SUMMER VISIT TO THE ROYAL GREENWICH OBSERVATORY, HERSTMONCEUX, SUSSEX

By kind permission of the Astronomer Royal, the Summer Visit this year was made to the Royal Greenwich Observatory at Herstmonceux, Sussex, on 29 June.

Arriving at the Observatory the party of 30 members was conducted by Mr Richards to the building which, in addition to housing the Nautical Almanac Office, accommodates the complex equipment providing our standard time. Mr Richards explained that, in the past, the accuracy of the time standards had been dependent on chronometers checked by star transits. Nowadays the ‘clock’ is purely an electronic device, the basic drive being obtained from a number of 100 kc/sec crystal oscillators, each of which is housed in a separate isolated compartment, partially evacuated and temperature controlled to the order of one part in a thousand. The outputs of the individual oscillators are also compared and checked against each other. The 100 kc/sec output is passed through Dekatron count-down circuits to provide a highly stable output a t I kc/sec, and is then fed to an electro-mechanical phonic motor which again reduces the frequency to I clsec, accurate to an order of I millisec. The times are checked by the use of a transit telescope, but the star transits used for time- checking purposes are now recorded automatically.

Fig. I . I’art of the main Observatory block, showing the dome housing the 36 in. Yapp telescope

The familiar six ‘pips’ are provided by the phonic motors and are passed to the BBC and other organizations every 15 minutes.

The time signals radiated by Rugby Radio are no longer derived from Herstmonceux, but come from another crystal source at Rugby. The signals, however, are frequently checked against the Royal Observatory standard, and in addition, checks are made by radio against the standard time-signals of other countries.

The party was shown the 7 in. Cooke transit telescope used for star- transit checks. As part of a long-term programme for checking star declina-

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tions, the transit times are recorded directly on punched cards for computer processing, and the declinations are recorded on film.

The six domes in the main Observatory block house five telescopes, com- prising 36 in. and 30 in. reflectors and 28 in., 26 in. and 13 in. refractors. The 26 in. refractor was built by Sir Howard Parsons of Dublin in 1896, and has a 13 in. refractor mounted alongside as well as a smaller ‘finder’ telescope. This telescope is used mainly for parallax checks-the main telescope being used for photographic work only, whilst the subsidiary 13 in. telescope provides the observer with visual means of checking any apparent slight inaccuracies in the automatic following mechanism, arising from the slight ‘wobble’ of the earth on its axis or other sources. Mr Richards took the opportunity of demonstrating the rotating dome and the rising and falling floor.

The largest telescope at present available at Herstmonceux is the 36 in. Yapp telescope of the Cassegrain type, which gives the advantage of a long focal length with comparatively short physical length. Made by Grubb-Parsons of Newcastle in 1932, it is now used almost exclusively for spectroscopic work.

Returning to the outside of the dome, Mr Richards pointed out the domes housing the other instruments, mentioning that the 28 in. refractor is now the only one used for visual work--on double stars. The 13 in. refractor is used for cataloguing work-again part of a long-term programme, whilst the 30 in. reflector is used with a Coude spectrograph. Work is being carried out on a building intended to house the new 98 in. Isaac Newton telescope now being constructed by Grubb-Parsons.

Finally, we noted with interest the Observatory Meteorological Station on the corner of the Observatory block, and returned to London after this very worth-while visit. N. MOORCROFT

BOOK REVIEW THE AMATEUR WEATHER FORECASTER. By. E. S. Gates. London (Harrap &

Co.). 1965. Pp. 94. 45 Figs. 6s. This compact and attractive looking booklet is designed for the popular market. The

text is very smple and there are few pages without ahiagram. Thd author’s aim is to encourage greater interest in weather study and to enable any intelligent layman to make some sense out of published weather maps and forecasts. The general layout is good. S i x short chapters on elementary meteorology lead up to a seventh on the central theme of ‘Making your own weather forecasts’, in which the reader is shown how to combine personal observation with an interpretation of daily weather maps. A t the end are six Appendices, including one on ‘Making your own meteorological instruments’.

Unfortunately, apart from its superlicial attractiveness there is little to commend in the book. If it were only a short popular exposition, much could be forgiven. But since the author claims a certain standing for his work by recommending it to schools, cadets and scouts, some minimum scientific standards must be observed. There is regrettably far too much in the book that is either out of date or quite erroneous. Amongst many other examples are: ‘The cloud-base is governed by the height of the dew-point . . .’; As the cloud thickens and lowers with the approach of rain the halo becomes larger.’ Fig. 23, entitled ‘A thunder cloud‘, shows a cumulonimbus-shaped cloud which is labelled Nimbo- stratus a t the bottom and False Cirrus a t the top. Fig. 30 shows the life-cycle of a typical depression extending over 8-10 days, with the occlusion process starting after 6-7 days. Appendix 11, on ‘The meaning of terms used in weather forecasts’, is almost wholly out of date and useless.

physics masters who wish to introduce their pupils to elementary meteorology, or readers of this magazine wanting to interest their uninformed friends in the weather, will be equally disappointed in this booklet. Despite its attractive production, the numerous faults of detail make it impossible for it to be recommended. P.G.W.

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