In the final month of winter, defy the chill and go exploring with the aid of:

Transcription

1 In the final month of winter, defy the chill and go exploring with the aid of: The times, circumstances and star charts to follow are configured for the Melbourne Observatory in line with other publications of the Astronomical Society of Victoria (ASV), for which these viewing notes are principally compiled: Longitude ' 23.8" E, Latitude 37 49' 54.1" S [" denotes arc second = 1/60 th of an arc minute (symbol ') or 1/3600 th of a degree (symbol )]. The notes contain many references to rise and set times, all configured for the co-ordinates given above; the following procedure will facilitate determining the correct times for other locations. The adjustment required for longitude is straight forward for each degree east (of Melbourne Observatory) subtract four minutes; conversely, add four minutes for each degree west. Adjustment for a difference in latitude is dependent on the declination of the object concerned how far north or south of the celestial equator it lies. The table below, from the yearbook of the ASV, gives the required adjustment (in minutes) for any object at a declination of between +30 and -30 (by convention, north is positive and south negative) when viewing from any location between latitudes -28 and -44 ; interpolate for intermediate latitudes/declinations. Note: add these values to times of rising and subtract from setting times. Whereas the declinations of stars and other deep sky objects are (very nearly) constant, those of the Sun, Moon and planets change considerably over time; a suitable resource for determining declinations is therefore required to obtain the adjustment for difference in latitude as described above.

2 While the reader may have ready access to such resources, I offer the following suggestions for those who do not: the ASV yearbook, free to members and available at reasonable cost to others (Sun and planets only); the yearly publication Astronomy Australia 2016 (Sun, planets and Moon); and various astronomical software packages (typically catering for all celestial objects). Other sources may be available on-line. Note that some resources give co-ordinates for epoch denoted as J 2000 whereas others may quote real time figures, denoted J Now. The discrepancy between the two systems will not be significant for the purpose at hand. Now a few notes defining terms which may be encountered in the text to follow: For those not familiar with the terminology used to describe phases of the Moon, note that it is referred to as waning (hard a ) when the phase is decreasing daily and waxing (soft a ) when increasing, and as a crescent when less than half lit and gibbous when more than half. Thus you may find it referred to in the text as, for example, a waxing crescent Moon. Appearances of the abbreviation au in the text denote astronomical unit, the average Earth-Sun distance, currently defined as 149,597,870.7 km. The abbreviation ZHR, where it appears in relation to meteor showers, refers to the zenith hourly rate, the number of meteors per hour which can be expected to be seen under ideal conditions, with the radiant (the point from which the meteors appear to emanate) at the zenith and a clear dark sky. The ecliptic, shown as a green line on many of the star charts to follow, is the path followed by the Sun and (very nearly) the planets as they arc across our sky daily. As the outer planets, those that orbit farther from the Sun than does Earth, move along their orbital paths, they move from west to east in our sky relative to the stars; this is referred to as direct or prograde motion. Around the time of opposition however, when we overtake them on our inner, faster orbital path, they change direction, moving east to west relative to the stars. Referred to as retrograde motion, this phenomenon is caused by the same effect as that seen when a car which is overtaken seems momentarily to move backwards in relation to a line of trees in the background. On any given night, a planet is said to be transiting (or culminating, there is a subtle difference between the two) when it reaches its highest point above the horizon in its passage across our sky that evening do not confuse this use of the term transit with the same word often used in these viewing notes to describe the passage of the moons of Jupiter across the face of their parent. Regarding the inner planets, Mercury and Venus, which never stray very far from the Sun in our sky, greatest eastern elongation refers to their maximum angular distance east of the Sun when they are visible in our evening skies; similarly, greatest western elongation refers to their maximum angular separation west of the Sun when visible in our morning skies. They are said to be in inferior conjunction when passing between Earth and the Sun on their inner orbital tracks, and in superior conjunction when rounding the far side of the Sun from our perspective. As a handy (excuse the pun) guide to estimating the angular separation of two objects, one finger held at arm s length typically spans a little over 1, a closed fist 10 and an open hand, thumb tip to tip of little finger, 20. Note finally that perihelion or aphelion of Mercury, Venus and other planets refer to the physical separation in space of the planet in question and the Sun, and are unrelated to their angular separation in our sky.

