Astronomy Essentials

What are star trails, and how can I capture them?

Light blue sky with short, concentric white lines and a white streak, with body of water below.
View at EarthSky Community Photos. | David Cox in Deep River Ontario, Canada, captured this photo of star trails and a Draconid meteor on October 8, 2021. He wrote: “Polaris time lapse captured a single, impressive Draconid meteor streak over the Ottawa River at Deep River Ontario, Canada, early in the evening of October 8, 2021.” Thank you, David!

What are star trails?

With a steady mount, long exposures and a few other tricks, photographers can take images of star trails, showing the motion of the stars over the sky during a period of minutes or hours. Often, the camera stays pointed at Polaris, the North Pole Star, or at the south celestial pole (not marked by a single star) in the Southern Hemisphere. Then, with an open shutter, the camera records an image as Earth turns on its axis and the stars move overhead. There are also many variations on star trail photos, as you’ll see here!

Star trails reflect Earth’s rotation, or spin, around its axis. The Earth makes a complete rotation relative to the backdrop stars in a period of about 23 hours and 56 minutes. So, as seen from Earth, all the stars go full circle and return to the same place in the sky after this period of time, which astronomers call a sidereal day – a revolution with respect to the stars.

Short streaks of light in concentric circles against a black background.
View larger at EarthSky Community Photos. | Cameron Frankish captured this image in Dartmoor, Devon, UK, on October 21, 2019. He wrote: “Polaris star trail with an Orionid meteor (possibly) in the bottom left.” Thanks, Cameron!
Concentric circles of light over a mountainous landscape.
Star trails over the planned site of the Giant Magellan Telescope in the Atacama Desert in Chile. Image via Yuri Beletsky Nightscapes.
Faint, short concentric streaks of light with one thin straight streak. Big cross in foreground.
View larger. | Star trails (plus meteor) photo taken by Guy Livesay. Thank you, Guy! If you aim your camera northward in a long-exposure photo, the star trails will be seen to track around the north celestial pole. In fact, the stars move counter-clockwise around the sky’s north pole in the course of every night.
Brilliant concentric streaks over distant buildings including a lighthouse tower.
Montauk Point lighthouse. Photo via Neeti Kumthekar.

Earth’s spin makes star trails

What this means is that, if you’re standing out under the stars, you see them move across the sky as the night progresses. The stars – like the sun during the daytime – move from east to west across the sky every night.

Stars near the celestial poles produce the smallest circles while those near the celestial equator produce the largest. Each and every star moves 15 degrees westward in one hour.

Star trails are really arcs, or partial circles, whose ever-circling motions forever tabulate the passage of time.

Concentric white streaks against medium blue background with wide linear white smudges.
Sometimes you can get cool non-star effects into your shot, as Michael A. Rosinski did in this photo.
Many thin concentric circles around point above horizon, with some trees in the foreground.
Ken Christison captured these glorious star trails around Polaris, the North Star. He wrote, “For the most common and often the most spectacular star trails, you want to locate Polaris and compose the image so it is centered horizontally and hopefully you can have a bit of foreground for reference.”
What are star trails? Dashes of light in a circle with black metal object in foreground.
View at EarthSky Community Photos. | Cameron Frankish in Longdown, Devon, UK, captured this photo of star trails on April 6, 2021. He wrote: “Originally planned to do a total of 1,000 shots but the cloud came in after 240…” Thank you, Cameron!

How to capture these time-lapse streaks

EarthSky Facebook friend Ken Christison has some wonderful photos of star trails. He said the equipment needed for making star trails is pretty simple:

First, a camera that allows manual settings so you can set your f/stop and shutter speeds, as well as ISO.

Next, a wide angle lens, the wider the better.

A good steady tripod is a must.

Some cameras will have a built in intervalometer which can be set to shoot the desirable number of frames. In some cases the intervalometer has a bit of lag between shots, which is the reason I use a separate remote attached to the camera that holds the shutter down and, when the camera is set in continuous shooting mode, will shoot 100 frames in succession with very little gap.

The remote I use is a simple one that can be found on eBay and uses a couple of AAA batteries that last quite a while. I just use the remote controller attached to the 10 pin connector. There is no need to use the wireless receiver in this case.

I use a shutter speed of 30 seconds, ISO of 400 to 800, and, with my 14-24mm lens at 14mm, shoot it wide open at f/2.8.

Next, he said, you’re ready to capture your star trail:

Make sure the camera is level, and after focusing on a star, make sure the autofocus is turned off. Then, using the settings mentioned above, click the shutter and stay around long enough to know that the shutter is actually actuating. I normally go back in the house, set the timer on our kitchen stove for 45 minutes, and do other things while the camera does its work.

When the timer sounds, go back out and reset the remote by turning it off, waiting for the shutter to close, then reset quickly.

Finally, you’ll want to process your photo. Ken said:

This is one of the most important elements in making star trail images. The program I use is free, works well and is simple to use:

One other program that I have heard works well and is also free is StarStax:

Thank you, Ken!

Visit Ken Christison’s Facebook page.

Read more: Long exposure star trail photography

Star trails and moon trails from our community

Curved white streaks against a dark brown sky with light on the horizon.
A 2-hour-and-15-minute star trail image from March 21, 2014. Our friend Ken Christison in North Carolina captured this image. Want to see what a single frame of this image looked like? See the photo below.
Dark brown sky with constellation Orion and seven stars labeled.
A single frame of the star trail image above, with the elements labeled. Thank you, Ken Christison of Conway, North Carolina!
Long white streaks with bright dots at lower end, looking like a rain of stars.
Composite image of star trails over Baja California, from EarthSky Facebook friend Sergio Garcia Rill. This image is the product of 80 separate photographs. Thank you, Sergio!
Pink sky with three images of the sun in a line behind a power line pylon.
You can also create a star trail of sorts with our local star, the sun. EarthSky Facebook friend Matthew Chin in Hong Kong created this sun trail on October 5, 2013. Thank you, Matthew!
Short white streaks with one thick, very bright white streak.
View larger. | Or you can create a moon trail. Star trails and moon trail over Monument Valley from Victor Goodpasture. The bright object is the moon. See more from Victor at Professional Digital Photography on Facebook.

Bottom line: Star trails are photographs of the sky taken with long exposures. The result is an image with stars trailing across the sky in concentric streaks, often whirling around one of the celestial poles, though you can also take photos that trail the sun, moon or stars as they rise or set.

October 13, 2021
Astronomy Essentials

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