Complex sentence: Its reentry has been suggested as a possible explanation of UFO sightings over the United States and Canada, centred around Kecksburg, Pennsylvania; however analysis found the spacecraft probably reentered several hours before the sightings.
Split into simpler sentences: Its reentry has been suggested as a possible explanation of UFO sightings over the United States and Canada, centered around Kecksburg, Pennsylvania. However, analysis found the spacecraft probably reentered several hours before the sightings.