3 What s in the sky this month; August 2017: 2 nd Mercury at aphelion (farthest from Sun, million km / au). 3 rd Moon at apogee (farthest from Earth, 405,025 km); Uranus stationary (begins retrograde motion). 8 th Full Moon; Partial lunar eclipse (visible from Australia and elsewhere). 10 th Neptune occulted by Moon (visible from WA, but not elsewhere in Australia,). 12 th Mercury stationary (ceases eastward movement relative to the stars). 13 th Perseids meteor shower peaks. 15 th Last quarter Moon. 16 th Aldebaran occulted by Moon (not from Australia). 18 th Kappa [κ] Cygnids meteor shower peaks; Moon at perigee (closest to Australia, 366,121 km). 22 nd New Moon; Total solar eclipse (not from Australia). 26 th Saturn stationary (ends retrograde motion). 27 th Mercury in inferior conjunction (swings in between Earth and Sun). 29 th First quarter Moon. 30 th Moon at apogee (farthest from Earth, 404,308 km). N.B.: When reading the following, refer back to the explanatory notes at the beginning of this article for information on terminology, angular separation approximations and adjustment of latitude & longitude. A lunar eclipse occurs when the Moon passes into the Earth s shadow. If the Moon is fully immersed in the umbral shadow (any point in space or on the Moon is within the umbral shadow if the Sun s entire disk is covered by the Earth from that point), the eclipse is total, if only part of the Moon is within the umbra and the remainder in the penumbral shadow (part of the Sun s disk is not covered by the Earth), the eclipse is partial, and if no portion of the Moon enters the umbra but part or all passes through the penumbra, the eclipse is penumbral. A partial lunar eclipse occurs in the predawn hours of the 8 th. Lunar eclipses theoretically can be witnessed from any vantage point on Earth the word theoretically is used here because the eclipse obviously can t be seen if the Moon is below the observer s horizon when entering Earth s shadow. From Melbourne, for which these viewing notes are configured, the Moon first touches the penumbra at 1:50 am, and the umbra at 3:23 am; maximum eclipse, with just under 25% of the Moon within the umbra, is at 4:20 am, and our satellite exits the umbra and penumbra at 5:18 am and 6:51 am respectively. During the penumbral phases (1:50 am - 3:23 am & 5:18 am - 6:51 am) only a very barely noticeable dimming of the Moon s surface will be visible, and because only 25% of the surface passes within the umbra at maximum eclipse on this occasion, the change in hue of the Moon s surface will be limited. The chart on the following page depicts the view at maximum, 4:20 am, showing the extent of the umbral (inner circle) and penumbral shadows, with the Moon at an altitude of 33 in the WNW. As a matter of interest, stars brighter than mag 5.5 are plotted (there are only two in the area covered by the chart); the brightest, mag 4.06 Theta [θ] Capricorni is labelled, but will not be visible to the naked eye in such close proximity to the Full Moon, albeit partially eclipsed. The eclipse will also be visible from New Zealand, the East Indies and part of Asia and Africa.

4 Those lucky, or determined, enough to be in North America on the 21 st, will be treated to arguably nature s grandest spectacle, a total solar eclipse. While lunar eclipses, as stated above, occur when Earth s shadow falls on the Moon, solar eclipses are the result of the Moon s shadow falling on Earth. Because the Moon is considerably smaller than the Earth, solar eclipses are of much shorter duration, and only part of the Earth s surface experiences even a partial eclipse, with totality limited to a narrow strip racing across the globe.

