The most dominant feature on the Sun the past week has been quite a large, dark coronal hole at the bottom of the Sun (Nov. 30 – Dec. 4, 2014). Coronal hole are areas where the Sun’s magnetic field is open ended and where high-speed solar wind streams into space.
The area appears darker there because there is less material being imaged in this wavelength of extreme ultraviolet. At its widest point, the hole extends more than 50 times the size of Earth.
Not to worry! As many of you may know, a gigantic hole in the Sun’s atmosphere is not terribly unusual. But you have to admit: This one is pretty dramatic.
The image above is actually a composite of three acquired by the Solar Dynamics Observatory spacecraft this past week. Each color highlights a different part of the Sun’s extended outer atmosphere — the corona. The coronal hole is that big, dark-blue splotch at the bottom.
Coronal holes are most common when the 11-year solar cycle is in a declining phase. Right now, the Sun is actually near the maximum of the cycle.
That said, this peak has been pretty weak compared to others since solar cycles have been observed in detail starting in 1755.
I’m hoping that the Sun continues to be feisty for a bit longer — at least until mid January, when I’ll be in Norway for the annual Arctic Frontiers conference. Solar tantrums (also known as coronal mass ejections) tend to produce great displays of the aurora borealis. Last winter I got to witness an awesome display in Norway in the form of a Viking ship!
