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.
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.
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: At the end of the film, when the comet hits, the tidal wave washes over New York City, smashing first into the Statue of Liberty, then Downtown and the World Trade Centre, then sweeping uptown, depositing Lady Liberty's head somewhere in Midtown. The only problem with this is the fact that Manhattan Island doesn't face East. It doesn't even face the South. It lies on an angle in a Northeast/Southwest direction, top to bottom (1:00 to 7:00 on a clock face). That means a wave that started in the middle of the Atlantic would have to take a pretty sharp right turn at Brooklyn (over 90 degrees) to travel uptown in a North-easterly direction.
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.
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: 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.
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.
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: During the scene where Jenny is on the dock trying to interview Secretary Rittenhouse, the sun changes position a few times during the scene. When Jenny is talking to the little girl, the sun is behind Jenny appearing to be the middle of the afternoon. When Jenny walks to look over at the cargo, the sun is now ahead of her to the west, getting closer to sunset. When Rittenhouse appears on the boat, the sun is back to the previous position, for a second until the camera pans back to Jenny with the sun out west again. Rittenhouse ushers off his daughter & she walks off as Jenny tries to talk to him, all the while the sun is now behind Jenny to the mid afternoon setting. When Rittenhouse walks off, the camera pans around and now the sun is in the west again near sunset and remains this way until the end of the scene.
Continuity mistake: When they are launched into space and change over to the other space craft they are all wearing street clothes, and then in a scene when they are getting closer to the comet they are all wearing NASA shirts.
Continuity mistake: When the boy takes the motorbike from the garage the mirrors are out of line. In the next shot before he rides out, the mirrors are all in line.
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.
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.
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.