Near the end the film Empire of the Sun (Spielberg 1987), the protagonist finds himself in (or near) Shanghai. He then sees the atomic bombing of Nagasaki. The bright light appears to be the pika flash, followed by what appears to be a shock wave:
Historically, was the atomic bombing of Nagasaki actually visible from Shanghai?
Absolutely not. The bomb dropped on Nagasaki detonated at an altitude of about 1,500 feet. Nagasaki is roughly 505 miles from Shanghai, and only about one degree of latitude further north. Assuming the character was near sea level, there is no way he could have seen the blast.
A point 1,500 feet above the earth's surface is only visible from distances up to 47.5 miles away. That's less than 10% of the distance between Shanghai and Nagasaki.
Why? Because the earth isn't flat. It is an oblate spheroid. Here's a rough model to demonstrate the problem. It is not to scale, and the earth is shown as a sphere rather than an oblate spheroid, but the general idea is the same:
Nope. Assuming we're talking about a cloud some 33,000 feet above the earth's surface, it would only be visible from a distance of 222.7 miles away at most.
No. The Nagasaki mushroom cloud was estimated to be 45,000 feet in height. This means it would be impossible to see from more than 260.1 miles away.
No, not in any strength that a human could detect. At a distance of less than 2.8 miles from the hypocenter (AKA, Ground Zero), the blast wave has already dropped to a pressure of less than 1 psi. Ambient atmospheric pressure at sea level is usually about 14.7 psi, so a person 500 miles from the hypocenter wouldn't feel or see any evidence of the blast wave.
Perhaps - you'd have to ask a physicist to answer this conclusively - but I doubt it.
Refraction might make some evidence of the bombing visible from distances greater than the calculations above would suggest, but this is unlikely for a couple of reasons:
The bomb was dropped over a valley, and the hypocenter is surrounded by mountains up to 1,400 feet tall (almost as high as the explosion itself). This makes refraction less likely.
The bomb wasn't dropped where it was supposed to be, because the military had decided to drop both bombs visually, which meant that they had to drop it in an area with clear skies. Much of Nagasaki - including the intended target - was covered with clouds that day. This cloud cover would diffuse light and reduce the likelihood of refraction.
I would also consider one more physical effect, light scattering from the atmosphere (quite different from refraction). It is the phenomenon explaining also twilight, the diffused light visible even when the sun is about 18° below the horizon (well, that is just about the limit). The flash of light from the Nagasaki explosion was certainly far brighter than the sun, though very brief. Perhaps not exactly as depicted in the movie (let us be nice, and grant some poetic license to Hollywood ...), but quite few photons might well have succeeded in scattering their way through the atmosphere above the stretch of East China Sea separating the two towns.
I just watched this movie. If the question is would the explosion be visible from Shanghai, then no, but the visible light from the explosion could travel much further. To be fair to the movie, the scene also shows the atomic blast far off on the horizon from a perspective that is very high altitude (not from the perspective of a person on the ground in Shanghai).
There's also historical accounts of light scatter: where the first atomic detonation, Trinity (in New Mexico), had the light that could be seen over 280 miles away in Amarillo, Texas. Whether there would be enough detectable light and refraction scattering through the sky to Shanghai: that could be creative leave. It's clearly a plot device where Jim thinks Mrs. Victor's soul has transcended, and an end to his conflict of his own survival vs well being of others.
