I love astronomy images, and I look at a lot of them, but this one from APOD last month is the most jaw-dropping image I've seen in a long time:
(Click for the desktop-worthy large version.) The photo, capturing almost the full 360-degree-by-360-degree spherical projection of space seen by a viewer floating in the Solar System, is a composite of two dark-sky photographs, from Chile in the southern hemisphere and the other from the Canary Islands in the North. What's jaw-dropping about this picture is the S-shaped band of light: it's not the Milky Way. In these images, the Milky Way is behind the mountains on the horizon. The band is actually the interplanetary dust between the planets in our own Solar System (or rather, sunlight reflected the dust orbiting along the ecliptic plane). Amazing. Also, the sight of the Magellanic clouds warms the cockles of my ex-Southern-hemisphere heart. There's something about seeing another galaxy with the naked eye that gives one context, y'know?
Astronomy Picture of the Day: A Tale of Two Hemispheres