Island and the main Hawaiian Islands, whereas the conjugate region was in the vicinity of the Samoan, Fiji, and Tonga Islands. It is in these areas that auroras were actually observed, in addition to those in the areas of the nuclear explosions." Beta particles are charged particles (usually with a negative electrical charge) that are released from nuclear explosions. These particles travel in a spiral along the magnetic field lines in the Earth's magnetic field. The nuclear explosions also release heavier debris ions, which also carry an electrical charge, and which also travel in a spiral along the Earth's magnetic field lines. The Earth's magnetic field lines arc high above the Earth until they reach the magnetic conjugate area in the opposite hemisphere. According to the DOD nuclear weapon effects reference, "Because the beta particles have high velocities, the beta auroras in the remote (southern) hemisphere appeared within a fraction of a second of those in the hemisphere where the burst had occurred. The debris ions, however, travel more slowly and so the debris aurora in the remote hemisphere, if it is formed, appears at a somewhat later time. The beta auroras are generally most intense at an altitude of 30 to 60 miles, whereas the intensity of the debris auroras is greatest in the 60 to 125 miles range. Remote conjugate beta auroras can occur if the detonation is above 25 miles, whereas debris auroras appear only if the detonation altitude is in excess of some 200 miles." Some of the charged particles traveling along the Earth's magnetic field lines cause auroras and other geophysical phenomena in the conjugate areas. Other charged particles are reflected back along the magnetic field lines, where they can persist for long periods of time (up to several months or longer), forming artificial radiation belts. According to the Operation Fishbowl planning document of November 1961, "Since much valuable data can be obtained from time and spectrum resolved photography, this dictates that the test be performed at nighttime when auroral photographic conditions are best." As with all U.S. Pacific high-altitude nuclear tests, all of the Operation Fishbowl tests were completed at night. This is in contrast to the high-altitude nuclear tests of the Soviet Project K nuclear tests, which were done over the populated land region of central Kazakhstan, and therefore had to be done during the daytime to avoid eyeburn damage to the population