Goofs

When Kirk is talking to Edith on the stairs, Edith stumbles and Kirk catches her. Before and after she stumbles, Edith is wearing two shoes. After she kisses Kirk and walks back up the stairs, her right shoe is missing.

Edith Keeler tells McCoy that her "young man" is taking her to a Clark Gable movie that evening. In the next scene, though, she tells Kirk that if they hurry, "maybe we can catch the Clark Gable movie," so seeing the film wasn't already planned.

When Kirk walks Edith home he tells her about a novel that will be written by someone from another planet, circling the far left star in Orion's Belt constellation which he points to. However, when the shot changes to the sky, it is overcast at dusk and no stars can be seen.

The color and density of Spock's make-up changes from scene to scene; sometimes very green or yellow, and other times closer to "white human" tone.

The makeup on Bones switches between light and heavy from scene to scene.

Goodnight Sweetheart, written by Ray Noble, Reg Connelly and Jimmy Campbell, was published and first recorded in 1931. This episode takes place one year before in 1930.

When McCoy changes history, the Enterprise vanishes because it no longer exists in this new time-line. But the landing party have not also vanished. Other Star Trek productions explain that people and objects are unaffected by time paradox if they are standing right next to the time travel mechanism. Star Trek: First Contact (1996) laboriously spells this out, and it was implied in a few earlier Trek shows as well, e.g. Yesteryear (1973), the animated sequel to this one.

With the "stone knives and bearskins" of 1930, Spock swiftly invents a small computer that can predict multiple possible futures. This achievement is unprecedented and speaks of infinitely greater potential - if he can do this with primitive technology, one can only imagine what he could do using the same process with the tools of his own 23rd century. Starfleet would never again be caught by surprise when Klingons or Romulans attacked, and a century later the Borg and Dominion conflicts would be over before they started. While the long-term ramifications of this machine would seem to be of galactic importance, it is used only as a convenient plot device in this one episode, and we never hear about this possibility ever again in any other episode of the Trek Universe. However, this is not a plot hole, because Spock made only a device with a monitor (not a computer with which it is possible to predict the future) which can be connected with his tricorder and show everything he recorded from the time portal - one record before and one after McCoy changed the time line.

When Kirk and Spock are running from the police, you can tell that they simply run around the block back to the exact same alley. The two barrels, one rusty and one yellow, are still in the exact same spot.

Script Supervisor George Rutter is written as "SCPIPT SUPERVISOR...GEORGE A. RUTTER" in the credits.

As Kirk and Spock are dressing in 1930s clothes, ironed creases can clearly be seen on the clothing. The clothes were stolen from a washing line and would not yet have been ironed.

During the early bridge scene, shots filmed from the front of the bridge clearly show a red uniformed female standing next to the center seat. When the shot switches to the view from the rear, she disappears, even though that section of the bridge is still in shot, and reappears when the view returns to the view from the front. In addition, Kirk looks different in the rear view shot, as if this section was filmed with a stand in for William Shatner.

When Edith is given her talk about future space travel to the men in her mission, Kirk looks to his right at Spock and the picture freezes for a second.

The landing party beamed down to the planet on a medical rescue mission but they brought no medical person with them.

The transporter only has six pads, but at the end of City on the Edge of Forever, seven crew members beam up to the ship at the same time, standing in the circular pattern.

In the beginning, after Bones injects himself, he falls backward into the railing and it breaks. Can only be seen for a brief few seconds.

In establishing scenes, the completed Empire State Building can be seen as part of the NYC skyline. Construction on the building didn't begin until early 1930, and wasn't finished until mid-1931.

One building front shows a fallout shelter sign, not used until after WWII.

In 1930, Edith Keeler offers to take Kirk to a Clark Gable movie and expresses surprise when neither he nor McCoy have heard of Gable. In 1930 Gable was a New York stage actor whose only film work was a few appearances as an extra in the 1920's. Gable didn't get his first credited acting role until in 1931, and he didn't become a star until 1934.

