Bright blue light observed in night sky

Hi there,
Here is a description of a very stange phenomenon I observed last
night. I have no idea what caused this. If anyone has any good ideas
please let me know. (A web search only reveals a couple of similar
experiences, but most of them seem to be posted on "UFO" type forums,
and hence the conversations tend to become a bit... muddy.)

I was in Cheltenham, Victoria (Australia), outside looking at the
stars. It was about 10:30 pm, Sunday June 4th. Conditions were clear;
there was no cloud and the stars were as bright as ever. The moon was
almost exactly half, and was towards the West - probably WNW about 40
degrees above the horizon.

My first observation was of the sky actually dimming. (This could have
been because I had just blinked and opened my eyes at the time that an
initial flash was fading. However, it left me with the impression that
the the light in the sky had been sucked away, and then emitted in the
flash that as to follow. In fact the more I think about, this initial
impression is also my considered lasting impression - it was as though
the light was being sucked into a single point and then released in a
huge silent explosion of light. Stupid as that sounds, read on...)

The flash followed almost immediately. I would estimate that between
the time I saw the sky start to fade until the blue flash began was
about half a second. The blue light flash was very bright, and it
filled probably 40 degrees of the horizon and to a height of about 40
degrees. It seemed to have a point source, but that was obscured by a
building so I can't say what was at the middle of it. I heard no
noise, but I was not in an entirely silent environment; I think I would
have heard a loud noise such as thunder, but not a quieter one such as
the sound of a distant flare. The glow seemed to come from ground
level or not much above, from a direction roughly SSE. It was more a
pulse than a flash, lasting less than a second.

The colour of the flash I would describe as not a natural colour. That
is not to say that this was not a natural phenomenon, but the colour
was not like any other you usually associate with the sky - it was not
the blue of the sky, lightning or stars. It was darkish, yet very
bright. Not dark blue, but tending more towards dark than light blue.
Perhaps a bit like a luminescent ocean blue.

Someone I was with also saw the light, although she had her eyes
half-closed so did not get a good look at it - she described it as
whitish. Perhaps she had seen the initial flash that I had missed?

My intial thoughts were that it might have been:
- a flare, but the spread was too wide and I saw no moving object.
- an explosion, possibly of an electrical station, but there was no
noise, the colour was wrong and the house lights stayed on!
- lightning, but it did not come from above and it did not flicker.

Perhaps it was some sort of "Aurora"? I have never seen anything like
it and I can't explain it.

-- ff