The night sky for August 2018

Northern Hemisphere

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

The Planets

• Jupiter - Jupiter can be seen in the southwest soon after sunset at the start of the month. It shines at magnitude -2.1 (falling to -1.9 during the month) and has a disk some 38 (falling to 35) arc seconds across. Jupiter's equatorial bands, sometimes the Great Red Spot and up to four of its Gallilean moons will be visible in a small telescope. Sadly, now moving slowly eastwards in Libra, Jupiter is heading towards the southern part of the ecliptic and will only have an elevation of ~15 degrees after sunset. 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 in the south at an elevation of ~15 degrees after sunset at the beginning of August. Its disk has an angular size of 18 arc seconds falling to 17 during the month. Its brightness reduces from +0.2 to +0.4 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 some 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 Triffid Nebula. Sadly, 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, having passed between the Earth and Sun (inferior conjunction) on August 9th, becomes visible after the 20th before reaching greatest elongation east of the Sun on August 26th. Then, some 18 degrees from the Sun, it rises before 5 am shining at magnitude zero.
  
  
• Mars - Mars, moving in retrograde motion westwards in Capricornus at the start of the month, made its closest approach to Earth since 2003 on the night of July 30th/31st. It moves into Sagittarius on the 23rd of August. Mars begins the month rising just after sunset shining at its peak magnitude of -2.8 but this falls to -2.2 by month's end. Its angular size exceeds 24 arc seconds until August 8th and falls to 21 arc seconds by the start of September. With a small telescope it should (but see below) 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? As I write this in July, a dust storm obscures much of the surface - let's hope it clears during August.
  
  
• Venus - Venus, can be seen low in the west after nightfall sinking towards the horizon as the month progresses. During August, its illuminated phase thins from ~57% to ~29% but, at the same time, the angular diameter of its disk increases from 20 to 29 arc seconds. The surface area reflecting the Sun's light does and so the brightness increases from -4.3 to an outstanding -4.6 magnitudes. Venus moves towards Spica in Virgo as August progresses and ends the month just one degree below the star. Sadly, however, they are then only ~10 degrees above the western horizon after sunset.
  
  

Highlights

• August - observe Mars.Mars came to its closest opposition to Earth since 2003 on the 27th July but, sadly two things conspire to limit our views. From the UK its maximum elevation when on the meridian will be only 12 degrees when observed from a latitude of +52 degrees. Thus the atmosphere will hinder our view and the use of an Atmospheric Dispersion Corrector may well help to alleviate its effects. The second problem is that, as sometimes happens, Mars is now suffering a major dust storm which, at the end of July, was making it very difficult to observe any features on the surface. These can happen every six to eight years and can last for several months. A small scale dust storm began on May 30th and, by the 20th of June, had engulfed the whole planet. Sadly, it could take as long as September for the dust to settle thus greatly inhibiting our view of Mars this apparation. However, it does look as though the South Polar Cap is still visible. Let's just hope that the dust storm subsides in time for other details on the surface such as Syrtis Major and the Hellas Basin to become visible in small telescopes. On the night of August 11th, these should be facing the Earth. A superb program, WinJUPOS can be downloaded for free and will give a view of Mar's surface for any time, showing what features should be visible.
  
  
• August - observe Saturn.Saturn reached opposition on the 27th of June, so is now low (at an elevation of ~14 degrees) in the west-southwest as darkness falls lying above the 'teapot' of 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 currently at an angle of 26 degrees to the line of sight. The rings will continue to narrow until March 2025 when they will appear edge-on again.
  
  
• August- 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!
  
  
• August - A good month to observe Neptune with a small telescope. Neptune comes into opposition - when it is nearest the Earth - on the 7th of September, so will be well placed to observe both this month and next. Its magnitude is +7.9 so Neptune, with a disk just 3.7 arc seconds across, is easily spotted in binoculars lying in the constellation Aquarius to the left of Lambda Aquarius as shown on the chart. It rises to an elevation of ~27 degrees when due south. Given a telescope of 8 inches or greater aperture and a dark transparent night it should even be possible to spot its moon Triton. (This is my objective around the end of the month!)
  
