Imagine yourself on a clear summer night, far from the city, admiring
stars you rarely see in urban areas. Then suddenly, from the corner of
your eye, you see a flash: brief, red, large, and high in the sky, like
an aurora turned on and off for an instant. Was it just your imagination?
had reported such sightings since at least 1886, but without producing
a photograph or videotape. What should science do with such reports, given
our proclivity to conjure up little green (or gray) men, report
Venus to 9-1-1 as a UFO, and read more into observations of natural phenomena
than facts warrant? Science needs to be patient, to wait for evidence.
As the late Carl Sagan often said, extraordinary claims require extraordinary
evidence. Science deals with facts, not forcing observations to conform
to fanciful speculation. Mystics, poets, and the ancients were adept at
speculation. And although they provided entertaining and amazing tales...that
is all they were.
On the night of 6
July 1989 a happy accident occurred. The late auroral physics
expert, Prof. John Winckler, and his grad students were testing a low-light
camera (like the night scopes on TV news) soon to fly on a research rocket.
Pointing out a U. of Minnesota observatory window (in central MN), the
camera should have recorded northern stars and some fireflies. But on
test tape playback came a total surprise: in two video fields appeared
giant pillars of light towering high above nearby trees. Assuming these
amazing events were associated with thunderstorms in northern MN 200 miles
away, geometry showed they extended tens of miles high, far above the
Kennedy Space Center have one key task-keeping spacecraft and lightning
apart. A tragedy was averted when lightning struck Apollo 12 just after
liftoff, but the vehicle survived to make the second successful moon landing.
Still, once was enough. The thought of lightning reaching up into space,
threatening the space shuttle, was unnerving. All the reports of strange
lights in the night sky above thunderstorms were suddenly reviewed-and
the hunt was on. But what to call these creatures? Rocket
lightning? Cloud-to-space lightning? Upward lightning? In science, terminology
is critical. One cant adopt a name that presumes more about the
physics of a phenomenon than is known, and no one knew whether this was
lightning, which way it actually traveled, or whether it was connected
to the clouds or reached space. The deliberately fanciful name sprite
was chosen. Fleeting spirits populate more than one of Shakespeares
plays. But these sprites were not myth-they were real.
One night in July,
1993, playing a hunch, researchers at Colorados Yucca Ridge Field
Station trained a low-light camera above a distant thunderstorm complex
over Kansas. On the TV monitors appeared hundreds of sprites, dancing
high above the cloud tops for hours. Soon sensitive color cameras in aircraft
found red sprites, with tinges of blue in the downward extending tendrils!
And sprites were huge, filling thousands of cubic miles of the thin atmosphere
between 20 and 60 miles above the ground. They were the same brightness,
and often similar in color to the aurora, but were fleeting, lasting only
a hundredth of a second or less. So, little wonder people who witnessed
sprites couldnt be sure if theyd seen something. Video cameras
proved they were there. But what caused them?
startled to find something so unexpected, began proposing, and disposing
of, theories. Soon it became clear that sprites occurred only above rare
positive cloud-to-ground lightning flashes (usually 10% of a storms
total). A theory proposed around 1925 by Nobel Prize winning physicist
C.T.R. Wilson suggested that when massive amounts of electrical charge
were lowered to ground, the event would briefly upset the electrical balance
of the middle atmosphere, causing a spark. Indeed observations
showed this spark occurred at around 45 miles altitude, followed by a
burst of upward and downward propagating electrical streamers. But for
Wilsons theory to be correct, the lightning involved had to be massive,
larger than textbooks claimed. So another hunt started. And during summer
2000, an NSF sponsored program, the Severe Thunderstorm Electrification
and Precipitation Experiment (STEPS), found such powerful lightning bolts
dwell in the huge thunderstorms roaming the central U.S. on summer nights.
to see sprites with the naked eye. If youre in a rural area, and
let your eyes become dark adapted, look above the area where large thunderstorms
are occurring 100 to 300 miles away. You just might glimpse the brief
life of a sprite-one of lightnings children dancing though the thin
air of the upper atmosphere near the edge of space.