Spring brings new vigor to the night sky scene. And the day sky too! After being spotless for weeks, two sunspot groups have popped into view. The larger of the two, named active region 2736, produced a flare early on March 20 that propelled a burst of solar plasma (electrons and protons) toward the Earth. It’s expected to arrive around noon Central Time this Saturday, March 23 and intensify to a G2 (moderate) geomagnetic storm during the afternoon and last into the early evening hours. With moonrise around 11 p.m. local time that night, we should have a good window of darkness for lights viewing.
A moderate storm usually means that skywatchers across the northern tier of states will see a northern lights display. That could mean anything from a sleepy arc 5-10° above the northern horizon to rays, arcs and pillars stretching and fluttering across the northern half of the sky. Most of the displays we’ve seen in the past year have been stoked by holes in the sun’s corona that allow high-speed solar winds to escape. This one, if it happens, points back to that flare-related burst, which produced a coronal mass ejection or CME.
At the equinoxes, cracks in Earth’s magnetic field are more likely to form. These allow the solar wind from CMEs and the like to find to get past the planet’s defenses and stream down into the atmosphere and excite atoms of oxygen and nitrogen to produce the northern lights.
“We’ve discovered that our magnetic shield is drafty, like a house with a window stuck open during a storm,” says Harald Frey, research physicist at the University of California, Berkeley. “The house deflects most of the storm, but the couch is ruined. Similarly, our magnetic shield takes the brunt of space storms, but some energy slips through its cracks, sometimes enough to cause problems with satellites, radio communication, and power systems.”
In other news, the International Space Station (ISS) is once again making passes during evening hours. With warmer weather now at hand, this is a happy time to be out at dusk to watch it go by. The space station looks like a bright star that rises in the western sky and travels east. If it’s not eclipsed by Earth’s shadow — when you’ll see it fade and disappear right before your eyes — a complete pass from west to east takes about 6 minutes.
Go outside a few minutes before a pass to get your eyes used to the dark and also to know in what direction to look. The ISS will first appear low in the west, southwest or northwestern sky (depending on the pass) and climb higher and higher into easy visibility.
The current round of passes continues through early April, so you’ll have lots of opportunities. You can find ISS pass times and maps showing its path at Heavens Above. Click the link, select your city and then tap the ISS link for a list of passes for the coming nights. Click on a date to see a map and timeline. Another option is NASA’s super-easy Spot the Station site for times. You can sign up there to get e-mail or text alerts whenever there’s a favorable pass over your city. Or you use an app like ISS Spotter for iPhone or ISS Detector for Android and customize your viewing.