When the number of days per year is zero, the same side of the earth perpetually faces toward the sun and the other side perpetually faces away. (Moon orbits Earth thus, leading to the Dark Side of the Moon.) If we were to live on such an earth, the most habitable region, being neither too hot nor too cold, would be the circle of longitude along which sunlight grazes the earth. Viewed from such twilight regions, the sun passes along the horizon.

When the earth’s inclination is greater than zero, the sun traces a figure eight, called a lemiscate curve, over earth’s surface. What would the sky look like from a habitable twilight region over the course of a year?¹ For a quarter of the year, the sun drifts northward just below the horizon, bathing the earth in semidarkness, and then, over the course of several days, the sun gradually rises north of where it had set. Over the next quarter year, the sun slides southward a bit above the horizon until it again meets the horizon. As it sets, the same cycle repeats over the next half-year, but this time the sun slides southward slightly below the horizon and then, after rising, northward slightly above the horizon. Each year, we would enjoy two prolonged sunsets and sunrises. No doubt, these would be occasion for extended holidays and feasts, at the very least.