I didn’t know that

13 jul 2026

A list of things I didn’t know before

Most of these I’ve forgotten once already. So now I’m writing them down.

Hinode XRT reports voltage for GND

I never thought to do this. The XRT instrument on Hinode reports a measurement of its ground voltage as part of the housekeeping data. You can see a plot of it here.

I’m not totally sure how to interpret this—what is the ground measured with respect to? But it seems like an excellent idea to check on your spacecraft ground.

Why does the level change over the years? Can’t say for sure. But it could be:

  1. Spacecraft charging (although I’d much faster drift in that case).
  2. Radiation damage, increasing leakage current somewhere.
  3. Drift in ADC calibration or reference voltage.

Very interesting.

Julia circular dependencies

The Julia language cannot handle declaration of types with circular dependency.

They fixed it! Hooray.

Cutting bread while holding a baby

If you’re holding a baby or even a big kid on your hip and cooking, sometimes you need to cut something. Of course, you should use the non-baby-holding hand to do this. But usually when cutting something, you’d hold onto it so it doesn’t slide (bread) away from you or roll (veggies).

The trick is: find a long object that is safe for a baby, such as a spatula or ladle, and hold it in the hand that belongs to the arm that is supporting the baby. You can use this extension now to hold the article down on the cutting board, and successully cut it with the other hand. Voilá.

Shell scripting

I started using fish shell recently. Procrastinating something. It’s a fine shell.

I used to run all my shell scripts like this:

$ source script.sh

but that doesn’t work now! Fish complains, because it wants different commands for variable assignment than bash and zsh.

So now I run scripts like this:

$ bash script.sh

and that works just fine. If I ever write a fish-specific script, I will run it like this instead:

$ fish script.sh

Maybe this is a good thing, because I’m being more specific about what I want the computer to do.