Abstract: An astronomical chart and projection system for mapping celestial movement plots the longitudinal positions of planets, as measured along the ecliptic, against time in a rectilinear coordinate system with each of the planets being represented by a line on the chart, such a line being designated the "major line" of the planet. The major line corresponding to at least one of the planets is repeated at fixed longitudinal displacements from itself to generate harmonic reproductions, typically at 45 degree intervals. These harmonic reproductions allow a user to immediately extract aspect information between the planet whose major line is harmonically reproduced and other planets, whether or not harmonically reproduced. The longitude and time axes preferably have a common origin at respective longitude and time coordinates corresponding to the vernal equinox, thus permitting sidereal and tropical time information to be extracted from the chart by simple linear scaling of coordinates.