This week, courtesy of dark skies, clean air, and panoramic views from our Welsh hideaway, markontour saw the planet Mercury for the first time (the glowing dot in the picture above).
As a lifelong urban dweller this has rarely been possible before and I was surprised, therefore, to discover that when you do get a decent line of sight, Mercury is really bright. Indeed, at a magnitude of minus 0.6 (for some reason astronomers have chosen to categorise the brightest stars in minus numbers, while the dimmest twinklers get a positive sign) this week Mercury was one of the very brightest objects in the night’s sky. For reference, the brightest star in the northern sky, Sirius, clocks in at -1.4, and the Pole Star only registers +1).
Due to its closeness to the Sun, Mercury is only visible low on the horizon just before dusk and dawn. This means you’re never going to have the pleasure of seeing the smallest planet in our solar system if you live in a city, where buildings hide the horizon and pollution makes everything fuzzy.
Probably because it is relatively hard to see, Mercury is often overlooked. It is relegated to the shortest movement in Gustav Holst’s ‘The Planets Suite’, for example, and it doesn’t even come first in the sequence, despite its premier spot in the Solar System line-out.
Yet there is a lot about Mercury that is interesting and unusual. What we consider today to the be planet closest to the Sun was in fact born 170 million miles further out, close to the current position of Mars. A very large impact kicked it further in and, in the process, dislodged most of the planet’s outer layer. Thus Mercury today is 85% of what we would consider ‘core’ in relation to the Earth.
I don’t recall if it was because of this primordial jolt, but if you spent a year on Mercury it wouldn’t last much longer than a day. That is, in the time it takes Mercury to orbit the Sun the planet only spins one and a half times on its own axis.
For ancient astronomers Mercury provided a different conundrum – the Greeks worked out from its passage across the sky that Mercury orbited the Sun, but how could that be when Earth was the centre of the universe and every planet existed within its own celestial sphere? The ingenious answer was that Mercury and Venus orbited the Sun and the three of them were together inside their own sphere, which itself orbited the Earth.
Four hundred years ago, after the motion of the planets was recalculated using Newtonian physics, it was concluded that only the existence of a yet unsighted planet between Venus and Mercury could explain the non-circular orbit of the latter. This planet they named Vulcan. It took Einstein’s theory of relativity, and an understanding of how bodies with mass bend the fabric of space, to provide an alternative explanation.
It is an example of how astronomers of old thought that the universe was as densely populated as terrestrial cities. In fact, most of space is empty, at least in the sense that the human brain can comprehend it. The artist Mishka Henner has produced a 12 volume ‘Astronomical’ book that depicts our solar system as it would seem if travelled through from the Sun outwards. Most of the pages are pure black. Each page represents a million kilometres of space and Mercury appears as just a speck in volume one.
Indeed, we have learned more about Mercury in the last 50 years than in the previous 5,000 (meaning humanity, rather than me and Ms Markontour, although we have also learned more about Mercury in the last five days than in our previous 40+ years). Yet only two objects manufactured by human beings have ever been within a million miles of the planet, starting with the Mariner probe’s fly-by in the mid-1970s, and most recently with Messenger’s kamikaze descent to the surface.
Perhaps that’s why Gustav Holst’s musical interpretation of Mercury still feels right, even though he derived his compositions more from his interest in astrology than understanding of physics – thus the un-astronomical ordering.
Listening to my 1970s vinyl recording of the Los Angeles Philharmonic Orchestera’s interpretation of ‘The Planets’ tonight, markontour’s untrained ear hears the Mercury movement as a call-and-response song, perhaps fittingly as Mercury was ‘the winged messenger’ of Roman mythology.
But mythological Mercury was a god of many talents, also representing avarice, or at least commerce and financial gain, as I recall from seeing his statue everyday from a former office window on the edge of London’s financial district.
Better, in my mind, is the Welsh mythological tradition, in which Mercury is synonymous with the magician god, Llew. You can’t imagine a god called Llew extracting surplus value by paying workers less than the value of the product of their labours, and a planet whose days and years are easy to get mixed up is bound to be able to pull off a decent card trick.
In any case, I am happy just to have had a decent look at Mercury from afar for just a few minutes. For those in Britain, Mercury will remain prominently visible just after dusk until February 14th or so. But you’ll need to get out to the country to have a chance of seeing it. I recommend Wales.
*The interweb has not been consulted in the writing of this blog. Instead, all information has been sourced from books in our house (some, admittedly, quite old, including a lovely 1960s version of ‘Astronomy With Binoculars’). It could be wrong, it could be right..