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Solar Highlights for August 15

Solar Rotation Nos: 2166 to 2168

Fairly low sunspot activity for much of the time but this month but we also saw the appearance of two sunspot groups large enough to be visible to the protected unaided eye.

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

A quiet start to the month with sunspots AR2390 nearing the (W)est limb and AR2393 and 2394 just moving away from the (E)ast limb. There was little change over the following days other than the daily shift of the sunspots westwards and the passage of AR2390 over the limb on the 4th.

On the 5th AR2396 was still near the E limb and was developing-up rapidly. So much so, that by the 6th it had grown substantially in size. As it approached the (C)entral (M)eridian around the 7th and 8th, it was becoming visible to the protected naked eye. AR2396 had grown again by the 8th and was seen with the protected naked eye up from then until the 10th. Strangely, for a substantial and complex sunspot such as this, it produced no major solar flares. Even as it went over the W limb around the 16th AR2396 remained quiet in terms of solar flares during its passage across the Sun’s disk.

With AR2396 now gone, this left AR2400 and AR2401 on the solar disk. Both were fairly small sunspots but AR2401 was flare active for a short while. We then went into a very quiet phase, with only one or two sunspots visible, and this situation lasted from the 16th until the 19th when AR2403 appeared over the E limb. This was another rapidly-developing sunspot group and was visible to the protected naked eye around the 21st. By the 23rd /24th as AR2403 crossed the CM it had changed from a cluster of smallish sunspots into a substantially long sunspot group with clear leader/follower spots structure. However, it had become clear the whole group was starting to decay by the 26th but despite this, it was still quite extensive as it went over the W limb on the 30th. This left an almost blank solar disk as the month ended.

SPA Sunspot Mean Daily Frequency (MDF): 2.68  
SPA Relative Sunspot Number: 39.78


There was plenty of prominence activity on the 1st in the form of a tall and complex group of prominences along the E limb (only a short distance away from AR2394) and part of the prominence became detached later that day. A number of low-lying prominences were seen along the E limb on the 4th as well as a long dark filament lying along the southern polar region.

The 6th saw a broad mound-like prominence on the E limb that was clearly seen extending on to the disk as a filament. On the 7th we had prominences along the limb, especially a tall curved prominence on the E limb that continued on to the disk as a filament, and a low hedgerow-type prominence along the NW limb with a detached prominence nearby. AR2394 and AR2396 showed plages around them and a broad curved filament near another tall sloping prominence on the NE limb. A beautiful tall curved prominence was seen on the SE limb on the 8th as was a hedgerow-type prominence along the N limb.  

By the 17th we had not much in the way of sunspot activity but plenty to see in H-alpha in the form of a two tall spike-like prominences and a smoke-stake prominence along the W limb.

On the 20th, as AR2403 was starting its passage across the solar disk we saw prominence activity along the E limb, in particular was a tree-like structure not far from AR2403. The 23rd showed lots of plage activity around AR2403 as well as some isolated plage activity near the SE limb. From the 24th to the 28th there was a great deal of plage activity around AR2403 and filament activity across the solar disk. Prominences were again showing up on the SE limb, on the 26th with another hedgerow-type, and on the 28th with three tree-like prominences on the E limb.

The 29th was somewhat unusual in that the Sun was nearly devoid of sunspots but in H-alpha we saw numerous filaments and a lovely prominence display along the SE limb. This situation continued as we reached the end of August.
SPA Prominence Mean Daily Frequency (MDF): 5.14 
6     1145UT    Flare at preceding limb
25   0800UT    Flare with Active Region (AR)
25   0900UT    Flare gone
28   0820UT    Flare with Active Region (AR)
28   0850UT    Flare still there
28   0045UT    Flare gone
All the above flares were observed by Alan Heath.

Well done to Brian Gordon-States who observed the Sun on 28 days in August and to Alan Heath and Jonathan Shanklin who observed on 26 and 25 days respectively.

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, Santanu Basu, Mark Beveridge, Carl Bowron, Paul Brierley, John Chapman-Smith, Mick Jenkins, Ian Lee, Cliff Meredith and Julia Wilkinson.

Welcome to Santanu Basu, who lives in Kolkata, West Bengal, India. Santanu has recently provided some very good whole-disk drawings of the Sun.

Geoff Elston

Solar Section Director

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