Our changing view of Mars over 2018, increasing in size as Earth got closer, than shrinking as we pulled away. Credit: Damian Peach

“Apparition” is the term astronomers use for the appearance of an object over some course of time. For Mars, it means when it first appears west of the Sun in the morning sky, after being lost in the glow. Earth moves faster in its orbit, so we catch up to Mars and pass it. When we’re closest to Mars and it’s opposite the Sun in the sky we say it’s at opposition. Mars rises at sunset and becomes an evening object. After that the Earth pulls ahead, Mars recedes, and some months later approaches the Sun from the east until it’s lost in the Sun’s glare once again, this time at dusk.