Old Omega watch, with calendar, gold, fully automatic, with a prominent constellation on the back, seems to have been bought in the 1970s.

That English word means that this is a series of watches and constellations. It is also the most successful series of Omega. The specific model is on the warranty card and tag of the watch. The English you gave is not the model.

To check the price, you can quote the model, call the local flagship store, and then the professional sales consultant will tell you the price. You can't find the price unless your watch is an old model and has been discontinued for a long time.