On Being Too Tightly Wound, Counterclockwise


Yes, that’s me.

One of the more interesting net-based projects is Galaxy Zoo, where anybody can help lend a hand categorizing some of the uncounted (and uncountable) galaxies found in obscure corners of SDSS and Hubble data collections. There, you can get a little quick training, and after a brief introduction, set to work doing real astronomy.

You quickly discovered (if you didn’t know already) that some galaxies are spirals, some are elliptical blobs and some are simply a random mess. Sometimes it’s hard to distinguish. The good people at Galaxy Zoo are hoping that many “amateur” eyeballs are more likely to be right than just one or two (alleged) experts.

So what did they find? According to Phil Plait, the Bad Astronomer,

people were finding significantly more counterclockwise-rotating spiral galaxies than clockwise. That’s a problem! We’d expect the numbers to be almost exactly the same. Did the GalaxyZoo folks stumble onto a new and previously undiscovered cosmological property?

They got real clever, and, since November, have been pseudo-randomly flipping some galaxies on us. If there are really more counter-clockwise galaxies in our view than clockwise, the discrepancy disappears. If we are biased to “see” more counterclockwise than are really there, the bias will remain. Easy enough. But according to the organizers, Murphy’s Law reared its ugly head.

So we basically wanted to compare the classifications for a galaxy before and after flipping, but we quickly realized that peoples behaviour in the last month or so is very different to the earlier datasets (see Anze’s post for an explanation of how we reduce the data). For example, recently people have been more likely to click the ‘Star/Don’t know’ button. This might be because we have lots of new users, recruited through our latest publicity drive. Or maybe lots of old members have come back after receiving the newsletters. Either way it meant we couldn’t simply compare before and after votes. Also, annoyingly, the original unflipped images are no longer on the site and so getting a handle on this behaviour change was a bit tricky (note that one of the first rules of scientific experiements is to have a control test, but accidentally a miscommunication amoungst team members meant that in this case our control sample got left out!). Fortunately though, we are able to use the monochrome images that are currently in the site to compare to (as we observe that being in black and white does not change how people choose between anti-clockwise and clockwise).

Well, I’ll spare you the details, but it gets worse before it gets better. Ultimately the project was able to remove a good deal of the “noise” in their data, and reveal something totally unrelated to astronomy (but intimately related to observing) – yes we have a bias. Why this shows up as seeing things as counterclockwise preferentially over clockwise is probably a fascinating psychological study. And hey! Is this related to our biological preference for being right handed?

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