Mariners often take Sun/Star sights just to compare the ship's position with GPS.
now as we all know that for sunlight to reach earth it takes about 8.5 minutes so that means the sun which i'm seeing is not acually there. this is the position where sun was 8.5 minutes before, but when calculating the sights the time is taken directly without any correction. also nowhere in the books which are used in the process (nautical almanac, norie's tables) any correction in this regard is mentioned. still mariners managed to get the right position. so where is the correction??
only serious answers please as i'm a mariner.
2006-10-22 23:09:02 · 3 answers · asked by amit v 2 in Science & Mathematics ➔ Astronomy & Space
OK, you take your sun sight at noon, traditionally right? Then you "Bring the Sun Down" on your Sextant down to the horizon- this tells you your lattitude, right?
If you've got the sailing almanac, and you're willing to do the calculations, the ships navigator is supposed to do this every 2 hours. Yeah. Right- NOT! Not when you've got GPS- they usually only "shoot the sun" for practice, and to make sure one is checking the other
2006-10-23 00:00:49 · answer #1 · answered by Anonymous · 0⤊ 0⤋
campbelp2002 has the correct answer. The keyword here is "apparent" position of the celestial object. Your nautical almanac gives all tables of positions in "apparent" form, meaning that they've already been corrected for light time travel. You may still need to correct them for atmospheric refraction when they are close to the horizon, but there is no need to apply light time travel corrections since those are always the same for all locations on earth. Now, if you plan on navigating beyond earth's orbit, you'll need to apply a different light time correction, but assuming you remain at sea level on earth itself, there are no additional light time corrections necessary.
For more information, see Jean Meeus' work "Astronomical Algorithms", or the earlier version of that same work "Astronomical Formulae for Calculators".
2006-10-23 15:05:17 · answer #2 · answered by Anonymous · 0⤊ 0⤋
I suppose that all tables are compiled based on the apparent position of the Sun, so they can be used with observations of the apparent position.
2006-10-23 09:01:09 · answer #3 · answered by campbelp2002 7 · 1⤊ 0⤋