A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Herbert Prinz
Date: 2018 Jul 25, 00:51 -0700
To achieve the specs of the longitude prize, the limiting factor for using anything slower than the moon is not computing power, but the theoretically required accuracy of the angle measurements. Not only can a normal sextant not provide it, but it exceeds the predictability of refraction.
At best, Jupiter moves a whooping 13' (prograde) per day (Moon: 60 times as much!). But even this happens only during conjunction with the Sun, when you cannot see the planet. It moves at half that speed (retrograde) when in opposition. While turning around between the two extremes, it stands virtually still for days.
Venus at maximum elongation basically follows the sun at 1° per day. This is better than Jupiter, but still only a twelfth of the speed of the moon. Needless to say, she is useless during both conjunctions.
The distance measurements would therefore have to be respectively at least 60 times or 12 times as accurate as those for the moon.