A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Steve E. Bryant
Date: 2020 Apr 1, 12:18 -0700
I made a trip to one of our city lakes yesterday evening for three purposes:
1. I'm re-working my PVC tubing for measuring eye height above water, and
2. to see if I could locate three objects in the evening sky all simultaneously, and
3. to perform a Venus Lunar measurement.
I used the Stellarium program to determine the azimuth and altitude of the Moon and Venus at a specific time. I set the sextant appropriately for each of the predetermined times (aided quickly and easily by the Stellarium program). The Program also provides an image of the sky showing the proximity of the Moon, Venus and of course the Sun along with the natural horizon. These images were useful in adjusting my gaze in search of the dimly lit Moon and the faint speck which was Venus. (I didn't bring my compass so the images from the app were useful). All three objects were above the horizon. The Sun and Venus were too far toward the West and therefore couldn't be brought down to the water's edge: trees etc., were blocking the view.
With the sextant set and the aid of the 7X35 telescope, I was amazed at how easy it was to find the dim Moon in the clear and brightly lit blue evening sky at 7:17PM CDST. Venus was located similarly and easily identified at 7:22PM. The Sun set occurred here at 7:51PM.
QUESTION: Given the good conditions of the day, would it have been possible to find and locate Venus throughout the day (second question: any day of the year)? And why is that? Does it have everything to do with the particular celestial positioning of objects this time of year or is it true that Venus can most often be seen during daylight hours?
I was able to evaluate and measure a Venus/Lunar distance by using Frank Reed's digital algorithm which revealed an approximate error in Longitude of 15°05.5'...extremely poor, I know, but the best I could do how. The error in the Lunar measurement, according to the algorithm, was -30.2'.
That was only the second Lunar I've ever taken. The other taken from my front yard months ago was appreciably better (or so I recall).
It's difficult for a novice to be very accurate especially given the great distance between the two at 39°17.1' and the altitude of the Moon, and the lower altitude of Venus as they were separated y that 39.3°. I'm convinced much of the error lies in my poor preparation for accurately observing the time. (I typically have no problem with this; it was a product of the complications of the day's events.)
The Lunar measurement was made at 8:04PM, Latitude 35° 31' 08"N; longitude 097° 42' 17"W' HE 4.5' (I was setting down near the water's edge) and IE: 0.2".