# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**Re: Jupiter-Venus angular separation**

**From:**Antoine Couëtte

**Date:**2022 May 6, 02:51 -0700

**(1) - Geocentric approximation:**

**1.1 -** 09:00 Geocentric Center to Center distance 1°31.1'

1.2 - 11:00 Geocentric Center to Center distance 1°35.2'

from which we derive **Geometric Center to Center distance at 08:43 to be quite close from 1°30.5' (which is our Topocentric Target value).**

Hence let's use 08:43 as a first - and probably rough - approximation for UT estimate, and see what actual sextant topocentric distance we get between Venus and Jupiter.

**(2) - 1st UT Estimate with UT = 08:43 and topocentric approximation**

From Atria and Venus published heights (15°07' and 27°52') considered to be measured both at 08:43, get S00°26.0' / W053°00.2' from which we compute (reverse engineering):

Venus observed Height 27°52.0' / Azimut 091.351° and Jupiter observed Height 29°14.7' / Azimut 091.673°,** i.e a sextant distance at 1°24.4' **(includes everything : refraction, parallax, ...).

Too low since our target sextant distance is 1°35.0'

**(3) - 2nd UT Estimate and topocentric approximation**

Assuming that the topocentric rate of change between Venus and Jupiter Distances is equal to its geocentric rate of change, let's try everything again through assuming that UT = 11:30

From Atria and Venus published heights (15°07' and 27°52') considered to be measured both at 11:30, get S00°28.0' / W094°44.7' from which we compute (reverse engineering):

Venus observed Height 27°52.0' / Azimut 091.279° and Jupiter observed Height 29°20.8' / Azimut 091.645°, i.e a **sextant distance at 1°30.8'**, (includes everything : refraction, parallax, ...).

Slightly too high since our target sextant distance is 1°35.0'

**(4) - 3rd UT Estimate at 11:22 and topocentric approximation**

From **(2) **and **(3)** above, we perform a third trial with UT = 11:22

From Atria and Venus published heights (15°07' and 27°52') considered to be measured both at 11:22, get S00°27.9' / W092°44.8' from which we compute (reverse engineering):

Venus observed Height 27°52.0' / Azimut 091.283° and Jupiter observed Height 29°20.5' / Azimut 091.646°, i.e a **sextant distance at 1°30.5'** (includes everything : refraction, parallax, ...).

*Here we are !*

**Computed Solution is close from :**

**UT = 11h22m at S00°27.9' / W092°44.8'**

**(5) - Comments :**

**(5.1) - **This result assumes a non moving observer.

**(5.2) -** Computed Position could be slightly refined through assuming that you observe Atria at 11h20, you then observe Venus at 11h21 and you carefully measure your Sextant distance of 1°30.5' at 11h22m . I leave this to other number crunchers. Should not change the result by that much.

**(5.3) - HOW ACCURATE ?** Between 08h43 and 11h30 the geocentric observed Sextant distance changes from 1°24.4' to 1°30.8' , i.e 6.4' in 2.8 hours. If we consider that our sextant distance built-in error cannot be less than 0.1', this translates into an uncertainty of slightly under 30 minutes on the UT determination, i.e. an uncertaintly of 7° on Longitude. If we assumed sextant error of .2' which would be already a nice and solid result - and a more realistic one - then our longitude guaranteed accuracy is just under 15°.

Longitude again, Longitude always ...

But use Lady Moon instead !

Antoine M. "Kermit" Couëtte