Mercury races around the Sun in just 88 days — the fastest planet, and the namesake of the fleet-footed messenger god. It has almost no atmosphere, so it bakes above 400°C in daylight and plunges below −170°C at night: the most extreme temperature swing of any planet.

Mercury never strays far from the Sun, so it is only ever visible low in the west just after sunset or low in the east just before sunrise, during the brief windows astronomers call greatest elongation. Look for a steady, slightly pink “star” in bright twilight. A flat, unobstructed horizon is essential — it never climbs high.