Description

Northern Hemisphere

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

The Planets

• Jupiter - Jupiter can be seen due south soon after sunset at the start of the month and over towards the southwest as the month progresses. It shines at magnitude -2.3 (falling to -2.1 during the month) and has a disk some 41.5 (falling to 38) arc seconds across. Jupiter's equatorial 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, moving slowly westwards 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, was at opposition on the 27th of June and so will be visible during all the (few) hours of darkness. It will highest in the south around midnight as July begins and a little earlier by month's end. Its disk has an angular size of 18.4 arc seconds falling to 18.0 during the month. Its brightness reduces from +0.0 to +0.2 magnitudes as the month progresses. The rings were at their widest some months ago and are still, at 26 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' slowly moving in retrograde to within a few degrees of M8, the Lagoon Nebula, and M20, the Trifid Nebula. Sadly, 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 shining at around zeroth magnitude early in the month reaches greatest elongation west of the Sun is on July 12th. It will be then be seen about 15 degrees down to the lower right of Venus but will have dimmed to magnitude +1 by the 17th and then rapidly fade from view into the Sun's glare.
  
• Mars - Mars, in Capricornus, is moving in retrograde motion westwards as it moves towards its closest approach to Earth since 2003 on the night of July 30th/31st. Mars begins the month rising about 2 hours after sunset shining at magnitude -2.2 but its brightness peaks at -2.8 during the final week of July. Its angular size reaches 24.3 arc seconds at closest approach but will exceed 24 arc seconds from July 24th until August 8th. With a small telescope it will be possible to spot details, such as Syrtis Major, on its salmon-pink surface. From the UK, it will only reach an elevation of ~14 degrees when due south and so, sadly, the atmosphere will hinder our view. Another reason for purchasing a ZWO Atmospheric Dispersion corrector?
  
• Venus - Venus, can be seen low in the west after nightfall sinking towards the horizon as the month progresses. During July, its illuminated phase thins from ~70% to ~57% but, at the same time, the angular diameter of its disk increases from 16 to 20 arc seconds. The surface area reflecting the Sun's light thus stays roughly constant and so the brightness stays at around -4.2. On July 9th Venus is close to Regulus in Leo and on the 15th to a waxing crescent Moon.
  

Highlights

• July - still a great month to view Jupiter. This is a still a great month to observe Jupiter which came into opposition on May 8th and will be visible in the south in the late evening. It is moving down the ecliptic and now lies in Libra so, 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?
  
• [I have imaged Jupiter recently and the Red Spot is very prominent and has a lovely orange/red colour. These can be seen in my article 'Imaging Jupiter at Closest Approach' to be found in my Astronomy Digest].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 but is less prominent than the North Equatorial Belt .
  
• Saturn in the evening Sky. Saturn is just past opposition, so is now due south and highest in the sky in the late evening. It lies close to the topmost star of the 'Teapot' in Sagittarius. Held steady, binoculars should enable you to see Saturn's brightest moon, Titan, at magnitude 8.2. A small telescope will show the rings with magnifications of x25 or more and one of 6-8 inches aperture with a magnification of ~x200 coupled with a night of good 'seeing' (when the atmosphere is calm) will show Saturn and its beautiful ring system in its full glory. As Saturn rotates quickly with a day of just 10 and a half hours, its equator bulges slightly and so it appears a little 'squashed'. Like Jupiter, it does show belts but their colours are muted in comparison. The thing that makes Saturn stand out is, of course, its ring system. The two outermost rings, A and B, are separated by a gap called Cassini's Division which should be visible in a telescope of 4 or more inches aperture if seeing conditions are good. Lying within the B ring, but far less bright and difficult to spot, is the C or Crepe Ring. Due to the orientation of Saturn's rotation axis of 27 degrees with respect to the plane of the solar system, the orientation of the rings as seen by us changes as it orbits the Sun and twice each orbit they lie edge on to us and so can hardly be seen. This last happened in 2009 and they are now well opened out, currently at an angle of 26 degrees to the line of sight. The ring's orientation is beginning to narrow until, in March 2025, they will appear edge-on again.
  
• July - Find the globular cluster in Hercules and spot the "Double-double" in Lyra. Just to the left of the bright star Vega in Lyra is the multiple star system Epsilon Lyrae often called the double-double. With binoculars a binary star is seen but, when observed with a telescope, each of these two stars is revealed to be a double star - hence the name!
  
• Early July: A very good time to spot Noctilucent Clouds! Noctilucent clouds, also known as polar mesospheric clouds, are most commonly seen in the deep twilight towards the north from our latitude. They are the highest clouds in the atmosphere at heights of around 80 km or 50 miles. Normally too faint to be seen, they are visible when illuminated by sunlight from below the northern horizon whilst the lower parts of the atmosphere are in shadow. They are not fully understood and are increasing in frequencey, brightness and extent; some think that this might be due to climate change! So on a clear dark night as light is draining from the north western sky long after sunset take a look towards the north and you might just spot them!
  
