Agreed that `LST` should not really be an `Angle`, but one disadvantage of it being a `Quantity` is that it cannot be typeset as hms. So, perhaps leave it as `Angle` for now? Hopefully, we'll have a proper sidereal time not too long from now (have just been wondering whether this is best done within `Time` or as a separate (sub-)class (where for the present purposes it might return a `TimeDelta` with 'scale=lst` or so).