Description

Northern Hemisphere

Ian Morison tells us what we can see in the Northern Hemisphere night sky during May 2018.

The Planets

• Jupiter - Jupiter reaches opposition on May 8th, so will be visible all night. It shines at magnitude -2.5 and has a disk some 44 arc seconds across throughout the month. Jupiter's equatorisl bands and sometimes the Great Red Spot (see 'highlights' for the times when it crosses Jupiter's central meridian) and up to four of its Gallilean moons will be visible in a small telescope. Sadly, lying in Libra during the month, Jupiter is heading towards the southern part of the ecliptic and will only have an elevation of ~20 degrees when crossing the meridian. Atmospheric dispersion will thus hinder our view and it might be worth considering purchasing the ZWO Atmospheric Dispersion Corrector to counteract its effects.
  
• Saturn - Saturn, now well into its new apparition, rises at around midnight on the first of May and a couple of hours earlier by month's end. With an angular size of ~17.5 arc seconds (increasing to 18.1 during the month) it climbs higher before dawn and so becomes easier to spot as the month progresses. Its brightness increases from +0.4 to +0.2 magnitudes during the month. The rings were at their widest some months ago and are still, at 25 degrees to the line of sight, well open and spanning ~2.5 times the size of Saturn's globe. Saturn, lying in Sagittarius, is close to the topmost star of the 'teapot'. It will been seen best just before dawn but, sadly, even when at opposition later in the year it will only reach an elevation of just over 15 degrees above the horizon when crossing the meridian. Atmospheric dispersion will thus greatly hinder our view and, as for Jupiter, it might be worth considering purchasing the ZWO Atmospheric Dispersion Corrector to counteract its effects.
  
• Mercury - Mercury reached greatest elongation east from the Sun on April 29th and might just be glimpsed low above the western horizon for the first few days of May, but for the remainder of the month will lie too close to the Sun to be visible.
  
• Mars - Mars starts the month in Sagittarius and moves into Capricornus in mid-May. Now a morning object, it rises at around 1:30 am BST at the start of the month and a little after midnight by May 31st. During the month, Mars has a magnitude which increases rapidly from -0.4 to -1.2 and has an angular size of 11.1 increasing to 15.1 arc seconds during the month so it should be possible to spot details, such as Syrtis Major, on its salmon-pink surface with a small telescope. It will only reach an elevation of ~10 degrees before dawn at the start of the month and ~131 degrees by month's end. Sadly, the atmosphere will hinder our view. Another reason for purchasing a ZWO Atmospheric Dispersion corrector?
  
• Venus - Venus, seen in the west after sunset, shines brightly at magnitude -3.9 all month with an angular size of 11.5 increasing to 13 arc seconds. Venus rises a little higher in the sky as April progresses, initially setting around two hours after the Sun but increasing to two and a half hours by month's end as its elevation at sunset stays at around 20 degrees - it will be very prominent in the evening sky. Venus starts the month in Taurus, not far above the Hyades Cluster, but passes into Gemini on the 19th before passing between the Hyades and Pleiades Clusters on the 27th.
  

Highlights

• May - a great month to view Jupiter. This is a great month to observe Jupiter which comes into opposition on May 8th and will be visible during all the hours of darkness. It is moving down the ecliptic and now lies in Libra and, sadly, will only reach an elevations of ~20 degrees when crossing the meridian. An interesting observation is that the Great Red Spot appears to be diminishing in size. At the beginning of the last century it spanned 40,000 km across but now appears to be only ~16,500 km across - less than half the size. It used to be said that 3 Earths could fit within it, but now it is only one. The shrinking rate appears to be accelerating and observations indicate that it is now reducing in size by ~580 miles per year. Will it eventually disappear?
  
• The features seen in the Jovian atmosphere have been changing quite significantly over the last few years - for a while the South Equatorial Belt vanished completely (as seen in Damian's image) but has now returned to its normal wide state.
  
• May: Look for the Great Red Spot on Jupiter. This list gives some of the best evening times during May to observe the Great Red Spot which should then lie on the central meridian of the planet. The times are in UT.
  
• May 5th and 6th before dawn: The Eta Aquarid Meteor Shower. The Eta Aquarids are one of the finest meteor showers that can be seen from the southern hemisphere but, in the northern hemisphere, may only be glimpsed in the pre-dawn sky in the south-east around 90 minutes before dawn. Sadly, this year the peak is when there is a waning gibbous Moon in the sky - so moonlight will hinder our view.
  
