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6 Unmissable Celestial Events in October 2016

October 2016 has been described as the Month of Conjunctions, which will be coming thick and fast throughout the month and especially as seen from the southern hemisphere in general, and Australia in particular.

Below are some details of a few of the more spectacular events, all of which are visible without optical aid of any kind, although some optical aid will be required to view details of some of the components of the conjunctions described.

3-4 October 2016; Venus close to Crescent Moon

Venus is always a spectacular sight, and especially if it is in close conjunction with another object to better show off its brilliance. Nonetheless, Venus will start October high above the western horizon in the constellation Libra, where it will approach star Zubenel Genubi (Alpha Librae), the star that in ancient times, marked the southern claw of the Scorpion. On the 6th of October, Venus and Alpha Librae will be less than 1 degree apart.

On the 18th of the month, Venus will pass into the constellation Scorpius, and by month’s end, it will set a full three hours after the Sun. On the night of 20/21 October, Venus will pass less than a degree to the northward of Delta Scorpii (mag. 2.3), the star that marks the head of the Scorpion, while during the last three days of October, Venus will be just to the southward of the planet Saturn.

6 October 2016; Crescent Moon close to Saturn

It is not difficult to spot Saturn against the star fields of the constellation Ophiuchus during October, shining as it does with a golden hue. Look for Saturn as it progresses eastward against the background stars, moving only about 2 degrees during the entire month of October. By month’s end, Saturn will set at about 22:10 Local Time as seen from Sydney.

On the 6th of October, Saturn will be separated from the waxing crescent Moon by only about 4 degrees, and on the 29th, Saturn and Venus will be in close proximity, being separated by only about five minutes of arc.

8 October 2016; Mars close to the Moon

Mars starts October within 0.5 degree of the globular cluster NGC 6553 (mag. 8.3). Moving eastward, the Red planet approaches another globular cluster, M28 (mag. 6.9), which it reaches on the 6th of the month. One day later, Mars passes within 0.5 degree of the star Lambda Sagittarri (Kaus Borealis), an enormous K0 IV-class orange giant located about 78 light years away, in the Teapot asterism.

On the 8th of October, Mars and the waxing Moon will be about 7 degrees apart, with Mars toward the southward of the Moon. Follow Mars throughout October as it traverses the bright star fields of the constellation Sagittarius.

9-10 October 2016; Mars close to the Globular Cluster M22

Shining at magnitude +5.1, M22 in the constellation Sagittarius is among the brightest globular clusters in the entire sky and the most luminous cluster in the Messier catalogue. Under dark skies, M22 is easily visible without optical aid, and only two other globular clusters, NGC 5139 (Omega Centauri), and NGC 104 (47 Tucanae) are more luminous. The image of M22 below was taken through a 10-inch Newtonian reflecting telescope.

The image of M22 above was taken through a 10-inch Newtonian reflecting telescope. Look for M22 2.5 degrees to the northward of Kaus Borealis (Alpha Sagittarius), where it marks out the top of the “Teapot” asterism. While M22 is easily visible with the naked eye, a pair of 10 x50 binoculars will reveal it as a distinctly diffuse ball of light, although no detail as to the distribution of stars within the cluster is visible.

However, observation the sky using a standard home telescope (80mm), it becomes possible to discern some detail, while a 150 mm aperture instrument will easily resolve individual stars in the outer regions of the cluster at high magnifications. Viewing M22 with a larger, 300 mm aperture instrument, an observer sees hundreds of stars spread out over the entire 32 arc-minute span of the cluster.

M22 contains an estimated 80 000 stars that seem to be evenly spread out over a distance of about 86 light years, which seen from our distance, covers an area that is bigger than the full Moon.  Although M22 is taken to be about 12 billion years old, it contains only one known planetary nebula, which makes it one of only four globular clusters known to contain planetary nebulae, the other three being M15, NGC 6441, and Palomar 6.

22 October 2016; Orionid meteor shower

So called because the shower appears to emanate from the constellation Orion, the shower will be best visible on the night of 19/20 October this year. The maximum hourly rate is expected to be about 20 or so. This year, a first quarter Moon means that the Orionids can be observed equally well from both the Southern and Northern hemispheres. Below is a table with details for the Orionid shower as seen from Sydney. Note that while the peak is expected on the night of 19/20 October, the Orionids is active from October 2nd to November 7th.

Orionid meteor shower for Sydney (Night of 19 Oct / 20 Oct)
Time Azimuth/Direction         Altitude
Thu 01:00   64°     10.3°
Thu 02:00   54°     21.0°
Thu 03:00   41°     30.2°
Thu 04:00   26°     37.1°
Thu 05:00   8°       40.8°
Along with the Eta Aquarids, the Orionids is associated with the Comet Halley, which will be visible again in 2061.

28 October 2016; Venus, Antares, and Saturn form a line 

The image aboveshows the relative positions of Venus, the star Antares, and Saturn as seen from Canberra at about 8:00 Local Time.

Saturn’s ring system is particularly well positioned at this time, being inclined to our line of sight by about 26.5 degrees. At this time, we are observing the “upper” or northern face of the ring system that will continue to tip towards our line of sight until October 2017, to reach an inclination of 27 degrees.

After this date, the ring system’s inclination will reduce as the planet tips on its axis, and by May of 2023, Saturn will have fully tipped the opposite way, to expose the southern face of its ring system that will be inclined towards our line of sight by 27 degrees.

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