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Compiled by Wayne Roberts th Thurs 5 New Moon. th Sat 7 Dark Sky Viewing Night, Benalla Sports and Equestrian Centre (adjacent to racecourse). Fri 13th First quarter Moon. th Mon 16 Moon at perigee (closest to Earth, 367,391 km). th Wed 18 Monthly meeting, Hockey clubrooms, Churchill Park, Waller St., 7:30 pm. th Thur 19 Full Moon. th Fri 20 Pluto stationary. rd Mon 23 September equinox. th Wed 25 Mercury at aphelion (furthest from Sun, 69.8 million km) th Fri 27 Last quarter Moon. th Sat 28 Moon at apogee (furthest from Earth, 404,308 km). Astronomy Benalla’s experience with the weather as of late has been reminiscent of our horror run last year; we have now been clouded out on each of our last two monthly viewing nights. The silver lining on, literally, the cloud was the success of two outreach ventures during the month – a solar viewing at a Shepparton primary school and an abbreviated night viewing of the Moon, Saturn, Venus and Omega Centauri at which we played host to a group of visiting Japanese students. Both events were well received, with the youngsters in Shepparton eager to examine the telescopes and view the Sun, and the Japanese students bowled over by views of, in particular, the Moon and Saturn. The 23rd of this month marks the September equinox, when the sun rises due east and sets due west and days & nights are of equal length. The transition from winter to summer is a double edged sword from an astronomical observer’s viewpoint – the nights are becoming warmer and more hospitable while at the same time starting later and finishing earlier. Slides and roundabouts. Our monthly viewing nights are held on the Saturday closest to New Moon unless it falls on a Wednesday; on these occasions we view on the preceding Saturday to avoid a Moon setting late in the evening. This month, with New Moon falling on a Thursday, it sets almost two hours after the Sun, giving us a relatively rare opportunity (averaging two months in seven) to observe the lunar surface. The extremely thin 3% waxing crescent will make an interesting target early in the evening. Set up 6:00 pm. Sunset 6:01 pm. (Twilight ends 7:24 pm). Moon sets 7:51 pm. Twilight begins 5:04 am. Sunrise 6:27 am. Moon rises 7:35 am. As September begins, Mercury is in the very early stages of its best evening apparition of the year. On our viewing night it is 10° above the sunset horizon and sets just under an hour later at 6:56 pm, its 94% illuminated disk spanning 5" [" denotes arc-second = 1/60th of an arc-minute (symbol ') or 1/3600th of a degree (symbol °)] and piercing the twilight at magnitude -0.7. Watch the inner planet as it climbs ever higher with each passing day throughout September and into next month before diving back toward the western horizon in late October. At the end of September, as Mercury’s inner orbit causes it to begin catching up to Earth, its apparent size has increased to 5.9", phase and magnitude have decreased to 74% and -.05 respectively (remember from last month that Mercury is the only planet which shines brighter when on the far side of the Sun than when on the same side as Earth) and elevation at sunset has increased to 23°. It reaches greatest eastern elongation (24°) from the Sun on October 9th, a couple of days after rising up past Saturn which is sinking slowly toward the western horizon. This month and next represent your best opportunity this year to follow the speedy ‘Messenger of the Gods’ as its size, phase, magnitude and altitude change at a rate far faster than any other planet. Brilliant Venus continues to dominate the western sky, climbing higher and shining a little brighter on each successive September night. As the month begins it stands 37° above the sunset horizon, its 15" disk 74% illuminated and shining at magnitude -4.02. On our viewing night, these figures read 38°, 15", 72% and -4.05 respectively; look for Spica (Alpha [α] Virginis, mag 1.0) 2° SW (lower left) of Venus, and Saturn 12½° east (upper right). By month’s end the respective parameters are 42°, 18", 63% and -4.17. On the morning of the 9th, the 12% lit waxing crescent Moon’s northern limb passes just 6½' – less than a quarter the size of the lunar disk – from Venus while still beneath the eastern horizon; use the Moon and Venus as mutual tools to locate each other in broad daylight – the planet runs ahead of the Moon’s illuminated NW limb by 1½° (three lunar disks) at 9 am and 2° at 10 am (one finger at arm’s length is approx. 