Understanding Equanimity

Hi, I'm trying to get a deeper understanding of equanimity as I am reading two books by or about S.N. Goenka: The Art of Living and The Discourse Summaries. From these two books, the working definition of equanimity seems to be "observing objectively without reacting."

But what that doesn't mention is the actual state of one's mind. Merriam-Webster defines equanimity as "evenness of mind especially under stress." Does one feel calm and peaceful as one observes the sensations in one's body? That seems to be implied without being explicitly stated, as far as I can tell.

And it seems like the quality of equanimity would develop over time, in the sense at that first, we might observe a sensation and control our reactions a little, but still have some reaction, but as we gain experience, we can observe with less of a reaction. But it would seem like by the same token, our sense of calm and peace grows stronger, and that's why we have more equanimity.

And what about feelings like compassion? If we are working through difficult sensations, does offering compassion (without attachment) to these feelings help, or do we just need to strictly not react at all?

Just curious if anyone has else has thought about this -- I just want to have a better sense of the mental attitude used in Vipassana.