It is only comparatively recently that much was discovered concerning the true nature of this mysterious little world.
It was long believed that Mercury spun once on it’s axis in the same time as it took to make one revolution of the Sun (88 Earth days) but radar investigations have established a correct value of just over 58 days.
This mistake was not really surprising as through the telescope, Mercury is very difficult to observe as the ‘messenger of the gods’ never strays further than 28° away from the Sun and has a maximum apparent diameter of only 13 seconds of arc.
Thus when a naked-eye object, Mercury is always low down and a clear horizon is necessary to see the planet in the dawn or dusk sky. For observers in the northern hemisphere, favourable elongations take place during the spring for evening observations and autumn for morning views but it is worth trying to locate Mercury at one of it’s less favourable elongations during the year.
Mercury is best seen through the telescope against a bright sky. Little will be seen apart from the phase but it is always a thrill to glimpse this elusive world for one’s self.
Full details concerning the current visibility of Mercury are given in “SkyDiary” in Popular Astronomy magazine.
Warning: When observing Mercury with a telescope or binoculars, only attempt to do so when the whole of the Sun’s disk is below the horizon. As Mercury lies close to the Sun in the sky, there could be a danger of getting the Sun in the view. This could result in eye damage, or loss of eyesight.