NIGHT SEXTANT OBSERVATIONS AGAINST A NIGHT VISION HORIZON*

Abstract

For years the air navigator has been supplied an instrument that permitted star observations at any time during the night. Bubble sextants have been given many wishful tests for marine work, yet to date, none of them have proven satisfactory. There are many times when morning and evening twilight conditions are not satisfactory for star observations ; however, an hour before morning twilight or an hour after evening sunset the sky may be cloudless and every star out, daring you to take observations. I have accepted the dare on ships equipped with a fire control system employing a stable vertical gyro. Many other naval officers, shipmates with such gunnery directors, have gotten reliable midwatch fixes. But all during the war submarine navigators and the merchant ship masters were screaming for a sextant that would permit accurate, reliable star observations at the navigator’s whim and not at the whim of the almanac time of morning or evening twilight, clouds and weather permitting. The officers manning our submarines during the war developed a highly reliable skill in taking star observations against a night-vision horizon that produced good fixes any time during the night.