Phoenix
posted: January 27, 2016

The phoenix is a large mythological bird with red and gold plumage, which has the most startling ability to regenerate itself. Indeed, when its body becomes old, it disintegrates in a fiery flash, soon to rise from its ashes as a newborn chick. Recently, it was most impressively featured in the Harry Potter movies as Professor Dumbledore's pet.

On 10 January, a small sunspot group appeared near the northeast limb at about 10 degrees in latitude and about 30 degrees to the west of two mature sunspot groups NOAA 2483 and NOAA 2480. This tiny region was numbered NOAA 2484 and, as small sunspot groups often do, it quickly faded out of view. The SDO/HMI images underneath show a full disk view of the Sun (left) and a zoom (right) late on 10 January resp. at 21:22UT and 20:39UT, and again on 15 January around 20:00UT. NOAA 2484 consists really only of those two puny dots 45 to 60 degrees to the west of the central meridian (top images), whereas it is spotless on the bottom images.



The images on the right are not only close-ups of the area around NOAA 2484, they actually are "fixed" over the location of the active region. This can be done with the remarkable "Track" feature of the JHelioviewer software. Simply put the feature of interest in the middle of the field of view, and the software then recalculates the position of the entire solar surface of the other images to fit in the original frame. It's a bit comparable to geostationary satellites that hover over a fixed point on Earth by moving with the Earth's rotation. In JHelioviewer, one can create the same impression by recalculating the position from the other images. One can see this tracking feature in action in the images above where the sunspot groups NOAA 2480 and NOAA 2483 stay at their fixed location in the right images, even though 5 days have elapsed and the "normal" images show how they have moved over the solar disk (left images).


This feature is obviously of great help in our story. Indeed, after the area was spotless for nearly 9 days, it started to show some small sunspots on 19 January that grew into a compact and dynamic sunspot region the next day. Was this emerging magnetic flux a regeneration of the old, disintegrated ashes from active region NOAA 2484, or was it a genuine new sunspot group at another location? JHelioviewer leaves no doubt as far as the location of the new group concerns: It emerged right at the same location as the puny sunspots that appeared on 10 January. This can be seen in the image above right, with the spots at 10 degrees latitude and 45 to 60 degrees to the west of the "10 January" central meridian. The strange, inward curve on the right is nothing else but the projected solar west limb. NOAA 2480 and 2483 have already rounded that limb, and obviously do not show anymore in this image. An annotated movie can be found here. NOAA 2484 would go on to produce a C1 flare on 20 January and another one on 21 January. As Professor Dumbledore might have said: "Fascinating features, those sunspot groups!"