The hunt for the elusive mercury

Astronomer, Neil Norman Picture: SARAH LUCY BROWN

Astronomer, Neil Norman Picture: SARAH LUCY BROWN - Credit: Archant

This month I thought I would set out a challenge to you all, the hunt for the innermost planet of the Solar System - Mercury, writes astronomer Neil Norman.

Before we go any further, here are a few facts about the planet.

Mercury takes just 88 Earth days to complete one orbit around the sun at a mean distance of just 58 million kilometres (the Earth by comparison is 93m km distant from the sun).

It is a terrestrial planet meaning it is a rocky body like Earth, Venus and Mars but unlike the latter planets, Mercury has no atmosphere.

Size-wise, Mercury is just 4,879 km in diameter, by far the smallest planet and for comparison, our own Moon is 3,474 km in diameter.

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Although it is the closest planet to the Sun, it isn’t the hottest. That distinction goes to Venus, but Mercury does have a wild temperature difference with the shaded areas of the planet seeing temperatures as low as -173C and extreme heat of 427C.

The surface of the planet looks very much like the Moon being heavily cratered due to asteroid and comet impacts from the period of the late heavy bombardment some 3.8 billion years ago.

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Mercury has no moons or rings and was first documented by the Assyrian astronomers in 14th century BC.

Mercury was known to be the fastest planet in Roman times and so they named it after the messenger to the Gods.

And finally, your weight on Mercury is 38% less than here on Earth, good news for those on a diet!

Mercury, though small is still a bright object but the problem is that it can never be seen in a dark sky because it is close to the Sun. It does however venture away from the Sun occasionally to a point where it becomes easily visible to us if you have a clear horizon and it passes a bright object like the Moon and Venus that can be used to find the planet.

This month sees Mercury make a close approach to both Venus and the Moon (visually from our point of view not in actual distance).

On May 15, Mercury is very low over the horizon but by the 20th it will be at the 5pm position from Venus at 9p , a day later on the 21st, it will be very close to Venus and directly beneath it at 9pm. On the 22nd, it will lie in the 9pm position from Venus at 10pm. On the 24th, a very young crescent moon will be beside it at 10pm making for a nice conjunction of Mercury,Venus and Moon.

When you find Mercury (it will appear as a yellow “star”) take pride in yourself because not many people even know what it is or can even find it, this is a great chance to tick the innermost planet off your Solar System list.

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