How the planetary lines are calculated
The calculator converts your recorded time and historical UTC offset to a single UTC instant. It obtains the apparent geocentric right ascension and declination of the Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto from Astronomy Engine. Greenwich sidereal time locates each planet's upper and lower meridians. At each sampled latitude, the geometric horizon equation gives the longitudes where the planet rises or sets. These lines describe the same instant viewed from different places on Earth.
MC means upper meridian; IC means lower meridian. ASC is the eastern rising horizon and DSC is the western setting horizon. At high latitudes a body may never rise or set on that date, so its ASC or DSC line can end before the pole. The flat map uses an equirectangular projection and stops angular lines at 85° north and south. The nearby-line estimate measures east–west separation along the checked latitude; it is not the shortest distance to a curved line.
Birth-time uncertainty matters: Earth rotates roughly 15° in longitude per hour, so an uncertain or rounded time can move these lines substantially. This map omits lunar nodes, topography, and atmospheric refraction. For a numerical two-line intersection, use the planetary line crossing finder; for latitude bands, use the paran finder. Angular geometry is not a destination prediction.