In space, next times are few and far between. Think about Pluto, and all those features we’d take a closer look at if only we could send a second spacecraft zooming by. Or Uranus and Neptune, two giant planets that just now, more than a quarter-century after our first quick visit, might be inching back onto the itinerary. The same is true for distant galaxies, exploding stars, and ghostly nebulae, which often appear in the eyepiece only after competitive observing time is awarded.
Each goodbye could be our last.