About two dozen satellite galaxies orbit the Milky Way. By far the brightest are the Large and Small Magellanic Clouds, both of which are within about 200,000 light-years of Earth. They’re best seen from the southern hemisphere, where they look like small, glowing clouds. In the past decade, our view of these two galactic neighbors has undergone a pretty big makeover. Astronomers used to think the Magellanic Clouds orbited the Milky Way once every one or two billion years. But in 2006, observations by Hubble Space Telescope suggested that the clouds had a wider orbit and thus a longer orbital period. And last year, new Hubble observations found that this period is at least four billion years and possibly much longer. Meanwhile, other studies show that only a few percent of giant galaxies like the Milky Way boast a pair of bright, star-making satellites as close-in as the Magellanic Clouds. The Milky Way’s other satellites are dead — they’re devoid of any star-making gas, so they no lon
