private static List<Star> stars;
...
public static void GetPlanetsInformation(int _starID)
        {
            if(WaitFor(ref stars, timeoutSec)) //ERROR
                netWorker.GetPlanetsInformation(_starID);
        }
private static bool WaitFor(ref object obj, int timeoutSec)
        {
            int times = 0;
            int tick = 100;
            while (obj == null)
            {
                if (times < timeoutSec)
                {
                    System.Threading.Thread.Sleep(tick);
                    times += tick;
                }
                else return false;
            }
            return true;
        }