To find HI, first eat cookies

Just a quick one because this is well outside my field but I absolutely cannot ignore it.

This simply wonderful paper starts with the utterly brilliant name of "WTH! Wok the Hydrogen" and it continues in that vein for the whole paper. It's all about building a radio telescope for public outreach purposes out of old bits and bobs you can find lying around in your kitchen. Of course, the main feature is the wok itself, which serves as the dish. Is it a parabola ? Is it a sphere ? They're not quite sure, but suspect it's neither because woks aren't normally built with radio astronomers in mind.

In any case it doesn't matter. With a diameter of 60 cm, only a few times the 21 cm emission this thing can detect, it has a 24 degree beam. The photo of the telescope sitting in a plastic tub that you could find in any hardware shop is by far and away the best observing setup I've ever seen. With a beam that large, you really just have to aim it vaguely in the direction of the sky and it'll do its thing.

It's not just a wok and the plastic containers though. There's also the cookie box, used for shielding the electronics. Apparently this makes a big difference to the sensitivity, allowing them to observe from the bustling metropolis of Hong Kong and still get a detection despite the billion or so mobile phones and other radio nasties in the area. They say this shielding is what makes the difference compared to other amateur radio projects that have had to go to quieter sites for detections.

Incidentally the use of the wok specifically is not just because of its ready availability in Hong Kong, but because its shape (whatever exactly that might be) is better than a traditional satellite dish because it has a better focal length. And one further piece of household equipment they use is a microwave oven, which is a ready source of copper wire for the dipole antenna itself.

How well does it work ? Look, this thing is never going to detect a pulsar. But it can detect the HI 21 cm emission from the Milky Way in 10 minutes. Point it towards the galactic plane for 10 minutes and BAM, a detection results. Point it away for the same amount of time and BOOM the signal goes away. For public outreach that's brilliant. You can't really do any more than that; they say it's just not good enough for mapping the galaxy or measuring a rotation curve. But who the hell cares ? They've taken a bunch of old junk and turned it into a $150 radio telescope that can detect gas in the Milky Way. That's a missed opportunity for Scrapheap Challenge (Junkyard Wars for Americans) if ever there was one.

And the best bit ? Our institute director wants to build one. Next year's open day should be interesting indeed.