  
• The mornings of August 12th and 13th - midnight to dawn: look out for the Perseid meteor shower - with no Moon in the sky! If clear, these mornings should give us a chance of observing the Perseid meteor shower - produced by debris from the comet Swift-Tuttle. The early morning of the 12th August will give us the best chance, if clear, of viewing the shower, but the peak is quite broad and so it is well worth observing on the nights before and after. Post midnight is best as then Perseus has then risen higher in the sky. Most meteors are seen looking about 50 degrees from the "radiant" which lies between Perseus and Cassiopeia. This year, the Moon is just after 'New Moon' (on the 11th) so will not hinder out view. NB: As we need to view a very wide area of sky, normal binoculars would be of no use, but the Vixen SG 2.1 x 42 that I have just reviewed in the Astronomy Digest, could be useful as it covers a field of view of 27 degrees. Do get to as dark a sky location as you can to the south of any major towns or cities. This dark sky map gives a very good guide to where to travel to.
  
  
• August 14th - Venus just below a thin crescent Moon.After sunset on the 14th, look for Venus, low in the west just below a thin waxing crescent Moon.
  
  
• August 31st - Venus just below Spica, Alpha Virginis. Soon after sunset and looking very low on the west-southwest you might be able to spot Venus just one degree below Spica. Binoculars may well be needed to lessen the light remaining in the sky, but please do not use them until after the Sun has set.
  
  

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

• Introduction.Kia Ora, Gabriela Perez here from Space Place at the Carter Observatory in Wellington, New Zealand. We are looking up at the month of August. The worst of winter is now behind us and our nights are getting shorter, but we still have plenty of long nights to look up at the stars. There are some spectacular sights in the sky this month. We have four visible planets in our skies in the early evening. They are so bright, they are outshining the surrounding stars and they become the focus point scattered across the night sky on the arch of the ecliptic backdropped by the zodiac constellations.
  
  
• Venus.Our evening star in the northwest is the brilliant planet, Venus. Because of its thick atmosphere it reflects a lot of light from the sun. It's so bright you will see it first in the sky before the Sun sets. High up in the north you will see Jupiter and following it is the planet Saturn followed by Mars. Mars is rivalling Venus's intensity in the East looking especially bright and red. It is still quite close to the earth as it was in opposition at the end of July and in the beginning of August it will continue to be the closest it has been to earth since 2003 a mere 58 million km from us.
  
  
• Scorpius and deep space objects.The most familiar of the constellations in our sky will be our 'winter constellation', Scorpius. It has a hooked tail and bleeding heart, Antares. Antares and the tail make the 'fish-hook of Maui' in Maori starlore, Antares becoming the bloody bait on the hook. Antares is a red giant star: 600 light years away. Scorpius is also home to four deep space object that were among the first to be catalogued by Charles Messier: M4, M6 also known as the Butterfly Cluster; M7, and M80. Below or right of the Scorpion's tail is 'the teapot' made by the brightest stars of Sagittarius. It is upside down in our southern hemisphere view. Saturn is near the teapot's lid. Between Scorpius and Sagittarius, we find the heart of our Milky Way in the 'bulge'. This area designated 'Sagittarius A' is believed to be the location of a supermassive black hole in the center of our home galaxy helping to hold it all together.
  
  
• The best viewing time for the deep sky objects will be mid-month as we will have the new moon the 11th. Full Moon will on the 26th of August.
  
  
• Dark Nebula.Mid-month will be the best time to look over at the South. High up in the Southwest we have the Crux constellation or the Southern Cross. On a dark moonless night away from the city lights, you might spot a dark patch nearby the Crux's second brightest star 'Beta Crucis'. This is the Coalsack Nebula, a famous dark nebula that is only visible because of the strong concentration of starlight we get along the edgewise view of our milky way. Dark nebulae block out the light from far away stars as they are densely packed pillars of frozen dust and gas. The Coalsack Nebula, much like coal itself, will ignite one day and in 3 or 4 million years, become one of the brightest patches in the sky. The Coalsack Nebula is sometimes known as the head of the Moa here in New Zealand, a large extinct flightless bird, and you can track it's long neck, body and feet formed by the other dark nebula you can make out across the Milky Way.
  
  
• Constellations.If you are awake in the early morning you can catch a glimpse of our dawn skies. We will have Orion and Taurus in the east, last month they were telling the tale of Matariki, the Maori New Year. There are some great views of 'The Pot' a small asterism in Orion with the base formed by Orion's belt. With three fainter stars that form the handle. The middle of these is in fact The Great Orion Nebula, a diffuse nebula and the closest stellar nursery to Earth. Here astronomers have witnessed the birth of stars and protoplanetary disk, the disks in which planets are formed around the young stars.
  
  
• That's all from me here in Wellington New Zealand and I wish everyone clear skies during the month of August.