5 As a matter of interest, astronomers differentiate between greatest eclipse and greatest duration, although the two typically differ by only about ⅒ th second google it if you wish. The longest duration of totality will be a mere two minutes and forty seconds, in parts of Missouri, Illinois, Kentucky and Tennessee, but that 2½ minutes plus will leave an indelible impression on all who experience it. The above map shows the path of totality and its duration at points across the continent; as the crescent symbols north and south of totality show, a partial eclipse will be visible throughout the USA, through the whole of North and Central America and beyond in fact. The greatest duration of the eclipse will be 2 min 40.2 sec, at latitude 37 35'N, longitude 89 7'W, in Kentucky. This occurs at 4:21:49 am on the 22 nd, our time; the limb of the Moon is never closer than ½ from the Sun s limb from our perspective, with the pair below our horizon. Back home, Neptune is occulted by the Moon on the 10 th. While the Moon passes in front of the planet from all parts of Australia south of, roughly, a line from Cairns in Queensland to Derby in Western Australia (as well as most of Antarctica), it will happen after the pair have set for all Aussies except those in WA (the far east of WA misses out also). Even there, re-emergence will happen below the horizon, and just to totally rain on the parade, it all happens in daylight. From our location, the event happens below the WSW horizon, between 9:31 am and 10:19 am, with the planet at altitudes of -12 and -20 respectively. The occultation of Aldebaran (Alpha [α] Tauri, magnitude 0.8) on the 16 th is even further removed from our potential viewing experience the planet is never closer than just over ½ from the Moon s limb, and that occurs 58 below the NW horizon, at 5:32 pm. Viewers in W. Asia, the Middle East, Europe and the Caribbean are favoured. Two meteor showers peak this month, the Perseids on the 13 th and the Kappa Cygnids on the 18 th. While the Perseids constitute a major shower, with ZHR s of as much as 150, it s predominantly a northern spectacle. The radiant s declination is 58, and almost 6 below our horizon at best, severely curtailing meteor counts; prospects are further degraded by the 76% illuminated waning gibbous Moon rising at 10:15 pm. The following chart shows the scene at 2:30 am on the morning of the 13 th, with the then 75% lit Moon flooding the sky with light from its altitude of 41 in the NNE directly above the radiant, which sits 15 below the horizon. While the afore-mentioned circumstances are not conducive to activity from our perspective, the shower s inherent strength is bound to throw a few specimens up over the NE to NW horizon, so if meteor showers are your thing, it s worth a look. The Kappa Cygnids are an extremely marginal shower from our perspective, even further north than the Perseids and having a ZHR of only 3. The Moon is a little more accommodative on the date of maximum, the 18 th, rising as a 20% waning crescent at 3:42 am; the radiant will, on that date, be 2 lower than the -22 depicted here. Uranus and Neptune are also plotted on the chart for later reference.

6 Mercury As August begins, Mercury is fully immersed in its best evening apparition of the year, having been at its greatest angular separation from the Sun on the 30 th of last month it is actually at its greatest sunset altitude on the 2 nd of this month, the lag being due to the angle of the ecliptic (the path across the sky followed daily by the Sun and, very nearly, the planets) gradually steepening in the evening as the days pass at this time of the year. It sets, on the 1 st, at 7:48 pm, having been at an altitude of 24 in the NW when the Sun set at 5:33 pm and 8 at cessation of evening twilight, 7:03 pm. Mercury s disk spans 8" [" denotes arc second = 1/60 th of an arc minute (symbol ') or 1/3600 th of a degree (symbol )], is 43% illuminated and shines at magnitude 0.5. The planet s easterly movement relative to the background stars continues to slow, and it is stationary in this respect on the 12 th ; its descent back towards the sunset horizon continues to accelerate and it re-enters evening twilight on the 17 th. With New Moon falling on the 22 nd this month (generating nature s grandest spectacle, in the form of a total solar eclipse, over a track across North America), we ll nominate the preceding Saturday 19 th as our viewing night. By the 19 th, Mercury has become a difficult naked eye capture, set against a brightening sky and shining far less brightly at magnitude 2.6. It sits 13 clear of the WNW horizon at sunset, 5:48 pm, subsequently setting itself at 6:59 pm. The span of Mercury s disk has increased to 11" at a reduced phase of 9% as it moves towards inferior conjunction on the 27 th, swinging in between the Sun and Earth on its inner, faster orbit. As the above figures show, Mercury counter-intuitively becomes dimmer as it approaches Earth, this being caused by the waning (thinning) phase decreasing the reflected sunlight incident upon Earth more than the increase due to the lessening distance from us. The following chart shows where Mercury sits at 6:18 pm, ½ hour after sunset (on the 19 th ); Jupiter is shown for reference, as is the bright star Arcturus (Alpha Bootis, mag -0.1).

