Through the Telescope

by James Baikie

Telescope House and 8½-inch 'with' Reflector.

Should it not be possible to obtain such a luxury, however, undoubtedly the next best is fairly outside. No one who has garden room should ever think of observing from within doors. If the telescope be used at an open window its definition will be impaired by air-currents. The floor of the room will communicate tremors to the instrument, and every movement of the observer will be accompanied by a corresponding movement of the object in the field, with results that are anything but satisfactory. In some cases no other position is available. If this be so, Webb's advice must be followed, the window opened as widely and as long beforehand as possible, and the telescope thrust out as far as is convenient. But these precautions only palliate the evils of indoor observation. The open air is the best, and with a little care in wrapping up the observer need run no risk.

Provide the telescope, if a refractor, with a dew-cap. Without this precaution dew is certain to gather upon the object-glass, with the result of stopping all observation until it is removed, and the accompanying risk of damage to the objective itself. Some instruments are provided by their makers with dew-caps, and all ought to be; but in the absence of this provision a cap may be easily contrived. A tube of tin three or four times as long as the diameter of the object-glass, made so as to slide fairly stiffly over the object end of the tube where the ordinary cap fits, and blackened inside to a dead black, will remove practically all risk. The blackening may be done with lamp-black mixed with spirit varnish. Some makers—Messrs. Cooke, of York, for instance—line both tube and dew-cap with black velvet. This ought to be ideal, and might be tried in the case of the dew-cap by the observer. Finders are rarely fitted with dew-caps, but certainly should be; the addition will often save trouble and inconvenience.

Be careful to cover up the objective or mirror with its proper cap before removing it into the house. If this is not done, dewing at once results, the very proper punishment for carelessness. This may seem a caution so elementary as scarcely to be worth giving; but it is easier to read and remember a hint than to have to learn by experience, which in the case of a reflector will almost certainly mean a deteriorated mirror film. Should the mirror, if you are using a reflector, become dewed in spite of all precautions, do not attempt to touch the film while it is moist, or you will have the pleasure of seeing it scale off under your touch. Bring it into a room of moderate temperature, or stand it in a through draught of dry air until the moisture evaporates; and should any stain be left, make sure that the mirror is absolutely dry before attempting to polish it off. With regard to this matter of polishing, touch the mirror as seldom as possible with the polishing-pad. Frequent polishing does far more harm than good, and the mirror, if kept carefully covered when not in use, does not need it. A fold of cotton-wool between the cap and the mirror will, if occasionally taken out and dried, help greatly to preserve the film.

Next comes a caution which beginners specially need. Almost everyone on getting his first telescope wants to see everything as big as possible, and consequently uses the highest powers. This is an entire mistake. For a telescope of 2½ inches aperture two eye-pieces, or at most three, are amply sufficient. Of these, one may be low in power, say 25 to 40, to take in large fields, and, if necessary, to serve in place of a finder. Such an eye-piece will give many star pictures of surprising beauty. Another may be of medium power, say 80, for general work; and a third may be as high as 120 for exceptionally fine nights and for work on double stars. Nominally a 2½ inch, if of very fine quality, should bear on the finest nights and on stars a power of 100 to the inch, or 250. Practically it will do nothing of the sort, and on most nights the half of this power will be found rather too high. Indeed, the use of high powers is for many reasons undesirable. A certain proportion of light to size must be preserved in the image, or it will appear faint and 'clothy.' Further, increased magnifying power means also increased magnification of every tremor of the atmosphere; and with high powers the object viewed passes through the field so rapidly that constant shifting of the telescope is required, and only a brief glimpse can be obtained before the instrument has to be moved again. It is infinitely more satisfactory to see your object of a moderate size and steady than to see it much larger, but hazy, tremulous, and in rapid motion. 'In inquiring about the quality of some particular instrument,' remarks Sir Howard Grubb, 'a tyro almost invariably asks, "What is the highest power you can use?" An experienced observer will ask, "What is the lowest power with which you can do so and so?"'