The first view of the soup kitchen shows a seated man, to the left, wearing a sort of greenish knitted baseball cap. That is the renowned US Army M1941 wool knit cap, AKA Radar O'Reilly cap, AKA jeep cap. First introduced as an under-the-helmet cap in 1942, it is still popular today; not only as military surplus but also in various civilian copies.

The calendar in the background at the mission (when Edith Keeler talks to Kirk about a place to stay) shows a 30-day month, with Wednesday the 14th in red, indicating a holiday. However, none of the 30-day months in 1930 started on a Thursday, and the only month in the United States with an observance that is always on the 14th is June (Flag Day). In 1967 (this episode was filmed in February of that year), Flag Day fell on a Wednesday, therefore it is likely that this is a 1967 calendar.

When Edith and Kirk leave the mission, you can hear Kirk say "Oh". However it is clear to see he is not talking. Also, Edith tells him they have to hurry to make it to the Clark Gable movie on time. Kirk responds with "What?". Again it is clear to see he is not taking.

Kirk and Spock run down a 21st Street in Manhattan that curves; the real West 21st and East 21st Streets do not.

Despite having a security alert aboard Enterprise to find Dr. McCoy--which everyone on duty at least would be aware of, Transporter Chief Kyle does not turn to face McCoy when he enters the transporter room and the sound of the doors opening is heard.

Adolf Hitler wasn't interested in wonder weapons, because he thought Germany would win the war with conventional weapons before they were ready. The V2 weapon was seen as nothing but essentially an artillery shell with a longer range and much higher cost. Only when Germany had to go on the defensive, with Soviet counterattack and the United States' entry in the war, did Hitler start giving the wonder weapon projects like the A-bomb (1942) and the V2 (1944) the funding long denied them. It was such that a conventional "dirty bomb," far weaker then those dropped on Japan, was slated for 1946. Moreover, the V2 simply wasn't able to carry such a weapon. So by delaying the United States entry into WWII you ALSO delay the very factors that got the German A-bomb and V2 programs better funding.

When McCoy enters the transporter room after being injected and temporarily insane, he knocks out the controller and beams himself off the Enterprise. He does not enter any coordinates or where he is going, but ends up on the planets surface, near the portal.

When Uhura and one of the security men are looking for Dr. McCoy on the planet they walk by a large rock that he is hiding behind. As they walk past the rock on their right, they are looking only ahead and to the left, but never to the right. Had they looked to the right they would have seen him squatting behind the rock. Not the normal "good work" you would expect from Uhura and a security man.

When McCoy jumps through the portal, Capt Kirk is next seen finishing a dive to try to tackle him. However, he was 2-3 seconds late. He ended up 3 feet away from the portal with Spock between him and the portal. He probably would not have dived after nothing.

Spock said the Guardian's age was on the order of "ten thousand centuries" (or, for the less-poetically-inclined, a million years). However, when the Guardian speaks, it says it has been "awaiting a question" since before the Sun started burning in the sky, which would be at least 5 billion years. Spock's estimate was uncharacteristically off by a factor of about 5000.

More than once, Spock refers to a "mnemonic memory circuit" when discussing the historical events he recorded during the Guardian of Forever's display of the past. For example, he uses the term when speaking to Edith Keeler when she inquires about the odd equipment he has set up in his and Kirk's "flop." The term "mnemonic" refers to something used to assist someone's memory (such as "ROY G. BIV" being an acronym for the colors of the rainbow). The term "mnemonic memory," therefore, is a redundancy, something that Spock, of all of the characters, would certainly not have used.

Kirk says that an author from a planet circling the leftmost star in Orion's belt wrote a novel that recommended the words "let me help" more than the words "I love you"; however, that star (Alnitak, or Zeta Orionis) is a trinary system, consisting of a twin primary of a blue supergiant and a blue subgiant orbiting at about the distance of Saturn, and an outer star orbiting much further away which is a blue giant. A planet in such a system would be far too hot to sustain life.

Leonard McCoy is a veteran doctor who has examined and diagnosed an untold number of sick and injured patients during his career, yet when Edith is hit by the truck, he just assumes that she's dead without even going to her to check her injuries. Any real doctor would not make such an assumption from several feet away.