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Solar Highlights for September 16


Solar Rotation Nos: 2180 to 2181

Very low levels of sunspot activity. Most sunspots were on the northern hemisphere.

Here are the highlights for September 2016 together with a selection of images from members of the SPA Solar Section.


1st to 10th September:
At the beginning of the month sunspot group AR2585 (sunspot type Eai on the 2nd) was close to the E (eastern) limb and AR2583 that appeared in late August was by now almost over the W (western) limb. AR2585 crossed the CM (central meridian) around the 6th and while it was quite large, it was also inactive and did not appear to change much from day to day until it finally disappeared on the 14th. There was, however, a light bridge seen across the main sunspot on the 8th.

On the 2nd there was an annular eclipse of the Sun visible mostly from Africa. This is where the Moon does not quite eclipse the Sun completely but leaves a bright ring (an “annulus”). Despite the low sunspot activity there were several high-latitude display of aurora caused by coronal holes in the Sun’s outer atmosphere and a gusty solar wind buffeting the Earth. While we cannot see coronal holes or the solar wind we can sometimes see their effect on the Earth’s atmosphere in the form of the northern (or southern) lights.

11th to 15th September:
Two new sunspots (AR2589 and AR2591) appeared wither side of the CM on the 11th. They were both small and inactive (sunspot types: Dai and Cro on the 11th).

16th to 23rd September:
Another small sunspot, AR2592 (type: Bxo) appeared on the E limb by the 16th and was joined by AR2593 and AR2594 (types: Cri and Cro) on the 19th. This was then joined by another Bxo type sunspot on the 20th and this was AR2595. 

24th to 30th September:
In the last week of the month we saw AR2597 appear near the centre of the Sun’s disk. Initially, the type Cao sunspot on the southern hemisphere, looked to be active and might generate some solar flares. However, it was not to be, and by the 26th AR2597 had already started to fade away. By the 30th several of our members saw a spotless Sun.    

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

SPA Sunspot Mean Daily Frequency (MDF): 1.92 (was 2.70)
SPA Relative Sunspot Number: 28.44 (was 36.31)


Some long dark filaments were seen this month.

From the 1st to the 10th there was a long-lived filament seen just to the north of sunspot AR2585. On the 20th a curved (almost “S” shaped) filament was seen near the SE limb. This was last seen on the 23rd when it began to fade. On the last day of the month another two filaments were see, one near the E limb and the other very close to the SW limb.

Most of the prominences seen were either small or low-lying in nature. There were a few exceptions however. The 10th saw a hedgerow type prominence on the W limb (near AR2585) that seemed to be part of the long-lived filament mentioned earlier. Such features are often termed: “filaproms”. There was a lovely arch-type prominence on the N limb on the 12th and on the 30th when despite the lack of sunspots there was plenty to see around the solar limb including a tall Shard-like prominence on the N limb.

SPA Prominence Mean Daily Frequency (MDF): 4.76 (was 6.37)

Well done to Brian Gordon-States who observed on 27 days in September. Jonathan Shanklin and Alan Heath were not far behind on 26 and 25 days respectively.

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

Images and drawings were supplied by: Carl Bowron, Mick Jenkins, Ian Lee, Cliff Meredith and Brian Woosnam.

Geoff Elston


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