Did anyone really see the Bikini nuke test from Japan?

[CC]

I've read again a reference to the 1954 Bikini H-bomb test and that people in Okinawa saw the flash - some 2300 miles away. Could this be so? I'm skeptical. And who would have been looking? Or was it a large enough flash that lots of people happened to notice it? Myth or fact? This teeming individual wants to know. Dopers?

[Squink]

That seems a long ways. 2300 miles is about 40 degrees.
According to this horizon calculator, the flash would have to arise at a height of about 380 miles to be directly visible at that distance.
The Teak explosion (altitude 48 miles) was visible from 700 miles away, while the horizon calculator gives a limit of 677 miles for that altitude. I've found no reports for anything beyond that distance.
However:

There are a number of interesting phenomena associated with a nuclear air burst that are worth mentioning although they have no connection with the destructive or other harmful effects of the explosion. Soon after the detonation, a violet-colored glow may be observed, particularly at night or in dim daylight, at some distance from the fireball. This glow may persist for an appreciable length of time, being distinctly visible near the head of the radioactive cloud. It is believed to be the ultimate result of a complex series of processes initiated by the action of the various radiations on the nitrogen and oxygen of the air.

This may be some sort of Sprite, Elf, or Jet phenomena, which might be visible at very large distances from the blast.

[CC]

A little searching tells me that the bomb was detonated at 6:45 am in Bikini. My atlas shows Japan to be two time zones west of that, meaning that in Japan, it was 4:45 am. So, was it so dark that there was a flash in the sky? And who was awake to see it? I've also found a site that talks about inhabitants of Bikini who had been removed to Rongelap atoll, some 135 miles east of the blast and they reported that they saw a glow in the sky from the blast. Ok. 135 miles - reasonable to think they saw light in the sky. I'm more doubtful than before. Does anyone know if it's true that someone actually saw this from 2,000+ miles away?

[CC]

Or, could the sky have been brightened in a huge diameter of light that could have been seen from Japan in the early morning hours? It seems almost impossible? Does anyone have any cites that could confirm or disconfirm the assertion?

[Alive At Both Ends]

The flash clearly could not have been seen directly from 2300 miles away. As has already been pointed out, the bomb would have had to detonate 380 miles above ground to appear over the horizon. 380 miles up would qualify as in space, three years before the launch of Sputnik 1. No missile in existence in 1954 could have reached that height (Sputnik 1 orbited at about 150 miles up). In fact the detonation was at near ground level.