Sky notes by Neil Bone 2006 April & May New Moon falls on April 27 and May Sun and Moon 27, putting the darkest night-time skies in The planets the opening and closing weeks in this inter- Spring’s lengthening days, with the Sun val. The ecliptic plane – close to which the Mercury is very poorly placed in the climbing to a higher northerly declination on Moon’s orbit lies – still cuts a fairly steep morning sky during early April, rising the ecliptic (its apparent annual path against angle with the western horizon in early barely 30 minutes before the Sun at UK the star background), bring extended oppor- evening at this time of year, making early latitudes. Superior conjunction, on the tunities for solar observing. Using the safe April and early May favourable times to Sun’s far side, is reached on May 18, and projection method, observers can follow the observe the young waxing crescent Moon. by the end of the month, Mercury can be comings and goings of sunspots and the as- In the interval from 3−5 days after New, glimpsed as a magnitude –1 ‘spark’ low in sociated bright patches of faculae (clouds of the day-night line of the terminator cuts the northwestern sky about an hour after hot hydrogen overlying spot-forming re- across some of the Moon’s most interest- sunset. Viewing conditions will be much gions, usually best seen near the solar limb). ing terrain, which is thrown into relief by more favourable in mid-June. At the moment, however, sunspot activity the interplay of light and shadow under low Venus is a ‘Morning Star’, but at a decli- in the current 11-year cycle (number 23) is local solar illumination. Around April 2−3 nation well south of the celestial equator is heading towards minimum; after a succes- and May 1−2, for example, the splendid quite poorly positioned for observers in the sion of surprisingly large late-cycle crater chain of Theophilus, Cyrillus and British Isles. Although in excess of 40° of spotgroups into the latter parts of 2005, the Catherina on the southwestern (lower left) angular elongation west of the Sun through- opening weeks of this year have brought fringe of the dark Mare Nectaris are excel- out this interval, Venus rises less than an many days when no spots whatsoever have lently presented on the terminator. The con- hour before sunrise, and even at mag –4 will been apparent on the solar disk – a situation trast between the bright heavily-cratered be difficult to spot low to the southeast in likely to prevail for the next 12−18 months. ‘highland’ regions of the Moon and the dark, the gathering dawn. Venus’ gibbous phase Nonetheless, daily observations should still relatively flat plains of the maria (lunar gradually increases as the planet recedes to- be taken whenever possible, and we may ‘seas’, filled with aeons-long solidified lava) wards the far side of the Sun. soon see the first, small, high-latitude spots is obvious even in a pair of hand-held 10×50 Last autumn’s favourable apparition now heralding the start of cycle 24. binoculars. a distant memory, Mars continues its east- Around Full Moon ward progress against the star background, (April 13 and passing through Gemini during April and May 13), absence of May. For a couple of nights around April shadows makes it 17 and 18, Mars lies about a Moonwidth to hard to pick out most the north of the open cluster M35. The features except the planet fades steadily from mag +1.2 at the maria. At these times, beginning of April, to mag +1.7 by late May: however, the high so- this, and the dwindling apparent disk diam- lar illumination makes eter (below 5 arcseconds in early May) re- the ray systems asso- flects the growing distance between Earth ciated with some of and the Red Planet at this time. the ‘fresher’ (still Jupiter is at its best for the year during many tens or hun- this interval, reaching opposition – 180° from dreds of millions of the Sun in Earth’s sky – on May 4. Around years old!) impact cra- this time, Jupiter will be visible from dusk till ters stand out. Most dawn, culminating due south at midnight. Seen prominent are the rays against the dim stars of Libra, the giant planet extending from Tycho presents a mag –2.4 slightly-flattened disk in the lunar south, and with a large, 45 arcsecond apparent diameter. around Copernicus Cloud features in Jupiter’s turbulent atmos- and Kepler in the phere take the form of dark belts and light Oceanus Procellarum zones, among which long-lived spots may also on the Moon’s west- be found. The current apparition, with Jupi- ern hemisphere. ter reaching a maximum elevation of