Tools Astrocalculator Horizontal Coordinates module The Horizontal Coordinates calculator module Horizontal Coordinates This module converts from Equatorial coordinates to Horizontal coordinates. First, select the date, time, and geographic coordinates for the calculation in the Input Data section. Then, fill in the equatorial coordinates to be converted and their catalogue epoch in the Equatorial Coordinates section. When you press the Compute button, the corresponding Horizontal coordinates will be presented in the Horizontal Coordinates section.