A talk by Nick James Director of the comet section of BAA.
Report of the meeting written up by Rob Maclagan from notes taken by Michael Reakes.
Nick gave an interesting talk to the Society at a recent Priory Street event. He showed how, originally, meteors were recorded visually, then by film photography, and now using digital cameras, including standard CCTV. Modern cameras mean that video footage can be shot in real time at high quality. Although these are currently expensive, CCTV and other cameras are affordable to amateurs and astronomical societies. Using software, data can be uploaded to sites, contributing to the recording of meteors. It also possible to use radio equipment to ‘see’ meteors.
Most ‘shooting stars’ are no larger than a grain of sand and come from the leftover debris of comet orbits. Astronomers are interested in the origin of meteors, so how do we calculate where the meteors come from? Triangulation from three sites is used to project back to find the orbit. This used to be done manually by visual observation but in the early twentieth century significant amounts of data was collected. Unfortunately there was a large margin of error because of the method used. For triangulation to work, accurate time of appearance needs to be recorded.
For accurate data, not only does the direction of the meteor need to be recorded but also its speed. This was not possible from visual observation, but this problem was solved by using several SLR film cameras set up in a circular array with images which were ‘interrupted’ by a rotating shutter that looked like helicopter blades. Because the speed of these blades was known, a meteor’s speed could be then be calculated. In addition accurate recording of the time of a meteor needs to take place
With the advent of digital cameras another step change in meteor astronomy occurred. Many serendipitous images are taken by amateur sky-scape photographers, often with accurate time and location of observations. One bright image was accurately tracked from Norway westbound across northern England. Special software is used to triangulate.
The Chelyabinsk meteor was not detected by professional optical monitoring stations since it approached the earth from the direction of the sun. Instead ubiquitous dashcam footage from cars in Siberia (where accident insurance is a dodgy business) provided footage of the incident.
Modern methods use low light surveillance cameras pointing up. These can be attached to a lap-top computer using software that only records when an incident happens. However this can include airplanes, satellites and even spiders! Any footage has to be monitored to remove extraneous footage. Data can then be processed by additional software and uploaded to the web. Example networks are NEMETODE and UKMon.
This makes a good project for an astronomy club for the price of a few hundred pounds and some dedicated people to monitor the footage. The EDMOND database can be used to match meteor photographs against the night sky.
Radio and spectroscopy can also be used with meteors as their trails reflects radio signals. It is possible to pick up scatter from a radio transmitter called Graves near Dijon in France on 140 MHz. You can also use Fun Cube USB Software, a Defined Radio (SDR) dongle and spectrum lab software. Additionally you can put a diffraction grating in front of a video camera and hence infer what a meteor is made of.
Now large sensor cameras can shoot video in real time and they are becoming more affordable. The Sony Alpha 7 low light camera (big pixels, greater sensitivity) is great. It is possible to use old Canon 85mm fast lenses with it. You can also shoot 25 fps colour videos on the Alpha 7. This will show green oxygen trails and even how upper level winds shift the trail in near real time. Starviz CCTV full camera low light cameras are also an option, but the images are compressed so they may not be so good for astrometry.
Lots of info online on how to setup a club station.