If you saw the aurora for the first time, and had no idea what it was, what would you think it was? Could you figure out how high it is, if it is higher than the clouds? Could you find out where its light comes from? Could it be sunlight reflected from ice crystals? What clues could you look for to help find the answers? It took scientists hundreds of years to gather the clues that led to our present understanding of the aurora. Here are some of the important clues:
- 1600 - English physician William Gilbert shows that Earth is a gigantic magnet. Nobody realized that this fact is crucial to understanding the aurora.
- 1774 - French scientist Jean Jacque Dortous de Mairan relates auroral displays to solar activity.
- 1860 - Elias Loomis of Yale University identifies the auroral zone, the region of greatest auroral activity. Eight years later, Anders Jonas Angstrom of Norway uses a prism to show that auroral light differs from sunlight. So much for the reflected sunlight theory!
- 1910 - Norwegian scientist Carl Stormer uses triangulation (observing the same aurora from different locations) to measure auroral heights. Measurements in Alaska (1930-1934) by Veryl Fuller confirm that auroras occur at the same altitudes throughout the northern auroral zone (typically around 100 km high).
- 1925 - Discovery of the ionosphere, an electrically conducting layer of the upper atmosphere starting at about 80 km above the earth, is announced by Merle Tuve and others at the Carnegie Institution. This means that the aurora is in the ionosphere!
- 1931 - Sydney Chapman and Vincent Ferraro put the clues together to form the first modern theory of the aurora. They explain how the earth's magnetic field guides particles from the sun into the earth's upper atmosphere, where the particles collide with air molecules and produce light. There are still a lot of unanswered questions about how all of these things work, though.
- 1939 - World War II intensifies research on auroral effects on communication, navigation, and detection systems. Auroras are known to wipe out radio communications, and they show up on some radar displays, obvious concerns during wartime.
- 1957 - Extensive auroral studies take place during the International Geophysical Year (IGY, 1957-1959); all-sky camera networks simultaneously record auroral displays from horizon to horizon throughout the arctic auroral zone. The first artificial satellite, Sputnik I, orbits Earth measuring density and other upper atmosphere features; the U.S. Explorer I satellite soon follows.
- 1964 - Information gathered during the IGY enables Geophysical Institute scientists to identify the auroral substorm, an intermittent surge of auroral activity. Several other important advances result from IGY data and satellite measurements. 1967 Geophysical Institute research shows that electrons causing northern and southern auroras come from the same source, creating simultaneous and often mirror-image auroras in each hemisphere.
- 1969 - Barium releases from rockets fired from the new Poker Flat Research Range paint the Earth's magnetic field in a way that Gilbert would never have dreamed of, creating a sort of artificial aurora seen across Alaska.
- 1974 - Scientists at the Geophysical Institute acquire observational evidence for electric fields existing parallel to the magnetic field, which provide current driving a massive ionospheric electrical circuit. They also lead a multinational expedition to the eastern Arctic to observe the daytime aurora (visible only during the high-arctic winter, when the sun does not rise for weeks) and its direct relationship to the solar wind. And through the present... Scientists at the Geophysical Institute are using rockets launched from Poker Flat, numerous instruments scattered around Alaska and the rest of the world, satellite observations, and supercomputer simulations of mathematical models to discover how the sun, the aurora, Earth's climate, and magnetic fields that fill interplanetary space interact and affect our life on Earth.