ABSTRACT
The phenomenon of the parallax is due to the finite distance of the planet or of the star from the observer. The determination of the parallaxes is therefore one of the most fundamental astronomical measurements. The horizontal parallax of the Moon, varies between 54' and 61' due to the strong eccentricity of its geocentric orbit. The diurnal parallax also has an interesting consequence on the apparent diameters. On closer examination, the methods based on Kepler's third law must provide the mass of the Moon in addition to the solar parallax, because it is the Earth-Moon barycenter to follow Keplerian orbit around the Sun. The measurement of the minute stellar parallaxes has always been a difficult task, quite often plagued by systematic errors. The astrometric satellite Hipparcos has enlarged this horizon by ten times, but still the volume of the Milky Way directly accessible to trigonometric distance determination is a very slight fraction of the total.
