# 2013 Russian meteor event, Sonic Boom or Explosion Boom?

In the lastest meteor event in Russia there was a big BOOM heard long after the meteor had passed. In this youtube video we can see at 4:30 the Meteor passing.. then hearing the BOOM at 7:00 , 150 seconds later, so what cause the boom? Sonic Boom from the meteor entering the atmosphere? or the big explosion that happens a bit later on its decent?

• There's good coverage at Bad Astronomy, the blog of the astronomer Phil Plait. Note this "UPDATE (23:00 UTC) After looking through more footage, it's become clear that the multiple booms heard were in fact explosions, and not just shock waves from the meteoroid's passing through the air. In some videos, you can see multiple flashes of light inside the contrail, which are clearly from the rock breaking up and then burning up very rapidly and with intense energy—the very definition of an explosion." – Michael Brown Feb 16 '13 at 6:47
The flash seen in this video may not be the glow of initial entry since the camera angle is angled somewhat along the path of the meteor; it is likely the active burning after the meteor has already entered the atmosphere. The mesosphere begins about 50 km above the earth's surface. However, the speed of sound in this region is a bit lower than the speed of sound on earth's surface, ranging between $280\text{m/s}$ and $330 \text{m/s}$. Coupled with the fact that we continue to hear less intense popping sounds for more than two full minutes afterwards suggests that the large boom heard is the shock wave, while the following sounds are actually from earlier events.
Meteors tend to enter the atmosphere at between 20 and 50 km/s, although they may be slower or considerably faster than this. This means that if their journey were straight down through the atmosphere, rather than across it, the trip would take 2 seconds or less. The trajectory of the meteor across the sky illustrates that it is a more glancing impact. The fact that the first sound takes 140 seconds to reach the camera indicates that the meteor is about 45 km from the camera. This is not reflective of the height of the meteor, but the absolute distance of the meteor path from the camera. There are estimates that the breakup altitude is around 20km. The following two minutes of reports reflect a linear distance of about 40 km of travel ($120\text{sec}\times300 \text{m/s}=40 \text{km}$), which probably took the meteor about 2 seconds to cover. So what we hear afterward is like a slow motion recording of the meteors breakup history, slowed down by a factor of somewhere between 40 and 100 times. If we could have heard these breakups in a frame comoving with the meteor, it would have sounded nearly like a single, continuous explosion. The first and loudest boom we hear is likely not from initial entry, but rather the sonic boom from the meteor's closest approach to the camera.