Summer Photo Op: The Perseid Meteor Shower

As you’re probably aware from the level of hype in your news feed, the Perseid meteor shower is approaching and you should get outside to see it now! Technically in late July, it is already active in our skies, but the reality is that there is a fairly narrow window of high activity only around the peak time. My own experience is that the number of meteors drops off dramatically a day before or after the peak evening. 

Of course, the absolute peak is not exactly predictable or may not be at night for many of us, but planning for the evening of the expected peak is the best we can do. This year, the best evening to be out there is August 11-12. And it is actually a favorable year for this shower because the Moon will set several hours before the show starts.

Why is the meteor shower predictable? The answer is that each year, the Earth is running into the dusty orbital path of a comet (Comet 109P/Swift–Tuttle), which returns to pass by the sun every 133 years. Each time it passes by the sun, a few more gas and sand grains are boiled off, leaving a trail of particles that the Earth runs into around mid-August.

For any given place on Earth, the activity on a night starts around when the radiant (apparent origin point) of the shower rises above your horizon, as shown in the Stellarium chart above. Your apparent horizon may be different from your actual horizon (a hill may block it), but start your watching and camera when the radiant starts to rise above the actual horizon. You need not be looking directly at the radiant point, but the Earth is rotating into that direction, so meteors may be visible in any direction, all seeming to come out of the radiant point. Think about driving through a gentle snowfall — streaks of snow appear all around you and may be more apparent slightly off to the sides than straight on.

If you’ve never seen a meteor shower, media reports may lead you to believe that you’ll see a spectacular storm of bright meteors flashing by. But the reality is that a meteor “shower” is much less of an event than a rain shower or even the barest drizzle of rain. Typically, the Perseid meteor shower yields around one meteor per minute somewhere in the entire sky, and these may come in bursts of two or three at a time with long periods of inactivity. But with an all-night shooting session, you can assemble an interesting record of the event (composite image or time-lapse video, for example), and there is always the possibility of a lucky bright bolide (an exploding meteor).

If you have some clouds during the night, unless they are blanketing you in a solid overcast, don’t give up on the night. Bright meteors may still be visible and will be more impressive as they light up the clouds, and a few clouds blowing through will enhance a time-lapse movie.

Photo Setup

A good photo setup is fairly simple:

• Photo tripod
• DSLR or mirrorless camera
• Wide, fast lens (e.g. 15mm f/2.8)
• Intervalometer (if necessary)

The lens should be fast (f/2.8 or better) and have decent image quality at the edges when wide open. The camera should preferably have a full frame image sensor so as to take full advantage of the field of view of the lens.

I recommend setting the camera up at a high enough ISO (typically ISO 1,600) to expose for 20 to 30 seconds (depending on the sky brightness) and to shoot raw + jpeg images all night. This allows you to use the full field of view of the camera and post-process the images to find the dim meteors, yet allows a quick look at the jpeg images to find the brightest meteors rapidly.

Don’t use a camera’s “time-lapse” movie feature. Although this seems convenient if you plan to create a time-lapse movie, this will crop the recording to a standard video format such as 16:9 and reduce the resolution of each frame. In addition, the frames will be compressed and limit your post-processing options. Instead, use the camera’s interval shooting mode if it is available internally or use an external intervalometer to shoot still frames continuously, but allow a few seconds of gap between frames to allow the image to be saved to the memory card.

Shooting All Night

Plan to shoot all night. Unlike just shooting during golden hour or a Milky Way composition, you need to shoot all night if you’re going to have much chance to capture a meteor. Fortunately, the right equipment will take care of itself for the entire duration, leaving you free to enjoy the show or go to sleep.

However, it’s essential to ensure that you have enough memory card space to run all evening. At a frame rate of two per minute or 120 frames per hour, a typical camera will generate about 3 GB per hour. So, a six-hour run requires some 18 GB of space. Higher-resolution cameras can require twice as much space. Fortunately, it’s no longer a problem to get high-capacity cards. But if you have an older camera model, first check to make sure your camera will be able to handle high-capacity cards.

Along with adequate storage space, you need to have enough battery capacity to last the night. With internal batteries, you’ll need to plan for one or two battery changes, which can be a nuisance as well as interrupt a potential time-lapse image sequence. External battery power or AC power should be considered as an alternative. Using external power has the additional advantage of minimizing the heating occurring inside the camera, an important image noise consideration for a warm summer night.

Running on a Tracker

If you have a tracker or telescope mount, you also have the option to follow the stars so that longer focal length lenses can be used without the problem of developing star trails in your shots. This gives you the flexibility of framing an interesting section of the sky during the night. A target region east of the meridian is best so that the region doesn’t set before sunrise, but this includes an interesting part of the summer Milky Way, so this is not much of a restriction. Using a longer focal length will reduce your chances of catching a meteor, but this should be kept in mind as a secondary setup if you have an extra camera available.

Above are Perseid meteors captured with a 105mm lens with meteor tracks that extend back to the radiant point. The prominent concentration of stars in the image is called the Double Cluster. This cluster is visible to the naked eye and is a good marker for locating the Perseid radiant.

Checking Your Frames

The next morning, be sure to back up all of your memory cards as you have your coffee, then check through the jpeg frames on a large monitor, noting the frames which include meteors. The brightest meteors should be visible on full-screen views, but after the first quick examination, import the raw images into a program such as Lightroom for a closer look after optimizing the lighting and contrast on the whole set of shots. Be sure to closely examine the frames following a bright meteor. Often, an ionization trail persists for a few minutes following a very bright meteor, and a sequence of these frames makes an interesting animation.

It’s essential to check the frames at 100% resolution and scroll around the frame since even the largest monitor will not show all of the pixels captured by a modern camera. At this stage, you will want to check each frame in this way. This can be a real test of your patience and persistence but is necessary if you want to make a composite of the night’s activity. You will also want to note frames that contain aircraft (look for flashing navigation lights) and satellites (colorless trails, especially if spanning more than one frame). Real meteors will show a hint of color, and if they are truly Perseid meteors, you will be able to trace them back to the radiant in Perseus.

The Luck Factor

An undeniable part of going out to shoot meteors is that luck plays a major role, so it’s important to set your expectations accordingly. Looking back over my attempts over 10 or so Perseid showers, my results come down to 10 to 20 frames with meteors (some bright, mostly dim) per outing. That’s 1-2 percent of my night's frames, but I still think it’s worth the experience. Best of luck to you!