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The Sky This Month - July 2014

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Written by Gary Boyle on
Post Date: 
Tue, 2014/07/01

The Mighty Hercules


As the sky finally darkens well after 10 p.m. on these summer nights, plan to hunt down some great objects in the constellation Hercules. The mythological son of Zeus is positioned directly overhead and well placed for observing and photography. At first glance, the asterism stars range from magnitude 2.2 to 4.4 and looks like a crooked letter H with its left side kicked in mid way up. These main stars reside from 35 to 408 light years from us. Hercules is the fifth largest constellation in area with 1,225 square degrees of sky. Within it boundaries lay a total of 93 NGC galaxies, 2 planetary nebulas and 3 globular clusters one of which is the famous M13. But more on M13 later.



At magnitude 2.8 the brightest star named Kornephoros and is 139 light years away. Its name is derived from the Greek meaning “club bearer” which makes sense since Hercules is actually inverted in the sky with head down and feet up. Kornephoros is a spectral class G8 star and part of a binary star system. Moving north we come to Zeta Herculis and a member of the four stars making up the Keystone. Zeta is an F9 subgiant star and is more than six times brighter than our Sun. It is located only 35 light years from us and has a close companion that orbits Zeta every 34.5 years.


Then we have Mu Herculis. It’s magnitude is 3.4 and lives 27.11 light years away. This G5 is a binary star system with its companion only 286 astronomical units away and orbits once in 43.2 years. To date many stars play parent to sibling planets that orbit around them. Another example is Delta Herculis, a spectral class A3 main sequence subgiant star believed to have from two to five planets dancing around it. In all Hercules have 12 stars that harbour exoplanets.


As mentioned, Hercules is home to only three globular clusters to which the most famous is catalogued as M13. At a distance of 25,000 light years, this snowball of stars is estimated to contain a million suns opposed to the typical 100,000. At magnitude 5.8 this cluster is on the border of naked eye visibility and is a good taste for sky transparency. Any telescope will reveal its wealth of stars with larger instrument seeing right down to the core.  M13 can be found two-thirds the way up from Zeta. From M13 move your scope about a degree to the north-east until you come across NGC 6207. This magnitude 11.4 spiral galaxy adds a beautiful contrast to both sp be sure to use a wide angle eyepiece. It has en estimated distance of 62 million light years.



Now here is your challenge. Sandwiched half way between these two is IC4617. A tiny spiral faintly glowing at magnitude 15.2 and is close to half a billion light years from us.  Another interesting object is Arp 272. This is a pair of interesting galaxies to which the two appear in a rich galaxy field. This area appears to the south-east corner of the constellation. The only planetary nebula within Hercules is NGC 6210. You are witnessing the final last gasp of a star that was less massive than our Sun. Solar winds from the hot radiation are causing the artwork of ionized oxygen over several time periods. NGC 6210 spans 1.5 light years across and is located about 6,500 light years from us.


Comet PanSTARRS (C/2012 K1) is now in the constellation Leo Major and should be brightening throughout July from magnitude 8.0 to 7.8 and well on its way to rounding the Sun on August 27. It is expected to reach naked eye limits of magnitude 6.0 in October of this year when it is a morning object. Another comet to keep tabs on is Comet Oukaimeden which is expected to peak on September 19, 2014 at magnitude 5.9. Stay tuned for that one. Over the next few weeks you should have an opportunity to observe a damocloid. A damocloid is simply a comet that has gone dormant and does not sport a coma or tail because of outgassing thus becoming an asteroid. Before now Comet C/2013 UQ4 Catalina was a +13 magnitude speck of an asteroid but since it rounded the Sun, Catalina has strangely reestablished its coma and tail. If and only if Catalina remains in comet mode will we have the luck to observe it before it fizzles out again. Comet C/2013 UQ4 reaches perihelion on July 6th only four days before its closest approach to the Earth at 47 million kilometres distant or half an AU, when it may well reach a peak magnitude of +7. At that point, the comet will have an apparent motion of about 7 degrees a day — that’s the span of a Full Moon once every 1 hour and 42 minutes.


I do not usually publish the positions of the big four asteroids but +8  magnitude Ceres and +7 magnitude Vesta will be converging in the sky on July 4 and 5. This is of course an optical close approach as the two will still be separated by some 50 million kilometers. Vesta measures 570 km wide whereas Ceres is double that size. The two are not too far from Mars and Spica in the sky so this might make for a great digital moment. Speaking of which we have another digital moment coming on July 5 when the first quarter moon will be centered between Spica on the left and Mars on the right.



Mars is still fairly prominent on these warm nights. Follow the red planet as it treks eastward against the back ground stars. Mars will slide above Spica on the 13 as the two will be 1.3 degrees apart or approximately three full moon widths. To give you a perspective on scale, on July 1st Mars is 8.2 light minutes from Earth whereas Spica is 263 light years away. Jupiter is bidding its final farewell as it disappearing into evening twilight and will be in conjunction with the Sun on July 24 and will glimpsed in the morning sky by mid August.


Saturn is by far the favourite planet at star parties. Its rings are nicely open and large scope will reveal its many moons. And let’s not forget Venus low in the morning sky as it teams up with Mercury on the 12th when they will be 7 degrees apart. July 12 also marks the Full Buck Moon at 11:25 UT. Next day will see large tides due to the moon’s close distance of 358,260 km at 8h UT. Two weeks later New Moon (lunation 1133) occurs on July 26 at 22:42 UT.


Until next month, clear skies everyone.


Gary Boyle


 Twitter: @astroeducator