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.
The Freemasons is a secret organization that began in the 1700s and is still in existence today. Who are the Freemasons? And what do they do in their secret meetings?
Every November, the Leonid meteor shower fills the sky with "shooting stars." This year, the shower is expected to peak twice. Learn how Leonid and other meteor showers work.