Sight Reduction 229 Interpolation tables

[dmccue]

I was explaining how the interpolation tables make it easy for us to look up data without having to remember a math formula to a Celestial study group. The sight reduction volumes have a good explainaition on how to use the tables if Dec. Int. is in range of 28.0′ to 59.9′ to correct Sextant Height calculated. I ran into a snag when i was trying to explain LAN Sun sights by sight reduction (local apparnet noon). Since LAN always ends up with the Local Angle Hour of 0 or 360 deg. The first differneces data ends up be d= +or – 60. Is it possible to use the 229 Interpolation tables for Hc correction in this situation?

[Tyler Szwarc]

Hi Dmccue,
It is possible to use the 229 Interpolation tables when LHA is 0, but in this specific situation, you don’t actually need them. When LHA is 0 and d = +/-60, your HC correction is simply the Dec. Inc, which is then added to or subtracted to Hc (as determined by the sign of d).
Hopefully I understood your question correctly; let me know if I didn’t!
Tyler

[dmccue]

Thank you , The response was clear. I can see now that by the formula Atltiude difference x del Increment / 60 that when the Alt Dif = 60 deg as in this case LHA=0, then the 60s would cancle themsleves leaving the remaining Declination Increment. Are the N.A.O. tables worth knowing how to use? Is there advantages for one or the other as far as precison goes or ease of use?
Del

[Tyler Szwarc]

Del,

Glad I was able to help. As for the N.A. sight reduction tables, I don’t have much experience using them. I use 229 to find Hc, Zn and d, and then I use a table from 249 to calculate the declination correction.

This table can be found here:
https://thenauticalalmanac.com/TABLE%205-%20Correction%20to%20Tabulated%20Altitude%20for%20Minutes%20of%20Declination.pdf

This table rounds the declination correction to the nearest 1′, but to me the ease of use is worth the minor loss of precision.

Tyler

[dmccue]

Thanks, I am familiar with the table 5 for the minutes corrections. I have a friend doing the Tom Tursi home study for celestial. He says he does not teach the tables but corrects by a calculation called Hci. I asked him to give me an example of how it is done. I will post it here when I get it from him.

[Author]

Posts