In 6BC, Jupiter, Mars and Saturn would all have been visible at the same time and close to the horizon. This would have made for an unusual and memorable sight, the sort of thing that we might expect to find recorded in any contemporary accounts of the time that may have survived. Is it possible that they formed the basis for a story about three wise men? Tales of planets being used by travellers to help them find their way are relatively commonplace, but the practicality of using them to find direction is a bit different.
The main challenge is that the planets do not behave in a way that is easy to predict without the help of paper or electronic tables. The reason for this is that they follow their own years, as they have their own orbit around the sun. This means that unfortunately there are no rules for planets that follow our year, we cannot for example say that Venus will be in the southwest in the early evenings of October. It will some years and not for many others. So how do we use the planets at all?
Like all celestial objects, planets rise broadly in the east and set in the west, so if we find a planet near the horizon, we must be looking roughly east or west. Unlike the stars, however, they do not rise on the same bearing from each location. Each planet can appear north of east at certain times and south of east at others, but will be consistent over the course of weeks, only changing over months and years. Saturn is currently in the constellation Virgo and is rising and setting very close to due east and west.
From the UK, all planets appear highest in the sky when they are exactly due south. Therefore if we see a bright object near the horizon moving upwards we must be looking roughly east, if it is moving down it must be roughly west. If, over a longer period, we see a bright object quite high in the sky, that arcs from left to right as it rises to its highest point and then begins to sink, then this must be the southern part of the sky. You will never see a planet in the northern skies from the UK.
Before we can use them, the first thing we have to do is recognize the planets. It helps to have some familiarity with the stars, because then any bright object that does not fit your reading of the stars will stir suspicions of a planet, but it is possible to recognize a planet even if you know no stars at all.
Planets tend to be brighter than stars and their light is usually steadier, it comes from a broader apparent source, and so planets do not scintillate or ‘twinkle’ in the way that stars do. Their brightness means they are usually the first objects to appear at dusk and the last to disappear at dawn. Jupiter, Venus and Mercury are white and usually very bright. Mars and Saturn are red and yellow respectively and can be quite bright, but often not much brighter than the stars around them.
The most useful things the planets can do is help us to hold a course. We might use the stars to find direction, let’s say we are heading southeast one morning and Venus is brightly showing the way then it is a great way to hold a steady direction, particularly if the terrain is confusing. I have used both Venus and Jupiter this way when moving through woodland on a moonless night. Without something to hold your course with at night, it is very easy to walk in circles otherwise.
In summary, the planets are not brilliant for finding direction compared to the stars, but they are useful in holding it and, besides, they add a lot of colour to our understanding of the night sky.
There is more information about using the planets to navigate naturally, as well as the sun, moon, stars, plants, animals and buildings in Tristan Gooley’s book, The Natural Navigator.