Lately, quite a few Milky Way images taken from airplanes have been popping up in social media. Nevertheless, many people are still astonished that it is possible to capture the Milky Way from a fast-moving plane without star trails. It is, therefore, time to look a bit deeper into the topic of airborne astrophotography.

Airborne astrophotography by Ralf Rohner
“Colors of Cygnus” by Ralf Rohner
Single exposure: 5s @ ISO6400 – f/2

Professional Airborne Astronomy

The concept of airborne astronomy is not new and has been applied by professional astronomers since 1957, when Stratoscope 1, a high flying helium balloon equipped with a 12-inch telescope took high-resolution images of the sun. Later, the focus shifted to infrared, UV, microwave, Gamma- and X-ray astronomy, as the dense lower atmosphere blocks these electromagnetic frequencies.

Skyhook_air_1957
At the whim of the winds, the Skyhook Baloon with Stratoscope 1 was the first unmanned balloon-borne telescope observatory. Photo courtesy US Navy.

In 1965 the first telescope was mounted on a jet aircraft. The NASA Galileo Airborne Observatory used a converted Convair 990; destroyed in 1973 in a mid-air collision. It was followed in 1974 by the NASA Kuiper Airborne Observatory (KAO) on a Lockheed C-141A Starlifter that operated until 1995.

NASA_C-141A_KAO
The NASA Kuiper Airborne Observatory (KAO)performed airborne astrophotography for over 20 years. Photo courtesy NASA.

NASA’s current observatory saw first light in 2010 and is called Stratospheric Observatory for Infrared Astronomy (SOFIA). It is an 80/20 partnership of NASA and the German Aerospace Center (DLR) and operates an extensively modified Boeing 747SP aircraft carrying a 2.7-meter (106-inch) reflecting telescope.

1920px-SOFIA_ED10-0182-01_full
The SOFIA Boeing 747SP airborne observatory examines comets, nebulae, star-forming regions, celestial magnetic fields, and the galactic center. Photo courtesy NASA.

As these professional instruments prove, it is possible to do astrophotography out of a flying jetliner, but how is this possible without producing star trails? Let us look into this.

Linear Motion is Irrelevant

Typically, jetliners cruising speeds are around 80% the speed of sound (Mach number: M 0.8). At 15°C (59°F) and sea level pressure, this is 272 m/s (980 km/h, 609 mph). As the speed of sound depends on temperature and as the temperature is much colder at the cruising level of an airliner, this figure drops to about 240 m/s (850 km/h or 530 mph) at 10,000 m (33,000 ft). To make things even more complicated, you have to add the wind into the equation. Wind speeds at this height can easily reach 300 km/h (180mph). To get the velocity over the ground, you have to add the tailwind or subtract the headwind from the true airspeed derived from the Mach number. In a strong tailwind, an airliner can reach ground speeds of about to 1150 km/h or 700 mph.

That speed is fast, but it is only about 1% of the 107,000 km/h (64,850 mph) at which earth is moving around the sun and not even this velocity is causing star trailing, because the stars are very far away. In other words: As long as you do not fly with warp speed, linear motion is irrelevant.

"Towards the core." Airborne astrophotography by Ralf Rohner
“Towards the core” by Ralf Rohner
Composite: 5s @ ISO6400 for the sky and 20s @ ISO1600 for the grond – f/1.4

What Causes Star Trails in a Long Exposure?

Star trails are caused by angular motion, i.e., the rotation of your camera or your mount. But you are using an extremely stable tripod and still get star trails after a few seconds, right? That’s because your tripod is standing on a huge rotating base called Earth, which rotates 360° in 24 hours. To take long exposures without star trailing, either you must limit your exposure time, or you have to use a tracking device that counters earth rotation.

An Airborne Tracking Mount

So all is good; you have to set up a tracker on your next long-haul flight, and you can expose virtually forever? Not quite.

An aircraft is not flying in a straight line; it follows the curvature of the Earth. If you are flying westward, the speed of the plane counters the effect of the Earth’s rotation while heading eastward makes things worse.

So how do the rotational velocity of earth and an airliner compare? With its circumference of 40,000 km (24,900 mi), the equator rotates with 1670 km/h (1038 mph). This figure decreases with increasing latitude, as the circumference decreases to 0 at the pole. Mathematically the rotational velocity is the cosine of the latitude multiplied with the Earth’s speed at the equator.

At mid-northern or southern latitudes, the Earth rotates at almost the same speed as the typical ground speed of commercial aircraft. This matching of ground spped and direction is the reason why, on a westward flight, you land at nearly the same local time as your time of departure.

So you can even leave your tracker at home, because the aircraft acts as an airborne tracking mount on westbound flights, while you better get some sleep on eastbound routes? In theory, yes, but unfortunately, reality makes things a bit more complicated again.

Airborne astrophotography by Ralf Rohner
“A Job with a View” by Ralf Rohner
Single exposure: 5s @ ISO6400 – f/1.4

What Limits Airborne Astrophotography?

