(Updated at 12:15 a.m. CST March 11: Kp index still stuck at 2. No aurora visible in Duluth, Minn. yet. The moon looks cool with its “companions” Saturn and Spica. Look for bright, red-colored Mars high up due south, the bright red star Arcturus in the east and twinkling Vega in the northeast.)
Are you ready for tonight? According to the NOAA space weather forecast, we’re still expecting a good solar storm to roll through late tonight with the potential for auroras. Arrival time is expected around 1 a.m. CST plus or minus 7 hours. Watch for the lights anytime from dusk through tomorrow morning by checking the northern sky periodically for any activity. If you see moving rays and bright greenish arcs of light, bundle up and plan to spend a little time under the cosmos. The same sunspot group responsible for tonight’s expected storm unleashed yet another large flare (M8-class) today around 11:30 CST. Expect that coronal mass ejection from that one to arrive at Earth midday Monday March 12.
The northern U.S., Canada and northern Europe are the best locations to see auroras, but if the storm is active enough, the auroral oval will expand southward toward the central states like Illinois, Kentucky and Colorado. Very strong shocks to Earth’s magnetosphere can even bring the dancing lights as far south as Arizona. I’ll stay in touch via the blog this evening, but don’t be surprised if I’m missing-in-action for a while; it just means I’m out under the stars. Clear skies are forecast for northern Minnesota tonight.
I know I’m repeating myself, but the best guides to whether the northern lights are likely to light up your life are the Kp index and the extent of the auroral oval. If the index equals 4, there’s a good chance of seeing an aurora in the northern U.S. and Canada. If it goes up to 6, auroras will likely be visible farther south into Wisconsin, Illinois, New York and the Dakotas.
The waning gibbous moon rises around 9:30-10 p.m. tonight, so it won’t dilute those pale auroral rays to the degree it did Thursday night. Still, there’s no need to turn your back on our shiny satellite. It forms a charming little triangle with the planet Saturn and Spica in Virgo this evening. Take a few minutes to look at Saturn, 825 million miles away, through a small telescope. Those rings are the equal of any auroral display in my opinion. Spica is a very close pair of extremely luminous blue-white stars with a combined light 1900 times brighter than the sun.
Don’t forget that tonight-tomorrow morning we switch over to daylight-saving time (DST) in the U.S. Instead of the sky turning dark around 7-7:30 p.m. as it will tonight, it will happen at 8-8:30 p.m. on Sunday. Lots of people look forward to this “extra” daylight in the evening hours. Conversely, we lose an hour of daylight in the morning and find ourselves waking up in a slightly darker world Sunday morning.
The hour shift also causes a shift in the stars. With DST in effect, the positions of the stars at 8 p.m. tonight will be the equivalent of their positions tomorrow night at 9 p.m. Think about a second and it makes sense. 9 p.m tomorrow is really the same time as 8 p.m. tonight, when we ignore the artifice of daylight saving time.
Another way to see it is shown in the illustration above. At 8 o’clock tonight, Sirius will be west of due south and Orion off to the right and out of the slice of sky I selected. Tomorrow at the same time, Sirius will not have reached its due south point at 8 p.m. on your clock. Instead it’s still off to the east, but Orion is now back in the picture.
That extra hour of daylight time has the effect of retarding the movement of the constellations by one hour. So you’ll have to stay up an hour later to see the spring stars in the east. This might make some of you sad, but if for those who still cling to the winter stars, DST is good news.