Of all the bodies in our solar system, the sun is probably the one we want to give the widest berth. It gushes radiation, and even though its surface is the coolest part of the star, it burns at about 9,940°F, hot enough to incinerate just about any material. As such, there are no plans to send a manned mission in its direction anytime soon (Mars is much more interesting, anyway), but it can't hurt to figure out at what distance a person would want to turn back. You can get surprisingly close.