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Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
An astronomic meridian is based on the rotational axis of the Earth and the direction of gravity. It derives its name from the means by which it is typically established: astronomic observation. The angular difference between astronomic and geodetic meridians is expressed in terms of the Laplace equation. For most practical purposes in plane surveying, this difference is negligible and both meridians are often collectively referred to as the “true” meridian.
Observations on Niccolò Tornioli’s The Astronomers
Published in Annals of Science, 2021
Susanna Berger, Sara J. Schechner
The globe’s focus on Hercules raises questions. As a scientific instrument, a globe should be tipped in its cradle so that the polar axis is parallel to the Earth’s axis at the user’s latitude.74 For Rome, that is forty-two degrees using the divisions on the meridian circle as a guide. When the globe is rotated in this position, the stars will rise and set as they do at the user’s location. The globe can be used as a star finder to identify bright stars and constellations seen at the time, and to determine the circumpolar stars that will never set at that latitude. It can also be used to solve astronomical problems such as the length of day or night on a given date, where along the horizon a star will rise or set, at what time it will cross the meridian, and what its maximum altitude will be. By tilting the globe to another angle, the user can learn how dissimilar the night sky would look at a different latitude; he or she could find out if the days might be longer or shorter there. Such manipulation of a globe would be an educational exercise, but it is not typically illustrated. In paintings of globes, the artist customarily shows the globe set for use at an angle close to the subject’s latitude or to display prominently an area of particular interest to the owner.