• July 3rd ~2:30 am: Mars and a waning gibbous Moon. In the early morning of the 3rd, Mars will be seen down to the lower left of the gibbous Moon.
  
• July 9th - sunset: Venus close to Regulus in Leo. On the 9th, one would, if clear, see Venus shining brightly just up to the right of Regulus in Leo.
  
• July 10th before dawn: the Moon in the Hyades Cluster. Before dawn, a thin waning crescent Moon will be seen amongst the Hyades Cluster.
  
• July 15th, after sunset: Venus to the left of a very thin crescent Moon. If clear after sunset and given a very low western horizon, you should be able to spot Venus over to the left of a very thin crescent Moon.
  
• July 19th after sunset: Jupiter below a waxing Moon. After sunset on the 19th if clear, you should be able to spot Jupiter below a waxing Moon. Alpha Libri is to its lower left.
  
• July 24th after sunset: Saturn close to a waxing Moon. After sunset on the 24, Saturn will be seen, if clear, to the lower left of the waxing Moon.
  
• July 27th after sunset: a Total Eclipse of the Moon.After sunset on the 27th, if clear, we will be able to observe a totally eclipsed Moon. All times in BST.
  
• 8:50 Moon rise on the horizon in the south east.
  
• 9:21 Maximum eclipse when the Moon is closest to the centre of the Earth's shadow. (The Umbra)
  
• 10:13 Total eclipse ends.
  
• 11:19 Partial eclipse ends - the Moon has left the Earth's umbra and lost its red colour.
  
• 12:28 Penumbral eclipse ends - the Moon has moved out of eclipse.
  

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

• Introduction. Kia Ora everyone, the winter continues here in New Zealand and with it come the season of Matariki, the Maori New Year as well as spectacular views of our planets and plenty of hours of night to gaze at the night sky.
  
• Planets - All the visible planets will be in our skies during the month of July. Mercury will set with the sun in the West appearing close to the brilliant evening star, Venus. High up in the sky will be the orange Jupiter in the constellation of Libra followed by Saturn in Sagittarius, in the bulge of the Milky Way in the location of the centre of our galaxy, and Mars which will be found in Capricornus. Mars will be the closest it has been to earth since 2003 when we pass by at the end of July.
  
• Stars and Constellations - The brightest stars in the night sky, Sirius and Canopus can be found in the Southwest both twinkling as they are close to the horizon. Canopus will appear to change colour as the light is dispersed and appears to separate into separate colours as it closer to the horizon marking itself as the traffic light of our South Skies.
  
• In the north we can spot Cancer, the Crab with Leo the Lion, looking a bit more like a coat hanger in his stick figure form. Cancer is the dimmest of the Zodiac constellations. The stars forming a shape of a Y, quite tricky to see with the naked eye as the brightest star in this constellation is only magnitude 3.5. Cancer is home to some famous deep sky objects including M66 and the Beehive Cluster. M66 can be found at the midpoint between Regulus in Leo and Procyon in Canis Minor. It is the oldest 'close' star cluster between 3.5-5 billion years old which is quite incredible as stars generally tend to pull away from their sister stars in an open star cluster quite quickly. And just below it we can see the Beehive Cluster aging at only 600 million years old.
  
• Milky Way - In the South we find spectacular views of our Milky Way, peppered with dark patches marking the location of dark nebulas made visible to us because of the high concentration of stars the their subsequent light in the edgewise view of our Milky Way, the most visible of these is the Coalsack Nebula. This densely packed pillar of gas and dust could ignite one day, much like coal itself, as within it our all the right conditions for stars to be born. For now one of the darkest patches in the sky but in a few million years it could be the brightest. Of course you can use this to find the Crux or Southern Cross but a more reliable method would be to use the pointer stars, orange Alpha and blue Beta Centauri. The brightest stars in the constellation of Centaurus. Alpha is a triple star system it's dimmest star being our closest stellar neighbor Proxima Centauri at only 4.2 light years away.
  
• Pleiades and Matariki - The heliacal rising of the Pleiades star cluster, Matariki, marks the time of the Maori New Year. The dawn sky has a particular importance to us in New Zealand as it was the dawn sky as opposed to the evening sky that was studied closely by early Maori astronomers. At this time of year the sky is held up by four pillars (Pou), three in the east (Sirius, Pleiades and Orion's Belt) and Scorpius being the lone pillar in the West with a curved back as the weight is crushing down on it. The belt of Orion is easily spotted just before sunrise and points us to Matariki. It is found in the shoulder of the bull in the constellation of Taurus. It is a young star cluster, only 100 million years old, mostly consisting of giant hot blue stars. It is a rare sight to be able to pick out so many stars in an individual cluster in our night sky with the naked eye.
  
• That's all from me here in New Zealand.To the New Zealand listeners remember to keep warm and I hope you have a happy Matariki season and I wish everyone clear skies in July.