In this recent period of cold, clear weather, it is possible to notice the procession of the lengthening days, the subtle shift of four minutes at the beginning and end of each day by which we edge towards spring. I can now walk over dusk-filled fields at five-thirty or later, observing the colours of the sky as they darken from cerulean to indigo, sometimes shot with clouds of improbable gold and rose. I learn to appreciate the beauty of the half-light, the sense of pause it brings to the start and finish of each day, that liminal time when birds, animals and the weather are all in a state of stasis, a lacuna in their restlessness.
Twilight has degrees; there are different forms of twilight,definitions precise enough to regulate the progress of the sun as it disappears over the horizon. Civil twilight, when the sun is less than six degrees below the horizon, gives us light enough to continue about our day-time tasks. It is the period of gloaming, as it is called in Scotland, a word that carries the weight of gloom but the freedom of roaming; a light sufficient to be still wandering the hills. Civil twilight is the time curtailed, for those of us in Britain, by Lighting Up Time; a ritual enshrined in the lighting of gas lamps on city streets: “and then the lighting of the lamps” as Eliot has it. The word dusk comes from the Old English for brown, and this memory of urban twilight conjures somehow that sense of colourlessness, like dark folds of cloth.
When the sun is further still below the horizon – six to twelve degrees, we have nautical twilight, a darkness in which mariners can fix their position from brighter stars, but when features on the shore have not yet melded into the gathering night. And then comes astronomical twilight; a form of darkness so indistinguishable from night that only astronomers may perceive it; a time when even the faintest of stars become visible on clear nights; the time when the faint light from distant stars reaches the earth through the thickening density of night. Beyond this period, when the sun is lower than eighteen degrees below the horizon, is true night. It is a condition that is alien to our northern skies in high summer; we are trapped in perpetual astronomical twilight, hovering in a limbo of almost-night like restless souls waiting for the dawn to return.
The importance of twilight is embedded in northern cultures in a way unknown in the tropics, where the sun sets so abruptly, like a performance in which one is still waiting for the final curtain call. It marks the shift from outside to inside, from activity to rest. It is also a time when many of the creatures which feature in our mythology are at their most active: badgers, foxes, deer, hares, bats, they are all crepuscular, creatures of the half-light.
I learnt that the twilight time in french is sometimes called l'heure bleue, as though there is an ineffable sadness which comes with the transition from day to night or night to day, a sense of loss which lasts only as long as the time taken for the light to change. Blue is also the colour of distance, of the far horizon when seen on a clear day, and we can imagine twilight as a gathering of this blueness, a slow creep of indigo from the edges of the world until it closes above our heads with the coming of night, like an ink stain on a sheet, a diffusion of blue.