Clicking 10 Billion Years Into The Past

Astronomers use funny units. We have the light-year, which sounds like a time but is actually a distance. There’s the parsec, a historical (but still used) unit of distance that was famously mis-used as a time in Star Wars. And then there’s redshift, which is actually a velocity — distance divided by time — but which, because of the expansion of the universe, astronomers get to use as a proxy for distance. 

While it may be convenient for us to use distance units where we set a mind-blowingly large number equal to 1, it doesn’t really help us communicate our work to the public. If I note that the galaxy images from CANDELS look a little different from the galaxies in the SDSS because the CANDELS galaxies are typically at a redshift of 2, that’s pretty meaningless. But it’s a little different to think of the fact that, when you classify a galaxy from CANDELS, you may be looking three-quarters of the way to the edge of the visible universe, and seeing the galaxy as it was 10 billion years ago. 

Okay, that's kinda cool.

Okay, that’s kinda cool.

During this hangout, we announced that your clicks and classifications of the CANDELS galaxies have been moving at such an impressive rate that the first round is finished. Every galaxy has enough classifications for us to get a very good sense of what its morphology is. It may be that, for some of the galaxies where there are clearly more details to flush out, we will ask for a few more classifications per galaxy. And there will probably be future CANDELS images from survey fields that are still being completed. So, don’t worry, there will still be plenty of opportunities to classify galaxies as they were 10 billion years ago!

In the meantime, though, we’re getting ready not just to do the scientific analysis, but to share Galaxy Zoo results with our colleagues around the world. The summer conference season is upon us, and many of us have given and are giving talks and posters at various meetings in various cities. This includes not just the recent meeting highlighting the importance of galaxy morphology in the era of large surveys at the Royal Astronomical Society and the upcoming ZooCon in Oxford and Galaxy Zoo meeting in Sydney, but also several more general conferences, including the 222nd American Astronomical Society meeting and the upcoming UK National Astronomy Meeting. Spreading the word about the scientific results we’re finding with Galaxy Zoo is one of the most important parts of our job — and it doesn’t hurt that in order to do that we have to visit some very interesting places. During the hangout we chatted a bit about that and also took some of your questions:

Note: although it was a beautiful sunny day in Oxford, the variable audio quality is not because I was occasionally distracted looking out the window. I don’t think it was the new microphone, either. We’ll look into it, but in the meantime I’ve tried to equalize the podcast version with some after-editing, so hopefully that is slightly better.

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5 responses to “Clicking 10 Billion Years Into The Past”

  1. Jean Tate says :

    It’s wonderful that there’ll be a Galaxy Zoo meeting in Sydney, Australia, in September!

    What are the plans to let Aussie zooites know of this? How do they register to attend the various conference sessions?

  2. kevinjardine says :

    Isn’t it the light-year which is historical? The International Astronomical Union adopted the parsec as the official unit of astronomical distance outside the solar system at its first meeting in 1922 and it’s been used by professional astronomers in scientific publications ever since.

    I believe that the parsec was chosen because its definition depends only on the Earth’s orbit whereas the light-year depended upon both the Earth’s orbit and the speed of light. So from a scientific point of view, the parsec was the simpler unit.

    So far as I know, the light-year is just used in press releases and science fiction novels now. I find it a bit strange that astronomers translate parsecs into light-years for press releases. If you are going to have an incomprehensibly large distance unit, why confuse matters by having two?

    • David Adams says :

      Most people don’t understand plane trigonometry and it is easier for them to comprehend how far light would travel in a year.

      • kevinjardine says :

        Does it actually matter how a unit is officially defined to understand it? For example, the official definition of a second is:

        the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom

        according to Wikipedia.

        We use seconds all the time despite the definition.

        When describing parsecs, I simply say that that the nearest star is 1.3 parsecs away and that the centre of the galaxy is roughly 8000 parsecs away. That gives the scale:

        And for anyone with high school trigonometry, there is the diagram I use here:

        which is a lot easier for me to understand than the definition of the second!

  3. Tom Freethesouls Zolotor says :

    Below are some conference’s mention in the blog. Will the FHB/CANDELS galaxies be talk about at these conferences?


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