The AAVSO Solar section and AAVSO headquarters are hosting a special guest this week and next, Leif Svalgaard (at center in this photo) of Stanford University/Solar Dynamics Observatory. Leif is here to digitize sunspot records from the original notebooks of AAVSO member Herbert A. Luft (1908-1988), housed in the Thomas R. and Anna Fay Williams Archives.
A year ago, our Solar section leader Rodney Howe started telling us about an international workshop series that both he and fellow solar observer Susan Oatney were attending. The SSN (sunspot number) workshop, established by Ed Cliver (Air Force Research Laboratory), Frédéric Clette (Royal Obs. of Belgium), and Leif, was designed to reconcile the numerous historical records of sunspot counts. As it turns out, records exist for sunspot counts going back to the 17th century at least, and those records can in principle provide us with a record of solar activity for several centuries. However, some parts of that record were likely corrupted over time by changes in observing procedure and the use of different averaging and weighting factors. (You can read former Solar Division Chair Carl Feehrer's article "Dances With Wolfs: A Short History of Sunspot Indices" on this same topic.) This is problematic, since it is difficult to understand long-term changes in the Sun without having a historical record that is self-consistent throughout. The scientific questions surrounding the sunspot record extend well beyond the Sun itself.
The goal of the group working on the problem now is to understand all of the changes in counting methodologies over the years, and to put the entire historical record on a single, self-consistent reference frame. Part of what they need to do that are raw observations of sunspot counts, and those have proven difficult to come by in many cases. This is where the AAVSO and the AAVSO Archives come in.
Leif is here at the AAVSO through May 16 to digitize the original raw observations by Herb Luft (seen on the right in this 1966 photograph). Luft observed the Sun for nearly 70 years, starting as a young man in pre-war Germany, then on to South America and finally to the United States where he and his wife Hilde eventually settled. The AAVSO was given Luft's original notebooks after he passed, and they're now archived at AAVSO headquarters where they and other similar materials can be used by researchers. Even the AAVSO Solar program doesn't have archives of raw sunspot counts for any of our observers prior to the year 2000, so Luft's notebooks are, as Leif says, "golden"! Below is an example page from one of Luft's notebooks from when he was in South America.
Leif Svalgaard's project is another neat example of the history and science that's coming from the Archives. We're happy to have Leif here, and we're looking forward to seeing Herb Luft's data being put to good use once again. We'll share more results about this ongoing project as we hear more.