J. Brit. Astron. Assoc., 106, 2, 1996
(Note: The British Astronomical Association is not responsible for individual opinions expressed in articles, reviews, letters or reports of any kind.)
From the Associate Director of the Minor Planet Center
I write in reference to the letters in recent Journals (106(1), 10 and 106(2), 110) concerning the object observed by George Sallit.
The Minor Planet Center does not attach any blame to Mr Sallit for the media fiasco surrounding 'Planet Sallit'. We were in e-mail communication with him at the time and he explained the situation to us. I even went to the lengths of defending Mr Sallit's role in a letter to the Guardian newspaper (Letters, Dec. 13, reproduced on The Astronomer World Wide Web site). The Minor Planet Center (and Central Bureau for Astronomical Telegrams) frequently have contact with the press with regard to new discoveries and we are well aware of the (usually unintended) misrepresentations that even experienced journalists make.
However, it is wrong of Mr Sallit to claim that the IAU reporting procedures for minor planets are 'complex, confusing, unfair and open to misunderstanding'. The procedures are both simple and fair: get two nights of observation of each object and report them to the Minor Planet Center. If the object is new, a new provisional designation will be assigned and the discovery credited to the observer. If the object is known, the identification will be communicated back to the observer by e-mail. Credit for a discovery is assigned to the first observer to report two nights of a specific object.
Accurate positions are also a necessity, but are easily obtained from CCD images using any one of a number of astrometric packages. Approximate positions were very common through the 1960s, as obtaining accurate positions from photographic plates was a time consuming and error prone procedure. An accurate position from a CCD image can be obtained within a few minutes of exposing the image.
We insist on a specific format for reporting astrometric observations because of the volume of observational material we receive. In a busy month we receive well over 10,000 observations: if all the observers were to use their own formats, we would waste a lot of time converting between formats. Most observers report material to the Minor Planet Center in the correct format. Publication of observational material in the Minor Planet Circulars counts as publication in the refereed literature, and it is quite normal for refereed journals to insist on specific formats for submission.
We do not give provisional designations to one-night stands for a good reason: it is a waste of time! When we have two nights on a new object, we can check the motion for consistency and look for identifications. We cannot do either of these checks reliably with only a single night. We do not ignore one-night stands, though. We keep them on file, check them against designated new objects and publish them as and when they can be identified with known objects.
The Minor Planet Center does work to encourage new astrometric observers, but we cannot lower standards. Astrometry is a field where amateurs can (and do!) make significant contributions, but it is also a field where bad results are next to useless. The standard of many amateur astrometrists is outstanding and they achieve a level of accuracy that is limited only by the poor quality of the Guide Star Catalogue used in the reductions. Our World Wide Web pages (http://cfa-www.harvard.edu /cfa/ps/mpc.html) contain guidance for new or potential astrometrists and also give details on the procedures for reporting observations.
Gareth Williams
Minor Planet Center, Mail Stop 18, 60 Garden Street, Cambridge, MA 02138, USA. E-mail: gwilliams@cfa.harvard.edu
From Mr M. Frost
As a new recruit to the BAA, I only recently came across the debate in the letters pages of the Journal on viewing Venus in daylight. This is of some interest to me, as I have recently been investigating the related subject of seeing stars in daylight. The published evidence strongly suggests that it is impossible to see objects as faint as stars with the naked eye in daylight, but readers may be interested in the discussion which followed the presentation of a paper on 'Stars in Daylight' to the BAA by Revd W. F. A. Ellison, eighty years ago. (JBAA, 26, 227 (1916)).
The discussion turned to observing Venus with a sextant, i.e. through a small (¾-inch) aperture telescope. Mr M. A. Ainslie reported that he 'had certainly seen Venus in the field of view of a sextant in the daytime on several occasions, but he had never been very successful in observing the planet under those conditions, nor had he ever met any navigating officer who placed much dependence on such observations.' He was about to! Captain Carpenter said he 'had done a great deal of surveying at sea off the coast depending entirely on astronomical observations. The officers of the morning watch were instructed to keep touch with any planet long after daylight appeared so they could get a good daylight horizon. There is no more accurate observation than that of a star or a planet with a daylight horizon.'
So daylight observations of Venus (albeit with some magnification) were part of the naval navigational repertoire. Are they still?
Mike Frost
70 Arbour Close, Bilton, Rugby, Warwicks. CV22 6EH
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From Mr B. R. M. Munden
When I read Dr Leyland's letter about finding Venus with the naked eye in broad daylight (J. Brit. Astron. Assoc., 106(1), 1996) , I found it hard to believe it was so easy. But only a week or so later on February 27 conditions were favourable to try for myself. The elongation of Venus was 43° and visual magnitude –4.1. The sky was an exceptionally deep blue with small white clouds. From the planet's RA and declination I knew where to look. I stood in the shade of the house and, using 8×32 binoculars, Venus was easily found at 13.25. I was able to see it with the naked eye before clouds came over. There was a break in the clouds at 13.48 and I again found the planet with binoculars. This time, using cloud edges as a reference, I was able to pick it up with the naked eye. I followed it until 13.59 noting its position relative to the tops of trees.