• May 5th - before dawn: Saturn, the Moon and Mars together in the southern sky. Before dawn on the 5th of May and given a clear sky and a low horizon to the east of south, you should be able to spot Saturn to the right of the waning gibbous Moon with Mars down to its lower left. Binoculars might be needed to penetrate the sky's pre-dawn brightness, but please do not use them after the Sun has risen.
  
• May 17th after sunset: Venus above a very thin crescent Moon. If clear after sunset on the 17th May and given a very low western horizon you should easily spot Venus! However it will be much harder to spot a very thin crescent Moon, just two days after new, down to its lower left. Binoculars may well be needed to see the Moon, but please do not use them until after the Sun has set.
  
• May 6th and 22nd - evenings: The Hyginus Rille. These evenings, should it be clear, are a superb time to view the Hyginus Crator and Rille as it will lie close to the terminator. For some time a debate raged as to whether the craters on the Moon were caused by impacts or volcanic activity. We now know that virtually all were caused by impact, but it is thought that the Hyginus crater that lies at the centre of the Hyginus Rille may well be volcanic in origin. It is an 11 km wide rimless pit - in contrast to impact craters which have raised rims - and its close association with the rille of the same name associates it with internal lunar events. It can quite easily be seen to be surrounded by dark material. It is thought that an explosive release of dust and gas created a vacant space below so that the overlying surface collapsed into it so forming the crater. The author's image of the crater and rille can be seen in the inset to the image of the 8 day old Moon below.
  

Gabriela Perez from the Carter Observatory in New Zealand speaks about the Southern Hemisphere night sky during May 2018.

• Introduction - Kia Ora, Gabriela Perez here from Wellington New Zealand. It's autumn here in the southern hemisphere and we can tell from the chilly night and fallen leaves but also from our skies. We can see the summer months sinking into the Western horizon with Orion and his companions making way for all our winter constellations. Quite a nice time year to see Orion and Scorpius on either sides of the sky knowing that they're doomed to chase one another forever.
  
• Orion - The best time to view the deep space objects will be around the middle of the month as new moon will be on the 15th of May and on the 29th we will round off the month with the full moon.
  
• The Planets - In the middle of May we will have sliver Venus setting 90 minutes after the Sun in the northwest once again becoming our evening star. The fainter planets, Saturn and Mars will also be in the sky in the constellation of Sagittarius.
  
• Scorpius - Another fantastic sight in the constellation of Scorpius is the Bug/Butterfly Nebula. It is a bipolar planetary nebula, having one the most complex structures ever seen with a star at its centre, also in its final stages but burning at some of the hottest temperatures recorded in the galaxy (for a star).
  
• Stellar Clusters - Between Scorpius and Sagittarius is the zone designated Sagittarius A and it is our galactic centre. The middle point of our Milky Way or the 'bulge' making up some of the brightest and star-rich regions of our night sky. We have noted some intense radio feedback form this zone as astronomers believe that in the centre of our galaxy (and in fact the centre of every galaxy) is a supermassive black hole holding it together. On a clear night you can follow the Milky Way up to the Crux constellation or the Southern Cross, the smallest constellation but arguably the most well-known in the South. Use the pointer stars, the reddish orange Alpha Centauri and the blue/white Beta Centauri to make sure you have the right cross shape in the sky. Nearby star clusters such as the Jewel Box cluster or the Southern Pleiades make for some stunning telescope observations. Pick out the different colours in the cluster depicting stars of different sizes and at different stages of their lives. For a little bit of a challenge, and for another look at a dying star, you can move towards the constellation of Carina and find Eta Carinae and the Carina Nebula.
  
• Meteor Shower - If you're up late enough, at about around midnight on the 6th till the early hours of the 7th of May you can catch the peak of the Eta Aquarids. This spectacular annual meteor shower is capable of producing up to 60 meteors per hour. They will radiate from Aquarius but can be seen in a lot of the night sky.
  
• Arcturus - And if you're up early enough soon after dusk Arcturus appears in the northeast, seen twinkling as it is close to the horizon with it's light being broken up. It is the brightest red object in the sky, only outshone by Mars and 120 times brighter than the Sun.
  
• That's all for me for this month in the South and remember to keep warm but not let that stop you from going outside and looking up!