Although you can observe sporadic meteors at anytime, there are certain times of the year when the Earth passes through the orbital debris trail of comets and asteroids, this leads to an increase in meteor activity. If you have ever been to a group meteor observing session, you will know that very often you will hear a cry of “Wow that was a good one, really bright did you see it”. Of course you didn’t because at the time you were looking the other way and the human eye can only cover so much sky ( your field of view ). It’s the same when trying to photograph meteors – unless you have enough cameras to cover the entire sky ( which has its own problems ) you will miss lots of meteors. The answer to missed meteors is the All Sky Camera. By using the now highly sensitive CMOS cameras, ZWO asi120mm for example and a fast wide angle lens such as the Fujinon 1.4mm f/1.8 fisheye lens with CS mount, DF1.4hb-L1, the entire 360° sky can be covered with a single camera. It’s not the same as seeing one with your own eyes – but at least you can watch the video afterwards and see what you missed. Ideally the camera and lens will be mounted in an enclosure to protect it from the elements and moisture, also the enclosure should have some form of mild heating to keep dew from forming on the dome window. A ready made all sky camera can be purchased, ranging in price from £700 to £3000.
Alternatively, it’s far cheaper and easier than you think to make one yourself – if you have some basic tinkering skills. Mine cost less than £200 to build and has lasted me a few years now. It consists of an asi120mm mono cmos camera and wide angle 1.4mm f/1.8 Fujinon lens, a 12v heater blower salvaged from an old cctv camera housing, ( the housing mounting bracket was also used ), a 100mm acrylic dome, a plastic sandwich container, ( the type with side clips and a blue silicone rubber seal ), an angle bracket and a camera 1/4 inch 20 UNC threaded screw, some speaker wire for the heater blower and 12v power supply and a 5m USB extension lead. The camera and fisheye lens are removed when finished with and a Christmas pudding tub protects the dome when not in use.
You will need to paint the sandwich container with grey plastic primer and white paint to protect it from the sun’s UV rays, the plastic will go brittle in a few months otherwise. A laptop computer, camera driver and capture software complete the setup. The software I use is HandyAVI Delux, from AZcendant and costs $59 ( about £45 ). It has a host of options ranging from timelapse to motion detection and of course meteor capture. The software works by comparing consecutive images or frames, any change between the frames such as a meteor or plane triggers a recording event, the number of frames before and after the event that are captured can be selected and the sensitivity can be calibrated to the camera noise, so that only motion triggers a capture event and not random camera noise. In the advanced tab, there is an option to mask off areas of the image, basically the software will ignore those areas – so for instance if a neighbour turns a light on, it will not trigger an event. It records video in AVI format and still frames in Jpeg. You will capture more than just meteors – planes, satellites and birds in flight if lit up from below by street lights and the odd spider crawling across the dome.
The all sky camera also comes in useful as a cloud monitor when deep sky imaging, as you can see if a cloud is going to cover the object you’re interested in.
When the meteor images are captured they can be used to make a composite image showing the activity for the night.
There are several showers each year, some more active than others and each has its own distinctive type of meteor; fast and bright like the Perseids or slow and persistent with many fireballs such as the Leonids. Meteor showers get their name from the constellation they appear to radiate from, i.e. if you back track the meteor trails they would seem to come from one part of the sky, and seem like spokes of a bicycle wheel coming from the radiant point. Each shower has a ZHR or Zenith Hourly Rate, this is the average number seen per hour, although sometimes there are outbursts when the earth passes through a denser part of the debris trail and many hundreds an hour can be seen.