Parallax of the moon, experiment update

With Proof 45 I asked readers if they would help perform an experiment to measure the parallax of the moon, and so derive a figure for the radius of the Earth. The experiment was more demanding than when we used Eratosthenes’ method, requiring helpers to stay up for much of the night and take specific photos of the moon and stars. Unfortunately this meant that only two readers contacted me to help perform the experiment, which simply isn’t enough to do it successfully, given the vagaries of weather. (The planned day was rainy here so I couldn’t be a third observer.)

So we don’t have any results to report. I may try this experiment again some time in the future, but I’ll need a significantly higher response from readers if we’re to get it to work.

4 thoughts on “Parallax of the moon, experiment update”

  1. I don’t have a camera as such. I doubt that a tablet, let alone a phone, without attachments that I don’t own either, would be up to the task.

    1. In my experience, a smartphone camera should be adequately capable, you should be able to set up the camera app to be sensitive enough to get what we’re after. Put the camera in manual control mode (on my phone that’s called “Pro” mode though I’ll bet that others use different names). Now you can drop the f-number as low as it goes and max out both the ISO and the exposure time. It’ll be an exposure of 10 or more seconds, depending on the details of your phone camera/app, so you’d need some kind of device to hold it steady for you. Just a simple stand would do the trick – maybe fold up something out of a cereal box, or build one out of LEGO – it just needs to hold your phone steady while it’s taking the picture.

      If you do want to take part I’d suggest trying it out in advance – no time like the present! If your photos show stars as points rather than drawn-out tracks then your stand is steady enough (I doubt any smartphone can manage an exposure long enough for any but the tiniest of star trails). And if you see at least as many stars in the photo as you do looking up, then you’re probably good to go.

  2. It was thickly overcast for me too, so we wouldn’t have had a second observer either. Though I’m perfectly willing to try again at some pont in the future.

    1. I was trying to do this, and took a few pictures with my smartphone camera (it has a “night” mode) but I couldnt see stars in the photos. I will try Christopher Seaton’s tips above next time.

      DMM, may I suggest posting on Twitter about this when you’re ready to do it again, it will be more easily shared and you may get more people interested.

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