Though at first glance the "Daylight" scenario appears unrealistic in the extreme, most of the effects described at Zero Hour have occurred on a number of occasions. Two enormous coronal mass ejections took place in 1859, producing Zero Hour on a small scale. The Sun could do much worse than that.

It should be noted that the Sun’s eruptions do not affect the orbits of the Earth or Moon in the slightest, nor the orbits of any other planet. The solar wind is more intense and chaotic, but this has little effect except on Earth’s magnetosphere. Volcanism, earthquakes, and continental drift are unaffected, going on as usual.

The links below offer greater detail on the scenario's background physics, with more detail on the 1859 superflares that inspired this shared world.