It's been nearly a decade since the closest planet to the sun sneaked between Earth and our blazing star. The European Space Agency says Mercury "boasts fascinating surface geology, including countless craters, ridges, highlands, plains, mountains and valleys," but you won't be able to see any of those details. It will look like a small black dot making its way across the disk of the sun.
Mercury last transited the sun in late 2006. If you miss the 2016 event, you will only have to wait until 2019 for the next round. The transit starts in the morning on May 9 in the US. Mercury will take its sweet time crossing the sun, racking up about a seven-hour journey. Most of the world will have the opportunity to see at least part of the transit. You can check in with NASA to follow the space agency's live coverage of the event.
Mercury is pretty tiny compared to Earth, coming in at less than half the diameter of our planet. Humans can't just stare at the sun and spot the little planet moving. You'll need to use your own telescope, make friends with a telescope owner or check to see if your local astronomy club has a Mercury viewing planned. Telescopes have to be equipped with a solar filter for safe viewing. The reward will be your participation in an uncommon astronomical happening along with fellow planet-watchers around the globe.