Solar Rotation Nos: 2242 to 2243
A substantial rise in sunspot activity from the middle of the month onwards.
Here are the solar highlights for April 2021 together with a selection of images.
Sunspots
The Sun was spotless from the 1st to the 3rd.
AR2813 suddenly appeared on the solar disc on the 4th between the Central Meridian (CM) and the northwest limb at latitude +21°, type Axx. It began to decay on the 5th and went over the solar limb by the 7th.
The Sun was again spotless from the 8th to the 12th.
AR2814 popped into view on the 13th just east of the CM at -22° and it was clear that this type Bxo group was not only developing but was also flare active. It developed to type Cro, of 7 spots, on the 15th and then type Dro, of 12 spots, by the 16th. It started to decay around the 17th and west over the west limb by the 19th.
AR2815 appeared west of the CM at -21° on the 17th but only lasted a day before disappearing on the 18th.
AR2816 also appeared on the 17th but over at the southeast limb at -24° and was seen to develop into type Cao by the following day. By the 23rd it was solar flare active.
AR2817 was seen near the northwest limb on the 20th at +18°. This was initially type Bxo but developed to type Dao by the 22nd and was by then was solar flare active with multiple C-class flares. It disappeared after the 23rd.
AR2818 came into view near the southeast limb on the 21st at -17°, type Hsx, and was visible until the end of April.
AR2819 came into view near the northwest limb on the 25th at +24° but only lasted a day and had gone by the 26th.
AR2820 also appeared on the 25th at -22°, near to AR2818, and remained visible up to the end of the month.
AR2821 popped-up near AR2818 and AR2820 on the 26th at -22°, type Cro, and remained visible up to the end of April.
At this point as we approached the end of the month, AR2818, AR2820 and AR2821 were all seen close to each other on the solar disc forming a group of small sunspots resembling, to my mind, a loose ‘W’ shape. They all seemed to decay after the 29th as they approached the southwest limb.
SPA Sunspot Mean Daily Frequency: 1.33 (was 0.73)
Relative Sunspot Number: 18.57 (was 9.99)
Solar Prominences, Plage, Filaments and Flares
There was plenty to see this month.
There were numerous small prominences throughout the month. In addition there were also detached cloud-like prominences, seen on the 5th, 10th, 11th, 19th and 29th.
A spectacular active prominence appeared on the east limb on the 12th, seen to change shape in real time, something that is exciting to witness if you are lucky to see it happen. It had gone by the following day.
Filaments were seen most days. A line of short dark filaments was seen with a filaprom lying along the southern hemisphere on the 3rd. A long dark filament was seen in the northeast on the 9th.
A filaprom was seen on the southeast limb on the 19th. This developed into a long broad filament over the following couple of days so that by the 21st it was seen near an impressive hedgerow type prominence on the southeast limb. On the 22nd both showed great detail particularly as the prominence had developed into a somewhat fragmented arch-type prominence. The filament remained visible until the 26th.
Plage were seen developing around AR2814, quite extensively around AR2816, AR2817 and AR2818. Some areas of bright plage were seen on their own too.
Extensive plage were seen clustered around AR2818, AR2820 and AR2821 on the 26th right up until the end of April.
SPA Prominence Mean Daily Frequency: 3.52 (was 3.81)
Congratulations to Alan Heath who observed every day in April, also to Brian Gordon-States on 29 days and to Ian Lee and Jonathan Shanklin who both achieved 27 days.
Detailed count records of Active Regions and Relative Sunspot Numbers came from: Simon Brown, John Chapman-Smith, Michael Fullerton, Brian Gordon-States, Mick Jenkins, Ian Lee, Lee Macdonald, Jonathan Shanklin, Brendan Shaw and Bob Steele.
Images and drawings were supplied by: Carl Bowron, Mark Beveridge, John Fathers, Mick Jenkins, Ian Lee, Cliff Meredith, Ian Morison and Keith Moseley.
Geoff Elston