How Hot is John? The chart below tracks astronaut John Grunsfeld's core body temperature as he moved up Mt. Denali to 17,200 feet. Climbers on Denali share a special bond: they are very cold. But are they cold to the core? A human's "core body temperature" is that of their vital organs. Amazingly enough, there is an accurate and relatively convenient way to measure this temperature continually. It involves swallowing a large pill (about the size of a large jelly bean) which contains a tiny radio transmitter. The frequency of the radio transmission changes depending on the surrounding temperature. A calibrated receiver placed nearby (for example, strapped around the waist) is able to pick up the radio frequency of the pill. The receiver then translates the frequency to an actual temperature, continually measuring the subject's core body temperature until the pill passes through the system. We've asked Astronaut John Grunsfeld, a first-time Denali climber, to measure his core body temperature during our trip using this method. We'll look both at the broad view - how core body temperature stays nearly constant despite dramatic changes in air temperature, wind speed and elevation. We'll also take a look at a full day's cycle of his core body temperature at several key stages of the climb up the West Buttress route and during the summit bid. We'll learn how his body behaves differently during sleep, find out whether it overheats when working hard in the intense sun, and observe how core temperature relates to skin temperature. Return here throughout the adventure -- we'll be adding data to the page at key junctions during the climb. Photos: (2) NASA. Climb | Expedition | Mountain of Extremes Denali for Kids | Dispatches | E-Mail | Resources Site Map | Surviving Denali Home Editor's Picks | Previous Sites | Join Us/E-mail | TV/Web Schedule About NOVA | Teachers | Site Map | Shop | Jobs | Search | To print PBS Online | NOVA Online | WGBH © | Updated November 2000