Astronomy Picture of the Day . Mercury on the Horizon . ... Because Mercury orbits so close to the Sun, it never wanders far from the Sun in Earth's sky . If trailing the Sun, Mercury will be visible low on the horizon for only a short while after sunset . ... So at certain times of the year an informed skygazer with a little determination can usually pick Mercury out from a site with an unobscured horizon. ... Publications with keywords: horizon - sunset . ... Little Planet Shadowrise . ...