ONE of the most iconic stars in the northern hemisphere is Polaris, also known as the North Star. If you can spot this star, you will always know which direction is north, because it is a steady point of light in a changing sky. No matter where you are in the northern hemisphere, it will never move. Or will it?
The North Star hasn’t always been, and won’t always be, Polaris. At the moment, it is our North Star because of the tilt of Earth: the north pole faces the same direction in space – towards Polaris – even as Earth moves around the sun and turns on its axis. In the same way, the south pole keeps facing the Southern Cross.
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But slowly, over thousands of years, Earth’s tilt – which is at 23.5 degrees from its plane of orbit around the sun – moves. This is a process called axial precession. You can think of it like a spinning top: Earth is spinning on its axis, but the direction in which it is tilted is also moving around in a circle, in a much slower process. It takes 26,000 years to complete a full circle. The extent to which Earth is tilted also changes, too, by a couple of degrees.
In 12,000 years, the North Star will no longer be Polaris, but a star called Vega. At the minute, Vega can be seen from most places in the world, so anyone can find the North Star of the future. It is one of the brightest stars in the night sky, and sits in the constellation Lyra.
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In the northern hemisphere, look north-east as soon as the sun has set. Vega will be the brightest star near the horizon. A few hours later, by around midnight, you will see three bright stars making a triangle shape in the east, near the horizon. This is called the summer triangle. Vega will be the furthest of these from the horizon. Vega is a summer star in the northern hemisphere, so look north-east any evening in May and you will see it.
In the southern hemisphere, it is a little trickier to spot. You will have to look quite late at night as it will rise in the north, 3 to 4 hours after midnight, but exactly when will depend on your latitude. Use a planner such as Stellarium to see when Vega will rise in your area.
Vega isn’t the only future North Star. As Earth’s tilt moves in a full circle, the north pole will face each point in the sky along that circle at some point in the future. Some of these regions contain no stars at all.
After Vega, Gamma Cephei, a star in the constellation Cepheus, will be the North Star.
Alderamin, the brightest star in Cepheus, will have a go a few thousand years later. Cepheus isn’t a prominent constellation, but it sits next to Cassiopeia, the W or M-shaped constellation, in the sky.
And what goes around comes around: 26,000 years from now, Polaris will be the North Star once again.
What you need
Your eyes
Stargazing software like Stellarium (optional)
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