While we were at the AAS, Jordan and I were interviewed by Pamela Gay of Astronomy Cast. You can hear the results over at Star Stryder. (The good news is it’s audio, so you don’t have to worry about my shirt…)

I’m back from the AAS meeting in Austin. Last week, Chris and I reported on some of our experiences at the meeting; I know many of you said you wished you could be there, so we wanted to give you a peek at what a scientific meeting was like. There were a lot of posts flying furiously, so this is an index of what we reported on, both here and on Chris’s blog. For more perspectives on the goings-on at the meeting, see the Astronomy Cast LIVE blog. The meeting went from Tuesday to Friday, so this is indexed by day.

Tuesday:

Chris wrote about the search for extrasolar planets, both the progress being made and the postponement of some other missions.

Then, Chris posted some highlights of research presented on Tuesday, including three results that have implications for Galaxy Zoo: a study of the importance of classifying galaxies by eye, the discovery of a spiral galaxy that appears to rotate backwards, and the discovery of a voorwerp-like blue blob.

Wednesday:

Chris posted some beautiful images of the infrared sky from the UKIRT.

Then, Jordan posted about his experiences at the Sloan Digital Sky Survey booth, answering questions about the survey while wearing a chef’s hat. The purpose of the hat was to advertise a session called “Cooking with Sloan,” which served up hot and fresh galaxy images like the ones you see on Galaxy Zoo.

Chris posted again, about how observers and theorists are both making important contributions to the study of extrasolar planets.

At the end of the day, Chris posted about a talk he went to with the intriguing title of How Astronomers Die.

Thursday:

Thursday was the day of the Galaxy Zoo poster presentation – much more about this tomorrow. We were busy in the morning, but several posts appeared in the afternoon.
First, Jordan posted about pub conversations with a researcher at the University of Alaska Anchorage about the role of scientific research in science education.

Next, Kate and Anze posted about the initial results of the Galaxy Zoo bias study, finding that the apparent excess of anticlockwise galaxies has something to do with human perception and not the universe. They also share some ideas about what we’re doing next.

Then, Chris posted twice in a row, about a study of a galaxy supercluster, then about an interview with him posted on Youtube.

Then, Jordan proudly noted that his chef’s hat had been complimented by a Nobel prize recipient, and later added a slightly embarrassing picture.

Friday:

Friday was Chris’s talk about the science results from Galaxy Zoo – more on that tomorrow as well.

Then, Kevin posted about one of the fascinating and unexpected results of Galaxy Zoo – Hanny’s voorwerp.

We hope you enjoyed our coverage of AAS. The next meeting is in St. Louis in early June; whichever of us is going to that will try to provide you with coverage of that meeting too.

‘Anyone?‘ asked Hanny from the Galaxy Zoo Forum. She came across a weird blue blob that none of us could really make any sense of. It’s right next to a rather massive galaxy that might be a spiral or a somewhat disturbed galaxy.

A highly scientific illustration.

At first, we had no clue. The mystery blob didn’t have a spectrum, so we couldn’t tell much about it at all. It could be in our Milky Way, it could be as distant as that big galaxy, or it could even be at the edge of the universe. Bill Keel enhanced the SDSS image a bit (see below) to reveal the intricate structure of what became known as ‘Hanny’s Voorwerp’ (object).

The five different SDSS bands (g,u,r,i,z), note the intricate structure in the g-band image.

The object seems to be very bright in the g-band image and virtually absent in the others. This led us to think that it must be an emission line object, i.e. an object which emits most of its light only in very specific atomic transitions. This usually means that what we are seeing is ionised gas, rather than stars. Still, it could be anything. Bill Keel kindly also obtained a multi-colour image with the 0.9m SARA telescope at Kitt Peak. The three colours here are much closer to what human eyes would see, so as Bill pointed out, it’s actually much more appropriate to call it the mystery *green* blob.

BVR image from the SARA telescope.

We’ve managed to contact a friend of ours who is currently observing at the 4.2m William Herschel telescope in La Palma and convinced him to take a spectrum of the Voorwerp for us. It shows us that the Voorwerp is…. *drumroll* at the same distance as the big galaxy. This implies that it’s really rather huge and luminous.What does all this mean? What is the Voorwerp? That’s not too clear yet. We have to properly analyse the spectrum to understand what exactly is going on. It’s likely forming stars at a huge rate, ionising lots of gas and making it shine. We’re also trying to get a deeper image to see if there’s evidence of an interaction between the big galaxy and the Voorwerp.So what’s next? We’ll have to do a lot of work to understand this mystery blob better. Right now, the Voorwerp is only slightly less mysterious than when we started, but I have a feeling that it’s going to be really good fun figuring out what is really happening here. It also shows the power of Galaxy Zoo and of having you guys go through the images by eye. If Hanny hadn’t spotted it and asked, we’d never have known about it!

The Bad Astronomer has an interview with me on his site, talking about the cosmology results.

