Tag Archive | time

The scourge of Daylight Savings Time

As Ali mentioned, we’re working on figuring out timing issues for all the images in Snapshot Serengeti. Each image has a timestamp embedded in it. And that time is Tanzanian time. You might have noticed that sometimes the time associated with an image doesn’t seem to match the time in the photo — especially a night shot with a day time or a day shot with a night time. We initially shrugged that off, saying that some of the times get messed up when the camera gets attacked by an animal.

But it turns out to be more complicated than that. All the times you see on Snapshot Serengeti — either when you click the rightmost icon below the image on the classify screen, or when you look at a capture in Talk — are on West Greenland (or Brazil) time. Why is that? Well, databases like to try to make things “easy” by converting timezones for you. So when the images got loaded up onto the Zooniverse servers, the Snapshot Serengeti database converted all the times from what it thought was Coordinated Universal Time (UTC) to U.S. Central Time, where both Minneapolis and Chicago are. That would mean subtracting six hours. But since the times are really Tanzanian ones, subtracting six hours sticks us in the middle of the Atlantic Ocean (or in Greenland if we go north or Brazil if we go south).

That wouldn’t be so bad, except for Daylight Savings Time. Tanzania, like everywhere close to the equator, doesn’t bother with it. It doesn’t make sense to mess with your times when sunrise and sunset are pretty much as the same time all year round. However, the ever-helpful database located in the U.S. converted the times as if they experience Daylight Savings Time. So on dates during “standard time,” the Snapshot Serengeti times are off by six hours; subtract six hours to find out the actual time the image was taken. But on dates during daylight savings, the times are off by just five hours.

blackboard

11:35am Tanzanian time. Shown as 4:35pm on Snapshot Serengeti.

And to make things more of a headache for me, those images that got taken during the hour that “disappears” in the spring due to Daylight Savings Time, get tallied as being taken the hour before. This might explain why we get some captures that don’t seem to go together: the images were actually taken an hour apart!

So now I’m focusing on straightening all the timestamps out. And when I do, I’ll ask the Zooniverse developers if we can correct all the times in Snapshot Serengeti so that they’re shown in Tanzanian time. Hopefully we’ll have that all set before Season 7.

By the way, I was able to figure this all out pretty quickly thanks to the awesome blackboard collection that volunteer sisige put together. You can see the actual Tanzanian time on many of the blackboards and confirm that the online time shown below the picture is five or six hours later, depending on the time of year. Many thanks to those of you who tag and comment and put together collections in Talk; what you do is valuable — sometimes in unexpected ways!