Ghost light, aka Will-o'-the-wisp, is a bluish green flame that would appear near graves at night. This horrifying phenomenon has been observed long long time ago and has even been recorded in some Chinese articles in the Qing Dynasty.
Don't believe it? Go to a graveyard at night and maybe you can really see some ghost light! ;) Anyway I can tell you it really exists.
Actually it is not that terrifying; it can be explained by science! It is because the bodies of human or animals contain phosphorus. As the corpses begin to decay, phosphine will be formed. When the surrounding air is hot, self-combustion of phosphine will be triggered, causing the phenomenon of ghost light!
During summer times, ghost light is more easily observed at the night. This makes sense since self-combustion should be more likely under hotter temperatures. Actually ghost light can also occur at day times, just that it is too bright to make the ghost light observable.
But I am sure even after you have understood the science of ghost light, next time when you see it you will still scream and run away ;)
Source: https://en.wikipedia.org/wiki/Will-o%27-the-wisp
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