Wallpaper Wednesday: SDO and Sunspots

16 07 2014
"Sweeping Arches and Loops", solar magnetic activity viewed in the ultraviolet, June 30, 2014.

“Sweeping Arches and Loops”, solar magnetic activity viewed in the ultraviolet, June 30, 2014.

Looking at some of the photos returned by NASA’s Solar Dynamics Observatory (SDO), you’d think contemporary solar observing had little in common with what was being done at Kodaikanal c. 1900-1910. But in addition to the dramatic images of solar loops like the one shown above, SDO also sends back sunspot records that closely resemble the photos and charts produced by C. Michie Smith, John Evershed, and company.

"Spots Galore," July 8, 2014. Image credit: Solar Dynamics Observatory/NASA

“Spots Galore,” July 8, 2014. Image credit: Solar Dynamics Observatory/NASA

According to SDO/NASA:

“The Sun sported a whole slew of substantial sunspots over the past 11 days (July 1-10, 2014). This movie and still show the Sun in filtered white light speckled with more and larger sunspots than we have seen in quite some time. Sunspots are darker, cooler regions on the Sun created by intense magnetic fields poking through the surface. The Sun may have passed its peak level of activity, but it will still be producing many more sunspots and solar storms during the rest of this solar cycle. The still image was taken on July 8 at 22:24 UT.”

Looks familiar!

Visit the NASA/SDO gallery to see more images of solar activity. Like the two above images, most are stills excerpted from videos. Click through each image to reach the links to .mov and .mp4 files.

Sunspots, 1903

14 07 2014
paper disc with handwritten notations of sunspots

Sunspot observation record, April 30-May 1, 1903. Image courtesy of Indian Institute of Astrophysics/JR

I was fortunate enough to spend some time studying the historic instruments and library collection at Kodaikanal Observatory in Tamil Nadu this past week. Run by the Indian Institute of Astrophysics, the observatory was founded in 1899 to facilitate solar observing. In 1907, John Evershed arrived on the scene to (quite famously) bring his “auto-collimating spectroheliograph” online. You can imagine my excitement when Mr. Selvendran, Senior In-Charge at KO, opened the door to the spectroheliograph room and slid open the shed roof to expose the instrument’s mirror. So cool.

But I’m getting ahead of myself. I spent my first day poking around KO’s fascinating library. Journals, books, catalogues, and ephemera stacked literally from floor to ceiling. So much stuff that I scarcely knew where to begin. But when I saw a stack of paper circles tucked into a corner shelf, I knew how I would spend the afternoon. I had only just read about these circles in one of C. Michie Smith’s (KO’s first director) annual reports.

Excerpt from Kodaikanal and Madras Observatories report for the year 1904.

Excerpt from Kodaikanal and Madras Observatories report for the year 1904.

Each of these 8-inch paper discs contains a record of 3-7 days of sunspot observations. Each spot was marked in pencil and assigned a letter (A, B, etc.). Every day, the observer recorded the new position and appearance of the lettered spots as they traversed the solar “surface”, i.e., the photosphere. For instance, in the following plates, sunspots A and B are shown moving from NNE to W between March 18 and 29, 1903.

Sunspot Observations, March 18-29, 1903. Image courtesy Indian Institute of Astrophysics.

Sunspot Observations, March 18-29, 1903. Image courtesy Indian Institute of Astrophysics/JR.

Sunspot Observations, March 18-29, 1903, detail. Image courtesy Indian Institute of Astrophysics.

Sunspot Observations, March 18-29, 1903, detail. Image courtesy Indian Institute of Astrophysics/JR.

The next image shows that those same spots continued westward between March 30 and April 2, 1903, breaking up as they went. You can also see a second line of spots traveling roughly parallel to the solar equator. They started out as indistinct patches at the eastern edge of the disc on the March 27-28. The March 30-April 2 disc shows how long it took for them to move half way across the Sun.


Sunspot Observations, March 30-April 2, 1903. Image courtesy Indian Institute of Astrophysics/JR.

According to C. Michie Smith, observers hand-recorded sunspots on 343 out of 365 days in 1904. What dedication, and this at a time when they didn’t really know what sunspots were. Observers just put in the hours and trusted that their efforts would one day lead to enlightenment.