7 Reappearing in the morning sky after inferior conjunction, Mercury is rising at 6:12 am at the end of the month, just over ½ hour before sunrise (6:44 am), when it sits 6 high in the ENE; its disk is 4% illuminated, spans 10", and shines unseen so close to the Sun at magnitude 3.6. The Messenger of the Gods (so named in earlier times due to its rapid movement across the sky) transitions from Leo into Sextans on the 4 th and then backtracks into Leo again on the 27 th. Venus August is the last month Venus can be seen clear of morning twilight, rising after the Sun s rays begin to brighten the eastern sky from Sept 2 nd ; it will, nevertheless, continue to be visible to the naked eye into December due to its brilliance. On August 1 st it rises at 4:52 am, and is 22 clear of the NE horizon when the Sun rises just under 2½ hours later, at 7:21 am; blazing at magnitude it dominates the pre-dawn sky, and a telescope reveals a 14.5" disk, 74% illuminated. Come our viewing night of the 19 th, it breaches the horizon at 5:09 am, and has attained an altitude of 17 by sunrise, 7:00 am; visual magnitude has declined only marginally, to mag -3.97, and the phase of the 13.0" disk has fattened a little, to 80%. Venus has two companions in the morning sky (on the 19 th ) the 11% waning crescent Moon 4 to its upper left, and, closer in, planetary nebula NGC 2392, aka the Eskimo Nebula, less than ½ above the planet. The thin crescent of the Moon should be easy enough to see without optical assistance; the nebula, very low in the pretwilight sky, will yield to a scope, but not be a compelling sight. Here s the scene as twilight begins at 5:32 am; Venus is at an altitude of just over 3½, the nebula 4 and the Moon 7½ (as a rough guide, one finger held at arm s length spans a little over 1, a closed fist 10, an open hand, tip of little finger to thumb tip, 20 ). The brightest stars in the area covered by the chart are also labelled with their magnitude ratings Wasat (Delta [δ] Geminorum), mag 3.50, and 56 Gem, mag At month s end, Venus is flirting with the twilight zone, rising 90 minutes before the Sun, 5:14 am vs 6:44 am, and being 15 high at sunrise; the planet s brilliant glare is further marginally eroded, down to magnitude -3.95, and its 12.5" disk is 83% lit.

8 Venus crosses the border from Orion to Gemini on the 1 st, then on into Cancer on the 25 th, finishing the month only ½ from the outskirts of that constellation s well known open cluster M44, The Beehive Cluster. Mars Having been in conjunction with the Sun late last month, Mars is not a viable target in August, or even for another couple of months for that matter. For the record, here are its rise and set times for the 1 st, 19 th and 31 st respectively: 7:22 am & 5:21 pm; 6:46 am & 5:07 pm; 6:21 am & 4:58 pm. The Red Planet moves from Cancer into Leo on the 17 th. Jupiter This evening apparition of Jupiter is now well advanced, setting in twilight very early in October and being in conjunction with the Sun (on the far side of the Sun from our perspective, the two rising and setting together in our sky) towards the end of that month, so views begin to deteriorate a little after August. On the 1 st, The King of the Planets transits (reaches its greatest altitude) in daylight at 4:45 pm, but remains well up in the sky, 45 clear of the horizon, when twilight fades at 7:03 pm; it dominates the night sky at magnitude -1.9 before setting at 11:04 pm, and is nominally out of round at an undetectable phase of 99%. As a matter of interest, Jupiter is superimposed on the spiral galaxy NGC 4941 the following afternoon, and in very close proximity that evening, but at magnitude 12.0, the galaxy will be swamped by the glare of the planet. On the 19 th, our designated viewing night, the King s altitude at the cessation of evening twilight, 7:16 pm, is down to 33, still in excess of the minimum 30 recommended by this column to comfortably avoid the murky views to be found near the horizon. The phase remains at 99%, visual magnitude is down a little, to -1.8, and setting time is 10:07 pm. No chart is needed to locate Jupiter in the early-mid evening, just look for the brightest star in the sky (the chart in the notes on Mercury shows where it sits ½ hour after sunset); here s a magnified view of the planet and its four Galilean moons at 7:16 pm, as the sky fully darkens.

