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Solar Rotation Nos: 2184 to 2185
January was a month of two distinct halves. For much of the first half, the Sun appeared quiet. It was not until later in the month that the Sun’s activity picked up a little.
My thanks to Alan Heath who provided me with an analysis he had compiled of sunspot longitudes for 2016 based on co-ordinates supplied by NOAA and the BAA Solar Section. It revealed that in 2016 of the 148 Active Regions (AR) that appeared, around 3 times more were on the solar northern hemisphere than south of the solar equator (an imaginary line drawn around the Sun’s globe to divide it into two equal halves). Greatest sunspot activity appeared between 20 and 170 degrees longitude on the northern hemisphere; between 140 to 160 degrees longitude, and at 220 degrees and 340 degrees longitude on the southern hemisphere. Seems as if 2017 is continuing this trend as most of the recent sunspots we have seen have appeared on the northern hemisphere.
Here are the solar highlights of January 2017 together with a selection of images.
1st to 12th
Active Region (AR)2622 was seen near the west limb of the Sun but by the following day this small northern hemisphere sunspot had gone. High latitude aurorae were seen by those living near the Arctic Circle on the 1st. Sadly, aurora displays like this one do not come far enough southwards for us in the UK to be able to see them but they occur quite frequently. The 2nd and 3rd saw no sunspots. There was, however, a large solar coronal hole facing Earthwards on the 2nd and while we could not see this visually, the effects of it being there were felt a couple of days later when the solar wind brought another display of aurorae at high latitude. On the 4th another small sunspot was seen close to the west limb. AR2624 was on the southern hemisphere of the Sun but it did not last and had gone by the 5th. The Sun then remained spotless until the 12th.
13th to 20th
AR2625 (sunspot type Cso) and AR2626 (type Hsx) appeared over the east solar limb, both were just north of the solar equator. Unlike earlier in the month, both sunspots remained visible for several days. Another Earth-facing coronal hole on the 16th gave rise to more high latitude aurorae here on Earth on the 18th. Sunspot AR2625 slowly drifted 3 degrees’ southwards, eventually ending up on the solar equator by the 19th.
21st to 31st
By now AR2627 and AR2628 had also appeared and both looked like they could be solar flare active (though only minor C-class flares at best). AR2625 had gone by the 24th and AR2628 was unfortunately starting to decay. Over the next couple of days both AR2626 and AR2627 disappeared but there was another new sunspot, AR2629, of type Cao, near the east solar limb. On the last day of January AR2628 had gone from view but we had two small sunspots AR2630 and AR2631, the first on the northern hemisphere of the Sun but the second just south of the solar equator. There were two more coronal holes, one on the 24th and 30th and there was another auroral display at high latitude on the 27th.
SPA Sunspot Mean Daily Frequency (MDF): 1.26 (was 0.90).
SPA Relative Sunspot Number: 16.78 (was 14.40).
Solar Prominences, Plage, Filaments and Flares
1st to 15th
Several prominences were seen along the northeast and western limb on the 2nd and a fine hedgerow prominence on the southwest limb on the 4th and 5th. On the 14th there were again some fine prominences to be seen on the east and west solar limbs.
16th to 31st
With the appearance of AR2628 and AR2629 we not only had prominences to look at but some dark filaments and bright areas of plage on the solar disc as well. AR2628 was particularly interesting to watch in H-alpha light as on the 20th as the three images taken by Carl Bowron of this sunspot group showed over 20 minutes of imaging. Then from the around the 25th onwards we saw more intricately-shaped limb prominences.
I am indebted to Ian Lee, Carl Bowron, Cliff Meredith and Julia Wilkinson who despite the low winter Sun at this time of year and the challenging UK weather still managed to provide some truly excellent images of the H-alpha Sun this month.
SPA Prominence Mean Daily Frequency (MDF): 4.13 (was 3.67).
Well done to Brian Gordon-States who observed 23 days and to Julia Wilkinson and Jonathan Shanklin who observed a total of 20 days and 19 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, Jonathan Shanklin and Bob Steele.
Images and drawings were supplied by: Mark Beveridge, Carl Bowron, Mick Jenkins, Ian Lee, Cliff Meredith and Julia Wilkinson.
The 2017 SPA Convention will take place at the Institute of Astronomy, Cambridge on Saturday 1st April. As usual I will be there on the Solar Section stand. Hope to see you there!