How to take jaw-dropping photographs of star trails
Can you find Polaris? It's the brightest star in the night sky, right?
Actually, it's not – it's the 48th brightest, but learn to find the North Star directly above the north pole and you can produce stunning star-trail photos that show how the Earth spins on its axis.
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Those swirls may look like the result of a highly technical procedure, but all you need to learn is how to take one long exposure photo on a clear, a starry night. Repeat that 50, 100 or 200 times, download some free software, and star-trail nirvana is yours.
Get ready, Instagram.
Finding Polaris
Even if you don't know the night sky well at all, finding Polaris is easy. You can use planetarium apps like Star Walk, The Night Sky or Google's Sky Map to help you find it, but double-check using this age-old technique.
First, find the two stars on the outside of the bowl of The Plough/Big Dipper; Merak at the bottom and Dubhe at the top. Draw an imaginary line from Merak to Dubhe, and carry on for about five times the distance between those two stars until you come to a reasonably bright star that's pretty much on its own. Bullseye.
Now search for a subject because star-trails alone will not produce an eye-catching photograph. The Rule of Thirds still applies to the night sky; put something in the foreground, ideally at least 10m away.
Star-trail travel
There are good reasons to travel to take star-trails images.
"It's about having Polaris low enough in the sky so you can frame a star-trail around something, such as a building or a tree," said Simon Waldram, star-trail tutor for Stars By Night in Fuerteventura in the Canary Islands, Spain. Fuerteventura has a latitude of 28° north, which puts Polaris 28° above the northern horizon, which is ideal for taking star-trails. In London at 51° north, or New York City at 41° north, Polaris is that much higher in the sky so you have to get in closer, almost underneath your subject to get it in.
Exactly the same applies in the south pole, though the southern hemisphere lacks a South Star.
What you need & when you need it
Producing a star-trail demands a clear night and a camera with manual controls, which means a DSLR, or at least a capable compact. What lens you use will make a difference to the composition; an expensive full-frame camera will always squeeze more in than the cheaper crop sensor cameras, but it's more important just to use the widest angle lens you can get your hands on. You'll also need a tripod and a good dollop of patience; a star-trail takes about at least an hour, but the longer the better (pack a fresh battery).
A super-dark sky location around New Moon, and about two hours after sunset, will maximise the density of stars, though during a Full Moon or in light-polluted cities like London, New York City and Sydney it's still possible to shoot a star-trail.
Setting up the camera
Using a wide angle lens on the lowest aperture possible (f/2 to f/3), set it to Infinity focus (the ∞ symbol on some cameras).
"You can do this by auto-focusing on something 20m away a few hours earlier in daylight, or by using a powerful flashlight in darkness, but remember to then switch to manual focus to fix it in position," said Waldram.
In manual mode on the camera, choose IS0 800, set the white balance to 2200K/Tungsten, and shoot a 30-second exposure in RAW format. Zoom-in on the LCD screen to check that it's sharp, and adjust the ISO until you're happy with the shot. Now take a minimum of 50 shots, putting a two-second delay on the shutter release (or using a remote shutter), and being careful not to kick the tripod.
"If you’re using a crop sensor DSLR, leave at least 15 seconds between each shot to let the sensor cool down, and for a full frame, about 10 seconds," said Waldram.
However, wait much longer and you'll get gaps in your star-trails. If it all sounds a little monotonous, get an intervalometer (or a camera with one built-in), which automates the entire process. Then you could sleep — or go for a beer — and come back later.
Stacking a star-trail
Speak to an old-school photographer and they will tell you to set the camera's aperture to around f/6, and to open the shutter for an hour. Don't listen to them; the results are noisy and horrid, especially on a crop-sensor DSLR.
"In the old days with analogue cameras that was the best way, but for digital cameras, the sensors heat-up too much and produce noise," said Waldram, who advocates taking multiple exposures and stacking them together. Each photo you've taken will be identical save for a slight movement in the apparent position of stars … and perhaps a plane flying over.
After using Photoshop or similar to batch-process your shots (handy for reducing noise and for making the stars stand out), download the free StarStaX software for Mac, Windows or Linux. Drag in your RAW files. Check 'gap-filling' then watch it gradually layer your photos to create a stunning star-trail.
All that's left to do is to give your photo the obligatory mock-meaningful title — "Circle Of Life" or "Time Traveller" should do it — before uploading it to a stunned internet.
Jamie Carter is the author of A Stargazing Program for Beginners: A Pocket Field Guide, published by Springer, and regularly uploads star-trails to Instagram and Twitter.
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