KEY POINTS:
Many people, not just astronomers, have been captivated by the display provided by Comet McNaught (C/2006 P1) over the last three weeks. It is ranked as the second-brightest comet since 1935, the brightest being Comet Ikeya-Seki in 1965.
The comet was discovered by Australian astronomer Robert McNaught last August but was lost to Earth-based observers in the Sun's glare for most of December. At this point there was no indication that it would become so bright, such is the unpredictable nature of comets. Satellites observing the Sun did follow its progress and they showed the comet was likely to get significantly brighter.
In the New Year, it became visible from the northern hemisphere by which time it was clearly going to be a very bright comet.
The comet reached its closest point to the Sun (perihelion) on January 12 and by this time the comet head was actually visible in broad daylight. As it continued to move further from the Sun and into our southern skies, the fine details of the tail, now perhaps 30 million kilometres in length, provided a spectacular display.
This comet is almost certainly a member of the Oort Cloud, a vast reservoir of small icy bodies that usually orbit between 30,000 and 100,000 times further from the Sun than does the Earth. While no instruments can see comets at these vast distances, in 1951 Dutch astronomer Jan Oort postulated the existence of this cloud based on his study of the orbits of the very long period comets.
Since 1951, many more comets with extremely long orbital periods (typically measured in millions of years) have been recorded and there is little doubt today that the Oort Cloud exists and contains billions of comets.
Currently, Comet McNaught is fading steadily as it moves away from both the Sun and the Earth. It is now 191 million km from Earth, 50 per cent more distant than when it was at its brightest on January 15, and just over four times further from the Sun.
The comet is only just visible to the naked eye but remains an easy target in binoculars. At 9.30pm over the next three days it will be 17 degrees above the SW horizon and no longer actually sets at our latitude.
Besides comets, there are other interesting objects to look for. By 10pm, Saturn is the brightest object in the northeast, outshining the star Regulus in Leo. Saturn is due north at 2am.
In the eastern sky before dawn Jupiter provides a fine sight below Scorpius.
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