observe function
Implementation
observe(String tle, Qth qth, start) {
var tles = tle.split('\n');
Map<String, dynamic> satrec = twoline2satrec(tles[1], tles[2]);
if (_badSat(satrec, qth, start)) {
return null;
}
return _observe(satrec, qth, start);
}