On Learning (and Un-Learning) the History of Astronomy

4 07 2014
Black and White drawing of Comet Biela soon after it broke into two pieces.

Comet Biela, February 1846. From E. Weiß: “Bilderatlas der Sternenwelt”, 1888.

One of the challenges of working on the history of science is that I’m constantly having to forget things that I only just memorized or figured out. This need to learn/un-learn has been particularly acute since my arrival in Bangalore. I’ve been buried in the ephemera of the founding days of astrophysics—correspondence, observational data, eclipse photographs, equipment—and on Wednesday, I’ll be going up to Kodaikanal Observatory to study the historical instruments in situ. I’ve spent a lot of time puzzling through C. Michie Smith’s thoughts on the D line in the solar spectrum, and reading along as John Evershed’s thoughts on sunspots evolved over the course of a few decades.

It’s fascinating, watching a scientific argument grow, falter, and grow again.

The Indian Institute pf Astrophysics has a small collection of Evershed’s letters to and from William Huggins, F.R.S. Although friendly, the two men (and presumably Margaret Huggins and Mary Evershed, who remain in the background as “wives” even though they had a great deal to do with the science successes of both men) were quite cagey in their correspondence. They shared data and floated ideas without ever committing to a particular theory or revealing everything they knew. Reading the letters against their published papers shows that both astronomers left out more than than they included in their personal discussions; Evershed saw Huggins as a competitor as much as a mentor and friend.

Interesting stuff. But what I’ve really had to focus on this past couple of weeks, as I dig more deeply into the history of solar physics, is the art of comprehension without retention. That is, I need to understand Evershed’s early theories, but also need to forget about them as they were eventually proved incorrect. For example, yesterday I found myself drawing a line through my notes on Hervé Faye’s claim that the sunspots were caused by an upflow of material too hot to radiate properly, just to remind myself that later Evershed demonstrated that the upflow was cooler than the surrounding area. Sometimes I can see a problem with a theory based on my own knowledge; sometimes I have to wait until I’ve read three more Monthly Notices of the Royal Astronomical Society before I realize I need to forget a few more things.

The first article I picked up this morning started this cycle up again.

I’ve been looking at Norman Pogson’s original observation logs and comparing them with his published papers and catalogues. This morning, I found an interesting notice of his observations of Comet Biela in December 1872 (click  on the image to download the entire notice):

Norman R. Pogson, "Madras Observations of Biela's Comet," Astronomische Nachrichten, Vol. 84, (August 1874), pp. 183 - 186.

Norman R. Pogson, “Madras Observations of Biela’s Comet,” Astronomische Nachrichten, Vol. 84, (August 1874), pp. 183 – 186.

Kind of cool. But a quick Internet search tells me that Comet Biela was last sighted in 1852—fourteen years before Pogson’s viewing. I know Pogson was an under-appreciated astronomer, but is it possible we’ve completely forgotten about his observations?

As it turns out, Pogson’s claim that he had spotted Biela was challenged as early as January 1873. Pogson may have been misled in his identification by another astronomer, Klinkerfues, who told him to search for Biela near Theta Centauri. Or he may have been encouraged to identify the moving object as Biela since it was roughly coincident with what would later be identified as a Bielan meteor shower, created by the comet’s disintegration. However the confusion arose, by 1892, it was accepted fully that Pogson’s comet, now known as X 1872 X1, was not Biela at all, but some other object in motion. Pogson was able to record only two locations for his comet, so it is impossible to determine X 1872 X1’s orbit or period. Today, we may know X 1872 X1 by a second name, or Pogson may have made the comet’s only sighting before it broke up like Biela.

W. H. S. Monck, "Pogson's Comet and the Bielan Meteors," Publications of the Astronomical Society of the Pacific, Vol. 4, No. 21 (1892), p.19.

W. H. S. Monck, “Pogson’s Comet and the Bielan Meteors,” Publications of the Astronomical Society of the Pacific, Vol. 4, No. 21 (1892), p.19.

So, this morning, I learned that Norman Pogson observed Comet Biela from the Madras Observatory in December 1872. Approximately ten minutes later, I began the process of unlearning this bit of information and replacing it with conclusions drawn in the last two decades of the nineteenth century. After lunch, I may need to unlearn those bits as well and absorb instead analyses of X 1872 X made in the twentieth—or even better—twenty-first century.

Observatories and Instruments