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Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during July 2017.

The Planets

  • Jupiter - Now three months after opposition, Jupiter still dominates the low southwestern sky after nightfall. It sets at about 1 am BST as July begins. As the month progresses its brightness falls from -2.0 to -1.9 magnitudes as its angular size falls from 37 to 34 arc seconds. It lies in Virgo some 10.5 degrees to the west of Spica, now moving eastwards again after its period of retrograde motion. It will pass Spica on September 11th on its journey towards the lower parts of the ecliptic. Next year it will only reach an elevation of some 25 degrees when due south and, in the following two years, just 18 degrees before it moves back towards the more northerly parts of the ecliptic. Even so, with a small telescope one should easily be able to see the equatorial bands in the atmosphere, sometimes the Great Red Spot and up to four of the Galilean moons as they weave their way around it.
  • Saturn - Saturn came into opposition on June 11th and so will be at its highest elevation due south at around midnight BST as July begins but by ~10 pm BST at its end. It will be visible throughout most of the short night. It shines initially at magnitude 0.1 falling to +0.2 during the month and has an angular size of ~18 arc seconds. With an angle of 26.7 degrees inclination to the line of sight, the rings are virtually as open as they ever can be. It is sad that Saturn, now lying in the southern part of Ophiuchus between Sagittarius and Scorpius, only reaches an elevation of ~17 degrees above the horizon when due south so hindering our view of this most beautiful planet. If imaging Saturn (or Jupiter), Registax 6 has a tool to align the red, green and blue colour images to largely remove atmospheric dispersion from the image. At somewhat over 100 GBP one can purchase the ZWO atmospheric dispersion corrector which uses two, contra rotating, prisms to carry out an even better correction - and which can also be used for visual observing.
  • Mercury - Mercury reaches greatest elongation east, some 27 degrees from the Sun, on July 30th. It can be seen low in the west-northwest around 30 minutes after sunset. Binoculars may well be needed but please do not use them until after the Sun has set. It fades slightly during the month from -1.0 to +0.4 magnitudes whilst its angular size increases from 5.3 to 7.8 arc seconds. No surface details will, of course, be seen.
  • Mars - Mars is hidden in the Sun's glare all month so cannot be observed.
  • Venus - Venus is visible in the east before dawn this month rising around 2.5 hours before sunrise increasing to 3 hours as the month progresses. It magnitude dims slightly during the month from -4.2 to -4.0 as its angular diameter shrinks from 18.2 to 14.6 arc seconds. However, at the same time, its illuminated phase increases from 63 to 74% which explains why the magnitude does not drop too much. Even though it will be moving back towards the Sun, as the angle of the ecliptic to the horizon increases at this time of the year, it elevation before sunrise will continue to increase until August. Venus passes the Pleiades Cluster on the 5th, the Hyades on the 13/14th and ends the month close to M35 in Gemini.
  • Highlights

    June - The best month to observe Saturn - Saturn reached opposition on the 14th of June, so is now due south and highest in the sky in the late evening. It lies in the southern part of Ophiuchus some 16 degrees up and to the left of the orange star Antares in Scorpius. 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.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 fully opened out, currently at an angle of 26.5 degrees to the line of sight. From this month the ring's orientation will begin to narrow until March 2025 when they will appear edge-on again.

    July - Find the globular cluster in Hercules and spot the "Double-double" in Lyra - There are two very nice objects to spot with binoculars in the eastern sky well after dark this month. Two thirds of the way up the right hand side of the 4 stars that make up the "keystone" in the constellation Hercules is M13, the best globular cluster visible in the northern sky. The 15 minute exposure image on right was taken by the author using a 127 mm APO refractor and SBIG 8.3 megapixel CCD camera. 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 frequency, 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 7th/8th - midnight: The Moon and SaturnLate evening on the 7th July, the waxing Moon will be seen to the upper right of Saturn.

    20th July - before dawn: Venus, Aldebaran and a thin crescent Moon - Before dawn on the 20th, Venus will be seen over to the left of a very thin waning crescent Moon. Aldebaran, lying in front of the Hyades Cluster, will also be seen to the upper right of the Moon.

    July 25th - after sunset: The Moon and Mercury - After sunset on the 25th July, given a low western horizon and clear skies, there is a chance of spotting Mercury down to the right of a very thin crescent Moon. Binoculars may well be needed but please do not use them until after the Sun has set.

    July 1st and 15th: The Alpine Valley - These are two good nights to observe an interesting feature on the Moon if you have a small telescope. Close to the terminator is the Appenine mountain chain that marks the edge of Mare Imbrium. Towards the upper end you should see the cleft across them called the Alpine valley. It is about 7 miles wide and 79 miles long. As shown in the image a thin rill runs along its length which is quite a challenge to observe. Over the next two nights the dark crater Plato and the young crater Copernicus will come into view. This is a very interesting region of the Moon!

    Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during July 2017.

