本帖最后由 人与自然 于 2012-12-28 01:03 编辑
http://www.dailymail.co.uk/sciencetech/article-2253659/The-comet-outshine-MOON-Sky-gazers-anticipating-unaided-eye-object-brightest-generations.html
Astronomers around the world are tracking with eager anticipation the arrival of a comet next year which could even outshine our Moon in the night sky.
Comet ISON is expected to draw millions into the dark to witness what is likely to be the most brilliant comet seen in many generations.
It is visiting the inner solar system for what is thought to be the first time and is set to put on spectacular views for the Northern Hemisphere across November and December as it heads towards the sun.
本贴大致意思是：翻译参见http://news.sina.com.cn/c/2012-12-19/080925845510.shtml
一颗彗星名为C/2012S1（ISON）。这颗彗星被不少人誉为是自百武和海尔波普彗星后又一颗可以震撼人心的彗星。根据目前的观测情况，到2013年11月这颗彗星将肉眼可见，最亮的时候甚至可以超过月亮的亮度。只是这个时候它距离太阳很近，很难被观测到。对于北半球的天文爱好者来说，11月至12月的清晨是搜寻这颗彗星的机会，到12月中旬，这颗彗星将在清晨从东方地平线上升起。如果一切顺利的话，届时市民可以观赏到一颗明亮的彗星。
不过，需要说明的是，由于彗星结构比较松垮，在靠近大行星的时候有可能会因为受到大行星引力的影响而破碎，再加上靠近太阳的时候受到强烈阳光的炙烤也可能引起解体等因素，是否真能如预报所言的出色表现还很难说。
Look to the skies next year: Comet ISON could produce a spectacular show when it flies by next year - similar to the 1997 appearance of Hale-Bopp (pictured)
How Hale-Bopp looked above Alaska: Next year's comet is predicted to be even more spectacular, and remain in the skies for weeks
It may prove to be brighter than any comet of the last century - visible even in daylight - and this may end up being its one and only trip to the solar system, as its trajectory may see it plunge into the sun in a fiery death.
It is currently moving inwards from beyond Jupiter, and as it approaches the Earth, the 'dirty snowball' could produce a dazzling display, burning brighter than the moon and potentially being visible in broad daylight.
Spotted in space: Two astronomers from Russia discovered the icy ball, pictured here dimly lit against background stars
'Its tail could stretch like a searchlight into the sky above the horizon,' Dr Whitehouse writes.
'Then it will swing rapidly around the Sun, passing within two million miles of it, far closer than any planet ever does, to emerge visible in the evening sky heading northward towards the pole star.
'It could be an "unaided eye" object for months. When it is close in its approach to the Sun it could become intensely brilliant but at that stage it would be difficult and dangerous to see without special instrumentation as it would be only a degree from the sun.'
The comet, which was discovered by astronomers using the International Scientific Optical Network (ISON) telescope in Russia, will pass within two million miles of the sun's surface - making it a 'sun-grazing' comet.
It is on a 'parabolic' orbit, which means it probably originated from the outer skirts of the solar system, perhaps from the Oort cloud - a mass of icy debris which lies 50,000 times further from the sun than the Earth does.
If comet ISON survives the encounter, it could take thousands - potentially millions - of years before the comet passes back through the inner solar system.
COMETS: THE REGULAR VISITORS TO OUR PLANET
Hale-Bopp sailed overhead, leaving two trails: An ionic trail of magnetically-charged particles facing directly away from the sun (left), and a trail of dust and debris (right)
Comets are dusty balls of ice, which generally originate from the Kuipler belt - a region of icy small bodies beyond Neptune.
Occasionally, a comet gets dislodged from its orbit, and plunges in to the inner solar system.
They differ from asteroids, which are made of metal or rock, and are usually the left over remnants of planets or moons.
Comets are not really reflective - they only reflect 4 per cent of the the Sun's rays, about the same as coal.
So although they look brilliantly white from Earth, they are black at the surface.
Halley's comet is the most well-known, named after Edmond Halley who noted the regular 75-76-year appearance of a comet, and predicted it would return in 1758, although sadly the astronomer died 16 years before he was proved correct.
Halley's comet has passed within a fraction of the Earth before - in 1910 the Earth even moved through the comet's tail.
Sadly, the 1986 re-appearance was the worst for 2,000 years, as the Earth and the comet were on opposite sides of the sun.
The comet will begin brightening once it gets within Jupiter's orbit, as the sun's heat begins boiling the ice locked within the comet, converting it directly into gas.
It is likely to recall the excitement of Comet Hale-Bopp, which sailed past the Earth in 1997, appearing as a static-looking smear in the skies across the Northern Hemisphere.
It is also set to outshine 'the greatest comet of the last century' - Comet McNaught, which shone brighter than Venus as it passed above the southern hemisphere in 1965.
Comets are known as 'dirty snowballs', although technically a better definition would be 'snowy dirtballs', as comets are generally rocky at the surface, with chemical-laden ice within the interior.
As the ice and chemicals heat up, they erupt as brilliant jets which can form tails lasting hundreds of thousands of kilometres in length.
The comet is expected to be bright throughout late November and early December.
Robin Scagell, vice-president of the Society for Popular Astronomy, said: 'This is a very exciting discovery.
'The comet looks like it could become a very spectacular sight in the evening sky after sunset from the UK in late November and early December next year.
'Our members will be eagerly following it as it makes its first trip around the Sun and hoping to see it shining brilliantly and displaying a magnificent tail as it releases powerful jets of gas and dust.'
Read more: http://www.dailymail.co.uk/sciencetech/article-2253659/The-comet-outshine-MOON-Sky-gazers-anticipating-unaided-eye-object-brightest-generations.html#ixzz2GH0yPt00
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