We often refer to the train/station analogy of inertial frames to determine the relativity of simultaneity. So, if the experiment was done on Earth, the train is one inertial frame, and the station is another inertial frame. But in reality the Earth is accelerating in a number of ways - revolving once a day, orbiting the sun once a year, and orbiting the galaxy centre once every 250mil(?) years. So both the train and the station are not in reality inertial frames. So my question is - can we treat them as inertial frames, because they are both subject to the same acceleration, or do we in reality need to invoke some other correction or indeed General Relativity?
Note, I'm not a physics student, so if it's possible to give a "for dummies" answer, that would be great.