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THE NIGHT SKY FOR JULY 2015

Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during June 2015.

Arcturis, the brightest star in the constellation of Bootes, is visible in the southwest. Meanwhile, in the northwest, Merak and Dubhe of the constellation Ursa Major may be seen pointing towards the Polaris near the North Celestial Pole. Further north the w-shaped set of stars which form Cassiopeia may be seen, while towards the east the Summer Triangle is clearly visible. It is composed of three bright stars: Vega of Lyra, Deneb of Cygnus, and Altair of Aquila. Just to the left of Vega lies the Double-double: what appears to be a binary star system when viewed with binoculars becomes two binaries when observed through a telescope. Below Albireo, the head of Cygnus the Swan, the Cygnus Rift, a dark, dusty region of the Milky Way may be seen. Within the Cygnus Rift you may spot Brocchi's Cluster, also known as the Coathanger, while to the lower left of the summer triangle lies a faint constellation known as Delphinus the dolphin. Halfway between Arcturis and Vega lies the constellation of Hecules. The Keystone of Hercules consists of the four stars in its center, and on its right hand side lies M13, the Great Globular Cluster, and the brightest in the Northern Hemisphere.

The Planets

  • Jupiter stays close to Venus following their conjunction on June 30th. They both appear low in the western sky just after sunset. It is currently shining at magnitude -1.8, but dims to -1.7 magnitudes towards month's end. Its angular diameter will shrink from 32.4 to 31.2" over the month. Up to four of the Galilean moons and the dark equatorial bands will be visible, however the Great Red Spot will be harder to see without good seeing and transparency.
  • Saturn is still well placed for observations in the south at nightfall. It moves slowly in retrograde motion in the eastern part of Libra, but still close to the fan of three stars which make up the head of Scorpius. It dims from +0.2 to +0.4 magnitudes, and its disk shrinks from 18.1 to 17.3" over the month. The ring system, tilted 24 degrees from the line of sight and spanning 40" across makes for a wonderful sight.
  • Mercury will be sinking back towards the light of pre-dawn sky for the first part of the month. It will be best seen at the start of the month, with a magnitude of -0.2 and a phase of 52 percent. Its 7" diameter disk should just be visible with binoculars on the east-northeast horizon as dawn breaks.
  • Mars is just 8' away from Mercury on the 16th of the month. Throughout the month it will be visible low above the north-eastern horizon before dawn breaks. It will brighten from +1.6 to +1.7 magnitudes over the month, while its disk, fully illuminated, will remain at an angular size of 3.6".
  • Venus, shining brightly at magnitude -4.6, dominates the western sky from half an hour after sunset for the first part of the month. First appearing 19 degrees above the western horzon, and setting at 11:35 BST, it lies in Leo and moves towards, and then beyond, Regulus. On July 18th it will be joined by Jupiter, and by a thin crescent moon. It then wanders westward from July 23rd, before returning towards Jupiter on the 31st, when it will be 6 degrees south of the gas giant. Throughout the month it will increase in angular size from 33 to 51", and decrease in phase from 34 to 8 percent.

Highlights

  • Saturn, and its moon Titan, are still easily visible this month. To find Saturn in the sky, follow the arc of the Plough's handle downwards to first find the orange star Arcturus and continue down to find the white, first magnitude star, Spica, in Virgo. Saturn, a little brighter than Spica, lies in Libra down to its lower left and will appear slighly yellow in colour. As it rotates its equator bulges slightly giving it a squashed appearance. Like Jupiter, it does show belts but their colours are muted in comparison. Over the coming years Saturn's rings will continue to open out due to its rotation until they reach their most illuminated in May 2017.
  • There are two very nice objects to spot with binoculars high in the south-western 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 brightest globular cluster visible in the northern sky. 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!
  • Noctilucent clouds are most commonly seen in the deep twilight towards the north from our latitude. 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. So on a clear dark night this month, as light is draining from the north western sky long after sunset take a look towards the north - you might just spot them!
  • Around one hour after sunset on July 4th, given a clear sky and low western horizon, you should be able to spot Venus 2 degrees to the left of Jupiter, with both down to the lower right of Regulus in Leo. Venus, shining at magnitude -4.6, should be easy to spot, but binoculars may be required to pick out Jupiter at -1.8 against the darkening sky.
  • About one hour before sunrise on July 12th look above the eastern horizon. You should, if clear, be able to spot a thin waning crescent Moon near to the Hyades Cluster in Taurus - in which direction is also seen the orange giant star, Aldebara.
  • After sunset on July 18th, there will be a very close grouping of the planets Jupiter and Venus along with a waxing thin crescent Moon close to Regulus in Leo. They would all lie in the field of view of a pair of low power binoculars and this is probably the best imaging opportunity this month if we are lucky enough to have clear skies. It will still be pretty light as they begin to set, so you will need a very low horizon towards the west.
  • July 9th and 25th are great nights to observe two of the greatest craters on the Moon, Tycho and Copernicus. At full Moon the rays of material that were ejected when Tycho was formed can be see arcing across the surface. Copernicus is about 800 million years old and lies in the eastern Oceanus Procellarum beyond the end of the Apennine Mountains. It is 93km wide and nearly 4km deep and is a clasic "terraced" crater.

Southern Hemisphere

Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during July 2015.

Venus and Jupiter begin the month as pair in our north western evening sky after dark. They will gradually move further apart as Jupiter sinks more quickly into the western twilight. Venus, too, sinks throughout the month and appears a thin crescent through a telescope. Through a small telescope Jupiter’s 4 largest moons: Io, Europa, Ganymede and Callisto, are visible, lined up to either side of the planet.

High in the north-east lies Saturn, its rings and largest moon, Titan, visible through a small telescope. Close by are the claws of Scorpius, with Antares a little further to the right. Lying along the tail of the scorpion 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, but in a dark sight, with a good pair of binoculars, NGC 6231 appears in an area of nebulosity, intermingled with open clusters Trumpler 24 and Collinder 316 to form a complex sometimes known as the Scorpius Lizard.

A little above the Scorpions tail, NGC 6193 is visible to the naked eye at magnitude +5.2, and nearby NGC 6167 may be seen with binoculars or a small telescope. Below Scorpius is an upside down teapot formed from the brightest stars in Sagittarius. To the left of the teapot’s spout, just visible to the naked eye, is the Lagoon Nebula (M8). Along with the nearby Trifid Nebula (M20), the Lagoon Nebula is a good target for binoculars or a small telescope.

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.

From its bright centre the Milky Way stretches overhead through the diamond-kite-shaped Crux, the Southern Cross, and on to Carina, Vela and Puppis, which together make up the great ship Argo Navis, famous in Greek mythology. To Maori the Southern Cross is known as Te Punga, the anchor of Tamareriti’s waka, which stretches out along the Milky Way.

Alpha Crucis, the brightest star in the Southern Cross appears to be a single star with a magnitude of +0.9, but a small telescope will reveal a double star with blue-white components of magnitudes +1.4 and +1.9. Beta Crucis, slightly fainter at +1.3 magnitudes, is also blue-white. Gamma Crucis, at the top of the cross, is easy to pick out by its reddish-orange colour. A little below Crux are the Diamond Cross and False Cross. To distinguish Crux, seek The Pointers, Alpha and Beta Centauri. Alpha Centauri is the third brightest star in the night sky at magnitude -0.27. Beta Centauri appears almost as bright, with a combined magnitude of +0.6. Using these stars to find the Southern Cross is as easy as ABC - Alpha, Beta, Crux.

Compiled by Ian Morison