Forty years ago this month, a celestial event came along – a bolt from the blue.
A brand new comet has made headlines around the world for days because of its exceptionally close path to Earth: less than 3 million miles (4.8 million km), or 12 times the distance from Earth to the Moon.
In fact, when the comet was first seen on April 25, 1983, it was not by human eyes or a telescope, but by a satellite: IRAS, short for Infrared Astronomy Satellite, launched from the former Vandenberg Air Force Base. January and placed in a 560-mile (900 km) orbit around Earth. The satellite is a joint venture between Great Britain, the Netherlands and the United States and is the first space telescope to survey the entire sky at infrared wavelengths. Its main purpose is to chart the thermal „signatures” of asteroids and observe the processes associated with the birth and death of stars.
Related: Comets: Everything you need to know about space’s 'dirty snowballs’
First seen by satellite
When the IRAS satellite picked up a fast-moving object on April 25, it was initially thought to be an asteroid. But then, a week later on May 3, Japanese amateur astronomer Genichi Araki announced to the Tokyo Observatory the discovery of a new comet in the constellation Draco the Dragon. This was followed by famous British comet observer George Allcock, who was scanning the sky with 15 x 80 binoculars. Surprisingly, Alcock – who had previously discovered four comets – was Inside his house and searching through a closed window, When he stumbles upon the comet Araki saw seven hours ago!
It soon became more and more clear that the object discovered by IRAS was not, in fact, an asteroid, but the same comet that both Araki and Alcock had discovered. It was deemed appropriate to name the comet IRAS-Araki-Alcock. When Araki and Alcock looked at it, the comet shone at the sixth magnitude—the threshold of visibility for someone without the use of any optical aid under a dark, clear sky.
Getting brighter…and getting closer!
Once the initial orbit for the comet was created, two things were determined.
First, intrinsically, it is a relatively small comet, perhaps no more than 2 or 3 miles (3 or 5 km) wide. And yet, by next week, it’s predicted to brighten more than 60 times faster, perhaps as bright as the second magnitude, Polaris, the North Star.
But for something That To walk, it would have to come very close to Earth. In fact, calculations indicated that it would miss our planet by only 2.88 million miles (4.63 million km) on May 11, 1983, the closest approach of any comet ever observed except for another comet, Lexell. It was in 1770!
Although IRAS-Araki-Alcock made its closest approach to the Sun (called perihelion) on May 21, 1983, at a point inside the Earth’s orbit, it had been at its closest approach to Earth since May 4 (perigee). .
In a way, it was like a call to arms for astronomers. A comet passed very close to Earth and appeared in a dark sky (the new moon on May 12), making close passes over familiar and easy-to-find celestial landmarks on subsequent nights. Mainstream news media.
Busy, busy, busy!
In retrospect, maybe a little Very good. . .
At the Central Bureau of Astronomical Telegraphs (CBAT) in Cambridge, Massachusetts – the global clearinghouse for astronomical discoveries – news of comet IRAS-Araki-Alcock spread like wildfire. Bureau Director Dr. Brian G. According to Marsden (1937–2010), he and his small staff were “overwhelmed” by hundreds of calls from reporters, planetarium workers, professional and amateur astronomers, and curious “humans.” Street, “all requesting the latest information about the approaching comet. During his tenure at the helm of CBAT, Dr. Marston clearly considered the passing of this comet „the most exciting time ever in the bureau’s history.”
The question most asked by reporters: „Are we in imminent danger of a collision?” (Nope!).
Timeline of close encounter
May 9, 1983: The comet, now shining a third magnitude brighter, can be seen passing near the bright orange star Kossab in the Little Dipper’s Bowl; The motion of the comet relative to the star was evident. In less than two hours, IRAS-Araki-Alcock approached Kochap, eventually passing less than half a degree from the star and gradually moving away from it. It was like looking at the minute hand of a clock. From all points north of the Tropic of Cancer, the comet is circular, meaning it is visible in the night sky. In essence, we were looking directly at the „bottom” of the comet from Earth.
May 10, 1983: It formed a broad, more or less equilateral triangle with the famous „pointing stars” Tuba and Merak in the bowl of the Big Dipper, and appeared high in the north-northwest sky to American observers. Sharp-eyed skywatchers can spot the comet without binoculars within an hour after sunset.
May 11, 1983: Approaching Earth Day – The comet revealed its closest proximity to the famous Beehive constellation in the constellation Cancer, although the comet was incomparably brighter, at magnitude +1.5. A narrow tail of gas was recorded in several photographs, but only the comet’s diffuse head (called the coma) was visible through binoculars and telescopes. and when seen against a dark sky it appeared absolutely enormous, measuring approximately three degrees across; Roughly equal in apparent size Six full moons! With large telescopes, spectacular structures appeared to illuminate the inner coma.
With IRAS-Araki-Alcock now so close to Earth, there was interest in trying to bounce radar signals off it. The 1,000-foot (305-meter) radio telescope in Arecibo, Puerto Rico, and NASA’s Jet Propulsion Laboratory in Goldstone, California, have both succeeded in obtaining such radar echoes. The nucleus of a comet.
May 12, 1983: Now receding rapidly from Earth, the comet – making a farewell appearance to Northern Hemisphere observers – is less visible in the southwestern sky after sunset, rapidly decreasing in brightness to third magnitude. By the next evening it was sinking below the horizon before evening twilight. The show is over as fast as it started.
Our next chance?
Will there be another chance to see a comet pass so close to Earth in the future?
Close approaches of comets to Earth are extremely rare. A comet approaches within 9 million miles (14.5 million km) of our planet – on average – once every 30 to 40 years. For a comet less than 5 million miles (8 million km) from Earth, such a close approach is still rare, occurring only once every 80 or 90 years.
So you can see how extraordinary a very close approach to Earth, 3 million miles (4.8 million km) is in the case of IRAS-Araki-Alcock.
However, interestingly, since 1983, many comets – or fragments of comets – may have made an even closer approach to Earth. A smaller comet, P/SOHO 5, may have come within 1.1 million miles (1.7 million km) of our planet on June 12, 1999, although this value is considered highly uncertain.
Another, 55P/Tempel-Tuttle – the comet that produces the annual Leonid meteor shower – was recently determined to have passed 2.1 million miles (3.4 million km) from Earth on October 26, 1366.
Only small, faint comets seem to pass exceptionally close to Earth, but there is one notable exception: Halley’s Comet.
On April 10, 837 AD, the most famous of all comets was 3.1 million miles (4.9 million km) from Earth. When viewed from China, Japan and Europe, the comet shone as brightly as Venus, stretching more than 90 degrees across the sky.
Oh, to see a comet That In our lifetime!
By May 7, 2134, when seen far away, Halley’s Comet will pass within 8.6 million miles (13.8 million km) of Earth, shining as brightly as Jupiter and once again displaying a spectacularly long tail.
Something our great, great, great, great grandchildren can look forward to.
Joe Rao works as an instructor and guest lecturer in New York Hayden Planetarium. He writes about astronomy Journal of Natural HistoryThe Farmers’ Almanac and other publications.
„Oddany rozwiązywacz problemów. Przyjazny hipsterom praktykant bekonu. Miłośnik kawy. Nieuleczalny introwertyk. Student.