Isn't there a lot of uncertainty about the mass of the milky way? I think if you are going to use something as a unit you really need an accurate figure.

There is indeed lots of uncertainty, and all Milky Way mass estimates are model dependent. Also, the ~10^12 solar mass figure referred to above is an estimate of the total galaxy + dark matter halo mass. Stellar or baryonic mass estimates are closer to ~6 x 10^10 solar masses. I'm using "~" to mean uncertainty to within a factor of 2 or so.

Stacy McGough wrote about this topic recently wrt the third Gaia data release: https://tritonstation.com/2023/09/19/recent-developments-con...

As long as we don’t measure length in football fields I won’t get triggered.

Me neither, as I prefer washing machines over football fields.

How would you go about doing this - just out of curiosity.

> How would you go about doing this - just out of curiosity.

Take the length and divide it by the length of a football field?

The first step would be defining what football means.

That would keep us entertained for many dog years.