The footage (video to the right) clearly shows a ball of light pulsing for around eight seconds on the horizon in Tokyo during the aftershock.
It registered 7.1 on the Richter scale and struck 40 miles east of Sendai along the same fault line as last month's quake.
We take a look at several theories as to what could have caused the bizarre phenomenon, from the plausible to the wacky, and get some insight from an expert seismologist.
The most widely circulating explanation is that this was an 'earthquake light' - literally a light that appears in the sky during times of seismic activity.
There have been a number of recorded instances of these - at Kalapana in 1975, L'Aquilla in 2009 and Chile in 2010 - but the phenomenon is not universally accepted in the scientific community.
Dr David Robinson, an earthquake researcher at Oxford University, told Yahoo! News one reason why these might happen.
"The idea is that just before an earthquake, you might get some build up of stress just prior to the event.
"People have invented all kinds of mechanisms whereby this stress gets released as an electromagnetic excitation of the upper atmosphere, which can cause things like lights appearing, similar to the Northern Lights."
The problem with this theory, said Dr Robinson, was that no-one has yet come up with a plausible reason for why this actually happens. "Anything which is caused by an unknown mechanism is dubious," he said.
A second issue is that while there have been several recorded instances of 'earthquake lights', they don't happen during every earthquake.
"There are satellites up there that record every thunderstorm that happens on earth. If you're getting something similar to a flash of lightning during an earthquake then they're going to measure it, but that's not happening."
There are a couple of other explanations that could explain this though. The first concerns quartz. When tectonic plates containing the mineral rub against each other, they create intense electric fields (called piezoelectricity). This could manifest itself as flashes of light.
A second, tantalizing possibility is these lights could actually predict upcoming quakes. This theory suggests that before a quake, the ground 'exhales' radon, which results in light emissions in the atmosphere. Dr Robinson says this is "clutching at straws" though.
He doesn't rule out earthquake lights, but feels the subject needs more study.
"Just because they can't be explained doesn't necessarily make them not true. But until anyone comes up with a plausible mechanism it will be on the fringes of earthquake study."
Another possible theory for the burst of light is that it was some kind of electrical explosion. It's been speculated that the flash was an electrical transformer exploding after being struck by the quake.
During Thursday'squake 3.6million homes in North East Japan area lost power, traffic signals and road lights also stopped working. 900,000 houses were still affected on Friday afternoon.
A spokesman for the Tohuku Electric Power Company said six power plants in the area went down after the tremor and power lines throughout the area were damaged, making this explanation a possibility.
A US 'superweapon'
We're into the outlandish territory now. Many commentators, including oddball conspiracy theorist David Icke, have said the footage was evidence of 'Haarp' (High Frequency Active Auroral Research Program).
Based in Alaska, this weather program was set up by the US Air Force, Navy and University of Alaska to research the upper atmosphere (the ionosphere) with a view to improving satellite communication.
Some have speculated that Haarp can physically change weather conditions, and the project's been blamed for triggering floods, hurricanes, droughts, the earthquakes in Haiti and Pakistan and even Gulf War Syndrome. Mind control is another one of its supposed capabilities.
Suffice to say the events in Japan have also been attributed to this 'superweapon' - with former governor of Minnesota and pro-wrestler Jesse Ventura telling Piers Morgan recently:
"The US's HAARP weapon system can cause natural disasters, including earthquakes and tsunamis like the one that happened in Japan."
Whenever grainy handheld footage of a glowing light in the sky surfaces, it's only a matter of time before it's held up as evidence of UFOs. This video is no exception.
A quick YouTube search reveals a spate of alien sightings in the build up to the Japan earthquake, with little green men spotted above Kyoto and the Sakurajima Volcano. Even Chinese news agency Xinyua reported UFOs flying over Mount Fuji in February.
An alien spacecraft was also spotted during recent Japanese news coverage of the Earthquake, but this was later confirmed to be a helicopter.
Written by Orlando Parfitt