These days I'm following groups AR3162, AR3163 and AR3166. At the beginning I had considered AR3162 and AR3163 as a single group, then measuring the extension with Helio Viewer it is 29.7°, so I reevaluated them as two groups. Have you also considered them as three groups?
Hi Maurizio -
If you look at this picture https://www.spaceweather.com/images2022/18dec22/hmi1898.gif and look at the alignment of the sunspots within each group, you can see that they really are pretty much parallel to the equator (which cuts horizontally across the picture). 3162 and 3163 are too well separated in longitude to be the same group, as you correctly surmised. You are also correct that it is not always obvious when they are coming over the limb (due to foreshortening - there is a mess today that I saw that I made a note to myself to look at over the next week as it gets closer to the center to determine how many groups it is) so you often change your mind when they get to the center of the disk and you can really see the extent in longitude. 3166 is definitely at a far different latitude than either 3162 or 3163 and has its own definitive bipolar-ish structure, so it is a well-formed separate group. So there are three separate groups there: 2 are too different in longitude, while the third is too different in latitude. 3160 and 3167 might confuse someone who was looking at them for the first time because they are closer to the limb (with more foreshortening) but again 3167 is a well-defined bipolar-ish group (and has the slight tilt towards to the equator in the leading spot due to Joy's Law).
- Kris Larsen
the number of…
the number of active regions (AR) is assigned by NOAA, after various solar observatories reported it. This numbering has been used since 1972. If an active region is very long-lived, it is given a different number with each rotation
excellent answer from David Svan
23 August 2022 at 3:07 pm #612067
I am not a member of the solar section, nor am I an expert on these matters. You may want to look here though:
I’ve seen reference to a formal naming system for sunspots. Where can this be found?
There is no naming or numbering system for sunspots. There is a system for numbering active regions, however. An active region can contain one or more spots. The National Oceanic and Atmospheric Administration (NOAA) numbers active regions consecutively as they are observed on the Sun. According to David Speich at NOAA, an active region must be observed by two observatories before it is given a number (a region may be numbered before its presence is confirmed by another observatory if a flare is observed to occur in it, however). The present numbering system started on January 5, 1972, and has been consecutive since then. An example of an active region “name” is “AR5128” (AR for Active Region) or “NOAA Region 5128”. Since we only see active regions when they are on the side of the Sun facing the Earth, and the Sun rotates approximately once every 27 days (the equator rotates faster than the poles), the same active region may be seen more than once (if it lasts long enough). In this case the region will be given a new number. Hence, a long-lived active region may get several numbers.
On June 14, 2002, active region number 10000 was reached. For practical, computational reasons, active region numbers continue to have only four digits. Therefore, the sequence of numbers is 9998, 9999, 0000, 0001, and so on. Active region number 10030, for example, is AR0030. This region will often simply be referred to as region number 30, with 10030 implied.
the provided weblink fails to open
must ask David