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Solar Highlights for May 16


We saw a slight recovery in sunspot activity this month compared to the previous four months of this year where the trend was downwards. However, it is clear that since the end of 2014 we are on the downward slope heading for Cycle 24 Sunspot Minimum, which is expected around 2019 or possibly 2020.
Here are the highlights for May 2016 together with a selection of images from members of the SPA Solar Section.


The first half of May actually saw a small increase in sunspot numbers. At that time several small sunspots were seen across the solar disk. Most of these were north of the solar equator but a couple (AR2533 and AR2537) were on the southern hemisphere and they were seen to last up until the 3rd when they both simply disappeared.

It was on this largely quiet solar disk that we saw the return of AR2529. This came over the E limb on the 5th but it was now re-classified AR2542. What was noticed was that this sunspot was not as active as it had been on its last appearance in mid-April. Even so, it was now classed as sunspot type Cko and was situated just north of the solar equator.

Of course, what we were all really waiting for was the transit of Mercury across the Sun on the 9th. Despite cloud a lot of our members were able to observe it and recorded the transit. This was my second Mercury transit, having seen the previous one in 2004, I was fortunate to catch the first half of this year’s transit until thickening cloud and then rain arrived late afternoon to end my observing session. If you have not yet seen the images of the Mercury transit, then they can be found on this website under “Solar Section News” (

Thank you to everyone who provided images and drawings of the transit.

On the same day as the Mercury transit, with the number of sunspots falling away, we saw just one sunspot appear on the southern hemisphere, a small Bxo type spot near the centre of the solar disk, classified by NOAA as AR2543. By the 11th another small southern sunspot had appeared, classified as AR2545, and this made up a total of four sunspot groups visible on the disk at that time.

AR2544 had appeared on the 10th and mostly went unnoticed until the 15th by which time it had developed from a type Cro into a type Dso sunspot. It had arrived at the CM (Central Meridian) and was crackling with small solar flares. Despite this, little came of the activity and it seemed that AR2544 was in decline. This is something we have before where sunspots are magnetically complex and there is the prospect of solar flares but after a day or so decline sets in and little happens.

On the 16th AR2544 was joined by AR2546 just over the SE limb. This was a big but quiet sunspot that was visible to the protected naked eye particularly around sunset. As it neared the CM on the 20th the sunspot (now larger than the Earth) could be seen with ease and it was easy to follow the sunspot as it was carried westwards towards the SW limb, arriving there on the 28th. At that time AR2546 was classified as Hhx throughout the time it took to travel across the solar disk, not showing any development or decay in that period.

If you want to know more about the sunspot classification, see the guidance on our website at:

SPA Sunspot Mean Daily Frequency (MDF): 2.57 
SPA Relative Sunspot Number: 34.06


In the light of Hydrogen-alpha, there was, on some days, plenty to see either on the solar disk or around the limb. Where there were sunspots, they were nearly always accompanied by bright areas of plage and mostly small filaments.

In the first week the disk was particularly active with plage and filaments associated with AR2535, 2536 and 2539 as well as 2540, 2541 and 2542. There were also several fine prominences seen particularly on the NE limb in the same week.

By the second week while the disk was still active the limb was quiet with just one or two very small prominences on view. AR2542, 2543 and 2544 all had areas of bright plage around or near them. On the 15th we saw disk activity in the form of bright areas of plage around AR2542, 2543, 2544, 2545 and 2546 (the last one was a recent arrival over the SE limb), but while there was not much in the way of filaments, we did have some low-lying prominence activity dotted around the limb.

From mid-May onwards we saw slightly less plage activity than before despite the passage of the “big” sunspot AR2546 across the solar disk at that time. There were days when some nice but small prominences were visible (such as on the 20th and 21st, 23rd, 28th, and at the end of the month). Filaments were particularly noticeable on from the 22nd to the 24th and from the 27th up until the end of the month.

SPA Prominence Mean Daily Frequency (MDF): 4.43

Well done to Brian Gordon-States who observed the Sun on 29 days in May. Alan Heath and Ian Lee each observed on 25 days and Jonathan Shanklin was close behind on 24 days.

Detailed count records of Active Regions and Relative Sunspot Numbers came from: Brian Gordon-States, Michael Fullerton, Alan Heath, Mick Jenkins, Ian Lee, Lee Macdonald, Jonathan Shanklin.

Images and drawings were supplied by: Carl Bowron, John Chapman-Smith, Michael Fullerton, Mick Jenkins, Ian Lee, Cliff Meredith and Brian Woosnam.

Geoff Elston


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