Adrian Dening's Stars Over Somerset

Wednesday, 4 October 2023 17:00

Monday 9th to Sunday 15th October 2023

On Thursday 12th, comet 103P/Hartley, also known as just Hartley 2 reaches perihelion - the point when it is closest to the Sun in its orbit.

Now you normally associate comets as coming from the Kuiper Belt in the far reaches of our outer Solar System and their orbits around the Sun can take hundreds of years.

Hartley 2 is a bit different in that it actually originates from the Asteroid Belt between Mars and Jupiter. Its orbit only takes six and a half years while it sweeps in close to the Sun and then heads back out to join its mates in the Asteroid Belt. It is known as a "Jupiter-family" comet because of this.

The comet is peanut-shaped and only has a diameter of about one mile. You will need binoculars at least to see it as the magnitude will be around +8.5

So how do you find it? Venture outside after 1am on the morning of 12th and look towards the east. You will see the obvious constellation of Orion. To the left of Orion is the constellation of Gemini, the "Twins", who will appear to be lying on their side.

Locate the star "Wasat" which marks the waist of the lower twin. Comet Hartley 2 will be situated just below Wasat with the comet's tail pointing towards the star.

I have provided an image of the comet, courtesy of NASA, but this was taken from only 435 miles away by their Epoxi mission in 2010. You will see a fuzzy blob! The good news is that the Moon will be below the horizon and so not creating any light pollution!