Never mind the new year fireworks, the start of 2015 happened with an even bigger bang, at least if you happened to be in Romania, Moldova or the Ukraine. The early hours of January 7th saw a massive fireball over the region, culminating in an explosion loud enough to wake people, and causing many to call the emergency services to report the event. In Romania reports of sightings have come in from across the country, putting the time of the explosion at 3:05 EET (01:05 UT), with people hearing the explosion in the counties of Buzau, Vrancea and Covasna.
So far over 50 recordings and eye witness reports have been collected by the IMO, many from surveillance cameras recording sudden brightening of whatever outside area was being monitored. A compilation of videos of the event, as recorded by security cameras, can be viewed on youtube at https://www.youtube.com/watch?v=WjS8GHu_0ZM. The map below shows the location of the reports received so far, red dots are from surveillance cameras, the blue markers are visual reports from witnesses, and the green dots are reports from those who heard the terminal explosion.
Fireballs are exceptionally bright events which happen when a meteoroid passes through the atmosphere. Stand outside on any clear night for more than a few minutes, and you will see a meteor somewhere in the sky. Meteors are caused by small pieces of rock, generally less than a millimetre in size. They range in brightness from too faint to be seen with the naked eye, right up to brighter than the full moon. The majority of meteors are at the faint end of this scale, while fireball events like this one are at the extreme upper end of this range.
The reports from Romania of the January 7th fireball put the maximum apparent magnitude of -16, brighter than the full Moon (-13). For comparison, the Sun has an apparent magnitude of -26, the brightest star in the night sky, Sirius, has an apparent magnitude of -1.4, and the human eye is capable of seeing as faint as magnitude +6 under good observing conditions from a dark site.
The magnitude scale is logarithmic; a star with magnitude +1 is actually 2.512 times brighter than a star with magnitude +2. The apparent magnitude above which a meteor is considered a fireball is somewhat arbitrary, with different publications defining it by different numbers. Roughly one in 1,200 meteors is brighter than magnitude -5, while only one on 12,000 meteors reaches magnitude -8 or brighter, so fireball events like this one are rare.
Almost all small meteoroids disintegrate during their passage through the atmosphere. But sometimes, very bright fireball events can result in a meteorite fall, where the meteoroid (or parts of it, in the case of an explosion) reaches the ground. If this happens, reports from people who saw the event are vital in determining the likely location of the debris.
So far, information on the event is sparse. The explosion appears to have occurred at a height of roughly 55 kilometres and it is likely that the meteoroid completely disintegrated. Whether a fall occurs or not, the details of events like this can only be determined from combining the information from many eyewitness reports. If you see a bright fireball event like this, you can help researchers by reporting what you saw in as much detail as possible. You can find further information on meteors and other related events, and advice on how to observe and report them, visit the IMO website at http://www.imo.net/