Milwaukee Astronomical Society


Planetary Conjunction - When & where was it taken?

By Gene Hanson

I ran across the photo above in the MAS archives while gathering photos for scanning and archiving. On the back there was simply this written note:

Though I can't be certain, my assumption is the photo is by Ed Halbach as he used his signature. I cannot assume the annotations as the handwriting doesn't seem to fix, but it's ultimately beside the point.

When and where was the photo taken?

I was immediately intrigued and wondered if I could pinpoint the date taken. I think I have it, but thought some of you might enjoy the challenge. I went on the assumption that it was Ed (although it could be some other MAS member) who took the picture and since it was in the MAS achieves it was taken on or after 1932. So when was this photo taken and where?

My Solution

The first thing that struck me is the angle of the planets. Ed's note says we're looking West and there is a "W" at the bottom of the picture. But the angle would indicate it would be taken in the southern hemisphere and I didn't check that further. Could it be that it was actually taken in the early morning in the East?

I figured I could use the Stellarium planetarium program to try to match the alignment, but that could take too long. So my next task was to narrow the date ranges that should be checked. I then did a search on planetary conjunctions and ran across this Wikipedia entry on Great Conjunctions. This was certainly a Great Conjunction as Jupiter and Saturn are fairly close together. These happen at roughly 20 year intervals so the first one to check was 1940-41. There was no correspondence in the East, but a very close match in the West, but at a different angle. At that point I it was clear to me that the photo had been reversed so it was a mirror image. Flipping the horizontal you get this:


To my eye the closest match occurs on February 26, 1940. Here is a screen shot from Stellarium.

Of course there's still an issue. Mars and Saturn do not correspond, but the simplest explanation is that they are flipped, obviously just mislabeled. 

So I think the photo was taken in the early evening of February 26, 1940. Though it could be the the day before or after, to my eye this is the closest match and on this evening the position of Omicron Pisces next to Saturn corresponds. Though I cannot be certain it was taken around Milwaukee (and probably the MAS Observatory as it had an excellent western horizon), it's highly probable.

Gene Hanson