The sun is about 93 million miles away from Earth, and if we think of that distance as a football field, a person starting at one end zone could get about 95 yards before burning up.
That said, an astronaut so close to the sun is way, way out of position. “The technology in our current space suits really isn’t designed to withstand deep space,” says Ralph McNutt, an engineer working on the heat shielding for NASA’s Messenger, a new robotic Mercury probe. The standard space suit will keep an astronaut relatively comfortable at external temperatures reaching up to 248°. Heat coming off the sun dissipates over distance, but a person drifting in space would begin encountering that kind of heat (the five-yard line) some three million miles from the sun. “It would then be a matter of time before the astronaut died,” McNutt says.
The space shuttle, however, has greater heat resistance than a spacesuit, so it could get to the two-yard line before cooking its crew.
http://www.popsci.com/science/article/2010-07/how-close-could-person-get-sun-and-survive | Photo: the Sun seen from Skylab, courtesy of NASA