From The National Geographic:
Going blind isn’t usually a worry when watching for comets passing near Earth. But that’s what astronomers say could happen if people aren’t careful when they scan the skies for a glimpse of comet McNaught.
The comet is currently visible in the Southern Hemisphere near the horizon at dawn and dusk. It passes close to the sun, so observers are being cautioned not to accidentally gaze directly at the rising or setting star.
The fiery apparition—shown this morning through a gap in the clouds above Christchurch, New Zealand—is being touted as the brightest comet in 40 years, prompting crowds of hopeful amateurs to train their eyes on the sky.