J. Brit. Astron. Assoc., 106, 1, 1996

Letters

(Note: The Association is not responsible for individual opinions expressed in articles, reviews, letters or reports of any kind.)


Seeing Venus in daylight

From Dr P. C. Leyland

In his fascinating short paper (J. Brit. Astron. Assoc., 105(6), 1995), Edward Ellis opened with the sentence 'It is not easy to find Venus with the naked eye in broad daylight'. I beg to differ. In certain circumstances it is very easy indeed.

On the morning of 1994 December 20 I saw Venus shining brightly in the southern sky as I brought in the milk from my doorstep at about 07.45. Around in the northwest the Moon was getting lower in the sky, it being two days after full. Shortly after 08.00 the Sun rose; Venus was still very obvious.

At around 08.30, I began my 13-mile motorcycle ride to Oxford University, arriving a few minutes before 09.00. Because I had taken care to notice the separation between the Sun and Venus, it was straightforward to find the planet again throughout my journey although, I must add, I attempted the observation only when stationary at road junctions or traffic lights! During this journey I had the great satisfaction of being able to see the Moon, Sun and Venus in the sky at the same time. The planet was still visible, although a little more difficult to spot, by the time I had to go indoors to begin work.

I reported these observations to the Usenet sci.astro newsgroup. In response I received several e-mail messages from others who had duplicated my observations. Better, I prompted a colleague at the University, Dr John Elder, to attempt the same. Two mornings later, he e-mailed me with the news that he also had followed the planet without any difficulty until almost 10.00.

Having checked in the Association's Handbook, I note that the planet was at magnitude –4.5 – almost its maximum. The great brightness, the favourable elongation of around 45°, and the low altitude of the midwinter Sun undoubtedly made the observation relatively easy.

Paul C. Leyland

18 Oxford Road, Oakley, Aylesbury HP18 9RE


From Mr S. Anderson

Please may I add to Mr Ellis' list of daylight sightings of Venus, and in my case Jupiter as well, from an 'unexotic site'(1): Luton, Bedfordshire in 1973. I was working at the Whitbread Brewery Research Laboratories on the third floor of the Oakley Road Brewery, with a clear western aspect over Dunstable Downs.

My intention was to observe Comet Kohoutek. Initially I picked up Venus and Jupiter with binoculars, and using a standard reference line on the floor I marked on the window the position of the two planets. Having three marks to go by, I observed both planets with the naked eye on successive days approximately 30 minutes earlier each day. Each time I marked their positions on the window and so had a trace line that I could note where to look on the next day. This procedure was continued over a period of two weeks – only interrupted once by an over-zealous cleaner who thoroughly cleaned all marks off the window!

Eventually both Venus and Jupiter were easily seen at 13.00 GMT – the British weather then took over and further observations were halted by cloud and rain.

The art of daylight observations of planets and bright stars is to train the eye to focus at infinity. If one looks at a clear sky there is nothing for the eye to focus on. In my case I used the hills at Dunstable to give me a relaxed and 'infinite' focus before I turned to the planets in question.

Steven Anderson

St. Kew Inn, St. Kew, Churchtown, Bodmin, Cornwall PL30 3HB

1: Muirden, James, Astronomy with Binoculars, Faber & Faber, 1976, p.59


More British impact craters

From Dr D. W. Hughes

I am afraid that R. L. Stratford (Letters, 1995 December) was being a touch too positive in his assertion that 'at the present time there are no known British impact structures'. His Midlands pair were preceded by another astroblem twin in Scotland. A paper by the Liverpool geologist Flinn (Proceedings of the Geological Society of London, No. 1663, 131 (1970)) suggested that St Magnus Bay and The Firth, in the Shetland Islands, are probably submarine meteorite craters. These have diameters of eleven and fourteen km respectively and both bays are about 165m deep – a quite unprecedented depth for coastal waters in this region. Both craters are oval in shape because of the east-west geological compression that the area has suffered.

It is suggested that the two craters were formed in late Tertiary times and that the subsequent ice age has severely eroded them, removing the rims and 'cleaning out' the centres. The craters are just over thirty kilometres apart.

David W. Hughes

Department of Physics, University of Sheffield, The Hicks Building, Sheffield S3 7RH


The sad tale of 'Planet Sallit'

From Mr M. P. Mobberley

The recent alleged discovery of an asteroid by George Sallit (reported widely in the national newspapers and on television on 1995 December 11) yet again proves that sensationalism almost always takes precedence over fact in the media. It also shows that a powerful telescope and CCD camera can be lethal weapons, capable of destroying the credibility of amateur astronomers.

The facts are these. In October of this year, Mr Sallit imaged a galaxy close to the ecliptic plane. A friend spotted a small streak on the image some time later. Nick James measured the two consecutive images which showed the streak and concluded that it was quite likely that an asteroid had been imaged. There was no obvious candidate for the object on the MPC (Minor Planet Center) files and so it was possible that a new asteroid, for which no calculated orbit exists, had been spotted. Mr James correctly cautioned Mr Sallit that his claim was unproven without follow-up observations. How can you prove to have discovered something when nobody else can ever find it again? This was, therefore, not an asteroid discovery and it is not an unusual event.

The telescopes and CCD cameras in amateur hands are easily capable of recording 'new' asteroids and they frequently do. The ecliptic is teeming with tens of thousands of uncharted asteroids within amateur CCD range, but without enough astrometric observations to determine an orbit, the object is unproven and lost for ever. Indeed Gareth Williams of the MPC has pointed out(1) that over 7,000 new minor planets have been 'discovered' so far in 1995, all of which have been observed on two or more nights. In addition, 21,000 reports have been received of objects seen on one night only, like George Sallit's object.

The kind of publicity generated by the media in this fiasco belittles the sheer hard grind of the likes of Brian Manning and Stephen Laurie who strive painstakingly to follow and measure their asteroids, month after month, year after year. It also damages our delicate links with professional astronomers, nurtured over many years of building up trust. Let us hope that we never again see such a ridiculous story unfold in the press.

Martin Mobberley

Denmara, Cross Green, Cockfield, Bury St Edmunds, Suffolk IP30 0LQ

1: The Guardian, 1995 Dec. 13, Letters section


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