A comet and a cluster of stars

Last Friday week amateur astronomer Jean-Luc Dighaye braved temperatures of -17°C at 5.35 a.m. in Munich to photograph Comet Garradd (C2009/P1).

The significance of this event was a close approach by the comet to globular cluster M92, as the comet sweeps through the constellation Hercules. The comet remains just below naked eye visibility though it is easily seen through binoculars or a telescope.

Such approaches, called conjunctions, occur since a comet is not a fixed object in space. Pulled towards the sun by its immense gravitational pull, Comet Garradd makes its closest approach to the Earth on March 5, when it would still be 190 million kilometres away.

M92 is a huge grouping of stars all orbiting around a common centre in what is known as a globular cluster. In this case the total amount of stars is thought to reach up to 330,000 ‘suns’.

Last week’s close approach between the comet and the globular cluster was only a visual illusion. This is because in reality M92 is over 25,000 light years away from Earth.

Comet Garradd, on the other hand, currently is situated only about 12.5 light minutes away – equivalent to around 225 million kilometres.

Images from dark sites would have revealed the comet’s broad fan-shaped dust tail and a much narrower ion gas tail, however, haze and heavy light pollution in the German town did not allow the comet to be seen in its full glory.

One can only imagine what a spectacle was put on display by bright comets, hundreds or thousands of years ago.

Unfortunately, nowadays light pollution takes its toll not just by ‘stealing’ away the night sky but also through energy waste as huge amounts of energy go wasted by external lighting which illuminates the night sky rather than the ground where it is required.

Architect Alexei Pace is president of the Astronomical Society of Malta. E-mail: info@maltastro.org.

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