Communication between bitcoin nodes and Blockstack nodes

I just have a little question about the communication between bitcoin nodes and Blockstack nodes. The Blockstack nodes need to connect to bitcoin nodes in order to get the transactions in the blockchain, how do the Blockstack nodes know the bitcoin nodes? Which node does a Blockstack node connect?

Another question is that if I run a light client, I need to connect to the Blockstack node, which Blockstack node do I connect by default? Can I specify one by myself. If I can, where can I find the information of public Blockstack nodes?

Hope someone will help me solve these questions. Thanks a lot.