Factual error: While the tidal wave is enveloping Manhattan, there is a scene where Washington Square Park is destroyed. A large arch is hit by the wave before reaching the rest of the park. The problem is the arch is on the UPTOWN side of the park, not the DOWNTOWN side which according to the movie was the direction the wave was coming from.
Continuity mistake: During a scene where the boss of the TV station is talking to his staff, when he finishes he takes off his glasses and starts to move off his chair. Yet in the next shot he gets off the chair still wearing his glasses. (00:07:30)
Factual error: When Sarah's family is fleeing Richmond, the highway sign says "Interstate 66." That highway is about a hundred miles north of Richmond; it starts in Washington DC. Another highway sign says "Virginia Beach 12 miles", which is the wrong way when fleeing Richmond westward.
Factual error: After the initial impact of the small comet, the clouds are all blown away. Yet in every further scene there is normal cloud cover, including the shots from space.
Factual error: When the asteroid crashes on earth you see people looking up at it, to see it fall. In reality the asteroid would burn everything on the ground due to the heat it develops.
Factual error: Leelee and Elijah are supposed to live in Richmond, Virginia. However, the hill supposedly behind Elijah's house is too high and too open for the Virginia piedmont and clearly looks like California. (Similarly, the hills around the Ark project, supposedly located in the Missouri Ozarks, also look very Californian.) When the couple are escaping the tidal wave on the motorcycle through the woods in the mountains to the west, they are going through a very open forest of what appears to be some kind of western pine trees found in semi-arid areas. In reality, the underbrush in the moist Virginia Blue Ridge would be too thick to drive through outside of a road or wide trail.
Plot hole: The government would have no chance of hiding the existence of the comet for a year. Most comets are discovered when they are very faint, literally thousands of times fainter than Wolf-Beiderman when Leo found it. Long before the events in the film take place, probably even before the government itself would be notified, the comet would have been discovered, an orbit calculated, and people panicked. The whole premise of the first half of the movie is thus based on flawed logic.
Revealing mistake: During the scene where the two teenage stars are outrunning the tidal wave through the hills, the girl is supposedly carrying her baby sibling strapped to her chest. However, the legs that can be seen dangling out of the baby-carrier belong to a dummy.
Factual error: Otis Hefter is introduced as the Director of the mission and prior to the launch of the Space Shuttle, greets someone with, "Welcome to Houston!" Hefter is then portrayed as the person "in command" of the mission, including the countdown and lift off. This is incorrect as Ground Control at Cape Canaveral, Florida commands the mission until the spacecraft has cleared the launch tower and actually begins its flight and mission. It is only then that the command of the mission who be handed over to Hefter and the crew in Houston.
Continuity mistake: Just after Jenny Lerner talks to her Dad in the rain, she hails a taxi with her left hand, in the very next shot she is hailing the taxi with her right hand.
Visible crew/equipment: When the kid is on the motorcycle looking for his wife, you quite clearly see a camera and crew filming another scene. It's when we see the traffic jam and the rental van shot.
Plot hole: The time and distance of the movie doesn't make sense. The comet was only 3.7 million miles away from Earth when the Messiah mission failed. That is about 1/10th the distance to Mars. They should have been able to put more contingency plans into place. Also, it took the Messiah 5 months to reach the comet which means it was only going 1,033 mph, which is very slow for spacecraft.
Continuity mistake: When the astronauts start drilling on the comet, they ask Spurgin Tanner how they are looking for time until the sunrise cooks them all, to which he replies "it's getting tight... 1:36:30." A few seconds later they show the display in the ship and in the bottom corner you can see "SUNRISE CLOCK 00:44:11." Moments later the camera zooms fully on the corner of the display and it shows "SUNRISE CLOCK 01:36:00".
Continuity mistake: When Leelee Sobiesksi gets on the motorcycle with her husband, the baby's head cushion moves from full coverage of the baby's head to partial coverage, to full coverage, back and forth, several times.
Factual error: Many scenes showing the tidal wave approaching land and buildings is factually inaccurate. Its already stated that the tidal wave will be moving faster than the speed of sound, and reach a height of over 1000 ft by the time it hits land. That being the case, there would be a massive pressure wave of air in front of the tidal wave, that would clear a path long before the tidal wave hits. Buildings would start to topple and crumble before the water struck, and certainly people would not be able to stand in the path of the tidal wave, because the air pressure would blow them away.
Factual error: When the comet is passing through the atmosphere it shines about as bright as your average bike-light, and the shot shows thousands of people looking directly at it without shutting their eyes. When a comet of that size goes through the atmosphere it does so at an incredible speed. The friction between the air molecules and the comet produces a light many times brighter than the sun, anyone looking at it would be blinded instantly.
Continuity mistake: When Orrin the astronaut is saying his good-byes to his wife and kid, we see him reach out to the screen as if to touch them with his right hand. When we switch to the shot within mission control, he's reaching with his left hand.
Factual error: The shock wave that hit Messiah when it detonated the nuclear bomb on the comet would not have existed in space. It may have been hit by debris, but that would have destroyed the craft.