The Angularsizeorator

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Back to the summer of 2015. A few of us (me, Jen Gupta, Megan Argo and Niall Deacon) worked on a project that wanted to address the problem with angular sizes in astronomy. When talking about how big things appear, it’s common to say things like “as big as a 5 pence peace at a distance of a mile” (that’s about 2.3 arcseconds, for what it’s worth). The problem is, even that analogy is hard to visualise – other than to say it’s really, really small – I can’t really imagine a 5p piece sitting a mile away, partly because a mile is hard to visualise.

I like examples that are possible to visualise. For example, the Hubble Deed Field is about 2.5 arcmin across, which is (roughly) about the size of a pinhead at arm’s length – I can imagine holding a pin at arm’s length so that’s OK.

The “Angularsizeorator”

Screenshot of the Angularsizeorator

Cue what was termed the “Angularsizeorator” (thinking up a name wasn’t a priority!). A Google spreadsheet that lets the user select an astronomical object (or an angular size), and then one or both of:

  • a object to compare it to
  • a distance at which that object is located

The spreadsheet does the simple maths (angular size = object diameter / distance), to tell you how many [objects] at [distance] the given size corresponds to. So, for example, Mars (at its closest approach) is about the same size as 2-3 grains of sand* at the other end of a train carriage. Which is small, but something it’s possible to visualise. (* actually 2.79 grains if you assume they-re 1mm across, but that kind of precisions isn’t necessary)

The neat bit is where you ask it to auto-select one of them, and it picks to other so as to being the number closest to 1. So if I select Mars (closest approach), and ask it to place an object at the other end of the Heathrow Runway, it tells me “Looking at Mars (closest) is equivalent to seeing 1.02 Cat(s) at the other end of the Heathrow Airport runway”.

If you’re wondering about the 5p at a distance of a mile (2.3 arcseconds, it’s about the same as a lime at the other end of the Heathrow Airport runway? I think that’s easier to imagine (though not necessarily any less ridiculous…)

We also added in comparisons for velocities/travel times and masses, but those were less well developed.

Why not make a web app

It’s tempting to make a snazzy web app for this kind of thing (and, hey, maybe one exists), but that would have taken us longer than the half day or so that we had. Plus, this is easily tinkerable with by others. You can even add in your own objects to the lists! (apparently we can blame Niall for adding Lorraine Kelly to the list of “everyday objects”*). If anyone does want to make a snazzy web app, then please be my guest.

(* Looking at Mars (closest) is equivalent to seeing 1.49 Lorraine Kelly(s) across Greater London)

Go on, try it for yourself!

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