Abstract
Abstract. The determination of magnetic declination angle entails finding two directions: geographic north and magnetic north. This paper deals with the former. The known way to do it by using the sun's calculable orientation in the sky is improved by using a device based on a WIDIF DIflux theodolite and split photocells positioned on its telescope ocular. Given the WIDIF accurate timing and location provided by the onboard GPS receiver, an astronomical computation can be effected to accurately and quickly determine the sun's azimuth and an auxiliary mark's azimuth. The precise sun's crossing of the split photocell, amplified by the telescope's magnification, allows azimuth accuracies of a few seconds of arc.
Highlights
The sun shot technique, potentially quick and accurate, is not very popular
– a theodolite with adequate precision, which can be the very DIflux theodolite used for magnetic measurements;
The sun shot add-on is clamped on the telescope at the ocular end
Summary
The determination of true north via the mark’s azimuth required for magnetic declination is an old problem which has received a number of solutions (Šugar et al, 2013): by sun shot, north-seeking gyroscope (Rasson and Gonsette, 2016) and GPS techniques (Lalanne, 2013). The sun shot technique is not cumbersome and basically needs only a few types of equipment:. – diagonal eyepieces (ocular and microscope) adapted for the theodolite in use so that steep sightings can be carried out (in case of high sun elevation);. The sun shot technique has notable advantages: it is rather easy to use, does not need much additional equipment, requires the occupation of a single station only and is fast – an experienced observer will not take more than a few minutes of time per sun shot (excluding the calculation by hand)
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