Some enchanted evenings

IT’S always fun to identify the planets in the night sky.

There are five that are clearly visible to the unaided eye, and a bit later this month we will have a special treat: all five will be visible at the same time in the early evenings. The best period for watching them all will begin in about a week’s time.

The five so-called nakedeye planets are Mercury, Venus, Mars, Jupiter and Saturn. They were all known to ancient astronomers — indeed, the origin of the word planet is planetes, the Greek word for “wanderer”. In 2006, much attention was given to the event at which astronomers finally scientifically defined what a planet is, leaving Pluto out in the cold as a dwarf planet.

You may already have noticed one of more of these recently. Jupiter, the largest of the sun’s planets, has been a prominent object in the evening sky over the past few months. As the twilight fades this month, it is a quite bright object high in the northern sky.

Another that has been capturing attention is brilliant Venus, low in the northwestern evening sky. Venus is the brightest of the planets, and it can even be seen in broad daylight, provided that you know exactly where to look. If you try this, always be careful to avoid looking at the sun — it’s best to shield your eyes to make sure you don’t do this!

Back to our evening sky. Mercury, the smallest of the sun’s plants since Pluto’s 2006 “demotion”, can also be seen in the northwest, below and to the left of Venus.

It is always fun to identify Mercury. Because it is the closest planet to the sun, when seen it never appears very far from the sun in our sky, and is therefore visible only in the evenings not long after sunset or in the mornings in the couple of hours before sunrise. Be careful not to confuse Mercury with the star Regulus, the brightest star in the constellation of Leo, the Lion.

Of the other three nakedeye planets, Mars is by far the brightest, at least for now. It can be seen low in the eastern sky as darkness falls, and is quite easy to identify because of its reddish-orange colour. At the end of the month, Mars will be at its closest to us since 2003.

Mars is currently a little brighter even than Jupiter, but there are two reasons why this may not appear to be the case. Firstly, Mars is quite low in our early evening sky, and its light is dimmed a little because it is passing through more of our atmosphere than Jupiter’s. The other reason is its colour: Mars and the reddish stars often do not appear to the eye to be as bright as yellow or whitish ones, even when their overall brightness is the same.

Appearing below the famous shape of the Scorpion, which looks rather like a reversed question mark on its side, is ringed Saturn. It looks just like a whitish, fairly bright star, but is not nearly as bright as Mars or Jupiter.

Beginning next weekend, the moon will add to the spectacle. On July 15, while an attractive crescent shape, it will be beautifully placed in the part of the sky where we find Mercury and Venus. On July 21, it will appear close to Jupiter, and then Saturn on July 25, when the moon will be nearly full. Finally, it will appear just to the left of Mars two days later.

If you miss this opportunity, a similar one will come up briefly in October with the planets rather closer together, although Mercury will be lower in the twilight and harder to identify. So go out later this month and have a look!