Much Ado About (Almost) Nothing

Whilst you can’t beat seeing a bright meteor with the naked eye it’s not usually practical to wait up all night for the occasional bright one, except during a so-called shower. Amateurs using low-light video cameras and suitable software can capture low resolution trails but even they need a clear sky, and darkness of course. Radio reflection allows meteors to be detected during the day provided there is a suitable strong transmitter over the horizon.

Some UK amateurs use reflections from the Graves radar based near Dijon in France and with such a strong signal thousands of echoes may be recorded per day. This makes it seem like there are a lot of meteors but most of them are really faint and wouldn’t show up to the human eye even under the darkest skies.

With visual or imaging methods you can work out which direction the meteor came from and decide whether it is a Perseid for example. With the simple radio setup that most amateurs have all you can do is record the reflection or echo. Unfortunately, there is no easy way of knowing which shower, if any, it came from or how bright the meteors would be visually. (There are professional setups that can do this, the Canadian Meteor Orbit Radar for example.)

Some of the meteor ablation zone illuminated by the Graves radar is visible from the UK making it possible sometimes to correlate a visual meteor with the radar echo. Here is an example of the echo from a relatively large Perseid meteor, the brighter patch in the left section, together with the matching video capture.

  • Radio meteor
    Radar echo from a bright Perseid meteor and a matching video capture.

The meteoroid was destroyed in a fraction of a second and it’s just the decaying trail of ionised gas reflected on the radio plot that shows it was once there, a bit like a smoke trail being caught in a searchlight.

It’s sobering to realise that all this was caused a bit of comet debris weighing a fraction of a gram - most of the echoes on the radio meteor plots are from particles in the microgram range. It’s just as well they are so small as all satellites and the International Space Station orbit well above the region where the meteoroids get destroyed!