![]() ![]() To get a star shot (at dawn or dusk), calculate the local time of Nautical Twilight (for dawn or dusk), and at that time (or preferably a few minutes earlier,) pre-set your sextant to the altitude of the star you wish to shoot, then go to your compass (gyro or magnetic, in which case you will have to correct for magnetic variation), line your sextant up on the bearing (i.e. You don't need to know them by sight, the sextant will find them for you using the following procedure. In that row you will find the tabulated Altitudes and Azimuths (True) for seven selected navigational stars at various azimuths. Then, find the page for your your Latitude (in whole degrees) in "Selected Stars" and look down the column on the extreme left marked LHA Aries until you get to your calculated LHA Aries. Now you have the Local Hour Angle of Aries. If it's greater than 360, subtract 360 degrees. If it's less than 360 degrees then add 360. LHA Aries = GHA Aries (for the Hour GMT, from Nautical Almanac) + Increment (Minutes, again from Nautical almanac) + Longitude East (OR - Longitude if you are West or Prime Meridian). However, Sirius usually rises early enough and it is nice to know the easily identifiable stars in the Southern Cross and Orion's Belt.įor stars, use "Selected Stars" (AP 3270/NP 303) Epoch 2010.0, and calculate Local Hour Angle of Aries at nautical twilight (time in GMT for nautical twilight taken from the Nautical Almanac) for your Assumed Position thus:. ![]() Stars are not as useful as you would hope, because you need a clear horizon and by the time most stars are visible, the horizon is not. Once you can get a reasonable sight with the sextant, and have accurate time, all you need is Bennett's Almanac and an ability to add and subtract.įorget the theory.just follow the directions in the Almanac.Īs for the bodies, start with sun, moon and planets. Bennett from one of our Aussie Universities published his own version of an almanac good for (I think) 10 years. In fact easier to hold than heavy metal jobbies when all is pitching and tossing, and if you do drop it in the drink it won't break the bank.Īs for tables, a guy named Prof. It will take all of 30 minutes to master it.įor what it's worth, the Davis Mark 2 (the one with the vernier scale) is quite adequate for use on a small boat. ![]() By default, the time is set to local time rather than GMT/UTC.Ozdork if you are ever in Tassie I would be pleased to show you how to use that Davis sextant. By default, the stars are sorted by e "Options" -> "Settings" -> "Sort stars alphabetically" to sort by name rather than number.Ģ. This allows each set of sights to be viewed separately without having to delete the previous set of sights.Ī "Starfinder" uses the device's GPS and orientation to show each celestial body.ġ. The calculated line of position can be saved to the "Records" and placed on the provided map via a single click.Īll calculated lines of position stored in the "Records" tab can be displayed or hidden from the map. * intercept distance and direction (towards/away)ĭetails of the calculation from sextant altitude to observed altitude are shown.ĭetails of calculation from assumed position longitude to LHA of body are shown. * calculated altitude of the celestial body body (Hc) * actual altitude of the celestial body (Ho) * altitude of the celestial body read from sextant entered by user (Hs) * celestial body selected by user from a list of sun, moon, planets and stars * date and time entered by user or taken from device's GPS chip ![]() * assumed position entered by user or taken from device's GPS chip The best app that I’ve seen for celestial navigation. There is no clutter of unnecessary “features”. This app has everything that one needs to resolve several sights into a fix. ![]()
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