No matter the destination, it’s a long walk. We make it easier on ourselves by using huge units to measure distance, such as a light-year, the distance traveled in a year by light—the fastest thing in the universe. A light-year is about 10 trillion kilometers (km). But that’s still fairly abstract to the typical person reading casually about “nearby” exoplanets or “distant” galaxies. One way to better grasp this scale is to take it step by step. The moon is the closest astronomical object to us in the entire universe. On average across its orbital path, it’s about 380,000 km from Earth. That’s already a pretty long way; nearly 30 Earths could fit side by side over that distance! Or think of it this way: the Apollo astronauts, traveling faster than any human before them, took three days to reach the moon’s vicinity.