Credit: Antti Kemppainen
Comet McNaught, or the “Great Comet of 2007,” was the brightest to appear in sky for 40 years. It blazed across the sky of the Southern Hemisphere, visible to the unaided eye even in daylight. Astronomers had to caution viewers to protect their vision when viewing it near the Sun, since it could even be seen close to our dazzling home star. Its huge tail could be glimpsed as far north as Colorado.
That tail looked spectacular – but we weren’t seeing the half of it, quite literally. On Feb. 3, 2007, the Ulysses spacecraft, a probe orbiting the Sun to study its atmosphere and solar wind, fortuitously happened to pass through the tail of the comet. Scientists seized on the opportunity to measure the region of space disturbed by the comet’s presence, looking for cometary ions, or electrically charged atoms and molecules, and studying their interaction with the solar wind. A comet’s tail of ionized gas is separate from its dust tail and reacts to the solar wind, changing speed or even bending. In fact, ion tails from comets are how scientists first discovered that the Sun was emitting a solar wind.
Comet McNaught ...