Do not be disappointed if your first views of celestial objects do not come up to your expectations. They seldom do, particularly in respect of the size which the planets present in the field. A good deal of the discouragement so often experienced is due to the idea that the illustrations in text-books represent what ought to be seen by anyone who looks through a telescope. It has to be remembered that these pictures are, for one thing, drawn to a large scale, in order to insure clearness in detail, that they are in general the results of observation with the very finest telescopes, and the work of skilled observers making the most of picked nights. No one would expect to rival a trained craftsman in a first attempt at his trade; yet most people seem to think that they ought to be able at their first essay in telescopic work to see and depict as much as men who have spent half a lifetime in an apprenticeship to the delicate art of observation. Given time, patience, and perseverance, and the skill will come. The finest work shown in good drawings represents, not what the beginner may expect to see at his first view, but a standard towards which he must try to work by steady practice both of eye and hand. In this connection it may be suggested that the observer should take advantage of every opportunity of seeing through larger and finer instruments than his own. This will teach him two things at least. First, to respect his own small telescope, as he sees how bravely it stands up to the larger instrument so far as regards the prominent features of the celestial bodies; and, second, to notice how the superior power of the large glass brings out nothing startlingly different from that which is shown by his own small one, but a wealth of delicate detail which must be looked for (compare Plate [XV.] with Fig. [22]). A little occasional practice with a large instrument will be found a great encouragement and a great help to working with a small one, and most possessors of large glasses are more than willing to assist the owners of small ones.

Do not be ashamed to draw what you see, whether it be little or much, and whether you can draw well or ill. At the worst the result will have an interest to yourself which no representation by another hand can ever possess; at the best your drawings may in course of time come to be of real scientific value. There are few observers who cannot make some shape at a representation of what they see, and steady practice often effects an astonishing improvement. But draw only what you see with certainty. Some observers are gifted with abnormal powers of vision, others with abnormal powers of imagination. Strange to say, the results attained by these two classes differ widely in appearance and in value. You may not be endowed with faculties which will enable you to take rank in the former class; but at least you need not descend to the latter. It is after all a matter of conscience.

Do not be too hasty in supposing that everybody is endowed with a zeal for astronomy equal to your own. The average man or woman does not enjoy being called out from a warm fireside on a winter's night, no matter how beautiful the celestial sight to be seen. Your friend may politely express interest, but to tempt him to this is merely to encourage a habit of untruthfulness. The cause of astronomy is not likely to be furthered by being associated in any person's mind with discomfort and a boredom which is not less real because it is veiled under quite inadequate forms of speech. It is better to wait until the other man's own curiosity suggests a visit to the telescope, if you wish to gain a convert to the science.

When observing in the open be sure to wrap up well. A heavy ulster or its equivalent, and some form of covering for the feet which will keep them warm, are absolute essentials. See that you are thoroughly warm before you go out. In all probability you will be cold enough before work is over; but there is no reason why you should make yourself miserable from the beginning, and so spoil your enjoyment of a fine evening.

Having satisfied his craving for a general survey of everything in the heavens that comes within the range of his glass, the beginner is strongly advised to specialize. This is a big word to apply to the using of a 2½- or 3-inch telescope, but it represents the only way in which interest can be kept up. It does no good, either to the observer or to the science of astronomy, for him to take out his glass, have a glance at Jupiter and another at the Orion nebula, satisfy himself that the two stars of Castor are still two, wander over a few bright clusters, and then turn in, to repeat the same dreary process the next fine night. Let him make up his mind to stick to one, or at most two, objects. Lunar work presents an attractive field for a small instrument, and may be followed on useful lines, as will be pointed out later. A spell of steady work upon Jupiter will at least prepare the way and whet the appetite for a glass more adequate to deal with the great planet. Should star work be preferred, a fine field is opened up in connection with the variable stars, the chief requirement of work in this department being patience and regularity, a small telescope being quite competent to deal with a very large number of interesting objects.