The Vela Incident

In 1979, a U.S. satellite, Vela 6911, detected the distinctive double-flash signature of a nuclear detonation near Bouvet Island, the most remote island in the world. The Navy's SOSUS array of underwater hydrophones also recorded a muffled thud at the same time in the same area. Various government investigations have only resulted in wildly-differing conclusions, but there is a trend among the naysayers to ignore vital evidence. Read on!

nuclearweaponarchive.org
The instruments used by the Vela satellites for detecting atmospheric nuclear explosions are called "bhangmeters". These are optical sensors that record light fluctuations on a sub-millisecond time scale. All atmospheric nuclear explosions produce a unique and easy to detect signature: an extremely short and intense flash, followed by a second much more prolonged and less intense emission of light.
No natural phenomenon is known that can imitate this signature. In fact it is reported that no false alarms have ever been detected with a Vela bhangmeter. Every other double-flash detection has later been confirmed to be an actual nuclear test.

Despite this, there has been a lot of controversy as to what the explosion actually was, including theories regarding fragmenting meteorites. The two separate bhangmeters recorded the second flash at different intensities. Although this was to be expected because each one had a different sensitivity, the ratio between them was not normal. This is the only bit of solid evidence that suggests that it wasn't a nuclear explosion. I think that, as the Vela system of nuclear-detection satellites was at least 90 months past its predicted 18-month lifespan, that various instruments were shutting down and as such the previously-established baseline for the deviancy between the two readings was now false due to the deterioration of the sensors (at the time the EMP-detector was completely offline, for instance).

After Vela 6911 detected the flashes, the U.S. government went into overdrive trying to find out what had happened, and who had detonated an atomic weapon if that was the case. Aircraft sent to find fission products - a sure sign of an atomic detonation - never made it into the low-pressure system the explosion occurred in. The official report handed to the President in 1980 came up with all number of flowery explanations, including lighting bolts with 400X more energy than ever before seen or space-debris hitting both of the bhangmeters at the same time and causing reflections to mimic the distinct double flash of an atomic bomb. The report also totally ignored the SOSUS detection, and other facts such as sheep in Australia having iodine-131 in their thyroids, something unknown at the time and since never repeated, plus a test conducted a few months after the event found an increase in radiation levels in Western Australia, and a radio telescope in Puerto Rico also detected an anomalous traveling ionospheric disturbance at the same time as the flashes occurred. In addition, an "unusually large" auroral light flared up a few seconds after the explosion, thought to be "a consequence of the electromagnetic pulse of a [surface nuclear burst]."

A report issued to the Los Alamos Laboratory regarding the possibility that natural phenomena had triggered the Vela instruments read '. . . make it unmistakable that this light signature originated in a nuclear explosion.'

Personally, I love the fact that all the accepted theories totally disregard the large explosion-like sound heard by the SOSUS system, instead rambling on about micrometeoroids.
There are a large amount of links on this page: National Security Archive. Make up your own mind

Oh come on! A hushed-up nuclear release incident and not one reply? Where's the ATS I used to know?

The ATS you used to know has probably fallen on to the couch by the
xmas tree, after consuming leftover ham sandwiches, and is presently
in a disbelieving state of panic concerning the total amount of money
spent on Christmas this year.

I find it hard to believe that the Velas, through 41 occurances, 12 of which
were by Vela 6911, only erred in this one instance, according to the panel ? Right ! Yet the sound was recorded by the U.S. Navy, and the
light flashes observed by inhabitants a thousand miles away, at roughly
the same time ? Something did happen ! The Carter administration has
peanuts to show for it though.

Dug this up through a search to see what ATS'rs had to say about this. I googled it and read up on what I could. Odd thing. I would imagine that if it was in fact a nuclear explosion, and the government didn't want to admit it, then it must of been one of ours?

What possible reasons could the military/government have that would cause them not to publicly finger another nation if they were the cause?

This is assuming it was not an electronic glitch.