JavaScript makes it tricky (a performance hit I think) to have actual, non-writable private variables that stay with a public instance of a class.  So our convention is to prefix with an underscore any variables that are meant to be private.

In this case, it means that `CesiumViewerWidget` shouldn't be directly manipulating the timeline's private `_scrubJulian` variable.  Instead, you can either add this line to an existing function in Timeline (such as `zoomTo` which is called on the next line), or you could look for an existing public function in Timeline that assigns a new value to `_scrubJulian`.

In this case, the line appears to be unrelated to the zooming of the timeline, which is only simultaneous by coincidence here.  Really it's the result of setting the clock above, and the timeline being unaware of it.  So I'm thinking you should take the latter approach, find an existing public function on `timeline` that already manipulates `_scrubJulian`, and call that here.