This month forty years ago, a celestial spectacle stopped—literally thunderous applause.
A brand new comet has grabbed headlines for days around the world because of its exceptionally close proximity to Earth: a distance of less than 3 million miles (4.8 million kilometers), or about 12 times the distance from Earth to the Moon.
In fact, when the comet was first seen on April 25, 1983, it was not with human eyes or a telescope, but from a satellite: IRAS, short for InfraRed Astronomical Satellite, launched from Vandenberg Air Force Base at the time. January and is placed in an orbit of 560 miles (900 km) around Earth. The satellite was a joint project of Britain, the Netherlands and the United States and was the first space telescope to survey the entire sky in infrared wavelengths. Its main goal was to catalog the heat “signatures” of asteroids as well as to observe the processes involved in the birth and death of stars.
Related: Comets: everything you need to know about the ‘dirty snowballs’ of space
First seen by satellite
When the IRAS satellite captured a fast-moving object on April 25, it was first assumed to be an asteroid. But then, just over a week later, on May 3, Japanese amateur astronomer Genichi Araki reported the discovery of a new comet in the constellation Draco the Dragon to the Tokyo Observatory. This was followed by a vision of George Alcock, a famous British comet-watcher, who was scanning the sky with a 15×80 binocular. Surprisingly, Alcock—who had already discovered four other comets—was inside his house and watch through a closed window, When he fell on the comet that Araki saw seven hours ago!
It soon became increasingly clear that the object IRAS had detected was not, in fact, an asteroid, but the same comet that Araki and Alcock had discovered. It was therefore deemed appropriate to name the comet IRAS-Araki-Alcock. When seen by Araki and Alcock, the comet was glowing with a sixth power — the threshold of someone’s vision without the use of visual aids under dark, clear skies.
Be bright…and soon!
Once a comet’s preliminary orbit was determined, two things were determined.
First, it was a relatively small comet, perhaps no more than 2 or 3 miles (3 or 5 km) across. However, over the next week, it was expected to brighten more than 60 times faster, perhaps to a second magnitude, as bright as Polaris, the North Star.
But for something like this To access, you must get close to the ground. Indeed, calculations indicated that it was destined to miss our planet by 2.88 million miles (4.63 million kilometers) on May 11, 1983, making it the closest point ever. And that was in 1770!
Although IRAS-Araki-Alcock made its closest approach to the Sun (called perihelion) on May 21, 1983, at a point just inside Earth’s orbit, during the period from May 4 it was at its closest approach to Earth (perihelion) on May 11 The comet aroused tremendous interest around the world.
In a way, it was a call to arms for astronomers. The combination of a comet passing very close to Earth and appearing in a dark sky (the new moon was May 12), while passing a series of familiar and easy-to-find celestial landmarks closely on consecutive nights, went very well with the mainstream news media.
Busy busy busy!
Looking back, maybe a little bit very good . . .
At the Central Astronomy Telegram (CBAT) office in Cambridge, Massachusetts — the clearinghouse for astronomical discoveries worldwide — news of comet IRAS-Araki-Alcock spread like wildfire. According to office director Dr. Brian J. Marsden (1937-2010), he and his small team were “absolutely overwhelmed” with hundreds of calls from journalists, planetarium staff, professional and amateur astronomers, and even the curious man on the street, “every request for the latest information on an approaching comet. When he was chair of the CBAT, Dr. Marsden clearly considered this comet’s passage “the busiest period in the history of the office.”
Perhaps the most frequently asked question by journalists is, “Are we in immediate danger of collision?” (no!).
Schedule a close encounter
May 9, 1983: The comet, now shining as bright as a tertiary magnitude, can be found near the bright orange star Kochab in the bowl of Ursa Minor; The comet’s motion relative to the star was quite evident. In less than two hours, IRAS-Araki-Alcock appeared to approach Kochab, eventually pass within half a degree of the star, and then gradually move away from it. It was like looking at the minute hand on a watch. From anywhere north of the Tropic of Cancer, the comet was circumpolar, meaning it was visible in the sky all night. Essentially, we were looking directly from Earth at the “underside” of the comet.
May 10, 1983: It formed a broad, somewhat equilateral triangle with Dubhe and Merak, the famous “pointer stars” in the Ursa Major basin, and appeared high in the northwest sky for American observers. Sharp sky watchers can find the comet without binoculars less than an hour after sunset.
May 11, 1983: On the day of its approach to Earth, the comet noticeably revealed its close proximity to the famous Beehive star cluster in the constellation of Cancer, although the comet was incomparably brighter, peaking at around +1.5. A narrow gas tail has been recorded in many images, but visually through binoculars and telescopes, only the comet’s diffuse head (called a coma) was visible. and, looking up against a dark sky, it seemed very enormous, about three degrees in diameter; Approximately equal to its apparent size Six full moons! Through large telescopes, fantastic structures have emerged that illuminate the inner coma.
With IRAS-Araki-Alcock now close to Earth, there was value 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, obtained these radar returns, which were used to provide details about the radius, rotation, and composition of the comet’s nucleus.
May 12, 1983: Now the comet is moving quickly away from Earth, and the comet – whose farewell appears to observers of the northern hemisphere – can be found low in the southwestern sky after sunset, after its brightness rapidly diminished at the third degree. and the next evening it sank below the horizon before the end of evening twilight. The show ended almost as quickly as it began.
Our next chance?
Will we have another chance to see a comet pass near Earth in the foreseeable future?
Comet close encounters with Earth are fairly rare. The approach of a comet located 9 million miles (14.5 million kilometers) from our planet occurs — on average — about once every 30 to 40 years. For a comet passing 5 million miles (8 million km) from Earth, such a close approach is rare, occurring about once every 80 or 90 years.
So you can see how unusual being close to Earth by less than 3 million miles (4.8 million kilometers) was in the case of IRAS-Araki-Alcock.
It is interesting, however, that since 1983 there have been many comets – or fragments of comets – that may have come close to Earth. A small comet, P/SOHO 5, “may” approached our planet within 1.1 million miles (1.7 million kilometers) 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 identified as passing 2.1 million miles (3.4 million kilometers) from Earth on October 26, 1366.
Only small dark comets seem to make exceptionally close passes to Earth, but with one notable exception: Halley’s Comet.
On April 10, 837, the most famous comet ever, passed 3.1 million miles (4.9 million km) from Earth. The comet has been seen from China, Japan and Europe, shining like a flower, with a tail that extends more than 90 degrees into the sky.
Oh, to see like a comet this in our lives!
Looking far into the future, until May 7, 2134, Halley’s comet will pass within 8.6 million miles (13.8 million kilometers) of Earth, likely as bright as Jupiter and once again displaying an astonishingly long tail.
Something our great, great, great grandchildren can look forward to.
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