Isotherm, in geography, a line drawn on a map connecting places that have the same average temperature for a given period of time. For example, an isotherm running through New York City, St. Louis, and Seattle would indicate that these cities, as well as any others along the line, all had the same average temperature for a specified period. Isotherms are useful in compiling and showing climate information. For example, for general farming, an average temperature of at least 60 F. (16 C.) is necessary during the warmest months. A map marked with an isotherm of 60 F. for the months of July and August would show the northern limit of the area where the temperature would permit general farming.
We take much for granted about our universe, like it's getting bigger. What if the universe stopped expanding and started collapsing inward with a giant crunch?
He is famous for a phrase he never said, for wearing turtlenecks and for hosting the original 'Cosmos' TV series. As enthusiastic about the stars as he was about marijuana, Carl Sagan led a very surprising life. Here are 10 cool facts.