Although they've been together for about 4.5 billion years, the sun and Earth still seem to have a downright electric relationship, based on a colorful show of northern lights seen on Valentine's Day. Above, a short but stunning aurora lights up the sky over Bø in Vesterålen, Norway.
Such displays occur when the sun sends a burst of charged particles coursing toward Earth. A recent uptick in these so-called coronal mass ejections, or CMEs, that started Sunday has increased aurora activity throughout the week.
The northern lights envelop the landscape of Sweden's Abisko National Park on Valentine's Day.
While still somewhat mysterious to most people, auroras are actually fairly common phenomena, occurring regularly in the high latitudes of both the Northern and Southern Hemispheres. But big solar blasts aimed at Earth can drive exceptional displays, sometimes creating auroras that are visible across a much wider region. (See pictures: "Huge Solar Storm Triggers Unusual Auroras.")
The similarity in appearance between auroras and neon lights is no coincidence. In every diner window where they flash, neon signs use electricity to create charged particles, which are sent through tubes filled with gases such as neon, argon, and xenon.
As with auroras, the charged particles temporarily excite electrons in the gas atoms, which settle back down by giving off the excess energy as light. Each type of gas produces a different color, just as the gases in Earth's atmosphere dictate the colors of auroral displays. (Also see "Auroras—Heavenly Lights" in National Geographic magazine.)
The windy appearance of auroras is an aspect noted from the earliest times, and it's reflected in the scientific names aurora borealis, or northern lights, and aurora australis, or southern lights.
In Latin, Boreas was the name of the northern wind and Auster that of the southern wind. Aurora was the goddess of the dawn, giving these heavenly displays the poetic name "dawning light of the winds."