Sky Notes by Neil Bone 2007 June & July
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Sky notes by Neil Bone 2007 June & July before sunrise, appearing against the stars of At magnitude –2.5, Jupiter is the brightest Sun and Moon western Gemini. object apart from the Moon in the summer Venus continues its very prominent show- midnight sky. Telescopically, it shows a flat- The Sun reaches its most northerly ing as ‘evening star’, reaching greatest elonga- tened disk with an equatorial diameter of position on the ecliptic on June 2, the date tion 45° west of the Sun on June 9. Around 45 arcseconds – sufficiently large that in- of the Summer Solstice. For a few days this date, Venus will show a half-phase (like struments as small as 60mm aperture will around this time the Sun rises as far north that of the first quarter Moon) in small tel- show some detail in the planet’s cloudy of east and sets as far north of west as it escopes. Half-phase – dichotomy – is nor- atmosphere. The dominant features are dark can, and the hours of daylight are at a mally reached a little before the date of great- belts and lighter zones and spots. The Great maximum for the year for observers at the est evening elongation, an anomaly known as Red Spot and its recently-evolved ‘Red latitudes of the British Isles. Even at the Schröter Effect. Around the time of great- Junior’ counterpart continue to attract much midnight, the Sun is never far below the est elongation, Venus sets three hours after observer attention. horizon at UK latitudes: from the the Sun. As June advances, Venus draws back Even for those with no more equipment Midlands northwards, astronomical closer to the Sun in line of sight, and by mid- than binoculars, Jupiter can be a fascinating twilight, with the Sun never more than 16° July sets about 90 minutes after sunset. Dur- object. A pair of handheld 10×50s are suffi- below the horizon, prevails throughout the ing this time, the planet will show an increas- cient to reveal the four bright (5th-magnitude) short nights of June and July. ing disk diameter (over 40 arcseconds by late Galilean satellites and their continually-chang- Sunspot activity – best observed using the July) and a steadily-diminishing crescent ing pattern, strung out to either side along safe projection method – currently remains phase. Small telescopes in the 60–70mm ap- Jupiter’s equatorial plane. low as we pass through the minimum be- erture bracket will show this clearly, and by Saturn’s apparition draws to a close during tween cycles 23 and 24. Observers have re- late July even a pair of steadily-held 10×50 this interval. At mag +0.6, the ringed planet ported a spotless disk on several days during binoculars should show Venus’ crescent. For lies west of Regulus in Leo. Right at the be- the opening months of 2007, and the few ac- most observers, Venus is probably at its most ginning of July, Saturn and Venus are close tive areas which have appeared have tended interesting at this time. together in the evening sky, less than a degree to be small, single spots. An upturn in activ- By mid-July, Venus is closing in on the (two Moon-diameters) apart on July 2. Like ity may arrive before the year is out. Sun by a degree per day, and it will become Venus, Saturn becomes lost in the evening The Moon is New on June 15 and July tricky to spot, even at a brilliant magnitude twilight before July is out. 14, around which dates the nights will be as –4, in the early evening twilight as the month dark as they can get at this time of year. Full draws to a close. Moon, languishing low in the southern sky, Having languished low in the bright pre- falls on June 1 and 30 (the second of these, dawn sky for much of the year so far, Mars being the second Full Moon of a calendar starts to become more prominent in this in- Minor planets month, is popularly described as a Blue terval, steadily brightening to mag +0.5 by Moon), and July 30. late July. Now seen against the backdrop of Earth reaches aphelion – the most distant western Taurus, Mars rises around midnight Brightest of the asteroids, (4) Vesta reaches point in its elliptical orbit around the Sun – UT. As Earth and Mars close towards each opposition in early June, slowly moving on July 7. other ahead of December’s opposition, the retrograde (westwards) against the stars of Red Planet shows an increasing apparent disk Ophiuchus, some ten degrees due north of diameter: at 7 arcseconds, Mars in late July Antares. During the first week of June, Vesta will reveal some of its dark albedo features to