miércoles, 5 de marzo de 2008

Aurora spring

Spring is usually the time for the Northern Lights like the one below.

So why Spring? Here is an explanation from NASA:

"It turns out that magnetic connections between the sun and Earth are favored in springtime. It’s a matter of geometry: As Earth goes around in its orbit, Earth’s magnetic poles wobble back and forth. (The poles don’t really wobble, but the combination of Earth’s 23-degree polar tilt plus orbital motion makes the poles seem wobble from the solar point of view.) Around the time of the equinox, Earth’s magnetic field is best oriented for “connecting-up” with the sun, opening the door for solar wind energy to flow in and spark Northern Lights.

But wait, there are two equinoxes, spring and fall, with similar magnetic geometry. Indeed, autumn is aurora season, too. Geomagnetic disturbances are almost twice as likely in spring-fall versus winter-summer, according to historical records."