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Wednesday 20 September 2017  •   30 Apple Moon 2017

Viewing the night sky in Apple Moon 2017

22 August - 20 September 2017

Map of night sky at full moon: 6 September, 07:03 UTC
Northern hemisphere perspective, aligned on the ecliptic. Morning sky to the left, evening to the right.

night sky map for Apple Moon 2017

Neptune comes to opposition on 5 Sep, and its nearest to Earth on 4 Sep, when it is 4329 million kilometres or 4 light hours away.
Like Uranus, it is an ice giant, and its diameter is about four times as large as Earth’s. Despite its size, it is too far away to be visible from Earth with the naked eye, but you can see it through a telescope or good binoculars.

Venus is the bright morning planet. During the month, Mercury and Mars come out of the dawn to join it. On 12 Sep, Mercury reaches 17.93°W of the sun. The planet, in its eccentric orbit, does not come very far out from the sun this time, but it is very favourable to be seen from Earth’s northern hemisphere, with the planet rising fairly vertically from the horizon, and the very bright Venus well above as a marker. If you have a good, clear view of the eastern horizon, you may be able to see the fainter Mars just below it, and the star Regulus just above it. The view from the south is poor. On 16 Sep, at around 17:51 UTC, Mercury passes within four minutes of arc north of Mars, best seen from the northern Pacific, but the planets rise soon after that in Japan, when they will still be close, and with Venus and then the moon above. On the morning of 18 Sep, there is a lovely view of the moon, Venus, Mercury and Mars, with the moon close to Venus and the bright star Regulus, and Mercury and the fainter Mars still close, nearer in towards the dawn. On the morning of 19 Sep, as seen from from Europe, the moon, Mercury and Mars are in a line in morning sky, with the moon nearest the sunrise. Further out are Venus and Regulus. On the morning of 20 Sep, Venus passes 0.5°N of Regulus.

Jupiter is now slipping towards the sunset, and much less bright than it was earlier in the year. On 25 August, the new crescent moon is nearby. By the end of the month, Jupiter is hard to see in the twilight, especially from the northern hemisphere.

Much further out from the sunset, round in Ophiuchus, is the fainter planet Saturn, setting mid-late evening. On 25 August, it resumes its eastward motion through the stars. The moon is nearby on 30 Aug.

The month ahead: Vine Moon 2017

21 September - 19 October 2017

Map of night sky at full moon: 5 October, 18:40 UTC
Northern hemisphere perspective, aligned on the ecliptic. Morning sky to the left, evening to the right.

night sky map for Vine Moon 2017

On 19 Oct, Uranus is opposite the sun as seen from Earth, 2830 million kilometres or 157 light minutes away. Although this is its nearest this year, it’s only eight years since its aphelion (furthest from the sun), and Uranus has a relatively eccentric orbit. At its closest in 2051, Uranus will be just 144 light minutes away, and quite a bit easier to see with the naked eye. Give it a go, though, even this year, if you have a good, dark sky.

Venus is the bright morning planet, though less prominent than earlier in the year as it heads towards the far side of the sun. The less bright Mars is in the eastern morning sky with Venus, and the two come together in the dawn twilight during the first half of the month, until on 5 Oct, Venus passes just twelve minutes of arc north of Mars around 16:50 UTC, best seen from Tonga and Midway in the Pacific. From Europe, see them close on the mornings of 5 & 6 Oct. The moon passes close north of Mars on 17 Oct and of Venus on 18 Oct.

You may just be able to see Jupiter in the western evening sky at the beginning of the month, especially when the new moon is nearby on 22 Sep. The view is better from the southern hemisphere. The planet then slips into the sunset, as Earth’s movement takes it round the back of the sun.

Saturn, in the constellation Ophiuchus, can be seen much more easily in the evening sky, albeit fairly low in the SW as seen from the northern hemisphere. The moon is nearby on 26 Sep. Although the planet is much less bright than earlier in the year, because of its greater distance from Earth, it is notable that the greatest northerly tilt of its rings for 29 years relative to Earth is on 16 Oct. If you have a telescope, look to see what a great view of the rings we have at the moment.

William Morris
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