Going, going, gone

Look toward the north during the early evening and you will see that the Plough is missing from the sky; it will return again standing on its end at around midnight

KEN CAMPBELL

Monday, 27 November 2017, 10:26

The North Star or Pole Star just happens to lie almost directly over the North Pole of the Earth, so as the Earth spins on its axis, this star appears to stay still while all the other stars revolve around it like the hands of a giant celestial clock. The Pole Star stays at the centre and all the other stars turn anti-clockwise.

Stars that are further out from the Pole Star have to travel further around the circuit, while stars that are closer to the Pole Star carve smaller paths as they circle the sky.

There are a few stars and constellations that are so close to the Pole Star that they are constantly visible in the northern sky and never set below the horizon; these are known as Circumpolar stars or Circumpolar constellations.

The height or altitude of the Pole Star in the sky varies depending on where you are on the Earth. If you were standing at the North Pole then the North Star would be directly overhead at altitude 90°. If you stood at the equator then the North Star would just be visible sitting on the horizon at altitude 0°.

From London the North Star appears slightly over half way up the sky at altitude 51°. But from Southern Spain the North Star appears much lower down in the sky at only 36°.

One of the most recognisable constellations is The Plough, or as the Americans call it, The Big Dipper. These are the seven brightest stars that make up a part of Ursa Major the Great Bear. The rest of the Great Bear is a bit indistinct but The Plough is very easy to spot.

At this time of the year the Plough lies directly below the North Star in the early evening sky. From the UK, because the North Star is quite high in the sky, there is enough room below for The Plough above the horizon. But in Spain, with the North Star being that much lower down in the sky, there isn't the same amount of room below and so the poor old Plough dips briefly below the Northern horizon and is no longer visible.

Look toward the north during the early evening and you will see that the Plough is missing from the sky; it will return again standing on its end at around midnight. I found this quite strange when I spent my first winter in Spain as suddenly an old familiar constellation as the Plough was no longer in the sky.

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