Black Friday: lifetime access is on a special offer in the app, until November 30. Black Friday: special offer on lifetime access, until November 30. Download
그레고리오식망원경은 천체 관측에 사용됩니다.geuregori-osik mangwon-gyeongeun cheonche gwanjeog-e sayongdoemnida.The Gregorian telescope is used for astronomical observations.