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Solar Rotation Nos: 2171 to 2172
December was a quiet month overall with most of the activity taking place late in the month. Overall activity was on the low side but the average was very slightly up on last month (sunspot MDF for Nov was: 2.43 against Dec which was: 2.57). The combination of short days and the continual stormy weather from the Atlantic has reduced the number of observations received.
Here are the highlights for December 2015 together with a selection of images.
December started with all of the sunspot activity near the (W)est limb of the Sun. The most prominent at this time was (A)ctive (R)egion 2458, a type Cao sunspot on the 1st on the northern hemisphere.
By the 3rd the Sun was almost spotless.
It was not until the 4th that two new sunspots came over the (E)ast limb, designated AR2462 and AR2463 (both initially type Hax). Both were fairly active with minor solar flares but over the following couple of days the chance of flares declined and the Sun was again quiet. AR2464 and AR2465 had by then appeared over the E limb but both were small and fairly inactive.
Overnight between the 8th and 9th AR2466 appeared on the disk (type Cro on the 9th) and this too was at first active with minor solar flares but again the chance of flares fell away over the following days.
It took until the 13th for sunspot activity to pick up when AR2469 and AR2470 came over the E limb. AR2469 was type Dso, while AR2470 was type at first type Hsx. Both were at first thought to be fairly solar flare active but once again nothing came of it. There was some development when AR2470 grew to a type Eko sunspot on the 17th. A couple of days later, on the 19th, it had reached the (C)entral (M)eridian.
As we entered the week of Christmas, AR2469 began to disappear but AR2470 was still prominent. Another two sunspots had come over the E limb, AR2472 and AR2473. Both were classed type Dao and Dac respectively on the 23rd. They were far more active than we had become accustomed to of late and it did not take long for something to happen. AR2473 gave rise to an M-class solar flare on the 23rd increasing the likelihood of aurora in the following days. However, after the 23rd the group seem to settle down and while it was thought likely to generate more flares it did not do so. Just when it looked like we would be disappointed once again, AR2473 generated a slow but powerful M-class solar flare at 1249UT on the 28th (by then it had crossed the CM). After releasing the flare, the sunspot group began to dissolve away as it headed westwards towards the solar limb. By New Year’s Eve we almost back to a nearly blank solar disk.
If you want to know more about the sunspot classification, see http://www.popastro.com/solar/solarobserving/chapter.php?id_pag=358 on the SPA website (items 4 and 5).
SPA Sunspot Mean Daily Frequency (MDF): 2.57
SPA Relative Sunspot Number: 37.98
PROMINENCES, PLAGE, AND FILAMENTS
There were not many observations to go on this month due to the poor weather. From those sent in it looks like much of the activity in H-alpha was seen towards the latter part of December.
Julia Wilkinson imaged some lovely plage and filament activity on the 7th and 8th. While Ian Lee recorded a lovely hedgerow-type prominence on the E limb while plage and filaments were seen around sunspots AR2470, AR2473 and AR2474 on the 23rd.
The 27th and 29th were days when there were not only prominences around the limb but a lot of plage activity at the centre part of the solar disk and a couple of interesting dark filaments too.
SPA Prominence Mean Daily Frequency (MDF): 4.33
Thank you to Alan Heath for sending me his solar summary for 2015. It makes interesting reading. From the summary, January was the most active month for sunspots while August and September the least. Three naked eye sunspots were observed (in January, June and August). Blank solar disks were seen in April (2 days), August (2 days) and October (2 days). Alan has clocked-up at grand total of over 12,000 solar observations to date.
Well done to Brian Gordon-States and Alan Heath who both observed the Sun on 20 days each in December. Jonathan Shanklin was not far behind on 15 days.
Detailed count records of Active Regions and Relative Sunspot Numbers came from: Richard Bailey, Michael Fullerton, Brian Gordon-States, Alan Heath, Mick Jenkins, Ian Lee, Jonathan Shanklin and Julia Wilkinson.
Images and drawings were supplied by: Richard Bailey, Carl Bowron, Mick Jenkins, Ian Lee, Cliff Meredith, Peter Paice, Julia Wilkinson and Brian Woosnam.