrounding the fovea, but approximately 20° away from its center. This fact has extremely important implications for our vision at night. When we look directly at an object at night, we are relying primarily on the cones within the fovea to create our vision. If, however, we look slightly to one side of an object at night, or about the width of your thumb at arm’s length, then the object’s image falls onto this donut-shaped area with its extremely high concentration of rods, instead. This process is known as averted vision.
Since the rods are so much better at resolving images at night than the cones, we are able to achieve much higher image resolution at night using averted vision. Practice this a few times and you will soon appreciate the difference!
Finally, the process of dark adaptation by your eyes is a crucial part of night photography. Dark adaptation is the name given to the physiological process by which the rods in your retina increase their level of photopigments until they are nearly a million times more sensitive to light than in full daylight.
Dark adaptation takes around twenty minutes to become completely functional, and increases with time after that. However, it only takes a few seconds of exposure to bright lights to reverse your eye’s dark adaptation. Also, since rods are relatively insensitive to red light, the use of red headlamps, or red cellophane taped over normal flashlights, allows the cones to function enough to assist with vision and yet maintain the dark adaptation of the rods.
READ PART TWO HERE.
