Here is a summary of the provided text in one paragraph: You can use RxJS Observables to track the International Space Station (ISS) position and send notifications when it's approaching specific geographic coordinates. The program uses JavaScript, Node.js, and Twilio Programmable SMS APIs to achieve this. It first loads information about stargazers from a JSON file and tracks changes with RxJS Observables. Then, it performs repetitive REST API calls to retrieve the current ISS position and checks if it's passing nearby each stargazer's location. When an approach is detected, it sends an SMS notification using Twilio Programmable SMS APIs. The program demonstrates how to use RxJS Observables for file changes and REST API calls, as well as how to send notifications with Twilio Programmable SMS.