On the evening of Tuesday the 10th, and on the morning after, the phones at the observatory were ringing busily. People from all over the Okanagan were phoning in with reports of something they saw in the sky. This account is distilled from all those reports, and describes a large fireball, or bolide.

At about 4:30 p.m., an extremely bright, starlike object appeared in the sky over the Northern or Central Okanagan, which was seen from as far south as Okanagan Falls, south of Penticton. Leaving a short, glowing trail, it crossed the sky heading in a westerly direction. Some observers reported that when it was close to the western horizon, it exploded into many fragments. One report came from 100 Mile House, About 80 km north-west of Kamloops, and described loud booms, like thunder. Obviously, something had come into the Earth's atmosphere at very high speed. Friction made it white hot and evaporated part of it, leaving a trail. Finally it exploded.

The two main possibilities are that it was either a piece of something of ours coming back to Earth, or that it was the arrival of a lump of rock or iron, material left over from the formation of the Solar System. At this point we don't know for sure, but there are strong clues. Firstly, it was going in a westerly direction. We rarely launch any spacecraft into orbit in that direction because if we launch them towards the east, we get several hundred kilometres an hour free from the rotation of the Earth. If we launch things the other way, we have to work against the Earth's rotation. That suggests the object was not one of ours. In addition, the sightings suggest the object was in a dive. Objects returning from orbit will be moving almost horizontally or in a very shallow dive during the burning up part of the re-entry. An exception could be a space probe or launcher rocket associated with an interplanetary space mission, but we don't know of any suitable candidate. It is most likely that the object was a lump of rock maybe the size of a suitcase, moving at somewhere between 30,000 and 100,000 km/h.

In space the rock was pretty cold. Then, when it entered the thin, upper atmosphere, friction heated the outside until it was white hot. Rock is not a good conductor of heat, so the inside remained cold. However, the temperature difference between the inside and outside would have produced a lot of stress. As the object dived more deeply into the atmosphere, the denser air imposed a savage drag on it, making it decelerate so hard that if one of us were sitting inside we would have been flattened. The object settled into a minimum drag configuration as it fell. Eventually the thermal and deceleration stresses became strong enough to break off a piece. This unbalanced the drag forces, sending the object into a supersonic tumble, which tore it to pieces. This probably caused the booms that were heard up at Hundred Mile House. As a very rough guess, the fragments would have landed somewhere close to the area defined by Kelowna, Penticton, Kamloops and Princeton. However in the thickly forested terrain, there's little chance of finding anything. Of course, I missed the event.

The planet Venus still dominates the southwestern sky until quite late in the evening. Saturn rises around 8 pm. The Moon will be New on the 24th.

Ken Tapping is an astronomer with the National Research Council's Herzberg Institute of Astrophysics, and is based at the Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9.