Sunday, October 14, 2012

Aurora Borealis

I promised I would bring you a more exciting post this week, and to prove it, I give you: the Northern Lights!  Friday night we had an awesome display in Anchorage. It's been many years since I've seen the Northern Lights (aka the Aurora Borealis), not just because we moved to Australia, but also because the sun was at a solar minimum.

What does that mean? Well, the Northern Lights are caused by solar flares -- when the sun releases great streams of plasma and electrons into space. As the stream of electrons hits the Earth, it interacts with our atmosphere and produces light. Many, but not all, solar flares are released from sunspots. The sunspots appear in 11 year cycles. It takes about 4 years for the sunspots to reach a maximum, and 7 to go back to minimum. The most recent minimum began in 2008, and lasted for about 2 years, which is longer than normal. (And that's your space weather lesson for today).

So, when we left, the sun was still at its minimum, but now it's heading back towards maximum again. The Aurora has come out a couple times this fall, but it's been cloudy, or the moon has been out. Friday was clear, and the display was active enough to see it from midtown, even with all the light pollution.

What is it like to see the Aurora? Imagine you have two different colors of water that are mixing together. They don't just instantly become mixed, one color will flow and stream into the other.

Green swirl

That's what watching the Aurora is like. It's a river of light in the sky.

Not just green; faint purple and red showed up as well.

Sometimes, it comes down straight over you, looking like a "rain" of light.

A whirlpool in the river

Other times, it goes off and does its own thing. It's constantly moving and changing, sometimes flashing on and off, sometimes marching down from above like other worldly beings.

Auroral curtains
These photos are adequate -- I wasn't really prepared, as I didn't have a flashlight to look at my camera settings, or my tripod to stabilize my camera. But judging from the space weather sites, I will have a few more chances this winter, so I hope to get some better shots next time!


Carlw4514 said...

Just recently found out that scientists think Mars lost its atmosphere due to the solar wind. Mars has no magnetic field to protect it. Or has one too weak, not sure which. Anyway our planet's magnetic field is really really important!

Uncle C

L said...

That's interesting, Uncle Carl. I always thought it had a thinner atmosphere because the gravity was slightly less. But I guess now that I think about it, the difference in gravity between the two planets. is not proportional to the difference in atmosphere.