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BAA Observing Sections Mercury and Venus

Venus in 2011–12: 1st Interim Report

Introduction

Venus entered eastern elongation from the date of superior conjunction, 2011 August 16. In 2012 June, at the next inferior conjunction, there will be another solar transit. To mark the special nature of this evening elongation we shall be submitting a short Venus report to each number of the Journal for the next four or five issues. Observers should therefore send in all their work regularly. We want good images in the ultraviolet (UV), the near-infrared, series with the usual visual waveband filters, and of course careful drawings (in white light and particularly with either a yellow W15 filter or a blue-violet W47 filter) submitted on the Section's standard report forms, which are available either from the Director or at our website. The Director can also supply gelatine filters to visual observers.

Venus near superior conjunction, 2011 May-August: cusps, ultraviolet rotation period and UV bright areas

Immediately prior to superior conjunction Venus exhibited a nearly full, though rather tiny disk. For the period May-August we have on hand a number of visual observations, especially from Gianluigi Adamoli (Italy) and Stanislas Macsymowicz (France), as well as UV and other images from Willem Kivits and Dennis Put, both in the Netherlands. Here we review them briefly. Adamoli was able to continue his daylight observations up till August 2. Put (18 years old) submitted an excellent report in addition to providing images, as well as maps made using WinJupos.

Put used a 279 mm SCT with a monochrome DMK21AU camera. Venus was imaged mostly in ultraviolet light using the Astrodon J/C UV filter, which provides transmission below wavelengths of about 395 nm. Until the end of May, a Wratten 47 violet filter had been used in conjunction with a Schott BG40 glass in order to eliminate the filter’s significant near-infrared leak. His ultraviolet images were all made between May 25 and July 20, when the planet's apparent diameter was about 10 arcsec. All images were obtained at dawn, the altitude of Venus being between 16 and 25º degrees.

The results from this epoch show a consistently bright S. cuspidal area, which had been remarked upon earlier in the elongation; there were occasional brightenings in the north, but the general impression was of a dusky N. polar region. On July 1 Adamoli found the NPR particularly dark visually, in accord with Put’s July 5 image, one atmospheric rotation later. On some dates specific bright UV clouds were recorded near the equator. On May 22 Detlev Niechoy found a small, very bright patch at the f. limb midway between pole and equator; this can be recognised on Put’s image two rotations later, on June 3. Macsymowicz visually recorded the bright patch N. of the equator on the f. side of the disk that was also imaged by Put on June 2. Arranging the images in rows with 4-day or multiples of 4-day intervals between each row reveals some similarities from one rotation to the next, but also a lot of variation. The characteristic Y marking, with its tail lying along the equator, can be recognised a few times, and a dark equatorial streak was drawn by Adamoli on several dates.

UV images often show the typical, long-enduring Y- and psi-shaped markings. If we take Put's image of 2011 Jul 5d 04h 47m (JD 2455747.6993) he shows the Y marking distinctly, and its fork is some 25o (0.06944 rotations) past the CM. This may be compared (for instance) with a similar image (published previously) of the Y marking with its fork at the CM by Tiziano Olivetti from 2004 Oct 29d 23h 17m (JD 2453283.4701). Dividing the 2464.2292-day interval by a rough period of 4 days we derive 616.0573 rotations, close enough to an integral 616 rotations to show that the same part of the planet was on show. Carrying out the precise division by 616 plus 0.06944 additional rotations for the 25o displacement, the average equatorial UV rotation period over the 2004-2011 interval is found to be about 3.999 days, in excellent accord with past work which gives a more precise period (measured over many years) of 3.99525 days. [1, 2] Later images on the morning of Jul 5 by Put and Kivits show this Y marking rotating to the right (with south at top).

The following also provided observations during the planet’s W. elongation: Paul Abel, Tomio Akutsu, Barry Clark, Peter Edwards, David Finnigan, Mario Frassati, Sadegh Ghomizadeh, David Gray, Simon Johnson, Willem Kivits, Stanislas Macsymowicz, Roy Panther, Jean-Jacques Poupeau, Andrew Robertson, John Sussenbach, John Vetterlein, Kenkichi Yunoki and the Director.

The next transit of Venus: 2012 June

As in 2004, the Mercury and Venus Section would like to receive your observations of this great event. We shall have more to say about it later. For now, the question for many observers will be to decide whether to travel abroad in the hope of seeing more of (or all of) the event, or remaining in the UK with the chance of seeing just the 3rd and 4th contacts. A word of warning for those travelling: do try to establish in advance the likely seeing conditions at the observing site. Some who travelled overseas in search of cloudless skies in 2004 succeeded in finding them, but seeing conditions were much less favourable than many stay-at-homes experienced.

For those wanting to know what sort of observations can be made, please see either our final reports in the Journal [3, 4] or the Venus transit CD-ROM published by the Association in 2004 (and still available from the Office). As for 2004, accurate timings of the event will be considered for publication in our BAA reports for the sake of historical completeness, even if such data are no longer able to improve upon our value of the Astronomical Unit.

The most interesting parts of the event will be to watch for the phenomena visible at ingress and egress, particularly the (irregular?) ring of illuminated atmosphere (often irregularly bright near the planet’s pole) that can be seen when Venus is only partly projected upon the photosphere. The chance of catching the planet as a black disk against the inner corona is also of interest, and is a phenomenon that has actually been observed with transits or near-transits of Mercury.

The 2012 BAA Handbook gives the circumstances of the transit in some detail.

A Venus transit website and newsletter

An organisation was established earlier this year with a number of aims (both current and historical) set out at its website. [5] The Director explained that he would be coordinating the BAA observations of the transit, and contributed an article about observing Venus, together with links to available pdf copies of our BAA Venus reports cited in this note. The website offers the chance to sign up to receive the newsletter.

Conclusion

Venus is a challenging but fascinating planet to study. There are still puzzles to be investigated by the BAA, and some of themes will feature in future reports. In the 2012 February Journal we hope to discuss any preliminary observations up to the end of 2011.

Richard McKim, Director

References

1 R.J.McKim, The Elongations of Venus, 1999-2006, J. Brit. Astron. Assoc., 118 (3), 131-144 (2008).

2 R.J.McKim, K.W.Blaxall and A.W.Heath, The Elongations of Venus, 1991-1998, J. Brit. Astron. Assoc., 118 (5), 254-269 (2008).

3 R.J.McKim, The transit of Venus, 2004 June 8: an introduction: J. Brit. Astron. Assoc., 115 (3), 128-129 (2005).

4 R.J.McKim, K.W.Blaxall and A.W.Heath, Venus 2004: east and west elongations and solar transit, J. Brit. Astron. Assoc., 117 (2), 65-76 (2007).

5 http://www.transitofvenus.nl

Venus_Put_2011-04 

Violet and ultraviolet images of Venus during 2011 May-July by Dennis Put (for details, see text) arranged so that the vertical columns show near-identical longitudes. (In this interval of time the average drift of equatorial features to the right would be just 8.6o.) An image by Willem Kivits (355 mm SCT, DMK camera, marked ‘K’), has been added for completeness.

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