about The just-past-Full 25° above the southern horizon, is the last Moon occults the mag- reasonably favourable one for a while as far as nitude +3.0 star Pi UK-based observers are concerned: in the next Scorpii around 02h UT couple of years, the planet will languish still (Universal Time; BST lower, against the stars of Scorpius and Sagit- minus 1 hour) on tarius, with all the accompanying problems May 14. Glare will of haze and poor seeing. make this a tricky event The four main Galilean satellites can be seen to observe, with the strung out in line to either side of Jupiter in star disappearing behind the planet’s equatorial plane. Even 10×50 bin- the Moon’s bright limb. oculars suffice to give a reasonable view. 102 J. Br. Astron. Assoc. 116, 2, 2006 Sky notes ent ionisation trains. Observed tude. Good constant-brightness compari- rates of maybe 6−8 Lyrids/hr can son stars are Delta and Gamma Herculis, be expected on maximum night, quite nearby in the sky, and with respec- and with a similar contribution tive magnitudes +3.1 and +3.7. from the contemporaneous spo- radic background, visual watches made by the Meteor Section’s standard methods (http:// www.britastro.org/meteor) Deep sky should be quite rewarding. Absence of moonlight also favours the Eta Aquarids in Late spring is surely ‘globular cluster sea- early May, with a broad peak son’, with several of the northern sky’s around May 4. From the UK finest examples of this class of object well perspective, however, the on show. Best-known, of course, is the shower is rather poorly posi- Great Globular M13 (NGC 6205) in tioned: the radiant is only just Hercules. Located on the western side of climbing into the eastern sky the Keystone asterism forming Hercules’ as dawn breaks. Nevertheless, torso, this is an easy object for 10×50 bin- patient, determined observers oculars, which will show it as a hazy cir- may catch a few of these swift, cular patch. Any small telescope will give The magnificent globular cluster M92, imaged by the Jacobus sometimes bright meteors in a pleasing view, showing the 17 arcminute Kapteyn Telescope on La Palma, with processing by Nik the last hour or so of the night. wide M13 flanked by a couple of sixth- Szymanek. Isaac Newton Group Heritage Project. Seen to best advantage from magnitude stars. Telescopes of 100mm and greater aperture start to resolve the outer Saturn continues to make an attractive more southerly climes, the Eta Aquarids are fringes into a mass of individual equally- binocular/low power pairing with the – like the Orionids, which will be favour- bright stars – perhaps as many as a million Praesepe open cluster (M44) at the heart able this October – associated with Comet are crowded into a volume of space 140 of Cancer, well up in the western sky in 1P/Halley. lightyears across – and the view in large the evening hours. At mag +0.2 to +0.3, instruments is simply breathtaking. Saturn remains prominent, and the ring Suffering somewhat by comparison with system is still well presented: any small its celebrated companion, Hercules’ other telescope will show it well. The planet’s Messier Catalogue globular M92 (NGC globe is rather bland in comparison with Variable stars 6341) is a fine object in its own right. This that of Jupiter, and with a smaller appar- mag +6.5 star-ball lies roughly midway be- ent diameter (less than 20 arcseconds) is tween the Keystone and the quadrilateral reluctant to give up much in the way of Corona Borealis returns to prominence in of stars marking the head of Draco. M92 detail to telescopes smaller than about spring skies, making it easier for observers has an apparent diameter of about 12 arc- 150mm aperture. With opposition now to keep a night-to-night watch on the con- minutes, and has a more condensed core some weeks past, the shadow cast onto stellation’s most famous variable, the ‘re- than M13. the rings by Saturn itself is prominent, to verse nova’ R CrB. Fluctuating only Ranked as fifth-brightest of all the globu- the west of the planet’s globe. slightly around sixth magnitude for much lar clusters, M5 (NGC 5904) in Serpens Titan, at mag +8 the brightest of Saturn’s of the time, this ancient, carbon-rich star, Caput, south of (below) Corona Borealis, many satellites, is visible in small telescopes, which is located inside the eastern (left) shines at an overall magnitude +5.7 – equal, due west of the planet around April 11 side of Corona’s ‘circlet’, is prone to sud- indeed, to M13. M5’s stars are less densely- and 27, and May 13 and 29; it lies due east den, unpredictable deep fades.