9 To the west (lower left on the chart) of Jupiter, Io and Callisto are both receding from their parent, while in the east, Europa is closing and Ganymede is moving away. The moons shine at magnitude 5.9, 6.5, 6.2 and 5.5 respectively; the brightest of the stars in the field of view are 13 th magnitude and so are not plotted. Europa will begin to transit across the face of Jupiter at 8:14 pm and will still be silhouetted against the Jovian cloud tops when the planet sets. Come month s end, Jupiter s altitude as twilight fades at 7:25 pm is down to 24, and its disk, now 100% illuminated, shines at magnitude -1.7; the planet sets at 9:30 pm. Jupiter will remain within the constellation of Virgo until mid-november, when it crosses into Libra in the company of Venus. Saturn The marvellous ringed wonder, odds on to win a popularity contest amongst those who have viewed the planets, is beautifully positioned for viewing these August evenings; with its fascinating ring system only a couple of months away from being as close to face on as they ve been in almost 15 years, it s a must at the eyepiece. At the start of the month, Saturn rises early afternoon and is at an altitude of 60 in the NE as twilight ends at 7:03 pm; it transits two hours later, 9:03 pm, before setting at 4:18 am. The planet s disk spans 17.8", the rings 40.4" at an inclination of ; together they shine at magnitude On our viewing night of the 19 th, the sky fully darkens at 7:16 pm, with Saturn 72 high NNE; it transits just a little over ½ hour later, at 7:50 pm, 74 clear of the horizon, then sets at 3:05 am. As the distance between Earth and Saturn is now increasing, its brightness is curbed slightly, to magnitude 0.35, as is the span of its disk, 17.3"; the eye-catching ring system spans 39.3", inclined at The chart below is configured for time of transit, 7:50 pm. It shows stars down to magnitude 5.5, and should allow naked eye identification of Saturn as the brightest star near the zenith (at this time) and the constellation figure of Scorpius, arguably the most recognisable star pattern of all. Saturn and Antares (Alpha Scorpii) are not unalike in appearance and are separated by 13 (remember a fist at arm s length spans around 10 ). While the nearby Teapot of Sagittarius is not as readily identifiable as the star pattern of Scorpius, its stars are brighter than others in the vicinity and you may find it useful to imagine the Teapot disgorging its contents into the catchment represented by Wei (Epsilon [ε] Sco, mag 2.3) through Shaula (Lambda [λ] Sco, mag 1.6). Pluto is also plotted for later reference.

10 Having identified the planet, examine it through the highest practical magnification to absorb the splendid sight of the ring system. The Cassini division should be visible as a black line a little over half way out from the centre of the ring plane; a good sized scope, high magnification, quality optics and clear, steady seeing may even pull in the Encke division out near the edge of the rings. When you ve had your fill of the planet itself, turn your attention to its retinue of moons, the seven brightest of which are shown in the following chart, configured for the same time. The labelled moons shine at the following visual magnitudes: Titan 8.6, Tethys 10.5, Rhea 10.0, Mimas 13.2, Enceladus 12.0, Dione 10.7 and Iapetus All brightness ratings are taken from Starry Night software bar that for Iapetus the software doesn t take into account the significant variation over Iapetus 79 day orbit, resulting from the starkly differing albedo (reflectiveness) of the moon s opposing hemisphere s, so the rating given here is my confident estimate. The brightest stars on the chart shine at magnitudes 13.7 (USNO J , circled at right) and 14.2 (USNO J , at left); all others are two, three or four magnitudes fainter still, so none can be mistaken for even faint Mimas, close to the ring system far flung Iapetus should be readily identifiable as well. Titan will show up in any telescope, even binoculars or a finder scope; Tethys, Rhea, Dione and Iapetus will yield to a six incher, Enceladus may require an eight incher, and Mimas a ten or even twelve inch instrument. As a matter of interest, the brightest of the barely visible points of light to Iapetus left on the chart is the magnitude moon Hyperion. As August draws to a close, Saturn transits at 7:03 pm, 74 clear of the northern horizon, and has descended marginally to 73 when twilight wraps up just over twenty minutes later (7:25 pm); it subsequently sets at 2:18 am. The span of disk and rings has reduced a touch further, to 17.0" and 38.6"

