Popular Astronomy

Share to Facebook Share to Twitter Stumble It More...

Solar Highlights for October 15

Solar Rotation Nos: 2169 to 2170

We are now definitely on the downward slope of the current Sunspot Cycle. Looking back at the observational data provided by observers in the SPA Solar Section, there was a first peak in sunspot activity in late 2011 and then we saw a second peak in early 2014 that continued more or less until the end of 2014. It then fell away sharply as we progressed through 2015. You can see a graph showing this activity on the SPA website at: http://www.popastro.com/solar/reference/downloads/index.php

Here are the highlights for October 2015 together with a small selection of images.


October was a mostly quiet month with mainly small sunspots to be seen on most days. The most active days were towards the end of the month.

As we started the month (A)ctive (R)egion 2422 was nearing the (W)est limb. This group was on the southern hemisphere and at that time of sunspot type Fkc but was beginning to decay. Nearer the disk centre was AR2427 a much smaller sunspot group. Over the next few days AR2427 looked like it might produce some solar flares but by the 7th as it, and all of remaining sunspot activity went over the (W)est we saw only small spots and pores.

Some very small spots appeared on the 12th in the form of AR2430, AR2431 and AR2432, quite near the (E)ast limb, and the sudden appearance of some very small sunspots designated AR2433 quite close to the W limb on the 13th but overall the Sun looked quiet.

It wasn’t until the 15th that activity picked up a little. By this time AR2431 and AR2432 joined by AR2434 a Cai type sunspot near the SE limb. This showed development over the next few days so that by the time it had reached the (C)entral (M)eridian it was type Dac and had the potential to produce flares. In addition, on the 18th AR2436, a pair of sunspots and type Dai, had come over the E limb along with AR2437. It was around this time that we saw the highest number of sunspots for the whole of October. AR2436 too, started to develop over the next few days becoming quite substantial as it headed westwards towards the CM. It was AR2434 on the 22nd, as it lying between the CM and the W limb, which suddenly produced a long-duration M-class flare. Most flares last maybe 15-30 minutes, some a bit longer but rarely that long. By the 23rd AR2436 was at the CM and it was thought likely to produce solar flares but this did not happen.

By the 29th there were only very small spots visible over the solar disk. However, over the E limb had come AR2443/AR2444. This was minor flare active and developing quickly so that it had grown in size by the 31st and looked promising.

SPA Sunspot Mean Daily Frequency (MDF): 2.75  
SPA Relative Sunspot Number: 39.94

The poor weather in the UK and the shorter days of Autumn took their toll in the number of observations we made. From those received, it seems there were some interesting prominences, most of them low-lying around the solar limb, while on the disk there was plage and filament activity associated with the sunspots that came and went throughout the month.

On the 1st we saw plage activity around AR2422 and AR2427 and while there were some small low prominences around the limb (including one that had an inverted ‘J’ shape) that was it. By the 4th the Sun was a bit more active with some tree-like prominences along the SE and NW limbs and with some fairly lengthy filaments across the disk. I’m grateful to Mark Beveridge who provided by email two short MP4 videos showing the flow of ionised gas along the line of magnetic force within the prominence on the W limb.   

Later on the 8th there was a large arch-type prominence on the W limb (possibly associated with AR2427) and smaller prominences on the SE and NE limbs. By the following day (the 9th) a large smoke-stack prominence had appeared on the W limb with part of the prominence seen detached from the limb.

The 12th was active with prominences along the SE and NW limbs and plage and filaments on the disk, especially around AR2430 and AR2431. By next day, all that was left of the prominences was a crowd of very low-lying prominences along the SE limb but plenty of plage and filament activity across the solar disk. It was a similar situation on the 14th but by the 15th, while nearly all prominence activity had declined, plage and filaments associated with sunspots AR2431, AR2432 and AR2434 had taken centre-stage.

By the 18th, AR2436 had appeared and the SE and NW limbs once again had prominence activity along them. There was plenty of plage activity around AR2434, AR2436 and AR2437 (just over the SE limb a few days earlier) but not much in the way of prominences on the 20th. By the time AR2436 was nearing the NW limb on the 26th (with AR2437 lying just to the south) there was a lot of plage activity around it. The southern hemisphere was particularly active with filaments on the 27th. 

On the 29th no filaments were seen but there was plage activity around AR2436 (at the NW limb) and AR2443 (over the E limb about a day and looked to be an active sunspot group) and that was about it. There was, however, a fairly impressive arch-type prominence sitting on the SW limb, the first we had seen for some days.

SPA Prominence Mean Daily Frequency (MDF): 5.21   
Well done to Alan Heath who observed the Sun on 23 days in October, Brian Gordon-States was close behind on 22 days and Jonathan Shanklin 21 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 and the Director.

Images and drawings were supplied by: Richard Bailey, Santanu Basu, Mark Beveridge, Carl Bowron, Mick Jenkins, Ian Lee, Cliff Meredith, Peter Paice and Julia Wilkinson.

Geoff Elston

Added by: