Morning Tea in February

Sometime in the next few weeks we will crank up the data acquisition for 2014. Since 2003 we have shot images of the same half-degree square patch of sky every clear night from late February to early October. Why? Well, why not. Don’t actually answer that. I can come up with plenty of reasons on my own. We start the images when the field clears the southeast corner of the observatory or it gets dark, whichever comes later. We stop acquiring data when the field dips below the southwest corner of the observatory or dawn arrives, whichever comes first. Given that our clock is based on the time it takes for the sun to go meridian to meridian and that we move a degree or so in orbit each day, our field of interest (any non-circumpolar field) rises about 4 minutes earlier each night. When we begin again in the next few weeks we will grab the last half hour or so before the coming daylight washes away the stars. Things will be reversed in October when we have the first fraction of an hour of darkness available for use.

We began this exercise knowing that we haven’t particularly transparent skies here deep in the atmosphere. What we do have is access every night. We asked what rare transient events or slow, subtle changes we might observe if we took hundreds or thousands of images, a few seconds each, whenever we could for a decade or two or three. The atmosphere would have posed less trouble had we chosen a field to study that was high in the sky, but we selected the field containing open star cluster M23 about 10 degrees north of  the more or less familiar teapot asterism of Sagittarius. This region never reaches 28 degrees above our southern horizon. At its highest, this field is below the minimum altitude of study for most researchers, but here the ecliptic plane of the solar system intersects the star-rich galactic plane. We figured this intersection might increase the odds, however slightly, that something rare and transient might pop up.

By now dozens of students have worked on this project – writing code, developing statistical tests, fitting curves, dreaming up possibilities. Three are working with the data right now. At least one new student will join this summer. This kind of slow, grinding project is continually generating new things to work on. We barely have the time to keep up. Some pretty typical things go on, like discovering about 60 pulsating variable stars and tracking them for evidence of pulsation mode switching. We are timing about half a dozen eclipsing binary systems to see if their periods are changing. We are always looking for elusive brightening events that are caused by something interesting and not by our normalization of the data. But we’ve also managed the less typical, like seeking evidence of increasing light pollution and checking to see if the average sky transparency is lower on Fridays and Saturdays in the summer when the campground about a mile south is likely to be fully occupied by people with campfires.

And it all starts again very soon. Will the pulsating stars be doing anything surprising when we get back to them? Will anything completely new crop up this year? Will all the equipment function? Am I ready for the sleep disruption? I’ve been working on this project for over a decade and I’ve been watching the sky with more than passing interest three times longer than that. Still, it surprises me too see the teapot asterism of Sagittarius, a symbol of balmy August nights, on a below zero February night. It’s not like I didn’t know it was coming. As long as it surprises me, by doing exactly what’s expected or some minute surprising thing, I’ll keep watching.