[attach id=571478 size="medium"]The king of the planets is seen in this image shot through the telescope by the author. The colourful spots and bands are constantly changing as they consist of storms and hurricanes – more than twice as fast as the strongest hurricane on the Earth. Also visible is the Great Red Spot in the lower right. This hurricane is three times the size of the Earth and has been raging on Jupiter for (at least) the past 400 years.[/attach]

This month sees the return of giant planet Jupiter in the evening skies. After appearing in the early morning skies for the past months, Jupiter now rises earlier as it approaches its closest position (666 million kilometres) with respect to the Earth, next Friday. This also means that Jupiter will be at its brightest, rising at sunset and setting at sunrise the following morning.

Throughout the month keep an eye on the separation between Jupiter and the nearby bright star Spica, and you will notice Jupiter’s motion in the sky as this giant planet slowly moves away. It was this motion that bewildered sky gazers of the past, who identified five points of light that did not remain stationary with respect to the starry background. They gave them the Greek name aster planetes, meaning ‘wandering stars’. They observed that these points of light, unlike the rest of the stars, did two things. First of all, they varied their brightness since the distance between them, the Earth and the sun varied as everything in our solar system is in continuous motion. Secondly, they noticed their motion. In reality, the stars themselves are also moving about around the centre of our galaxy, the Milky Way. However, since the stars are very far away, their motion from our perspective appears very small and is only apparent over the course of thousands of years.

The planets still lie hundreds of millions of kilometres away from each other, but it so happens that they all trek on the same plane around the sun. Our solar system is therefore flat, so all the planets follow the same path across the sky, through the constellations of the zodiac.

With the naked eye, we see Jupiter only as a point of light, however a common pair of 10 x 50 binoculars will reveal four smaller and closer points of light around it. These are its four largest moons (out of a total of 67 moons) and are the same moons seen by Galileo Galilei when he first observed them 407 years ago. Each one of them is a distinct world – some covered by water ice, others volcanically active.

Currently the Juno spacecraft is exploring Jupiter. This is a Nasa probe that arrived last year with the aim of studying Jupiter’s composition, gravitational and magnetic fields and polar magnetosphere. It will also try to find more details on how the planet formed, including whether it has a rocky core and the amount of water present within its deep atmosphere. In fact, what we see when looking at Jupiter is simply the tops of the cloud formations in its atmosphere.

More planetary motion is evident when watching Mercury and Venus. This evening, Mercury will be bright enough to see at nightfall, setting after sunset on the western horizon, in the darkening twilight. But in just a few days it would have moved and will no longer be visible, too faint to see in the bright twilight. The same thing happened with Venus which previously dominated the evening skies – but now shines brightly before sunrise.

Astronomical events during the month of April

3th at 9pm: First quarter moon.
7th at 11pm: Jupiter at opposition.
10th at 11pm: The moon close to Jupiter.
11th at 8am: Full moon.
16th at 8pm: The moon close to Saturn.
19th at 12pm: Last quarter moon.
22nd: Peak of Lyrids meteor shower.
23rd at 8pm: The moon close to the planet Venus.
26th at 2pm: New moon.
28th at 9am: The moon close to the planet Mars.

Last article

Sadly, this is my final article for what was a regular monthly feature running for more than 10 years. The feedback received was a constant reminder of how, despite our daily struggles in life, many of us still look up to the stars in awe and wonder how insignificant – and yet how precious – is this tiny planet of ours in the grander scheme; and how ego-shattering is the consideration that our lifetime is just a split-second in the history of the Universe. Observing the night sky is a humbling, inspiring experience and I hope that you keep looking up!

Alexei Pace is a member of the Astronomical Society of Malta.