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For sky-watchers in the northern hemisphere, there is a great chance to see Mercury in the evening sky in the first half or so of the lunar month, especially on 8 April, when it shines brightly to the right of the new crescent moon. It reaches 19.93°E of the sun on 18 April, when it is not far below Aldebaran and the Pleiades. By then, it is a little less bright, and if you look at it through binoculars or a telescope, you should be able to make out that we are seeing it as a fat crescent. In the second half of the month, Mercury falls rapidly into the sunset, and indeed will move across the solar face on 9 May.
Venus is on the far side of the sun, but may be seen just before sunrise for the first part of the month, before it gets too near the sun in the sky.
Saturn and Mars rise near to each other in the late evening, and are both very bright in the night and morning sky, with Mars the brighter and redder of the two. Both are coming towards opposition and maximum brightness next month. On 17 April, as Earth moves round in its orbit towards Mars, and begins to ?catch it up?, Mars halts in its westward progress through Ophiuchus towards Saturn, and begins to swing back the other way. On 25 April, the waning gibbous moon is near Mars, Saturn and Antares, the great red star of Scorpius that is currently outshone by the neighbouring planets. On 30 April, Mars crosses back into Scorpius.
By contrast, Earth swings further away from Jupiter, and the giant planet continues to grow gradually less bright, night by night, and sets in the early hours. The moon is nearby on the night of 17/18 April.
Look out for the Lyrid meteors on 21/22 April, though the full moon will make them harder to see, and the Eta Aquarid meteors in moon-free skies on 5/6 May.
Although Venus is behind the sun, there’s a lot happening with the other planets.
Mercury moves across the sun on 9 May. The transit begins at 12:12 BST (11:12 UT) and ends at 19:42 (18:42 UT), and is visible for all of that time from Western Europe, South America and eastern North America. Elsewhere in the world, except for Australasia and far E and SE Asia, some of the transit will be visible. The best way to see it is to project an image of the sun on to white card through a telescope or binoculars. Use a mask around the telescope or binoculars to create a bigger shadow on the card. Do not look directly at the sun through any optical equipment unless it is specifically designed for you to do so. It is safe to use mylar eclipse glasses (though check for damage first), and you should be able to see Mercury through them, but it will appear as quite a small dot. The next transit of Mercury is in November 2019, and the one after that is in November 2032. By the end of the lunar month, Mercury moves into the morning sky, well seen from the southern hemisphere, but from the north, it is still very low in the east when the sun rises. On 3 June, the very old crescent moon is nearby, and indeed passes in front of Mercury (occults it) as seen from southern Africa during daylight, and parts of the South Atlantic before sunrise.
There are three very bright planets in the evening sky, a wonderful spectacle.
Both Mars and Saturn, close in the sky, come to opposition and maximum brightness this month, and shine together prominently all night. Mars’ opposition is on 22 May, the day the full moon is near it and Saturn. At this close pass to Earth, Mars is 76.2 million km, or 4.24 light minutes away. Note that Mars will be considerably closer and brighter at its next opposition in July 2018 (oppositions in or near August occur when Mars is near perihelion, and Mars has a relatively eccentric orbit). On 28 May, with Earth overtaking on the inside, Mars is seen to move back into the constellation Libra and, for the moment, away from Saturn.
Saturn is at opposition on 3 June, and it comes as close as 1349 million kilometres or 75 light minutes. It’s still a couple of years before Saturn’s northern summer solstice and, with Earth and the Sun well north of Saturn’s equator, the rings are on brilliant display if you look through good binoculars or a telescope.
Jupiter, round to the west from Mars and Saturn, in the south of Leo, is (just) the brightest of the three on view. Night after night, all three bright planets adorn our skies. Watch as they gradually move in relation to each other. On 9 May, with opposition well past, Jupiter stops moving slowly westwards through the stars, and turns back towards the east. The moon is near Jupiter on 14 & 15 May.