Halley's Comet Makes Its Closest Recorded Passage by the Earth
Halley's Comet, named after the English astronomer Edmond Halley, made its closest recorded passage by Earth on May 10, 1910. This remarkable event provided a stunning display for observers across certain regions of the planet. Halley's Comet is notable for its periodic appearances, having been documented since at least 239 B.C. by ancient Chinese astronomers. Historically, comets were often viewed as omens, but scientific inquiry revealed them to be natural celestial phenomena. Halley’s groundbreaking work in the early 18th century established that comets, including his namesake, orbit the Sun in elliptical paths, with Halley’s Comet returning approximately every 76 years.
The comet's nucleus, composed of ice, dust, and debris, becomes visible as it approaches the Sun, creating a brilliant tail that can extend millions of miles. Advances in technology allowed for close-up study during its last approach in 1986, when several spacecraft were sent to gather data. Halley's Comet remains an object of fascination due to its size, historical significance, and the insights it offers into the formation of our solar system. The next anticipated return of Halley's Comet will be in 2061, continuing its legacy as one of the most famous comets observable from Earth.
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Halley's Comet Makes Its Closest Recorded Passage by the Earth
Halley's Comet Makes Its Closest Recorded Passage by the Earth
Possibly the world's favorite visitor from outer space, Halley's Comet made its closest recorded passage by the planet Earth on May 10, 1910. It created a brilliant nighttime display for those lucky enough to live in the right parts of Earth during the weeks when the comet was visible.
The comet is named for the English astronomer Edmond Halley, who first proved that comets orbit the Sun just like the planets. We know now that the periodic passage of Halley's Comet has been recorded since at least the year 239 b.c., when the ancient Chinese wrote of the appearance of a “broom star” in the night sky. (The “broom” was what we would call the comet's tail.) In ancient and medieval times comets were regarded as signs—heavenly portents of great earthly events. The first scientists, however, realized that they might be natural phenomena, and in 1577 the Danish astronomer Tycho Brahe showed that they were objects in space. Halley determined that they often travel in highly elliptical paths, coming very close to the Sun and then swinging far out to space. His groundbreaking treatise on comets was published in 1705, and he also predicted that what we now call Halley's Comet would return in 1758, because it was the same comet that had been seen in 1456, 1531, 1607, and 1682. (Halley determined this on the basis of similarities he found in the observations made during the comet's passages in those years.) The comet was named after him when his prediction proved to be accurate and the comet was sighted on Christmas day, 1758. Halley's Comet has attracted great interest ever since, and its passage by the Earth is always a widely followed event.
Halley's has become famous because of its size, the number of times it has been seen from Earth, and the fact that it was one of the first comets whose orbital cycle was plotted with a reasonable degree of accuracy. It visits the neighborhood of Earth roughly once every 76 years, although the cycle can vary from 75 to 79 years, depending on the gravitational influences of the nine planets in the solar system. The comet's orbital path takes it from the frozen depths of space beyond the planet Neptune to the scorching heat of the Sun.
By the most recent approach of Halley's Comet in 1986, the technology existed to launch satellite probes in order to study it, and five such probes were launched. The probe sent by the European Space Agency, named Giotto, made the closest approach to Halley's Comet. Equipped with a wide variety of scientific instruments, it traveled to within 340 miles of Halley's nucleus and transmitted pictures and other forms of data to scientists on the Earth. The former Soviet Union launched two probes, Vega 1 and Vega 2, which came within roughly 5,000 miles of the comet. Japan also sent two probes, Suisei and Sakigake, but they did not come very close to the comet.
These probes helped confirm the theory that an American astronomer, Fred L. Whipple, had advanced in 1950—that the core of a comet is essentially a “dirty snowball,” a solid nucleus composed of frozen gases, ice, rocks, dust, and debris. This nucleus is rarely larger than a few cubic miles (Halley's Comet has a nucleus of roughly nine by two-and-a-half miles). As a comet approaches the Sun, much of the frozen matter in the nucleus boils off. These particles spinning off from the nucleus reflect the Sun's light, which is how the comet becomes visible to observers on Earth. Its big hazy head and long tail can extend for millions of miles. The tail will vary in size depending on the comet's orbital position and reaches its greatest magnitude when it is closest to the Sun. Because of the prevailing solar wind, the tail is typically directed away from the Sun, no matter which way the comet itself is traveling. One comet has been recorded with a tail more than 200 million miles long, although others seem to have almost no tail at all. Fewer than one-tenth of those now known to exist can be seen without a telescope.
Residual matter left over from the formation of the Sun and the planets, called the Oort Cloud after the Dutch astronomer Jan Hendrik Oort, who developed this concept, is what forms comets. The gravitational influence of the Sun and its planets then draws them into and out of the solar system. Some comets have enormously long orbital cycles, such as the comet Kohoutek, which takes approximately 75,000 years to make one round-trip journey. On the other hand, some comets have been trapped by the Sun's gravity so that they never leave the inner solar system: The comet Encke takes only 3.3 years to complete its orbit.