Hey guys and girls,

So, as you probably know, the last month or so of Galaxy Zoo has been dedicated to testing whether we have any bias in our classifications (and if you want to know why we are interested in looking at the rotation of galaxies then please have a read here). By ‘bias’ we basically mean some systematic error in the way people classify (you can get a good explanation in Jordan’s post), and this is different from just random general scatter of results. For example, we know that when a galaxy is faint or small then people are more likely to think it is an elliptical galaxy – and this particular mophology bias is something that Steven must compensate for in his work.

It has been really exciting to work on the rotation classifications of Galaxy Zoo, and as many of you know early on in the project we realised that people were classifying more galaxies as anti-clockwise (see the Telegraph article for example). Specifically, if we take those galaxies that are well classified (ie. more than 80% of people agree) then we find we have an anti-clockwise:clockwise ratio of about 52:48. This may not sound particularly significant, but as you increase the number of galaxies that you have in your sample (as more of you lovely people classify for us) then this ratio becomes more significant, and is highly unlikely for the ~35,000 galaxies that we have. [For those of you who like probability, the number of anti-clockwise galaxies that we expect is distributed according to a Binomial probability distribution. And if we assume that the ratio is really 50:50, then out of a total of N galaxies we expect N/2 to be anti-clockwise, with a standard deviation of sqrt(N/4).]

In the plot below we show the relative excess of clockwise votes (for users that classified more than about 300 galaxies) – this is the number of clockwise votes minus the number of anti-clockwise, votes divided by the sum of the two. For example, this number would be 1 if a user always clicks clockwise, and zero if they click both clockwise and anti-clockwise equally.

This graph confirms that everyone is generally clicking anti-clockwise more often, because we see that the mean tends to lie below the zero line. But this plot cannot distinguish between intrinsic excess of anti-clockwise galaxies on the sky or human bias, and it is obviously very important for our rotation results that we get a handle on this as we could not announce our possible anti-clockwise excess result to the scientific community without doing these bias checks. So the basic idea is to look at the votes for a galaxy before and after a galaxy image is flipped. For example, if 6 out of 10 people thought it was originally clockwise, then after flippping we expect about 6 out of 10 people to now think it is rotating anti-clockwise (if there is no rotation bias).

Since the end of November many of the images in Galaxy Zoo have been flipped for this purpose (and we’ve been monitoring the status here), and we now think that we have enough data to measure the levels of bias. This week Anze has flown over from Berkeley (in California) especially to crunch the numbers with Kate (in Oxford); it is quite a job – with over 7 million classifications to go through! And during our analysis some rather subtle points arose… as with most science, things don’t go exactly to plan!

So we basically wanted to compare the classifications for a galaxy before and after flipping, but we quickly realised 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).

So we want to know what the average votes per button are, for the average galaxy in Galaxy Zoo. This is where we encountered our second problem – our bias sample does not cover all of the Galaxy Zoo galaxies, but just 10% of them, and this 10% was not selected at random. In particular we know that we have more anti-clockwise galaxies in the bias sample (on the site at the moment). Therefore we needed to careful undo what we did when we selected this subsample, so to then construct an effectively random subsample of our full database. Then we could look at the average weights.

In the figure we show the average fraction of votes that a galaxy gets for clockwise (class=2) and anti-clockwise (class=3). We show the result for the original classifications in black (before December), for the monchrome images in red, and for the flipped images in green. We also show the 1 standard deviation errorbars from sampling.

So what we see is that the class=3 points are always higher than the class=2 points, and crucially this is true even after we flip a galaxy image! Looking at the red points, we find that before flipping there is a 6.0% chance of hitting anti-clock and 5.5% of hitting clock for our sample. Then after flipping (green) there is a 5.9% of hitting anti-clock and 5.6% of hitting clock. So the point is that those numbers stay the same (within 1 standard deviation) when they should actually reverse if there is no bias. It is easier to think in terms of the ratio of fractions:
anti/(anti+clock)=0.522 before flipping
anti/(anti+clock)=0.512 after flipping.
And if we had:
a) no bias and no excess then these should both be 0.5.
b) no bias and a real excess then one should be the opposite of the other (ie. 0.52 and then 0.48)
c) a bias and no excess then we would expect them to stay the same and not equal 0.5.
But what we actually find is that 0.522 is 5 standard deviations away from 0.5, 0.512 is 3 standard deviations away from 0.5, and 0.522 & 0.512 are within 1 standard deviation of each other. So you see we appear to be convincingly in situation (c).

So what next? Well – it is fantastic that we have been able to get a handle on the bias even if it did turn out to be effecting our results. Only with Galaxy Zoo which has so many contributors were we able to detect the bias (and it may turn out to be an inherent bias in the way people see galaxies, which an interesting psychology result). Without so many classifications the excess result would have always remained uncertain. And while we no longer think we have an overall excess of anti-clockwise galaxies (which we never expected in the first place!) we can still do a lot of interesting work and pursue our original scientific aims, as explained here and here.

Thanks guys! And keep up the good work. Current classifications remain useful, and we hope to give you some more images next week (possibly returning to the full catalogue!).

Cheers, Kate & Anze

I’ve just realised that everything I’ve just written in this blog post over at my personal site is relevant to Galaxy Zoo. Enjoy.