The Occasional Spark: Newsletter Challenge (October 2016)

Caused by a buildup of static electricity....Corona discharge results when the electric field is strong enough to create a chain reaction: electrons in the air collide with atoms hard enough to ionize them, creating more electrons which ionize more atoms....

St. Elmo's fire.

https://en.wikipedia.org/wiki/St._Elmo%27s_fire

St. Elmo's fire is what it's called, but the question asked what caused it.

In 1965, I observed St. Elmo's fire off the tip of my index finger, held high above my head, when I was on the very pointed top of Bishop's Peak near San Luis Obispo, CA. I quickly moved to a lower point under a large boulder, and lightning struck the very point where I had been standing only a few minutes later.

Expanding on SolarEagle's post, what caused it was droplets of water carrying charge as they fell, and creating an electric field, together with the sharp point (my finger, in the above case) rapidly spraying out opposite charges attracted by that field. Those charges ionize molecules of air, and the ionized molecules emit light when the extra charge is lost.

St. Elmo

Yes it is called St. Elmo's Fire

I really should stop trying dry humor online.

I don't understand!

I Suspect that he was joking that what caused St. Elmo's Fire was St. Elmo...

OK, that makes sense.

Thanks!

Yes. Sadly, my jokes aren't much better in real-life.

OMG, I thought this was real life. Is there something, someones not telling me?

Well, maybe there is, and maybe there isn't. Either way it's amazing!

...I'll show myself out now...

yes, my socket's are not washed yesterday! want anything more you are not told?

What is this?

top secret

OK...

During my high school days as a part time job of doing antenna installations experience...

while installing antennas up high on the roof tops of tall buildings, it was normal occurences For me to get and feel electrical shocks! A very good reminder for me to don a pair of gloves! Especially on windy days, as the strong gust of wind hit the long antenna pole I was trying to erect vertically...

My thoughts was that highly ionized air molecules, electro-magnetizedly charged by different radio waves as propagated by transmitters were inducing high energies onto the long metallic antenna pole..... Similar concept applied on generators, electrical transformers alike!

To prevent from getting shock, I was told to keep the metal pole electrically grounded using braided grounding wires.... Otherwise potentials will build up on the metal pole high enough that either a Spark or an electrical shock can be observed!

when the high energy seeks for a low resistance path to discharge....

Part of the reason is exactly as Rixter describes so well; electric field strength is roughly inversely proportional to effective radius, so structures with small effective radius can more readily experience electric field strength sufficient for ionized molecules to interact and ionize neutral air molecules triggering a breakdown and discharge.

..

Another factor is the Earth being negatively biased compared to the atmosphere varying with the vertical component (as well as with season, locality and weather) yielding around 50 volts per vertical meter to 500 volts per vertical meter.

...which is why you typically observe discharge at greater height off the ground, i.e. ship masts, but not so often mail box flags or wrought iron fence tops....no matter how dry and windy it might be.

static electricity