Daylight recedes as the setting sun moves west into China. On the Asian mainland beyond, it is still late afternoon, and twilight awaits. Before disappearing entirely, the sun descends to between four and eight degrees below Tokyo’s western horizon. Though no longer visible and its direct rays gone, a diffuse glow persists in the atmosphere. Shorter blue wavelengths come to the fore as they scatter through the air, giving rise to the cool, liminal interval between day and night we call the blue hour.

Blue hour came to structure my days last June, when I spent a week walking west to east along the Chūō Line. The walk followed Tokyo’s longest unbroken stretch of railway track, a distance of 142 kilometres, amounting to 222,524 steps at around 31,500 per day. Keeping to schedule meant being on the streets from first light until dark, and over the week, I grew attuned to the city’s patterns.