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SKY DIARY Last quarter 23 Sep, 10:56 22 Oct, 20:14 Moon phases Apsides Date Apsis 06 Sep, 20h Apogee 18 Sep, 18h Perigee Occultations Date 18-Sep 20-Sep 21-Sep 21-Sep 21-Sep 23-Sep 24-Sep 17-Oct 19-Oct 19-Oct 19-Oct 19-Oct 20-Oct 25-Oct 26-Oct Object nu Piscium mu Ceti 89 Tauri, NSV 16124 sigma 1 Tauri sigma 2 Tauri 130 Tauri 26 Geminorum Hyadum I, gamma Tauri, NSV 01553 71 Tauri, V777 Tauri theta 2 Tauri theta 1 Tauri, NSV 16016 111 Tauri 31 Leonis 56 Leonis, VY Leonis A summary of the main sky events, September to October 2016 (UT times) New 01 Sep, 10:03 01 Oct, 01:11 Dist (km) Size 405,055 km 29’ 31” 361,896 km 33’ 00” Date 04 Oct, 12h 17 Oct, 01h Bright limb Disappearance Reappearance Dark limb First quarter Ma 09 Sep, 12:49 09 Oct, 05:33 Apsis Apogee Perigee Full 16 Sep, 20:05 16 Oct, 05:23 Dist (km) 406,096 357,861 Size 29’ 26” 33’ 23” The position angle (PA) of the occultations given below is measured anticlockwise from the northpoint of the Moon’s disc (use the Moon’s north pole as a guide). 0° 270° 90° 180° ZC 249 405 699 Mag 4.4 4.3 5.8 Phase RD RD RD Data for Greenwich Time PA⁰ Alt⁰ 22:01 201 24 00:29 165 40 22:55 273 16 Az⁰ 114 133 84 Data for Edinburgh Time PA⁰ Alt⁰ 22:10 211 22 00:49 196 38 23:01 282 15 Az⁰ 115 137 84 702 704 878 1029 5.1 4.7 5.5 5.2 RD RD RD RD 23:05 23:19 03:44 01:59 208 237 267 243 17 19 49 28 86 88 136 96 23:16 23:27 03:44 02:06 220 246 280 256 17 19 45 26 87 89 135 97 462 635 6 3.7 RD RD 20:27 00:12 240 272 19 45 95 130 20:34 00:12 248 286 18 41 95 130 661 4.5 RD 03:11 203 49 189 671 669 3.4 3.8 RD RD 04:41 04:45 229 250 47 46 226 228 04:39 04:39 244 263 45 45 218 219 806 1486 1589 5 4.4 5.9 RD RD RD 01:39 03:35 03:18 238 302 233 50 24 11 137 104 94 01:42 03:34 03:30 252 317 252 45 21 11 137 103 95 These are the only occultation for this period, based on the following criteria: Mag: Visual magnitude. Phase: (R)eappearance, (D)isappearance or (G)raze at (D)ark or (B)right lunar limb. Alt: Altitude. The Moon’s height. Az: The angular position along the horizon measured clockwise from true north (through E, S, W back to N). PA: Position Angle, measured anticlockwise from the direction of the celestial North Pole. This listing shows lunar occultations of stars brighter than mag +6, observable with small telescopes in a sky dark enough to be seen without difficulty. For data specific to your own locality or details of fainter occultations, contact Occultation Section Director Mell Jeffery (address on p46). A s mentioned in previous editions of Popular Astronomy, during this two month period 16 occultations can be observed, in fact if you are in the far south west of England (Devon/Dorset) you can add an extra one to the list! On 20 September mu Ceti is occulted. For much of the country the reappearance takes place at the dark limb of the 85% illuminated waning gibbous Moon. However, further south, e.g. Greenwich, you are more likely to see the event take place at the lit portion of the Moons southern cusp. The Moon moves by the asterism of the Hyades during 21 September. The +5.1 and +4.7 mag. stars sigma 1 and sigma 2, are occulted with a 10 to 14 minute gap between the events, late in the night, with the waning gibbous Moon still rising in the east. During the morning of 19 October, the Moon passes through the Hyades, occulting the stars theta 1 and 2 Tauri. 44 Popular Astronomy For observers in the south of the country there is a four minute interval between the two occultations. For those further north, e.g. in Edinburgh, the events take place within 50 seconds of each other. A little over an hour prior to the theta 1 and 2 Tauri event, there is a graze of the +4.5 mag. star 71 Tauri. The graze path for this event runs from the Welsh coastline between Llangrannog and New Quay, passes across country between Walsall and West Bromwich, to the north of Leicester, cuts across the Wash and out to sea on the Anglian coast just north of Cromer. North of this graze line an occultation is visible. Later that morning, approximately 07:41 UT, the Moon occults the +1.0 mag. star alpha Tauri, Aldebaran. However this event is only visible from the far south western area of England. The 86% illuminated waning gibbous Moon is at a reasonable altitude but the Sun is just rising in the east, so this is a www.popastro.com daylight event. The graze line for the event runs from the north Devon coast, just south of Croyde, clips the very north of Barnstaple and cuts across the country to the southern coastline, between the entrance to Poole Harbour and Swanage, in Dorset. South of this graze line an occultation is visible, north, a conjunction (07:42 UT for Greenwich). The next event involving Aldebaran takes place in December and is a country-wide event. Please see page 43 for maps showing the graze path for the occultations 71 Tauri and Aldebaran. For further information regarding any of the events mentioned, or others listed in the table, please contact me. Observations of events, listed or otherwise, are more than welcome. Mell Jeffery September - October 2016 SKY DIARY Planets T his period offers an excellent opportunity to observe the outer “ice giants”, which are very well placed and Mercury gives its best morning show of the year for UK latitudes. Mercury starts the period in inferior conjunction, between the Earth and the Sun, on 13 September, but rapidly moves into the morning sky becoming noticeable as a bright spark above the eastern horizon. Climbing higher each morning, it reaches its greatest elongation to the west of the Sun on 28 September, when it will lead the Sun by 18 degrees. On that date Mercury will be obvious, due east, around 10 degrees above the horizon at 05:25 UT, some 35 minutes before sunrise and shining at a magnitude of -0.5. Mercury can be followed each morning into the second week of October, its altitude steadily reducing. Its brightness changes noticeably