Mercury reaches magnitude -1.9 at brightest but never strays more than 28 degrees from the Sun, making it one of the harder naked-eye planets. Look for it low on the horizon during twilight — best seen at greatest elongation, roughly three times per year from each hemisphere. Its tiny disk (5-13 arcsec) shows phases like Venus but demands at least a 150mm telescope to resolve. Ancient Sumerians recorded it around 3000 BCE, calling it Ubu-idim-gud-ud. The Romans named it Mercury after the swift messenger god for its rapid orbit (88 days). Mariner 10 made three flybys in 1974-75, mapping about 45% of the surface and discovering a global magnetic field. MESSENGER orbited from 2011 to 2015, revealing water ice in permanently shadowed polar craters and a surprisingly dynamic magnetosphere. BepiColombo, a joint ESA/JAXA mission launched in 2018, is en route and will arrive in 2025. Mercury's surface is heavily cratered like the Moon, with the Caloris Basin (1,550 km) as its dominant feature. The planet has no atmosphere to speak of, just a thin exosphere of sodium and potassium that creates a faint cometary tail detectable in large telescopes.