Solar Rotation Numbers: 2205 – 2206
No sunspots were seen this month. Why is this, and how can there be no visible sunspots at all? First, we are near to, or at, Sunspot Minimum. This is when sunspots are traditionally absent. This is not to say we will get no sunspots at all in this phase, but they will mostly be small and only last a few days at most (this is something we have seen a lot of recently). There may well be the occasional sunspot that ‘bucks the trend’ so it pays to keep looking so as not to get caught-out. Gradually, new Sunspot Cycle sunspots will appear at the higher solar latitudes and will slowly, in time, take the place of the old Cycle sunspots. Secondly, there are other regions of the Sun, the Chromosphere and the Corona, are two examples, that are still active despite the lack of sunspots. The Corona is only visible either naturally during a total solar eclipse or using specialist equipment. However, modern technology has given us the Hydrogen-alpha (sometimes called the “Ha” or “H-alpha”) filter and this allows us to see some of the Chromosphere.
Here is a summary together with a selection of images made by our observers in July 2018.
No sunspots were seen throughout July. Indicating we are very close to, or at, Sunspot Minimum.
SPA Sunspot Mean Daily Frequency (MDF): 0.00 (was 0.81)
SPA Relative Sunspot Number: 0.00 (was 13.82)
Solar Prominences, Plage, Filaments and Flares
For those with H-alpha filters, there was more to see than in white light. While there were no sunspots, there were some varied and attractive prominences and some sizable filaments.
The 3rd saw several prominences on the solar limb, the largest being on the on the north limb.
A highly filamentary prominence was imaged on the north limb by Carl Bowron on the 5th.
The images for the 7th and 8th show two prominences on the west and south limb as they developed from one day to the next.
A filaprom (the combination of a dark “filament” usually seen on the disc and a bright “prominence” normally seen along the edge of the Sun) was seen lying across the south solar limb on the 9th. As the Sun rotated, and the prominence came more into view, it became much taller and impressive by the 10th.
Ian Lee reported witnessing the development of a bright active prominence on the south east limb on the 12th. He saw the prominence slowly change appearance while watching it over some 70 minutes.
Throughout the month, while several patches of bright plage appeared on the Sun’s disc they never developed any sunspots.
The was the possible sighting of a very faint pore in H-a light by Carl Bowron on the 14th. This tiny sunspot would not have been seen in white light.
By the last week of July there were several isolated filaments here and there and a diverse number of prominences had also appeared especially on the 30th.
No solar flares were reported.
SPA Prominence Mean Daily Frequency (MDF): 2.64 (was 1.21)
Well done to Michael Fullerton who observed every day in July! Brian Gordon-States and Bob Steele were not far behind on 30 days and 28 days respectively.
Detailed count records of Active Regions and Relative Sunspot Numbers came from: Michael Fullerton, Brian Gordon-States, Alan Heath, Mick Jenkins, Ian Lee, Jonathan Shanklin and Bob Steele.
Images and drawings were supplied by: Carl Bowron, Paul Brierley, Mick Jenkins, Ian Lee and Cliff Meredith.