11 respectively, while the rings have opened just a tiny bit more, to (the inclination will peak at in October). Saturn is in Ophiuchus until the second half of November, when it will cross the border into Sagittarius; because it is stationary on the 26 th as it ends retrograde motion (see the explanatory notes above), Saturn doesn t move a great deal against the starry background throughout August. Uranus Uranus is now rising before midnight (as of July 31 st ), and so has become an evening object, albeit marginally. At the beginning of August, it rises at 11:55 pm, then transits at 5:25 am, just 24 minutes before twilight commences; spanning 3.6", its disk shines at magnitude On August 19 th, it is rising considerably earlier, at 10:44 pm, subsequently transiting at 4:13 am, and remaining at an altitude of 39 in the NNW at the commencement of twilight (on the 20 th ), 5:31 am; the span of the disk remains at 3.6" and brightness is also virtually unchanged, at magnitude Here s an overview at time of transit, labelling Neptune as well; the earlier chart in the meteors section also shows both planets (when positioned farther east). The astute reader may notice that Uranus is not at the crest of the ecliptic when transiting I invite you to resolve what may seem to be a contradiction, feel free to contact me if you are unable to do so (the reason will be apparent to seasoned observers, but this column also caters to newly cast amateur astronomers). Use the chart to identify Algenib (Gamma [γ] Pegasi), magnitude 2.8, the star at the top right corner of the Great Square of Pegasus, as well as Eta [η] Piscium, mag 3.6 and Menkar (Alpha Ceti), mag 2.5. Noting that Uranus lies almost precisely on the midpoint of a line joining Algenib and Menkar, and is 6 a little over half the span of a fist at arm s length from Eta Psc, will give you a good fix on the

12 planet s location in the sky (although not bright, Eta should be readily identifiable, as the only other naked eye stars within 5 are very faint, and the two brighter stars to its lower right point towards it). You should also be able to spot Omicron [ο] Psc, magnitude 4.25, the (unlabelled) star just to Uranus upper left on the chart; while fainter again than Eta, Omicron is still comfortably naked eye under a dark sky. When you re ready to proceed, refer to the magnification below, which is delimited by Eta & Omicron Psc and intended for use in conjunction with a finder scope, to hone in on your planetary target.

13 The blue marker for Uranus position (on the 19 th ) appears between the white crosses marking its location on the 1 st (at lower right) and 31 st (upper left). Note that the planet actually moves, imperceptibly at this resolution, further to the right from the 1 st to the 3 rd before changing direction as its period of retrograde motion begins. The chart plots only those stars brighter than magnitude 9.5, at or beyond the reach of a finder scope, so many of the faintest stars shown here will be extremely faint or unseen through your finder. Use the chart to first identify Pi [π] Psc, magnitude 5.5, halfway between Eta and Omicron, then position your finder so that Pi and Omicron are equidistant from opposite edges; Uranus will then be easily identifiable as the bright star to the upper right of centre (on the chart, remember that your finder scope will probably invert the view), intermediate in brightness between Pi and HIP8588, magnitude 5.9. Identification of the planet will be further aided by its relatively steady glow as compared to the twinkling stars (another test for those new to the hobby why is it so?) and its subtle blue-green hue. Confirm capture by switching to the main eyepiece at a magnification at 150x or more to resolve its very small disk (the higher the magnification the better, conditions and equipment permitting) the colouration of the disk will be much more noticeable than through the finder. On August 31 st, Uranus continues its march towards views earlier in the evening, rising at 9:56 pm before transiting at 3:25 am; the span of the disk is marginally improved, to 3.7", as is its brightness, to magnitude The planet will slowly traverse the star fields of Pisces until 2018/19. Neptune Officially the outermost planet (regular readers will get my drift), Neptune is at opposition early next month and so is becoming more viewer friendly, attaining a respectable altitude above the horizon earlier in the evening. As the month of August gets underway, it s still far from optimal, rising at 8:15 pm, nearly 1¼ hours after evening twilight fades, and not transiting until 2:40 am the following morning; the span and brightness of its disk, which don t alter very much over the course of a year, stand at 2.3" and magnitude 7.83.