through this period: being +1.1 on 22 September, reaching -0.6 by month’s end, and -1.1 by 14 October. This is due to the steadily increasing visible phase being just 28% illuminated four days before greatest elongation, 50% on the day, and 94% illuminated by mid-October. Venus will be hard to see from UK latitudes during September and October as it first appears close to the setting Sun in the western evening sky. As the period progresses Venus increases its separation to the east of the Sun but the reducing angle of the ecliptic at this time of year places Venus lower in the sky. From the UK the best time to glimpse Venus is towards the end of October shortly before sunset, when it will appear as a bright magnitude -4.0 spark around southwest, just above the horizon and slightly below much dimmer Saturn (mag +0.5). Mars keeps company with Saturn, at least from the start of September, the pair being briefly visible as darkness falls, low in the SSW. Mars has a prograde (eastern) motion against the background stars in this period and will rapidly separate from Saturn, appearing very slightly further south each night as darkness falls. Sadly Mars also suffers from the declining position of the ecliptic, being around 10 degrees up as darkness falls throughout the period. Just like Venus and Saturn, Mars improves in visibility the further south your location is. Its apparent size falls below 10 seconds of arc in early September, so really detailed observation will be very difficult by the end of October. The apparent proximity of both Saturn and Jupiter to the Sun means that they too are lost to detailed night time observation but, Saturn in particular, may be found and observed in daylight as long as sensible precautions are taken to ensure the Sun can never enter the field of view of either the telescope or the finder-scope. Jupiter is just too close to the Sun for this to be safely attempted. Which brings us to the outer ice giant planets of Uranus and Neptune: Neptune reaches opposition, due south at midnight UT, on 2 September and Uranus reaches opposition on 15 October. This means that both planets are visible during nearly all of the available darkness on any night in the period, with Neptune up first and Uranus following on. Neptune will be a telescopic object, little more than 2 seconds of arc in apparent size, shining at a faint +7.8 magnitude against the background stars of Aquarius. In small telescopes it will appear as a defocused pale-blue or blue-green “star” but larger instruments and high magnification will start to show a visible disc. From mid-UK latitudes Neptune will be around 28 degrees above the southern horizon as it transits due-south and will be worth seeking out if the seeing is steady. On the evening of 15 September, the Moon and Neptune are in a very close conjunction and from mid UK latitudes Neptune will be hidden behind the nearly full Moon until around 19:54 UT, when it will appear from behind the mountains on the southeastern limb – an interesting observational challenge. Uranus will be even better placed than Neptune, transiting some 2 hours and 40 minutes later and noticeably higher, around 46 degrees up throughout the period. Uranus will also appear both slightly larger and considerably brighter, on the edge of naked eye-visibility at magnitude +5.7, against the background stars of Pisces, the planet should appear as a bluegrey disc in visible light under steady seeing conditions. Alan Clitherow Meteor notes September: Although background sporadic and minor shower rates are quite good during September, there are no major meteor showers active. October: The highlight of October is the broad peak of the Orionid meteor shower during 20-24 Ocober. A good number of Orionids are bright and leave persistent trains. Be aware that the Orionid radiant actually lies midway between the main patterns of Orion and Gemini, rather than within the main stars of Orion itself, and doesn’t rise above the horizon until around 21:00 UT (22:00 BST). The disappointing news for 2016 is that a waning gibbous moon will be rising soon after this. Activity from the Taurid meteor shower can also be seen throughout October, typically producing a few meteors per hour, rising as the month progresses. For additional information, see www.popastro.com/meteor/reference/meteorshowers/index.php Tracie Heywood Variable Star notes Eclipsing Variables: RZ Cassiopeiae can be seen in eclipse during the evenings of 3, 9 and 15 September, with the first eclipse being centred near 22:00 BST (21:00 UT) and each successive eclipse in the sequence occurring approx. 35 minutes earlier. Another series of evening eclipses occurs on 4, 10, 16, 22 and 28 October, with the 4 October eclipse being centred just before midnight BST (23:00 UT). Eclipses last for just under five hours. The most favourable eclipses of Algol (Beta Persei) will be centred at the following times (UT): 6 September 22:42, 9 September 19:54, 29 September 21:12, 19 October 23:00, 22 October 19:48. Eclipses last for approximately. ten hours. Mira type variables: Best placed for observation is Chi Cygni, which is due at maximum in mid-September and should be readily visible in binoculars during September and October. It may also be visible with the naked eye for a while from good observing sites. R Ursae Majoris is due at maximum in early September and is usually just below magnitude +7.0 at maximum. T Ursae Majoris should reach maximum in early October, with its average peak brightness being around magnitude +7.7. Mira (Omicron Ceti) will be closing in on its 9th magnitude minimum, but should be visible in larger binoculars. Finder charts for these and other variable stars on the SPA VSS programme can be found by clicking on the name of the star in the section’s programme listing: www.popastro.com/variablestar/observingprogramme/index.php Tracie Heywood September - October 2016 www.popastro.com Popular Astronomy 45