Two faint Perseid meteors streak across the sky above Selsey. Image Credit: Pete Lawrence
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.