Practical Astronavigation

Good pointers, the culmination of the Sun


What far

You received the positional line but you don't know where you are. Remind yourself what they taught you of bases of the coastal navigation: position of around two nonsimultaneous bearings on 1 object.. Wait 2 hours and do the second positional line into the identical way.

Draw it everything so:       

Good pointers

1. Note the state of the log directly after the measurement of the height!!!

2. For the bigger accuracy, do at least 3 measurements with the sextant, employing the second person by the chronometer. The first measurement - for example 37°18'. Shout 'now' for catching the time. Turn the screw propeller up about 5' and place on 37°23'. When the Sun reaches up to the horizon in the telescope, shout 'now' and turn the screw propeller up against more distant 5'(37°28'). You must not in this way have around three heights the arithmetic mean. The other measurement is an average: 37°23'. You are only counting average of around three times. The temporal difference between the first and second measurement should at the accurate measurement be identical, as between second and third. If so - it too average you are taking the time of the second measurement.

3. At big waving of the sea, make measurements with the sextant from the big height from the sea level, in order to not take some of waves for the range.

4. At very big waving of the sea, when the hull of the yacht is butting against waves, but you with eye against the telescope, twist the telescope off and leave her in the box. Do measurements 'from the free hand'. It concerns observation of stars and planets alone at night. The telescope is only disturbing. Curiosity: no textbook familiar to me astro is leaving out, what the telescope is in the sextant up to. Reply: there is this device for short-sighted, if only they could without glasses see the horizon.

5. You can for correcting the measured height use for example Polish navigational boards TN-74, but do it consistently then. Why all amendments of the Nautical Almanac, why all from TN-74. Taking for example an amendment from TN-74 to the height of the eye, and he is giving amendments from RA to the edge essentially nonsense, because zero points are in both systems somewhere else.

6. If you are on the eastern hemisphere, remember that it is necessary to add the longitude to GHA.

7. If you are doing astro on the northern hemisphere after 23 September, and before 21 March remember to go the right side up to HD 605 (contrary name). Check by the Moon, planets and stars each time whether the declination is north or south. (letters N or S).

8. ATTENTION! Trap on novice! If you are to the west of Greenwich far, but the Sun 'you caught' right after the culmination on the Greenwich meridian, you can receive for example such a result:

GHA = 6°37,5'
- λ = 34°37,5'

Results: LHA is negative what is impossible by definition. Solution: add to GHA in such a case 360°. You will receive 366° - 34° = 332°. Test: The sun is right after the culmination in Greenwich so GHA is small, but before the culmination at you, so LHA is approaching 360°.

9. Try to adopt some constant principle of writing measurements and calculations. You won't already have to after a dozen or so examples write labels at individual numbers, well place on the page, which the given number is written down, with is determining every it too number. Try to write what you designed until now according to of diagram:

It is looking out on numbers this way:

As can be seen don't need the sheet of paper to one positional line!



Culmination of the Sun

1. Entire dose of the theory:

2. Entire practice:

14.08.1980, The place are like in the previous example.

  • Calculate the time of the culmination: enter RA into the table SUN Mer. Pass. and read out 12h 05m. This hour, alike entire RA he is treating GMT
  • Open RA on the first yellow page (Conversion of arc to time), enter with your longitude there (10°). 0h Read out 40m.
  • Add it according to of GMT pattern - (± λ). You are receiving:
  12h 05m  
  + 0h 40m  
  12h 45m at this hour (GMT) the Sun will be culminating on your meridian.
  • Catch the height with the sextant. You received 57°23,1' (bottom edge).
  • Correct the height:
    + 0,1'   (from the certificate)
    - 3,0'   (mistake of the index)
    - 3,3'   (height of the eye)
    + 15,3'   (bottom edge)
  hs = 57°32,2'  
  • Calculate declension: from RA
      hour 1200 - N 14°13,8'
      hour 1300 - N 14°13,0'
    Interpolate in the memory: per hour 1245 : Dec.=14°13,2'
  • Calculate: φ = 90 - h + δ = 90° - 57°32,2' + 14°13,2' = 46°41'.
  • Cross the latitude off on the map!

Attention! He doesn't have trouble with the azimuth because he is obvious: 180° or 0°, if the Sun is culminating to the north of you.




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Practice - algorithm of acting in seven points
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The Moon, Planets and Stars



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