NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Modris Fersters
Date: 2023 May 7, 07:49 -0700
Hello, Jan!
You wrote: “Has anyone used Venus this Spring for sights?”
Yes I had. But not for real navigation at sea. Therefore I don’t no if it is of any interest to you. But I will try to describe my own experience this Spring and will give some recomendations.
I measured the angle between Venus and the near limb of the Sun on 7 April from latitude 57°N (just like lunar distance sights). The altitude of the Sun was about 35°, the altitude of Venus: about 53° (these numbers are from Stellarium, I did not measure them with sextant). My purpose was to measure acurately only the distance between these two celestial bodies (it was about 38°).
How did I find Venus? I simply preset sextant to the approximate angle which I measured in Stellarium (or you can use any appropriate software to calculate separation angle; or you can calculate this distance from celestial coordinats by yourself; great accuracy is not needed).
Then I put shades on horizon mirror and looked to the Sun through my sextant telescope. Then I slowly (THIS IS ESSENTIAL, BECAUSE IT IS EASY TO MISS THE PLANET WHEN MOTION IS TOO FAST!) rotated sextant around telescope axis (all the time keeping the image of the Sun in the field of view) till I found reflected image of Venus. Besides a good guide is the angle of the ecliptic with the horizon. You can easily see it in Stellarium (press “,” button to show ecliptic). The sextant tilt angle will be the same as the angle of ecliptic with horizon in this direction.
Ones you have found Venus in the field of view, adjust micrometer, so far as it is necessary.
Now you see how Venus look through the telescope in the given situation (depending on weather conditions). If you want to measure the altitude of Venus, I would recomend to do the following:
-Repeat the procedure I described above (but this is not obligatory; you can start with the next step too).
-Preserve the index arm position (don’t change it’s position; sextant must be preset to the Venus/Sun separation angle), look at the sky in direction where you are expecting Venus is, and try to catch the image of the Sun in the field of view. (You can start with sextant tilted horizontally (90° to its usual position) and looking at the same altitude as the altitude of the Sun. Then move sextant away from the Sun horizontally until you find the reflected image of the Sun.)
-Then you rotate sextant vertically keeping Venus in the field of view.
-Then bring Venus down to the horizon and measure the altitude.
At first glance all these steps may seem complicated, but in practice this is very fast and easy.
Modris Fersters