14 By the 19 th, the situation has improved a little the planet rises at 7:02 pm, almost ¼ hour before the end of twilight, then transits at 1:27 am; span and brightness have improved incrementally to 2.4" and mag Charts in the meteor and Uranus sections show where Neptune sits in relation to the Great Square of Pegasus, the Circlet in Pisces and the Y of Aquarius the three asterisms (ultimately the Y ) useful for pointing the way to the planet. The Circlet and Y are composed primarily of 3 rd and 4 th magnitude stars, and so are visible to the naked eye, albeit faintly so. Having identified the Y, refer to the magnified view above, which is configured for 11:00 pm with Neptune at an altitude of 45 in the NE; the chart enlarges the portion of sky between the asterism and the area past Neptune. Only those stars of magnitude 5.5 or brighter are shown, duplicating what you may expect to see, without optical aid, under a dark sky; the chart is intended to allow you to identify Phi [φ] Aquarii, mag 4.21 and, primarily, Lambda Aqr, mag As it shows, there is only one naked eye star, Kappa Aqr, between the Y and this pair of stars (and even it is very faint, at mag 5.0), so both Phi, and particularly the brighter Lambda, should be readily identifiable. With Lambda & Phi in your sights, proceed to the final magnification below; delimited by those two stars, and labelling, with their magnitudes, all stars above the ecliptic (and thus in the area of concern) which are brighter than Neptune, it should facilitate identification of the planet. The chart, which is intended to be consulted while viewing the sky through your finder scope, also includes white crosses marking Neptune s location at the start (lower right) and end (upper left) of the month. This chart plots all stars brighter than magnitude 9.5, and so, as with the final magnification in the previous section on Uranus, the dimmest stars shown will be either extremely faint or unseen through your finder. Begin your final search by identifying the star of magnitude 5.43 (83 Aquarii), the brightest star on the chart other than Phi & Lambda, and only 3 SE of the latter; as such, Lambda and 83 will comfortably fit within the field of view of your finder. Neptune should then be an easy capture, almost on a line joining the two stars and just a little closer to Lambda than 83, and therefore close to the centre of the view through your finder. If you are looking at a spot halfway between the two aforementioned stars,

15 you re virtually looking at Neptune, as there are no other stars of comparable brightness in that area; its subtle blue-grey hue and steady shine will also give it away. Confirm that you have found your quarry by switching to the main eyepiece at the highest practical magnification (250 x or more, if possible) to resolve its tiny disk through careful examination. On the last day of the month, Neptune rises at 6:13 pm, just ¼ hour after sunset (5:58 pm), before transiting soon after midnight, at 12:39 am; the span of its disk remains at 2.4" and it is undetectably brighter, at magnitude The ice giant sails slowly through Aquarius until 2022/23. Pluto Pluto having been at opposition last month, August is prime viewing time for those up for the challenge of tracking it down in the frozen outer reaches of the solar system proper (it s the real outermost planet ). On the first day of August, Pluto is 38 clear of the eastern horizon when evening twilight wraps up at 7:03 pm; it then transits at 10:55 pm before setting at 6:08 am (just under 20 minutes after twilight starts to paint the sky). Pluto s disk, far too small to be resolved by other than professional instruments, spans just 0.098", and glows dimly at magnitude It is better positioned on our viewing night of the 19 th, 55 high in the NE at the end of twilight, 7:16 pm. Time of transit is a more convenient 9:42 pm, after which the planet sets at 4:56 am. The span of the disk now registers 0.097", and its brightness magnitude The wide field view depicted in the notes on Saturn shows where Pluto sits, below (from our southern perspective) the handle of the Teapot asterism of Sagittarius, just east of three naked eye stars; here s a closer view, configured for 9:42 pm (as it transits), the time affording the best opportunity of catching it in the eyepiece.

