How to photograph meteor showers

Plan your shoot close to the shower’s peak activity for the best chance of truly stunning pictures.

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Image Credit: 
Pete Lawrence

Two faint Perseid meteors streak across the sky above Selsey


July and August are arguably the best time to see meteors. The reason for this is undoubtedly the presence of the Perseid meteor shower, which peaks just before mid- August. However, this is not the only active meteor shower at this time of year. Others include the Southern and Northern Delta Aquarids, the Southern and Northern Iota Aquarids, the Alpha Capricornids and the Kappa Cygnids. Although less active than the Perseids, it’s the overlap of each shower’s activity that not only helps to raise the number of visible meteors but gives you the best possible chance to take some truly stunning photographs.

Understanding why meteors happen also helps you to make your pictures that little bit more special. They occur when a small particle called a meteoroid, which is typically the size of a grain of sand, gets pulled towards Earth. Its first encounter is with our atmosphere. Friction causes the meteoroid to heat up and, when its boiling point is reached, it begins to vaporise. Molecules from the vaporised particle interact with the atmospheric molecules and temporarily raise them to an excited state. They don’t stay like this for long, though, and when they return to normal they give off energy in the form of light. From the ground we see the light given off from these interactions in the form of a meteor trail. The ‘burn-up’ process, called ablation, typically occurs at a height of around 96km (60 miles).

The trail leaves behind it a tube of ionised molecules which can persist for many minutes. If you look carefully at the sky following a bright meteor, it’s sometimes possible to make out this tube while it glows subtly against the background of night. This is known as a meteor train: particularly bright examples can last for several seconds.

A burst of activity

Meteoroids originally come from comets. When a periodic comet’s orbit takes it close to the Sun, it bursts into activity and particles are ejected from the comet’s nucleus to form its head and tail. This material eventually gets spread around the comet’s original orbit. When the Earth passes through this meteoroid stream, we see a meteor shower in which all the meteors appear to come from the same region of sky, known as the shower radiant. Different densities of meteoroids in the stream result in different rates of meteors seen on Earth.

Random meteoroids encountering the Earth’s atmosphere produce what are known as sporadic meteors; these can appear at any time without warning. Shower meteors, however, are different as their activity can be predicted. This allows you to tip the odds that you might actually see or take a photograph of one in your favour.

To optimise your photographic chances, it’s best to plan a shoot close to a shower’s peak activity. A perspective effect means that meteors closer to the radiant appear shorter than those that start further away. Pointing your camera approximately 20° to 45° from the radiant will allow you to catch meteors of a decent length and, depending on your camera’s field of view, hopefully ones that will stay in frame. To do this, align the long axis of the camera’s frame so that it points to the radiant.

Another factor to consider is the fact that the Earth in rotates the same direction as it orbits the Sun: anticlockwise. This means that in the UK, between midday and midnight, meteors play catch-up with Earth. Between midnight and midday they hit the Earth head-on. Consequently, they are brighter and appear more frequently.

Any camera with a bulb setting marked B can be used to catch a meteor, but you will need a lockable shutter release cable, or remote, to allow you to keep the camera’s shutter open for minutes at a time. Aim to use a ‘normal’ focal length lens, eg 35 to 70mm; if you own a digital camera, divide these figures by your camera’s multiplication factor to find the focal length of a suitable lens. Then prepare to open your lens to its widest stop value.

Using rolls of film

Film users should use a fast film (egISO 400 or above) but remember that the higher the ISO rating, the grainier the results. Sky conditions dictate the best exposure length, but between 10 to 20 minutes is ideal for film. It’s a good idea to take an initial shot of something bright – perhaps a sheet of paper with the date and time on it – to help film processing machines find the first frame.

As you must hold the camera shutter open, a DSLR camera is really best for the job. Set it to its highest useable setting (eg Canon 350D; ISO1600) and keep the exposures to around one or two minutes each. The aim is not to take a beautifully exposed star background, it’s to capture a meteor. If your camera is equatorially mounted and driven, then take a couple of properly exposed shots (use a less noisy ISO setting, eg ISO 400) of the star background alone for later composition with your meteor shots. For the main shots, multiple exposures of one or two minutes will generate a lot of images. A couple of large memory cards which can be swapped between camera and computer will allow you to maintain a continuous shooting regime.

Meteor photography can be frustrating, but with such impressive rewards, it is definitely worth the effort. So, one evening this month, why not relax, lie back, and see if you can catch yourself
a spectacular meteor.

Step 1

Make plans: take the trouble to find out what showers are active and make sure the Moon is out of the way. A high radiant will produce more meteors than a low one, so take this into consideration as well. In the UK, more meteors tend to occur after midnight (UT) as the meteoroids are hitting the atmosphere head-on after this time. This year, the Perseids shower peaks on the evening of 12 August, giving a chance to capture some memorable images.

Step 2

Pick an observing spot where you will be comfortable and where your camera can get a clear, unobstructed view of the sky. Then mount and point your camera. A distance of 20° to 45° from the radiant and around 50° to 60° altitude is good. Align the long axis of your field of view so that it points to the radiant. Do take the trouble to wrap up sensibly – even though it’s summer, the nights can still get cold here in the UK, so don’t just wear shorts and a T-shirt.

Step 3

To ensure the best results, use a lens in the range of 35mm to 70mm. A wide-angle lens can see more of the sky in one go, but a longer focal length lens will typically have a larger maximum aperture, allowing you to capture more light. Remember – you’re after a balance between sky coverage and light collection. With the camera mounted, focus on the brightest object you can see in the sky. Accurate focus is important, so do take your time to get it right.

Step 4

Use the lens’s lowest f/ stop to open the aperture right up. Film (eg Ilford HP5, Fujifilm Superia, Konica Centuria) should be ISO400 or above. Digital cameras should be set to the highest ISO setting that produces tolerable noise. Use a lockable shutter release and the bulb (B) mode. Expose for 10 to 20 minutes for film and one to two minutes for digital. Stick to one area: don’t move the camera around chasing meteors that have already happened.

Step 5

It is important to make a note of the time and frame number for bright meteors that you may have recorded. In addition, always keep an eye out for dew forming on the camera lens. If this does happen, directing warm air from a 12V hairdryer is an excellent way to remove it. Another precaution you should take is to have some spare camera batteries on hand in case they are needed. It’s an elementary thing to do,  but sometimes it’s overlooked.

Step 6

If you see any really bright meteors that may have crossed the camera’s field of view when the shutter was open, remember to make a note of the time and the frame number. Also, consider ending the exposure early just in case something happens to ruin it. Don’t forget to look out for a faint meteor train following a bright meteor. If there is one, end the exposure with the trail on it and reopen it to try and capture the train.


This article first appeared in the August 2006 issue of Sky at Night Magazine

 

 

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