1°) Mars has just cleared morning twilight and continues to pull painfully slowly away from the eastern horizon throughout September, with the pace picking up slightly as the month progresses. On the morning of the 8th (following our viewing night) it rises at 4:44 am, just under 1¾ hours before the Sun and stands 17° above the sunrise horizon, its 4.1" disk 96% lit and shining at magnitude 1.64. Look for it 15° SE of Pollux (Beta [β] Geminorum, mag 1.15) and 22° east of brilliant Jupiter (thumb to little finger of an open hand at arm’s length is approx. 20°). The Red Planet’s ruddy hue and the fact that it shines far more vigorously than any star in its vicinity should make it fairly easy to locate. If you turn a telescope or binoculars on Mars at this time you will see that it stands only ½° west (upper left) of M44, the Beehive Cluster; on the following morning it is even closer, skimming the SW (upper) edge of the cluster. Under a dark sky, M44 is quite easy to see with the naked eye; can you still see it close to the horizon and with Mars shining nearby? By month’s end it rises at 4:00 am and is 19° above the horizon at sunrise (5:54 am), its size, phase and magnitude are 4.4", 95% and 1.61 respectively. Our neighbour’s leisurely climb above the eastern horizon continues to accelerate at a very modest rate throughout the year; by years end it rises about ¼ hour after midnight. Mighty Jupiter is king of the morning sky. On the 8th it rises at 3:22 am, more than three hours before sunrise, at which time it is 26° above the horizon. Its 35" disk is 99% illuminated and blazes fiercely at magnitude -2.1. Scan Jupiter’s trailing edge with a telescope to catch its inner Galilean moon, Io, emerging from an occultation between 5:36:46 am and 5:40:22 am, having passed behind its parent body just before it cleared the eastern horizon; note that this event occurs a little over ½ hour after twilight commences (but still more than ¾ hour before sunrise). Jupiter, which shares the morning sky with Mars, is pulling away from the eastern horizon at a considerably faster rate (due to Mars’ smaller orbit carrying it eastward against the starry backdrop of our sky at a greater rate than Jupiter) than its little brother. By month’s end it is rising at 2:07 am and is over 29° clear of the horizon at sunrise; it is a little bigger at 37" and brighter at -2.2. Saturn and its wondrous ring system are now well advanced in this apparition but still a captivating sight in the early evening sky. This beauty sets on our viewing night at just 10:13 pm, so target it as soon as the sky fully darkens (evening twilight nominally ends at 7:24 pm, but the slim crescent Moon will brighten the sky slightly until it sets just under ½ hour later) in order to minimise the blurring effects of Earth’s atmosphere. Saturn shines at magnitude 0.7, its disk spans 16" and it stands 49° clear of the horizon when the Sun goes down. The magnificent ring system, spanning more than twice the diameter of the planet’s disk, is now inclined at almost 18½°. To locate 2 Saturn with the naked eye early in the evening, note that it is about /3 as far above Venus as the latter is above the Moon. As Venus continues to pull away from the western horizon daily, it closes the gap with Saturn; on the 18th the pair stand side by side with Venus 3½° to Saturn’s south (left). How many of Saturn’s brightest moons can you see? Here are the circumstances at 8 pm on our viewing night (they won’t change appreciably before Saturn sets): Titan, the largest and brightest at magnitude 8.8, lies 2½' to Saturn’s east (upper right); Rhea (mag 10.2) is on the same side a little under half as far 2 from the planet and Dione (mag 10.9) is closer in again, slightly left of, and /3 of the way along, a line from Saturn to Rhea. On the opposite side of the planet to this trio, and about as far out as Dione, lies Tethys (mag 10.7); depending on your optics and seeing conditions, you may see Enceladus (mag 12.2) just 8" closer in than Tethys. Finally, look for Iapetus (mag 11.6) which lies 2' (80% as far out as Titan) NNW (lower right) of Saturn.

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