Popular Astronomy

Share to Facebook Share to Twitter Stumble It More...

Solar Highlights for October 17


Solar Rotation Nos: 2195 to 2196

A sharp drop in activity from last month. Overall, a very quiet month until the end of October when activity picked up slightly. We saw two old sunspot groups reappear twice more and the sky went a strange colour (not because of the sunspots)!

Here are the solar highlights of October 2017 together with a selection of images.


1st to 8th October
As the month began, we still had sunspots AR2681 (a southern hemisphere sunspot at latitude S14°); AR2682 (formerly AR2673, at S11°) and AR2683 (formerly AR2674, at N13°) crossing the disc of the Sun. None of these were particularly active during their second transit. AR2681 disappeared over the west limb on the 3rd, AR2682 and AR2683 followed on the 8th leaving behind a blank solar disc.

9th to 21st October
Apart from AR2684, a small Bxo type sunspot, which briefly appeared at N11° on the 16th the rest of the time the Sun was devoid of sunspots between the 9th and 21st. Unconnected was the strange weather phenomenon of the orange-red Sun seen across large parts of the UK on the 16th. Both Sun and daylight sky were a strange copper-hue for several hours. The cause, according to meteorologists, was fine dust particles swept-up from the Sahara Desert by Hurricane Ophelia, which was near the UK in mid-October.

22nd to 31st October
By the 22nd we saw AR2685 emerge from the east solar limb. This small Hax type sunspot at S11°, was formerly AR2682 (and AR2673) seen earlier in the month, making another trip across the disc. By the 24th AR2686 had also come over the east limb. This was AR2683 (and AR2674) but by now a small type Hax sunspot. These much diminished sunspots were seen to cross the Central Meridian of the Sun around the 28th and nearing the west limb by month-end.
SPA Sunspot Mean Daily Frequency (MDF): 0.93. (was 2.43).
SPA Relative Sunspot Number: 10.88 (was 34.45).

Solar Prominences, Plage, Filaments and Flares

Some beautiful prominences were seen this month.

1st to 6th October
A very long snake-like filament was on the 2nd near AR2682 as it moved away from the Central Meridian and towards the west limb. Meanwhile on the south limb was a broad tree-like prominence. As AR2682 and AR2683 approached the west limb, numerous bright areas of plage were also seen along with some small prominences. 

7th to 20th October
Most of this period there was not much in the way of filaments and plage because of the lack of sunspots but there were several prominences.  Notably, a hedgerow prominence on the north west limb on the 8th, a tall tree-like prominence on the west limb on the 16th, and on the solar disc that same day, a long straight filament. This filament developed in intensity and had a distinct bow-shape middle by the 18th. It was still visible by the 20th but by then a magnificent hedgerow prominence had appeared on the east limb.

21st to 31st October
With the return of sunspots in the form of AR2685 (was AR2673), we saw a few more filaments and area of plage on the solar disc. By the 25th AR2686 had appeared and so too had an impressive hedgerow prominence on the east limb! By the 27th there were several (smaller) prominences around the solar limb and plage and filament activity around AR2685 and AR2686 as they crossed from east to west over the Central Meridian of the Sun. The situation was little changed as the close of the month.

No flares reported.

SPA Prominence Mean Daily Frequency (MDF): 3.32 (was 3.23).

Well done to Brian Gordon-States, who observed 28 days and to Jonathan Shanklin who achieved 21 days observed.

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 and Bob Steele.

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

Geoff Elston


Added by: