Star magnitude and manual navigation sighting accuracy using the Apollo T2 sextant.

This laboratory study investigated the effect of four star magnitudes (0, +1, +2, +3) upon the angular sighting accuracy attainable between a star and a lunar limb using a space-rated sextant with an 8-power telescope. Four males were tested. The results indicated that over a series of daily sightings sighting accuracy increases as star magnitude decreases; i.e., the angle between the actual lunar limb and the perceived lunar limb decreases as the intensity of the star increases. The significant subject and day main effects that were found indicate that each individual must be calibrated against himself and that extreme care must be taken to center the various images correctly within the sextant's field of view each time the instrument is set up. These findings are discussed in relation to further refinement of a graphic model of the distribution of energy on the retina. A discussion is also presented on the differences between sextant sighting research conducted in the laboratory and in the real, high-altitude or space environment.