Comet's tail is incorrectly directed. It is caused by solar wind, not friction, because the latter doesn't exist in vacuum. Therefore the tail should be directed away from the Sun, rather then left straight behind the comet.
As there's no friction in the middle of space, the comets will not have a tail.
Only in the neighborhood of e.g. a planet with atmosphere or the sun, the tail will be there.
Nuclear explosions in space will not divert the comet. Since there's no atmosphere in space, there will be no shock wave either.
One of the first scenes pinpoints what the movie identifies as Shannon Airport on a map. In fact it is Galway City which is indicated. Sometime later a similar map purports to indicate Dublin City, but in fact shows Dundalk.
The geography of Ireland is completely messed up. The film implies that both Shannon Airport and Queen's University are in Dublin, whereas the former is near Limerick and the latter in Belfast, both of which are over 100 miles away, in different directions.