Planets putting on show as they line up in night sky

It is not often that all the planets in the Solar System other than ours are lined up across the night sky for us to see.

The show is in progress now and will climax at the end of February, when Mercury sneaks up through the sunset glow to complete the cast of the show.

Moving outward from the sun, the Solar System's known planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Mercury, Venus, Mars, Jupiter and Saturn are easily visible to the naked eye. Uranus and Neptune need binoculars or a telescope and knowing exactly where to look.

Today’s column focuses on the five that can be found without any optical assistance.

Having all the planets other than ours lined up across the sky is quite rare, but not really scientifically special. Imagine seeing the Solar System from above, with the sun in the middle and all the planets moving around it in concentric circles (or near-circles), in the same direction.

The speed with which they move around their orbits decreases with increasing distance from the sun. All the planets are moving in the same plane, like marbles rolling around on a plate. We live on the third marble out from the centre. In such an arrangement, there will be times that from our position on planet 3, we will see the other bright planets strung out to the left or the right of the sun.

Having the sun on the end of the line means we can have the sun below the horizon, giving us a dark enough sky to see the planets. That happens after sunset, when the planets are to the left of the sun and before sunrise, when the planets are to the right of the sun.

Because Mercury and Venus—being the two planets closest to the sun—can never be far from it as viewed from Earth, start observing soon after sunset, as soon as the stars become visible.

At first sight the planets look like stars, bright point-like objects in the sky. But if you look at them carefully, you will see they shine steadily, whereas the stars twinkle. This is because the stars truly are points of light, whereas the planets are actually tiny discs, as binoculars or a telescope will show.

At the moment, starting in the southwest after sunset, there is Saturn, moderately bright and golden coloured. Next, to the left, is Venus, brilliant white, like an escaped aircraft landing light. Further to the left and higher in the sky is Jupiter, almost as bright and a little bit yellowish. Then there is Mars, less bright than Jupiter and obviously reddish in colour.

All these planets justify getting out the binoculars or better yet, a small telescope. Saturn is surrounded by a system of rings, normally making it the most spectacular planet in the Solar System for anyone with a small telescope. At the moment, we are seeing the rings almost edge-on. Venus appears as a glaringly bright crescent. Jupiter is always worth a look. Binoculars will reveal a tan-coloured disc, with its four largest moons in line with the planet, like beads on a wire.

Mars, the “red planet,” requires a bigger telescope to reveal any of its surface features. However, even with binoculars or a small telescope, it is intriguing to look at that red disc and think about what our spacecraft are telling us about that world, which long ago was so much like ours, and still resembles ours enough to attract intense interest.

In late February, Mercury—the closest planet to the sun—will be far enough to the left of the sun to be above the horizon to be seen against the post-sunset glow. It the sky is clear the planet should be visible as a starlike dot. Binoculars or a small telescope may help, however, only if the sun swell below the horizon.

The only effect this lineup of the planets will have on us is to give us a fantastic opportunity for planet watching. The next lineup will be at the end of February 2048. Then the planets will be lined up to the right of the sun and much lower in the sky so don't waste this opportunity.

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• The moon will reached its first quarter on Feb 5.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.