    Kia ora and welcome to the July Jodcast from Space Place at Carter Observatory in Wellington, New Zealand.
    Jupiter is still high in our evening skies this month, midway up the northwestern sky after sunset. Shining at magnitude -2.1, with its bright golden glow, Jupiter will be the first star-like object you'll see as the sky begins to darken. Just above is bluish Spica, representing the "ear of wheat" held by Virgo. The waxing crescent moon will pass close to Jupiter on both the 1st and 29th of the month.
    Lower in the west, Mercury is making an appearance in the evening sky. At the start of the month it sets just an hour after the Sun, but by the end of July, when it reaches its greatest elongation from the Sun, it will remain in our skies until 8pm. On the 25th Mercury will form a close group with Regulus, in Leo, and a thin crescent Moon.
    Saturn is high in the northeast and is a great target for a telescope of any size, with its rings still at almost maximum tilt. Look out for Saturn's largest moon Titan looking like a star at around 4 times the ring diameter from the planet. Saturn continues to sit just below Antares in Scorpius, with the claws of the scorpion to the left and his tail curling around to the right. In New Zealand we see this as the fish hook of Māui, Te Matau a Maui.
    Below Scorpius is an upside down teapot formed from the brightest stars in the constellation of Sagittarius. The bright centre of the Milky Way runs through Scorpius and sagitarrius, so there are many stunning objects to explore in this part of the sky.
    Lying along the tail of the scorpion, close to the orange 3rd magnitude star Zeta Scorpii, is NGC 6231, a bright cluster of stars which looks like a small comet. At magnitude 2.6 this is easily visible to the naked eye. Estimated to be only 3.2 million years old and nearly 6000 light-years away, NGC6231 covers an area of the sky similar in size to the Pleiades, but its stars are much more luminous. If the cluster was placed at the same distance as the Pleiades then some of its stars would be amongst the brightest in the night time sky. With a good pair of binoculars, from a dark sight, NGC 6231 appears in an area of nebulosity and intermingled with open clusters Trumpler 24 and Collinder 316 to form a lovely complex sometimes known as the Scorpius Lizard. Also nearby is NGC 2642. With binoculars its three brightest stars stand out from a faint background glow.
    A little above, NGC 6193 is also visible to the naked eye at magnitude 5.2, and nearby NGC 6167 is worth a look in binoculars or a small telescope.
    Below, about halfway between the scorpion's sting and the spout of the teapot is M7. This is another open cluster of stars easily visible to the naked eye at magnitude 3.3, and a lovely sight through a good pair of binoculars. It contains about 80 stars brighter than 10th magnitude and covers an area of 1.3 degrees diameter. Current estimates suggest a distance of 980 light years and an age of 220 million years old – still pretty young in astronomical terms. M7 has been known since ancient times and was first recorded by Ptolomy in 130 AD, who described it as a "nebula following the sting of Scorpius", because of this it is also sometimes referred to as the Ptolomy cluster. Nearby and somewhat fainter, the Butterfly cluster, or M6 is also a nice sight in binoculars. The stars will all appear to be at around the same brightness, and the open winged shape that gives the cluster its name should be easy to pick out.
    To the left of the teapot's spout, and just about visible to the naked eye, is another lovely Messier object, the Lagoon Nebula, or M8. This is a huge cloud of interstellar gas and dust where new stars are being formed. M8 is a great example of an HII region, where the UV radiation from hot young stars is ionizing the leftover hydrogen gas and causing is to glow. These emission nebulae often appear pink in colour photographs and the Lagoon Nebula is a good target for binoculars or a small telescope.
    Another good target is the Trifid nebula, discovered by Charles Messier in 1764, and famed for the three-lobed appearance, which earned it it’s name. It is an interesting object to observe as it combines both an emission and reflection nebula along with an open cluster of stars.
    There are also a number of globular clusters in this part of the sky. The brightest is M4, and this is also one of the easiest to find, lying just 1.3 degrees west of Antares. Appearing as a small fuzzy ball in binoculars or small telescopes, a slightly larger telescope will begin to pick out individual stars.
    Also in this region, near the top of the teapot, is M22, one of the first globular clusters ever discovered in 1665, and one of the closest at just 10,600 light-years.
    From its bright centre the Milky Way stretches overhead through Crux, the Southern Cross, and on to Carina, Vela and Puppis above the southwestern horizon. Together these three constellations make up the great ship Argo Navis, famous in Greek mythology as that used by Jason and the Argonauts in their quest for the Golden Fleece.
    Just to the left of the Milky Way is Carina’s brightest star Canopus, or Alpha Carinae, the second brightest in the nighttime sky. Its Maori name is Atu tahi or Au tahi, which means to stand alone, because of its position just outside the main band of our Galaxy. In the other direction , the Milky Way drops down to the eastern horizon and the bright star Altair in the constellation of Aquila, the Eagle, which rises around 9pm at the start of the month.
    In the morning skies our last visible planet, brilliant Venus, rises after 4am. Venus is so bright that you can really only mistake it with the headlights of an airplane and provides a useful pointer to help find Matariki/the Pleiades as the cluster rises before dawn. Venus sits just above Matariki at the beginning of the month, but slowly moves down between Matariki and Taurus' brightest star Aldebaran as the month progresses, sitting just below Aldebaran on the morning of the 18th.
    Wishing you clear skies from the team her at Space Place at Carter Observatory.

    Compiled by Ian Morison