Sky Notes by Neil Bone 2004 June & July
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Sky notes by Neil Bone 2004 June & July and no-one alive today has ever seen one. Transits of Venus occur in pairs separated Sun, Moon and Earth The 2004 transit will be intensively covered by 8 years: the second in the series is in 2012, by those wishing to photograph and image and only the closing stages and egress will be The Sun reaches its greatest northerly decli- it, as well as by visual observers keen to visible from the British Isles on that occasion. nation for the year at 00h 57m Universal Time witness a rare astronomical spectacle. After 2012, there is a long wait until 2117. (UT=GMT; BST minus 1 hour) on June 21, The usual cautionary note with respect to the northern hemisphere Summer Solstice. solar observing applies to the transit. Projec- The hours of daylight are at a maximum for a tion is the safest way to view the event. Objec- week or so to either side of this date, and with tive filters can be used, but only if the observer the Sun never very far below the horizon even is absolutely sure, via the manufacturer’s speci- The planets at midnight, the short midsummer nights never fications and instructions, that these are safe. really become properly dark at the latitudes Advice on safe observing, along with other as- of the British Isles. Particularly in Scotland, pects of the transit, can be found on the website Mercury is at superior conjunction on the Northern Ireland and the Northern Isles, the at http://www.transitofvenus2004.org.uk/ far side of the Sun on June 18, then emerges nights are brief and twilit. The transit, starting early on this Tuesday into the evening sky to a rather unfavourable Long days afford plenty of opportunity morning, is visible in its entirety from the apparition, reaching greatest elongation east for solar observing by the safe means of pro- British Isles; stay-at-home observers are hop- of the Sun on July 27. Setting only an hour jection. After the spectacular revival of last ing for a repeat of he generally fine weather at most after the Sun, Mercury is unlikely to autumn, sunspot activity in the current Cy- conditions which greeted the transit of Mer- be visible from the UK. cle 23 is now winding down towards mini- cury in 2003 May. Locations in southern Following the June 8 transit, Venus moves mum, expected in 2006/7. Nonetheless, ob- Europe, North Africa and the Middle East are rapidly into the morning sky, west of the servers should still find a reasonable number also favoured, and many will be travelling there Sun. By late June, Venus will have pulled of active areas on the solar disk, with per- in search of more dependable out to nearly 30° elonga- haps three or four spot groups on most days. clear skies. tion, rising about 80 min- The Moon is New on June 17 and July Precise timings for the key utes before sunrise, and un- 17, placing the darkest nights into the mid- events in the transit vary with mistakeable at magnitude dle fortnight of the month. Full Moon falls geographical location: the cal- −4. Through July, Venus’ on June 2, and July 2 and 31. In American culated values given in the BAA elongation continues to in- parlance, a second Full Moon in the same Handbook and on p.119 are crease, and the planet will calendar month − like that in July − is often geocentric, but observers will be a truly prominent referred to as a ‘Blue Moon’. Midsummer find the Earth’s surface a like- ‘Morning Star’ rising 2h Full Moon occurs at southerly declinations lier location for their view... 30m before the Sun to- close to the ecliptic, against the stars of Observers in the British Isles wards the end of the Scorpius in June and Sagittarius in July. Con- (there is little variation from month, among the stars of sequently, for UK observers, the Moon at one region to another) can ex- Taurus. Through this in- Viewing the Sun by the terval, Venus will show an these times is as low in the southern sky as pect first contact between Ve- projection method. (Neil Bone) the winter Sun, and with twilight prevailing nus and the Sun’s southeastern increasingly broad cres- in any case, seems to have less impact in limb at 05h 19m UT; as Venus continues its cent phase in a telescope, brightening the sky. Earth reaches aphelion westwards motion, a growing ‘nick’ will be but its overall diameter will appear to shrink − the farthest from the Sun in its slightly apparent in the solar limb over the next few as it recedes around its faster orbit inside elliptical orbit − on July 5. minutes. Venus’ appreciable 1 arcminute disk that of the Earth. will take up to 20 minutes to completely pass Mars is still just about keeping pace east- onto that of the Sun (second contact). The wards ahead of the Sun along the ecliptic, but time around second contact will be followed is now lost into the evening twilight as the with particular interest. As a result of Venus’ current apparition comes to the usual linger- The transit of Venus thick atmosphere, and unsteady seeing (tur- ing end. Jupiter, too, is becoming poorly bulence) in our own, second contact is not placed in the evening twilight, already quite clear-cut. Instead, Venus’ dark body appears low by the time dusk deepens in mid-June. A For amateur astronomers of a certain vin- joined to the solar limb by an extended ‘stalk’, bright mag −2 against the stars of Leo, Jupiter tage, this interval brings the finale in a series producing what is known as the black drop is too low for effective observation by July. of long-anticipated landmark celestial events. effect. Recording this will be a target for many Saturn, meanwhile, is at conjunction on the Those of us who grew up with the ‘Apollo imagers. Remember that BST (local) times will far side of the Sun on July 8, and will not re- Era’ of the 1960s always had marked in our be an hour later than those given here. emerge to easy view until late August. wish-list the return of Halley’s Comet in Once onto the solar disk, Venus will track For observers with binoculars, Uranus and 1985/6, the total solar eclipse of 1999 Au- steadily westwards on a chord across the Neptune − in Aquarius and Capricornus re- gust 11, and the Leonid meteor storm later Sun’s southern hemisphere, taking until 11h spectively − are becoming better placed. the same year, together with the 2004 June 8 08m UT to reach the western limb. As at Uranus, around mag +5.5, is an easy binocu- transit of Venus. ingress/second contact, the egress/third con- lar object about 1.5° northeast of the fifth- As outlined on page 119, this is of course tact is expected to produce a black drop ef- magnitude star Rho Aquarii, a few degrees an event of great historical significance: the fect. Venus finally departs the solar disk south of the ‘Water Jar’ asterism. Neptune previous transit of Venus occurred in 1882, (fourth contact) at 11h 26m UT. is 1.5° northeast of fourth-magnitude Theta J. Br. Astron. Assoc. 114, 3, 2004 169 Sky notes Capricorni (more or less in the middle of 2001 Q4 Capricornus), and at mag +7.7 should be rea- (NEAT) sonably easy to find in, say, 10×50s. will have Charts for these two outer ice/gas giants been a rea- can be found on pp.70−71 of the BAA Hand- sonable na- book. Magnitude estimates, made using back- ked eye ob- ground stars as comparison objects will be ject during welcomed by the Director of the Asteroids mid-May, and Remote Planets Section, Andrew Hollis. and if it lives up to the more optimistic forecasts, it Noctilucent clouds will still be so through NLC photographed from Chichester in 1995. (Neil Bone) June and July are the traditional ‘season’ for to mid- seeing high-atmosphere (82km altitude) June. As it noctilucent clouds (NLC), which many be- tracks northwards during late June and into night, and report details − even if no activity lieve to form as traces of water vapour con- July, heading towards the Bowl of the is noted − to the Meteor Section. dense onto suspended residual meteoritic Plough, the comet will start to fade, but July sees an upturn in overall meteor ac- material. Often distinctively banded, NLC should remain a good binocular object. tivity, with several Capricornid and Aquarid have a characteristic silvery-blue colour. The Nightly drawings can be made to show radiants coming ‘on stream’ south of the clouds are very tenuous, and can only be how the tail behaves as the comet recedes Square of Pegasus. Bright moonlight in the seen after the Sun (which illuminates them) from the Sun, and these will be welcomed, closing week of July will prevent fruitful has sunk more than 6 − but no more than 16 together with magnitude estimates and observation of these showers, but the good − degrees below the observer’s horizon, ap- other observational details, by Comet Sec- news is that August’s Perseids will enjoy pearing in contrast with the twilight. Ob- tion Director Jonathan Shanklin. Those dark skies close to their maximum. servers in the south of England will find NLC, wishing to make detailed observations are if present, restricted to the low northern sky advised to consult the BAA Observing below Capella.