16 The chart shows stars down to magnitude 6.4, a little dimmer than visible to the unaided eye for most folk and labels, with their visual magnitudes, the three stars referred to above Albaldah, aka Pi Sagittarii, mag 2.87, Omicron Sag, mag 3.75 and Xi 2 [ξ 2 ] Sag, mag 3.50 as well as Nunki (Sigma [σ] Sag), mag 2.03, the second brightest of the stars of the Teapot. The cut-off point of mag 6.4 has been chosen in order to as closely as possible represent a naked eye view while depicting the star just to Pluto s left on the (above) chart mag 6.37 HIP94372, which is labelled on the following magnification: This view, configured for the same time (as will be the final magnification to come), labels stars brighter than magnitude 8.0 with their brightness ratings. White crosses are included to show Pluto s position on all other Saturdays in August (the marker for August 12 th is partly concealed by the to of Pluto s label) and the first Saturday in September, the left most cross. The chart shows stars down to around magnitude 13 (still considerably brighter than Pluto), and is best suited to be used in conjunction with a low power eyepiece. Relate it to the previous view using Omicron Sag ( 3.75 ), Albaldah ( 2.87 ) and HIP94372 ( 6.37 ); as the chart shows, the last of these is an excellent reference point for launching a final assault on Pluto. The final chart on the following page shows stars down to magnitude 16.0, much fainter than Pluto, and labels those brighter than magnitude 13.0; as the angular distance from the HIP designate to Pluto is only 11', not much more than ⅒ th of a degree, and your target shines dimly at magnitude 14.2, you ll want to use it in conjunction with a highly magnified view through the eyepiece. First, star hop from 6.37 to the double star marked with mag s and 11.59, which will appear to be one star of mag Continue then to that of mag 11.18; these 11 th magnitude signposts are the brightest in the chart s area, apart from 9.81 at top left. From 11.18, veer slightly right and travel a similar distance to arrive at the mag star shown to Pluto s upper right on the chart. Once you ve identified & (TYC & USNO J respectively), Pluto is yours, as it s the brightest star roughly between them and close to (it s less than 1' away) as shown. The two faint

17 stars to Pluto s immediate lower left on the chart shine at mag s 16.0 and 15.9, so along with many of the other faintest stars plotted you probably won t see them unless you ve got a large scope. In the absence of the ability to resolve Pluto s disk, you may wish to return the following night or shortly thereafter to confirm capture by seeing which star moved to this end, the chart includes white crosses marking the planet s location on the 20 th and 26 th, respectively a day and week after our viewing night. On the last day of winter, Pluto is at an altitude of 65 as twilight slips away at 7:25 pm, transits at 8:54 pm, and sets at 4:08 am on Sept. 1 st ; span is unchanged from the 0.097" quoted above for the 19 th, while visual magnitude now stands at The tiny frozen orb will remain in Sagittarius until 2023/24. Our feature this month is Messier 57, the Ring Nebula, the planetary nebula also catalogued as NGC Unsurprisingly, given its small span of 1.5' x 1', most amateur instruments see just a ring, but larger instruments, and in particular professional instruments, reveal more structure of course, even a small instrument used for time lapse imaging can reveal far more than a visual inspection. The Ring Nebula was discovered independently by Charles Messier and the French astronomer Antoine de Pellepoix in early The nebula is situated some 2300 light years away, and has been expanding for about 7000 years (currently at a calculated speed of km/sec) since its progenitor star exhausted its nuclear fires and cast off its outer layers, leaving behind a white dwarf about the size of Earth, glowing dimly at magnitude 15.8.

18 Locating the nebula is actually a breeze, despite its northerly declination and the fact that it will appear stellar and very faint through your finder scope it is just barely visible (through the finder) from my rural back yard, a touch more obvious under a darker sky. Here s a wide field chart configured for 9:22 pm, when M57 transits and thus offers the best views. First use the above chart to identify Altair (Alpha Aquilae, mag 0.75), and Vega (Alpha Lyrae, mag 0.0). Most observers will need no assistance to locate these two prominent stars; note that Altair, in conjunction with Tarazed (Gamma Aquilae, mag 2.7, the star just to Altair s lower left on the chart), points virtually directly at Vega. Refer then to the chart opposite Use this chart to find Sheliak (Beta [β] Lyrae), mag 3.50 and Sulafat (Gamma Lyrae), mag 3.25, respectively 6 and 7½ from Vega; while not bright, these two are easy naked eye captures, straddling the Vega-Altair line and being the brightest stars in their immediate locality. (Sulafat is poorly labelled here; it s the star just above the h of Sheliak ). Finally, consult the last chart on the next page to nail the nebula.

19 All star charts courtesy of StarryNight Pro TM Version /Simulation Curriculum Corp. As you can see, M57 lies just off a line from Sheliak to Sulafat, a little closer to the former; slowly sweep the sky between the two (they re less than 2 apart), with a low-medium power eyepiece and you can t miss the planetary (a 17 mm yielding a magnification of 88x works well for me). Once you ve located it, experiment with different magnifications to see which gives the best view. That s all we have for this month folks; as usual, questions, comments or suggestions are welcome and may be directed to: waynerobertsau@yahoo.com.au Until next month: