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Solar Highlights for December 16

Solar Rotation Nos: 2183 to 2184

We sometimes think that the Sun’s activity is all about the sunspots that we see on the solar disk, but this month was a clear demonstration that this is not always so. While there have hardly been any sunspots to see on the disk, there have been numerous aurora-filled night skies within the Arctic Circle. Why is this? The answer is that whether there are sunspots, or not, the Solar Wind is always reaching out from the Sun into planetary space and influences the planets in the Solar System. Unsurprisingly, this includes the Earth. Sometimes, it is a gentle flow but gaps in the solar Corona (typically called ‘Coronal Holes’) can lead a virtual howling gale. It is the blast of charged particles from the Sun, within the Solar Wind, that causes the Earth’s magnetic field to deform and react. As the particles are funnelled down the magnetic poles of the Earth, the northern (and southern) lights are the result. This happened at three times in December (8th to the 10th, 21st to 26th, and the 31st) but you had to be within or at least near the Arctic Circle to witness these spectacular displays.

Here are the solar highlights of December 2016 together with a selection of images.

Sunspots

A very low level of sunspot activity persisted throughout December. In terms of the sunspot activity graph we are at a similar level last seen in 2010. This is not unexpected as we are heading towards Sunspot Minimum (expected around 2020) within the current Sunspot Cycle No. 24.

1st to 10th December
At the start of the month sunspots Active Region (‘AR’)2612, AR2614 and AR2615 were clearly visible across the solar disk. Of these, AR2615 (the only sunspot on view that was south of the solar equator) was the most active and was thought it might produce solar flares of low intensity but this did not come about. AR2616 appeared on the 3rd and while it lasted several days it soon disappeared over the West limb.

11th to 18th December
The 11th saw no sunspots at all.  Two very small sunspots appeared (AR2617 and AR2618) on the 12th and 13th both close to the West limb but by the 17th and the 18th the Sun was again spotless.

19th to 31st December
AR2619 appeared as a tiny sunspot (called a ‘pore’) but it was hard to see and easily overlooked. The second southern hemisphere sunspot of the month (AR2620) appeared on the 21st. This had gone by the 24th leaving the disk blank. AR2621 then came into view near the West limb of the Sun, but another blank solar disk was seen on the 30th. On the last day of 2016 only one small sunspot was visible and this was AR2622 and it too was near the West limb.

SPA Sunspot Mean Daily Frequency (MDF): 0.90 (was 1.31).
SPA Relative Sunspot Number: 14.40 (was 17.59).

Solar Prominences, Plage, Filaments and Flares

Poor weather impacted on the number of observations received this month but there were some interesting prominences particularly on the 3rd, 4th, 17th, 22nd, 26th and 29th. There were also several filaments and plages on the disk especially on the 3rd and 4th (associated with AR 2615).

SPA Prominence Mean Daily Frequency (MDF): 3.67 (was 3.60).

Well done to Brian Gordon-States who observed 19 days and to Jonathan Shanklin not far behind at 13 days.

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

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

Geoff Elston

Director

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