Abstract: Celestial navigational instrument and method of determination of local latitude and local hour angle of Aries by a single sighting on the night sky. Greenwich hour angle of Aries and latitude are obtained by simple reference to the instrument's scales and to a watch and Nautical Almanac; sight reduction tables, plotting boards and charts are not required. The instrument comprises a sky assembly and a horizon assembly. The sky assembly includes a closed central axial tube on which are rotatably mounted a combined periscope/telescope tube for sighting a first star and a periscope tube for sighting a second star, the siderial hour angular positions of both of which are set with respect to a single sky wheel and the polar distances of each periscope turret with respect to protractor scales. The horizon assembly comprises a periscope/telescope assemby mounted on the central axial tube and indexed to a horizon wheel and protractor scale to read the local hour angle of Aries and local latitude.