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A Spectacular Guy Fawkes Comet

Written by Tony Marsh and Tony Questa.

On the 24th of October comet Holmes increased in brightness a million times.

Astronomers all over the world are watching to see what happens next.

Normally a very faint comet that needs a large telescope to see, Comet 17P Holmes was discovered in 1892 and comes round approximately every 7 years. But after its sudden brightening you can now find it easily with the unaided eye.

Its high altitude in our Northern-Hemisphere sky means it’s visible all night long if the weather is kind.

You will find it in the constellation of Perseus. Look at it through a pair of binoculars and you’ll see it as a nebulous ball nearly the size of the full moon. In a telescope it’s a splendid sight.

The Guilford Astronomical Society have been imaging the comet at their Holmbury Observatory – here is one of the images.

The tail of the comet must be spectacular but it cannot be seen from Earth - the comet, Earth and Sun are roughly in line and as the tail of a comet always points generally away from the Sun. So we see the comet head-on as though it were heading straight for us.

Don’t worry it won’t hit us. It’s orbit takes it well outside that of Mars.

The GAS CCD pictures show the comet at about 60% of the apparent size in the sky of the full Moon. But remember it’s over 600 times further away.

In the few days since the outburst that caused the original brightening the comet’s outer regions at first expanded at an average speed of over 5000 kilometres per hour to a diameter of 1.3 million kilometres.

The expansion slowed a bit but in a few more days it reached over 1.5 million km. That’s bigger than the visible part of the sun (photosphere). Of course it’s only a tiny fraction of the sun’s mass.

What we are seeing is sunlight reflecting back to Earth from the gas and dust thrown off from a sudden disruption in the comet’s solid core - itself only 3 kilometres in size – a type of celestial firework for the November skies!

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