Fireball Observing
I thought I would share with you an email I received a while back. It’s very interesting…..read on
Dear Graeme,
Many thanks for your fireball (= notably bright meteor) report. Much appreciated, and congratulations on spotting such an impressive event!
If you can recall the time you saw this object, that may give a clue as to which date it was on, as there were brilliant fireballs seen on each of January 14-15 (at about 22:25 GMT), 15-16 (circa 22:57 GMT) and 16-17 (around 20:15 GMT) from Britain.
I appreciate the problems of trying to remember the event’s details some time later now, and that you had other things to concentrate on at the time, but it would be very helpful if you could pin down more closely just where the meteor’s track you could see started and ended in the sky. The true azimuths (that is, angular compass directions around the horizon, not just magnetic compass bearings) and elevations in degrees would be ideal, but even an indication of the directions of the first and last points you saw based on compass points, and approximate elevations in degrees above the horizontal would help. You can use your hand held at arm’s length from your eye to estimate these, as the distance across your clenched knuckles is about 10 degrees, while your outspread hand (outer edge of thumb to outer edge of fourth finger) is about 22 degrees. Your index finger’s tip is roughly one degree wide. Please don’t be concerned if you can’t recall all this information, but anything more you can manage would be most welcome!
Should you need it, there is further advice on what to report from fireball sightings generally on the SPA “Fireball Observing” webpage, at:
http://www.popastro.com/sections/meteor/fireball.htm .
In terms of the fireball’s distance from you, most meteors occur around 90-120 km (about 55-75 miles) altitude above the Earth’s surface. Even a very bright fireball will only rarely get closer than 30-50 km (20-30 miles) away before it vanishes, and that’s without regard to any horizontal distance the object may have been away too, so in general, if you see any meteor that isn’t virtually overhead, you know it must be at least 100 km (60 miles) distant or more (possibly a lot further for one seen very near the horizon). It’s extremely difficult to estimate the size and distance of such things by-eye, as we simply have no markers to judge by.
Most such brilliant fireballs seen away from a couple of major shower maximum nights each year are sporadics, that is, non-shower meteors. Although there has been a good number of such events spotted from the UK recently, this seems to be just one of those lucky coincidences, rather than because they all had a single origin (there’s no evidence they did, at present).
As regards the terminology, the object seen brightly glowing in the sky is a meteor. If a solid body fell to the surface from it, after the meteoric fireball had ceased to glow, and was subsequently recovered, we would call that a meteorite. While the object is in space (or indeed within its fiery cocoon, blazing through the atmosphere), we call it a meteoroid.
If you’ve recalled anything additional about your fireball since, or if you’ve learnt of anyone else who saw it (or indeed, any other fireballs), please do let me know with full details.
All best wishes,
Alastair McBeath,
Morpeth, Northumberland.
Meteor Director, Society for Popular Astronomy.
Meteor homepage: http://www.popastro.com/sections/meteor.htm