Triangulum Galaxy

M33 sits roughly 2.7 million light-years from Earth — slightly farther than Andromeda — and forms, along with M31 and the Milky Way, the gravitational backbone of the Local Group. From dark skies it is a naked-eye object, but its low surface brightness makes it notoriously elusive: it is large but diffuse, easier to find with averted vision than through high magnification. The galaxy is rich in star-forming HII regions, the most prominent being NGC 604, a glowing pink complex ~1,500 light-years across — large enough that it appears as a distinct catalogued object in many surveys. For imagers, M33 rewards generous total integration. Long exposures with broadband filters bring out the loosely wound spiral arms, while pure Hα captures pull the HII regions out from the spiral background like a constellation of pink jewels. Recent radio observations suggest a tidal bridge of hydrogen connects M33 to M31 — they may have had a close encounter billions of years ago.