A weather balloon is prepared for release at the Cape Canaveral Air Force Station weather station.

A weather balloon is prepared for release at the Cape Canaveral Air Force Station weather station. The balloon is equipped with a radiosonde, an instrument that transmits measurements on atmospheric pressure, humidity, temperature and winds as it ascends. The data will be used to determine if conditions are acceptable for the launch of NASA's THEMIS mission. THEMIS, an acronym for Time History of Events and Macroscale Interactions during Substorms, consists of five identical probes that will track violent, colorful eruptions near the North Pole. This will be the largest number of scientific satellites NASA has ever launched into orbit aboard a single rocket. The THEMIS mission aims to unravel the mystery behind auroral substorms, an avalanche of magnetic energy powered by the solar wind that intensifies the northern and southern lights. The mission will investigate what causes auroras in the Earth’s atmosphere to dramatically change from slowly shimmering waves of light to wildly shifting streaks of bright color. Launch is planned from Pad 17-B in a window that extends from 6:01 to 6:19 p.m. EST. Photo credit: NASA/George Shelton