“The Sky This Week” appears regularly. It is written by Ian Clarke, Director of the Hatter Planetarium at Gettysburg College. The planetarium offers regular educational presentations about the stars and the skies; there’s something for early elementary through adults. Public shows have concluded for the academic year, but we are still accepting field trip requests for the summer!
In this post, I am going to look back to the night of April 23-24 when the northern lights were seen in the local area and, in fact, as far south as Virginia. Full disclosure: I missed them. I was aware of the potential activity from online reports. I scanned the sky before bed and saw nothing and thus missed the show. So what are the northern lights, and how can you know when to look for them? The northern (and southern) lights are caused by charged particles from the sun (called the solar wind) hitting and interacting with the magnetic field of the earth. When the solar wind increases, such as after a Coronal Mass Ejection (CME), the intensity and visibility of the aurora increase. A sudden increase in activity is called a geomagnetic storm, and these are rated on a system called the Planetary K Index, or KP Index, from 0 to 9. Only strong storms can be seen in the continental US. For example, a KP=7 may be seen in New England. The storm in April peaked at KP=8. Such storms are uncommon. I personally have seen the northern lights only twice, once around 1980 and once in the early 00s. If you want to keep track of “space weather,” including the aurora forecast, NASA’s Space Weather Prediction Center is great.
Ian Clarke is the director of the Hatter Planetarium at Gettysburg College. In addition he has taught introductory astronomy labs and first-year writing there for over 30 years (not necessarily all at the same time). He was educated at Biglerville High School, the University of Virginia, and the University of Iowa. He lives in Gettysburg.