NavList:

Antoine, you got intercepts of 0.1,0.5,0.5,0.6,0.4 nautical miles. Since we're interested in the fine details of the tenths here, note that I got -0.35,+0.1,+0.15,+0.15,0.0 for the same sequence after correcting for oblateness (unless the USNO online calculator already includes the oblateness in which case add back 0.15' to each). Your numbers would be the same as mine with an offset of 0.4' (within a tenth). I'm wondering where that came from... Even if we back out the 0.15' for oblateness, my numbers are still uniformly less than yours by about 0.25'. It's no concern in practical terms, but it really shouldn't be there.

Antoine you wrote:
"I am asking simply because our standard CelNav Formula "sin(Height)=sin(Lat)*sin(Dec) + cos(Lat)*cos(Dec)*cos(Body Local Hour Angle)"
is not best suited to determine "Body Local Hour Angle" as its cosine starts becoming close from 1, as is the case here."

Maybe I misunderstood you here, but as you've written it, I don't agree with this. The sensitivity of the LHA to the inputs is simply the nature of the problem. It's not an issue with the "standard celnav formula". Some decades ago, when trig problems were done with tables (and even on computers if they had mediocre math libraries), the resolution of the values of the cosine (near one) for small angles was an issue, but that's no longer the case. Bruce shouldn't be trying to get LHAs (and thence longitudes) from sights near the meridian because the geometry ITSELF is very sensitive to small changes in the input values of the altitude, latitude, and declination. The fact that the cosine is nearly one is a symptom of that problem, not a separate issue. And just to reiterate, the sensitivity of the formula is EXACTLY the same sensitivity that we see in a plot of LOPs. If I have a latitude line, and I cross this with an LOP that's perpendicular to azimuth 165, the shallow crossing angle will yield a large change in longitude, at rate of about 5-to-1, for a small change in altitude, declination, or latitude.

-FER

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