OBSERVATION OF T H E A U R O R A BOREALIS (An article on " Aurora Borealis '' by Mr. Paton appeared an " Weather ", pol. 1, p . 6 .

Readers may be interested in the technique of auroral observation and this article has bean Provided to assist amateur observers.)

During the next few years, it is expected that the Aurora Borealis or Northern Lights will occur more frequently and will be visible at places much further south than usual. This is due to the fact that the aurora is associated with sunspots. The area of the sun's disc covered by these spots waxes and wanes in a fairly regular mannner, reaching a maximum every 11 years. The next maximum is expected in 1948-49. Simultaneous photography at different stations allows the determination of the exact position and rate of movement of auroral features.

VISUAL OBSERVATIOK OF AURORA

Pmelj- visual observation of the aurora from widely scattered places over the country is a useful supplement to photography. This may be done most readily in country places. where artificial light and smoke do not interfere with observations of the night sky. Suitably situated observers should make a point of taking an occasional look at the night sky and should note when an!- unusual illumination is present. This may merely be a dawn-like glow above the northern horizon (aurora borealis means literally " northern dawn " 1 or it may be the feverish activity better described by the name " merry dancers ", by which it is known in North Scotland and the Orkney and Shetland Islands. Of course, it can be seen only on clear nights or through breaks in cloud, for it occurs in thc atmosphere at heights above 60 miles, well above the levels a t which clouds are present. Observers should be very careful to distinguish it from reflexions of moonlight or the artificial light of towns on low clouds. The auroral log might take the following form (e.g. on six consecutive nights) :-

1st : Sky cloud-covered. 2nd: Ditto. 3rd : Clear sky. No aurora observed. 4th : Ditto. 5th : Clear. Well-marked glow on the northern horizon. 6th : Bright quiet arc across the northern sky observed first at 19.30 G.M.T.

The summit of the arc passes through the Great Bear. [A sketch showing the position of the boundary of the arc against the star background would be useful.] The arc is white in colour with just a tinge of green here and there. At 20.10 streamers observed darting upwards from the arc reaching overhead to Andromeda. The summits of these rays are red. All activity ceases by 21.05 leaving only a weak glow above the northern horizon.

If the observer is free to observe continuously for a period, his observations may be of great value, especially if accurate times and positions against the stellar background are kept. I t is difficult to keep a log while observing out of doors in semi-darkness, but if a helper is available the observer may stand outside, near a window or door (or even inside at a window in a darkened room) while his assistant, sitting in a lighted room with a watch or clock available, records the observations.

20.08 : Lower edge of arc passes exactly half-way between the pointers

20.10: The sharply-defined lower edge of the arc passes now exactly

20.12 : A bright ray passes overhead through the Pole Star. The exact position of the observer should be given, i.e. latitude and longitude

to within a minute, and the watch or clock should be checked against the next B.B.C. time signal, corrections to give exact time G.M.T. being applied.

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For example :-

It is moving higher. of the Great Bear.

through the upper star of the two pointers.

SKETCHES OF THE AURORA ON STAR MAPS Specially prepared star maps are used to assist in making accurate observations

and when features are very sharply defined. The observer's watch should be checked against a B.B.C. time signal or the telephone speaking clock if this is .available. The auroral features should be drawn in pencil on the star maps, just as they are seen among the stars in the sky. A record covering a much larger .area of the sky than is photographed by the auroral camera is thus obtained.

I I

I I Fig. 1. Typical sketch of aurora on star map.

The star map may be used : 1. To show the occurrence and general distribution of auroral activity

across the sky, giving an indication of the colours appearing in different parts of the sky, as in Figure 1.

2. To show accurately the position among the stars of a particular auroral feature at a specified time. The position of a quiet homogeneous arc may be precisely indicated by this method. When drawing such an arc on the maps be careful to mark accurately the position of the lower border at either end (i.e. at the horizon) and where it is highest in the sky at the same moment. If there is ray activity, try to record carefully the exact position of the highest points of the ray. It should be emphasized that these observations are of value only when (a) the auroral features are sufficiently sharply defined to be drawn accurately relative to the stars ; (b ) the time is given accurately to the nearest half-minute for each feature drawn ; and (c) the position of the observer is given, i.e. the latitude and longitude to within 30" and the height above M.S.L. to within about 25 feet.

VACANCIES I N THE METEOROLOGICAL SERVICE

JAMES PATON

The Meteorological Office is in need of some hundreds of assistants during 1947 for plotting charts, taking meteorological observations and similar work. Candidates must be holders of a School Certificate with credit in Mathematics or a Science subject. Entrants will serve initially as unestablished temporary assistants on a weekly wage, but suitable candidates will have an opportunity of being considered by the Civil Service Commission for establishment and permanent retention.

Special consideration is being given to ex-airmen and ex-W.A.A.F. meteorologists who have served satisfactorily for two years in the Meteorological Service. It is understood that rates of pay for established staff will not be less than : Men LlSO at age 18, rising by increments of f;15 to L380 per annum ; Women A180 at age 18, L195 at age 19. rising by increments of ,I10 to L320 per annum. There are promotion prospects, but full particulars can be obtained from the Under-Secretary of State, Air Ministry, S.Z(b) , Cornwall House, Waterloo Bridge Road, London, S.E. 1.

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