Most people are well aware that camera shake destroys any astrophotography. Unfortunately, even a 300,000kg flying camera mount is not completely stable. In addition to hand-holding your camera, there are two leading causes of camera shake with airborne astrophotography.

Turbulence

Turbulent air causes short term non-linear motion of the aircraft. Even if you managed to fix the camera to the aircraft structure, this makes the stars jump around in your image, causing erratic trails or blurred stars.

Clear air turbulence destroying a 5-second exposure out of a side window.   Photo by Ralf Rohner.
Clear air turbulence destroying a 5-second exposure out of a side window. Photo by Ralf Rohner.
A 100% Zoom of the image above showing erratic star trails caused by turbulence.

Dutch Roll

Dutch roll is a type of aircraft motion, consisting of an out-of-phase combination of “tail-wagging” (yaw) and rocking from side to side (roll). Swept wings of commercial transport aircraft tend to increase the Dutch roll tendencies. This yaw-roll coupling usually is well damped by the installation of a yaw damper, but it nevertheless causes a slight motion of the stars in a long exposure. Dutch roll is most pronounced when shooting out of a side window and, depending on its strength, it can cause stars to appear as doughnuts instead of points.

Although taken in perfectly still conditions this image appears slightly blurry. Arborne Astrophotography Photo by Ralf Rohner.
Although taken in perfectly still conditions this image appears slightly blurry. Photo by Ralf Rohner.
A 100% crop reveals doughnut-shaped stars, caused by aerodynamic
oscillations (dutch roll).

Exposure time, therefore, usually is not limited by conventional star trailing, but by the rocking and rolling motion of the aircraft. Even though you may be sitting in a flying tracking mount, you have to keep your exposure time as short as possible.

Too Much Glass

For airborne astrophotography, I recommend having as little glass in the light path as possible. In other words: get rid of all your filters! For airborne astrophotography, however, you will hardly have the privilege to have an open hatch available, like in those professional flying observatories. Depending on where you sit, you will be shooting through thick glass or even some plastic. These layers not only can introduce distortions, but the windows are also very prone to reflections, mainly because you will always have some light in the cabin. There are two ways to try to avoid this:

– You can make a total fool out of yourself and hide under a blanket. This trick works surprisingly well, but your fellow passengers might consider your behavior extremely suspicious. I therefore strongly suggest informing your neighbors and the cabin crew about what you are planning to do. Furthermore, you better dress lightly, as it can get rather stuffy in the long run.

The Lenskirt XL will help block cabin lights from your airborne astrophotos. Image courtesy of Lenskirt.com.

– You can use a lens skirt such as the Lenskirt XL. It is a flexible hood which you attach to the end of your camera lens and on the other side to the window with suction cups. It lets you breathe better and does not nearly look as silly as the blanket.

Strobes and Beacons

Most astrophotographers do not especially like the aircraft trails produced by the strobes, beacons, and navigation lights. They can be an even more significant nuisance when shooting out of the aircraft.

Unfortunately, you cannot merely ask the pilots to shut down all these lights, as they are essential for flight safety. You have to live with them. The red and green navigation lights on the wingtips usually are not a problem, and the strobe lights can even have a pleasing effect. The biggest challenge is the red beacon light which tends to cast an ugly red hue. Fortunately, you can correct this during post-processing, or you can also try to use the light for something creative.

Airborne astrophotography by Ralf Rohner
Beacon light and fuselage shadow while skimming the cloud tops.
Single Exposure: 10s @ ISO6400 – f/2

Stabilizing the Camera

You are undoubtedly aware that it is not best practice to handhold your camera for long exposures, but if you have no other option, you might as well give it a try. In this case, try to press your lens to the window and operate your shutter with a self-timer or a cable release.

A better solution is to use a tripod to position your camera correctly, but depending on how tightly packed the seats are, you might have a hard time to set it up.

Suction cup mounts like the Delkin Devices Fat Gecko Triple can help stabilize your camera for airborne astrophotography.

There is a massive selection of different suction mount models with one, two, or three legs. My preferred way is to use a Delkin Devices Fat Gecko Triple Mount. This 3-cup model is the most stable. You can also remove one cup to convert it to the 2-cup model if needed.

Of course, I have the privilege to have big windows in the flight deck, but with the larger cabin windows of the new generation of airliners, you might be able to install one of these in the passenger cabin as well.

Dreamliner Dreams

One word of caution: Boeing’s new 787 Dreamliner not only ditches classic small windows with pull-down plastic shades and replaces them with large, dimming windows that can be adjusted to let in various amounts of light. These windows can be individually controlled by the passengers, but the flight attendants can also change entire sections of the plane. I know that certain airlines are remotely dimming all windows during night flights to avoid stray light entering the cabin. You may, therefore, have to convince your cabin crew to give you control over your window.

