Solar Highlights for October

Solar Rotation Nos: 2208 to 2209

Very quiet, with a few very small sunspots appearing at the start and middle of the month but the Sun was spotless on most days.

According to Spaceweather.com, scientists have recorded a cooling of the top of the Earth’s atmosphere in relation to the low level of solar activity that we are seeing on the Sun. It seems that through research they have discovered that when the Sun is active the thermosphere heats-up in response but during solar minimum it cools down too. There is a new space weather metric called the ‘Thermosphere Climate Index’.

Here are the solar highlights of October 2018 together with a selection of images.

Sunspots

1st to 5th
Active Region (AR) 2723 was just west of the solar Central Meridian (CM) only a few degrees south (latitude -08°) of the solar equator. As AR2723 headed westwards to wards the solar limb, it initially grew a little bit but it then went into decline on the 4th and disappeared on the 5th.

6th to 12th
The Sun was spotless.

13th to 18th
AR2724 a small Hrx type sunspot group appeared at latitude -08° around the 12th / 13th showing faculae around it, and this was joined by another small sunspot, AR2725, the following day. AR2725 was also at -08° and type Axx. AR2724 decayed so much that it vanished by the 16th, leaving just AR2725 only just visible. On the 17th both had gone but AR2725 briefly reappeared on the 18th before finally disappearing.

19th to 31st
The Sun was spotless.

SPA Sunspot Mean Daily Frequency (MDF): 0.15 (was 0.08).
SPA Relative Sunspot Number: 1.93 (was 1.15).

Solar Prominences, Plage, Filaments and Flares

In a similar trend mirroring the current low level of sunspot activity, prominence and filament activity were also reduced. The H-alpha features that were seen, were quite dim and weak looking. The only exceptions during the month were two hedgerow-type prominences seen on the solar west limb from the 9th to 19th and on the north limb of the Sun on the 18th.

2018 October 9 @ 0955UT Ha disc drawing made by Ian Lee.
2018 October 18 @ 0815UT. Ha disc drawing made by Ian Lee.
2018 October 10 @1322 UT Ha Prom. Image taken by Mark Beveridge.
2018 October 11 @0955UT Ha Prominence. Image taken by Carl Bowron.

Bright plage were seen around sunspot group AR2723. Bright plage were seen on the solar disc on the 15th (with some faint filaments mixed-in) but no sunspots were seen.

The last two days of October saw a resurgence of prominence activity around the limb.

2018 October 31 Ha Prominence. Image taken by John Fathers.

No solar flares were reported.

SPA Prominence Mean Daily Frequency (MDF): 2.99 (was 3.21).

Despite the low Sun at this time of year and frequently cloudy skies, well done to Brian Gordon-States, who observed 25 days in October, and to Jonathan Shanklin and Alan Heath who both reached 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, Jonathan Shanklin and Bob Steele.

Images and drawings were supplied by: Mark Beveridge, Carl Bowron, John Fathers, Mick Jenkins, Ian Lee and Cliff Meredith.

Geoff Elston

Director