Welcome to the April night sky. This is the month when we have the chance to spot the elusive planet Mercury. It will be visible during the first two weeks of the month just after sunset, low on the western horizon, and will appear as a bright pinkish-coloured “star”.
Mercury is the closest planet to the Sun and its orbit never allows it to move very far away from the glare of the solar disc, so it’s not easy to see. But this month Mercury will be at its furthest distance from the Sun on April 18. After that date, it will rapidly move closer to the Sun and, in fact, on May 9 will actually pass between the Sun and the Earth in an event called a transit. These occur approximately every seven years or so.
As Mercury is much closer to the Sun than to the Earth, its surface temperature can be more than 400°C, but on the night side of the planet the temperature can drop to -170°C.
Mercury rotates very slowly on its axis with one day lasting 58 Earth days and, consequently, the Sun rises very slowly so if you walked at 10kph away from the sunrise you could outpace it and avoid the scorching heat.
The gas giant planet Jupiter is still big and bright in the southern sky during the early evening and the moon will be close to it on the night of the 17th.
At midnight over the southwest, the planets Saturn and Mars can be seen rising in the constellation of Scorpius. The just past full Moon will be close to them on the night of the 24th.
Scorpius the Scorpion – the southernmost constellation of the Zodiac – is a major showpiece of the starry sky. This J-shaped assemblage of stars actually looks like its namesake.
The red star Antares is fortuitously placed in the sky just where the Scorpion’s Heart should be. It is a constellation of the Zodiac that is in the direction of the sky that has one of the densest concentration of stars visible, but it never rises very high in the southern sky when seen from Europe.
There is a minor meteor shower between April 16 and 25, but the Moon is bright on those nights so only the brightest meteors will be seen.
The Moon is new on the 7th, first quarter on the 14th, full moon on the 22nd and last quarter on April 30.
By Clive Jackson
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Clive Jackson is the Director of the Camera Obscura (next to the Castle in Tavira), specialising in education and public outreach.
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To see the April Sky Map click on the pdf link below