Development of constant‐altitude instruments for astronomical observations

Abstract

This paper describes the split‐telescope astrolabe and the pendulum‐astrolabe, which the author invented and assisted in bringing into use for the determination of astronomical longitudes and latitudes from observations of stars whose positions relative to other stars are determined on other instruments, and describes the system of the prospective constant‐altitude transit‐circle for further use of the principles of these instruments in the fields of geodesy and fundamental astronomy, including the determination of the spherical coordinates of all celestial objects. The most useful form of the constant‐altitude transit‐circle is expected to be an observatory instrument of about 15 inches aperture for the direct determination of much more accurate spherical coordinates of stars and other objects down to about the 11th or 12th magnitude, along with the latitude, longitude, and azimuth at the observatory. These more accurate star‐coordinates are expected to contribute fundamentally to the solutions of many problems of practical and theoretical interest. It is judged that there should be one or more constant‐altitude transit‐circles in each hemisphere, north and south, and that there should be about 15 photographic zenith‐tubes distributed throughout the world in addition to the one at the Naval Observatory in Washington, which has been the best standard of time and frequency and the best base station for the determination of longitudes since 1934. An Indefinite number of field‐instruments, probably pendulum‐astrolabes or photographic zenith‐tubes, are needed for determining astronomical longitudes and latitudes to be used in conjunction with geodetic observations for determining the shape of the Earth.