can be found 4° south of the 3rd-magnitude larger telescopes (200mm aperture upwards). star Zeta Ophiuchi. At mag +5.5, Vesta is The planets Naked eye observers may find it interesting to readily visible in binoculars. compare the red of Mars with similarly-bright Aldebaran’s Mercury is briefly visible in the evening sky hue in the early morning sky at the start of June, reaching greatest at June’s close. elongation 23° east of the Sun on June 2. Jupiter reaches opposition Around this time, Mercury sets some 90 – 180° from the Sun in Earth’s minutes after the Sun, and will be visible as sky – on June 5. Located a magnitude –1 ‘spark’ in the gathering against the stars of Ophiuchus, twilight: binoculars will help in locating it. to the northeast of Antares in For a few evenings, Mercury stands 6° high Scorpius, Jupiter is rather low in the westnorthwest an hour after sunset, in the sky for UK-based ob- fading steadily from night to night: by the servers in 2007. Even at its end of June’s opening week, the planet will midnight culmination the gi- be difficult to find. ant planet is only 17° above By June 28, Mercury has arrived at infe- the horizon from southern rior conjunction, between Earth and Sun. It England. This low in the sky, then emerges into the morning sky, reaching the view is especially prone greatest elongation 20° west of the Sun on to the adverse effects of at- One of the brightest noctilucent cloud displays of recent years July 20. Around this time, Mercury will reach mospheric turbulence – ‘see- occurred on 2006 July 14–15. This image, taken at 22:00 magnitude 0, and rise a little over an hour ing’ – on warm summer nights. UT, was obtained near Chichester by Neil Bone. 154 J. Br. Astron. Assoc. 117, 3, 2007 Sky notes Meteors Variable stars June’s twilit skies are far from ideal for meteor observing, although by this time the background sporadic rate will have picked The long-period (Mira- up somewhat. Patient observers may also type) variable Chi Cygni detect a trickle of activity from the should brighten into Ophiuchid radiants low in the southern sky binocular range during during June: this near-ecliptic activity is June and July, ahead of never prolific, giving rates of only one or its September two meteors per hour. maximum. Located a July brings a marked upturn in activity, as few degrees from eta several radiants south of the Square of Cygni on the Swan’s Pegasus come ‘on stream’. Most obvious are ‘neck’, the star was the Alpha Capricornids and Delta Aquarids notably bright at its last peaking towards the month’s end. These peak in the summer of maxima unfortunately coincide with July’s 2006. Weekly estimates Full Moon, but conditions will by the same suffice to follow its M56 imaged by Paul Brierley in 2006 July. Orion Optics SPX 200 token be much more favourable for summer’s variations, and making a F5.6 and Atik 2-HS CCD camera with an Atik focal reducer, 6×15 seconds. main event – the Perseid maximum in August. start now should allow observers to assemble their own extended lightcurve stretching well into the autumn months. Deep sky R Scuti, brightest of the RV Tauri class Noctilucent clouds of pulsating variable stars, is well-placed Led by the bright (mag +0.04) blue-white for observation during the summer. Found star Vega, the distinctive, compact just west of the ‘Wild Duck’ cluster (M11), constellation Lyra is high overhead on June The twilit nights of June and July offer R Sct like others of the class shows alter- and July nights, and is home to three summer optimal viewing conditions for noctilucent nating deep and shallow minima in its light showpiece objects. First of these is the clouds (NLCs), a summertime phenomenon curve. For much of the time it is around 6th celebrated ‘Double Double’ star, Epsilon of the high atmosphere, forming at altitudes magnitude, but deep minima can take R Sct Lyrae, just a couple of degrees to Vega’s close to 82km. These tenuous clouds cannot as faint as magnitude +8. Again, this is a northeast. To the naked eye, Epsilon appears be seen in daytime, becoming visible only star that can be followed adequately by as a pair of 4th-magnitude stars, separated when the Sun is between 6 and 16° below weekly observation. by a testing 3.5 arcminutes: if your eyes the observer’s northern horizon – conditions One to check on a nightly basis aren’t quite up to splitting them, binoculars that obtain throughout the summer night at through the summer is, of course, R Co- will easily do so. Telescopically, each of these latitudes north of the Midlands.