Airborne astrophotography by Ralf Rohner
A really smooth ride makes it possible to stack several exposures for noise reduction.
Stack of 3 x 5s @ ISO6400 – f/1.4

Airborne Astrophotography Recommended Technique

As mentioned above, for airborne astrophotography, you will have to keep your exposure time as short as possible. A fast lens will help you to gather as much light as possible in the short time available, but you will also have to increase your ISO as high as practical. I use a Canon EOS 6D with 24mm f/1.4 prime lens and expose for 5sec @ ISO6400. Depending on your lens and camera, you will have to adapt to these settings, but try to keep exposure times short.

Nevertheless, most of your images will inevitably be blurred. In reasonably smooth conditions, I usually get only about 2 – 5% sharp exposures. That means that you’ll have to acquire a long sequence to ensure that you get a few keepers.

High ISO Comes With A Price

High ISO shooting comes at the price of increased noise. As in terrestrial astrophotography, stacking several exposures helps to lower these noise levels. Unfortunately, it is much harder to get a sequence of clean exposures for stacking from an airplane, but as you will capture a long series anyway, check if you have several good shots that can be stacked. For this, you only need the exposures to be sharp, as you can align the stars with specialized software like Sequator (PC) or Starry Landscape Stacker (MAC).

Airborne astrophotography by Ralf Rohner
The lights on the ground show the fast linear motion that leaves the stars unimpressed.
Stack of 10 x 10s @ ISO6400 – f/2

If the conditions are too turbulent for stills, consider capturing an extended sequence, and make a time-lapse movie. The high frame rate and the lower resolution of a video will hide much of the blur in each individual frame, and fast-moving lights and clouds guarantee a stunning sight.

“Night Flight”, a time-lapse video by Ralf Rohner.

Just the Milky Way?

As in terrestrial nightscapes, the Milky Way is the most prominent target, but there are other exciting things out there. Northern lights, thunderstorms, or constellations can keep you shooting on every night flight without the need for onboard entertainment.

Airborne astrophotography by Ralf Rohner
Northern lights over the Hudson Bay.
Handheld stack of 6 x 0.8s @ ISO6400 – f/1.4
Airborne astrophotography by Ralf Rohner
Thunderstorms over Brazil.
Single exposure: 10s @ ISO6400 – f/2
Airborne astrophotography by Ralf Rohner
Orion, Taurus, the Pleiades and the California Nebula over Poland.
Single exposure: 10s @ ISO6400 – f/1.4
Airborne astrophotography by Ralf Rohner
The Big and Little Dipper over Poland.
Stack of 5 x 5s @ ISO6400 – f/1.4

Give Airborne Astrophotography a Try

Take your camera and have fun on your flights! I wish you a smooth ride.

You can see more of Ralf’s awesome airborne astrophotography by visiting his gallery here at MilkyWayPhotographers.com.

4 COMMENTS

  1. Capitan Rohner,
    I salute you for opening a new and fascinating field of photographing Milky Way from airplanes.
    I am entirely new to this are of photography, but so is everybody else.
    How much indulgence do you have to answer a few questions?
    My wife and I will be night flying from Munich to Cape Town on October 24. Sony A7R and Sony A7Rriii together with Voightlander 40mm F1.2 and Contax Zeiss C/Y 21mm F2.8 will be by my side to be used at any time.
    Do you think there may be a chance to shoot Milky Way and if so what camera/lens would you suggest using? Single or multiple shots?
    So far I photographed the Swiss Alps out of Martigny where I live.
    Best wishes for now.
    Henryk
    https://500px.com/henrykkierzkowski

    • The Voightlander is very fast, which is excellent, but it is not very wide. Turbulence and oscillations will show more at longer focal lenghts. The Zeiss is wider, but also slower, so there is no clear favorite. Both bodies are good as well. The newer A7riii has probably better high ISO performance (I am guessing, as I am not a Sony shooter), but the higher resolution will show any oscillation more clearly. I’d probably first give it a try with the A7riii, as you can always lower your resolution in post.

      The question, whether you will be able to see the Milky Way, is a bit more tricky. By end of October the core will not be visible anymore from the lattitude of Munich, but further south it is still visible. At the Equator, it will set in the SW around 9 p.m. and at a lattitude of 25°S at about 11 p.m.

      It therefore depends on when your filght departs. If take-off is in the afternoon (like 3 p.m.), you have a good chance if you your seat is on the right side. If your flight leaves in the evening, it will be too late for the Milky Way.

      In this case you can try to shoot Orion, which will rise in the east around 10:30 p.m. For this, a seat on the left side would be necessary.

      I hope that helps.

  2. Thank you very much. I could not have hoped for a more useful answer. Our flight will depart in the evening, so Orion will is the only hope.
    On this flight, I will make my first attempt at photographing the Milky Way, or Orion for that matter, and therefore I want to stick to the lenses I already have. They will probably turn out more useful in South Africa and Namibia where the conditions will be less hectic.
    Thank you again for your suggestions.

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