You might be interested in knowing that Venus is often used by celestial navigators to derive an exact position at sea during daylight hours. Lines of position (LOPs) from the sun and Venus, and if available, the moon, can be intersected to yield a precise location on earth. As you know, Venus is often easily visible in daylight, but it is hard to find against a bright sky unless you know exactly where to look. Navigators can use the nautical almanac or other tools to derive a rough azimuth and elevation from an estimated position so that precise sextant observations can then be made to calculate the exact position.

This is important because observations of at least two celestial bodies are required to get a precise latitude and longitude, and a third body is highly desirable because it helps verify the accuracy of the other two observations. At sunrise and sunset, there are numerous stars available whose angular elevation above the horizon can be measured (at night there is no horizon and observations are impossible). But in daylight, only the sun, moon and Venus can be seen, and rarely are all three available at once. The size of the triangle on the chart formed by the crossing of the three LOPs is an indication of the accuracy of the position.

The LOPs are not azimuths to the celestial bodies, azimuths cannot be measured to an accuracy of better than half a degree (30 nautical miles!). However, elevations above the horizon can be determined to an accuracy of half a minute of arc with a sextant (about a 1000 meters). The LOP is at right angles to the azimuth, and represents a tiny segment of a circle on the earth where the celestial body would appear to have the same elevation. Under good conditions, a skilled navigator can calculate his ship's position to within a half mile: not as good as GPS, but it doesn't require batteries.