At 14.52 I resumed the search, but now with the unaided eye only. I estimated the position of Venus relative to the tree tops, reckoning on about 13° movement since I last saw it. I found the planet almost at once and followed it easily until 14.56 when it was again obscured by cloud. In those four minutes it was still visible as it passed behind thin wisps of cloud.
I would rate my eyesight as only average such that, with light pollution in these parts, my magnitude limit even on a good night is around 4.5. If it is possible to make the comparison, the visibility of Venus in daylight was for me about the same as a star of magnitude 3.5 to 4. In transferring from binoculars to naked eye, small clouds are a great help, not only for positional reference but also as an object on which the eyes can focus.
Michael Munden
67 Lilliesfield Avenue, Barnwood, Gloucester GL3 3AH
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From Mr P. Wade
Edward Ellis' paper about naked-eye sightings of Venus in the daylight sky and subsequent correspondence prompted me to look again at some naked-eye observations I made in the early 1980s. Each of my attempts at a naked-eye sighting of Venus was made after the completion of observations with a telescope at or near to the time of Venus' transit, the telescope tube being used as a guide to where to look. During evening apparitions the observing site was shielded from the direct light of the Sun. However, morning apparitions were observed in direct sunlight though some shade could be produced by holding a board at arm's length to blot out the Sun.
Naked-eye sightings were recorded from the 1980 evening and morning apparitions as well as the 1981 evening apparition. The planet was generally seen at elongations of 36° or more though on one occasion (1980 May 29) it was spotted at an elongation of only about 25°. The lowest magnitude of Venus when sighted was –3.6 (1980 October 12 and 18).
Venus' altitude above the horizon when seen varied from 54° to 64° for the first apparition, 43° to 55° for the second and 13° to 17° for the third. The Sun's altitude for the last was only 2° to 6° (zenith angle 88° to 84°) but for the others was much greater: 26° to 49° (zenith angle 64° to 41°) for the 1980 evening apparition and 16° to 43° (zenith angle 74° to 47°) for the 1980 morning apparition. Thus, for those who know where to look and with the ability to pick out a point of light in a daytime sky of good transparency, these results suggest that Venus should be visible at all apparitions as it transits when at elongations of over about 36°.
Peter Wade
24 Manor Grove, Morecambe, Lancashire LA3 1JA
From the Director of the Comet Section
Members may have noticed the display of nacreous or mother of pearl clouds, which were widely seen across the country on the evening of February 16, and wondered what they were. These clouds form in the stratosphere, at heights of between 10 and 30 km, when the temperature there falls below –80°C, and are probably composed of ice particles with a liquid coating of nitric acid trihydrate. They appear bright because they are high enough to be illuminated by the Sun long after local sunset. The pastel colours arise through diffraction or interference effects in much the same way that colours appear in a film of oil on a puddle of water. Occasionally seen from Scotland during the winter months, they are a once in a lifetime sighting from southern England. They are more frequently seen from the southern hemisphere, particularly from locations along the Antarctic Peninsula where the mountains create lee-waves in the upper atmosphere.
Stratospheric clouds are associated with ozone depletion as they create the necessary environment for the chlorine based catalytic photochemistry that destroys ozone at around 1 percent per day. Fortunately the conditions rarely last more than a week in the northern hemisphere, but temperatures in the southern hemisphere are around 10° colder and the clouds can persist for several months, creating the Antarctic ozone hole.
Jonathan Shanklin
11 City Road, Cambridge CB1 1DP
From Dr R. G. Stuart
On 12 October of this year a partial solar eclipse will be visible over Great Britain and Europe. During the last two partial eclipses I have observed I have found it rewarding to focus attention on lunar limb features that can often be seen silhouetted against the solar disk during such events.
Only relatively modest equipment is necessary to view the largest features. Using 20×80 binoculars fitted with mylar filters I was able to observe the walls of the craters Drygalski and Amundsen during the eclipse of 1993 May 21. During the eclipse of 1994 May 10 the Montes Rooke that encircle Mare Orientale on the Moon's western ridge were clearly seen. A given limb feature can be positively identified by accurately recording the time that it is seen to make contact with the solar limb.
I developed a method for calculating the selenographic coordinates of the limb features from these times by using the Besselian elements of the eclipse. The details can be found in Mon. Not. R. Astron. Soc., 276, 476 (1995). By consulting a suitable lunar atlas, such as Atlas of the Moon by A. Rückl, that contains detailed maps of the libration zones the observed features can be precisely identified.
I have written a BASIC program employing this method and would like to make it as widely available as possible. Given the observer's position and the local time, the program outputs the selenographic coordinates of features at the contact points of the solar and lunar limbs. The results are accurate to about a kilometre on the lunar surface. The program, called 12OCT96.BAS, may be obtained via anonymous ftp from the internet site feynman.physics.lsa.umich.edu (141.211.96.169) in the directory /pub/astro/eclipse/solar. A detailed description of the program is contained in the file eclipse.ps.
I encourage your readers to take advantage of the upcoming eclipse to add a new dimension to their observing programmes and explore the details of the lunar limb.
Robin G. Stuart
Department of Physics, University of Michigan, 2071 Randall Laboratory, Ann Arbour, MI 48109-1120, USA
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