Read Ebook: Half-hours with the Telescope Being a Popular Guide to the Use of the Telescope as a Means of Amusement and Instruction. by Proctor Richard A Richard Anthony

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But the telescope is out of focus, therefore we must turn the small focussing screw. Observe the charming chromatic changes--green, and red, and blue light, purer than the hues of the rainbow, scintillating and coruscating with wonderful brilliancy. As we get the focus, the excursions of these light flashes diminish until--if the weather is favourable--the star is seen, still scintillating, and much brighter than to the naked eye, but reduced to a small disc of light, surrounded with a slight glare. If after obtaining the focus the focussing rack work be still turned, we see a coruscating image as before. In the case of a very brilliant star these coruscations are so charming that we may be excused for calling the observer's attention to them. The subject is not without interest and difficulty as an optical one. But the astronomer's object is to get rid of all these flames and sprays of coloured light, so that he has very little sympathy with the admiration which Wordsworth is said to have expressed for out-of-focus views of the stars.

We pass to more legitimate observations, noticing in passing that Sirius is a double star, the companion being of the tenth magnitude, and distant about ten seconds from the primary. But our beginner is not likely to see the companion, which is a very difficult object, vowing to the overpowering brilliancy of the primary.

Orion affords the observer a splendid field of research. It is a constellation rich in double and multiple stars, clusters, and nebulae. We will begin with an easy object.

The star is an interesting object, on account of its colour and brilliance, and as one of the most remarkable variables in the heavens. It was first observed to be variable by Sir John Herschel in 1836. At this period its variations were "most marked and striking." This continued until 1840, when the changes became "much less conspicuous. In January, 1849, they had recommenced, and on December 5th, 1852, Mr. Fletcher observed Orionis brighter than Capella, and actually the largest star in the northern hemisphere." That a star so conspicuous, and presumably so large, should present such remarkable variations, is a circumstance which adds an additional interest to the results which have rewarded the spectrum-analysis of this star by Mr. Huggins and Professor Miller. It appears that there is decisive evidence of the presence in this luminary of many elements known to exist in our own sun; amongst others are found sodium, magnesium, calcium, iron, and bismuth. Hydrogen appears to be absent, or, more correctly, there are no lines in the star's spectrum corresponding to those of hydrogen in the solar spectrum. Secchi considers that there is evidence of an actual change in the spectrum of the star, an opinion in which Mr. Huggins does not coincide. In the telescope Betelgeuse appears as "a rich and brilliant gem," says Lassell, "a rich topaz, in hue and brilliancy differing from any that I have seen."

Turn next to , the brightest star below the belt. This is a very noted double, and will severely test our observer's telescope, if small. The components are well separated , compared with many easier doubles; the secondary is also of the seventh magnitude, so that neither as respects closeness nor smallness of the secondary, is Rigel a difficult object. It is the combination of the two features which makes it a test-object. Kitchener says a 1-3/4-inch object-glass should show Rigel double; in earlier editions of his work he gave 2-3/4-inches as the necessary aperture. Smyth mentions Rigel as a test for a 4-inch aperture, with powers of from 80 to 120. A 3-inch aperture, however, will certainly show the companion. Rigel is an orange star, the companion blue.

Turn next to the northernmost of the set of three stars in the head of Orion. This is a triple star, though an aperture of 3 inches will show it only as a double. The components are 5" apart, the colours pale white and violet. With the full powers of a 3-1/2-inch glass a faint companion may be seen above .

The star , the lowest in the belt, may be tried with a 3-1/2-inch glass. It is a close double, the components being nearly equal, and about 2-1/2" apart .

For a change we will now try our telescope on a nebula, selecting the great nebula in the Sword. The place of this object is indicated in Plate 2. There can be no difficulty in finding it since it is clearly visible to the naked eye on a moonless night--the only sort of night on which an observer would care to look at nebulae. A low power should be employed.

The nebula is shown in Plate 3 as I have seen it with a 3-inch aperture. We see nothing of those complex streams of light which are portrayed in the drawings of Herschel, Bond, and Lassell, but enough to excite our interest and wonder. What is this marvellous light-cloud? One could almost imagine that there was a strange prophetic meaning in the words which have been translated "Canst thou loose the bands of Orion?" Telescope after telescope had been turned on this wonderful object with the hope of resolving its light into stars. But it proved intractable to Herschel's great reflector, to Lassell's 2-feet reflector, to Lord Rosse's 3-feet reflector, and even partially to the great 6-feet reflector. Then we hear of its supposed resolution into stars, Lord Rosse himself writing to Professor Nichol, in 1846, "I may safely say there can be little, if any, doubt as to the resolvability of the nebula;--all about the trapezium is a mass of stars, the rest of the nebula also abounding with stars, and exhibiting the characteristics of resolvability strongly marked."

It was decided, therefore, that assuredly the great nebula is a congeries of stars, and not a mass of nebulous matter as had been surmised by Sir W. Herschel. And therefore astronomers were not a little surprised when it was proved by Mr. Huggins' spectrum-analysis that the nebula consists of gaseous matter. How widely extended this gaseous universe may be we cannot say. The general opinion is that the nebulae are removed far beyond the fixed stars. If this were so, the dimensions of the Orion nebula would be indeed enormous, far larger probably than those of the whole system whereof our sun is a member. I believe this view is founded on insufficient evidence, but this would not be the place to discuss the subject. I shall merely point out that the nebula occurs in a region rich in stars, and if it is not, like the great nebula in Argo, clustered around a remarkable star, it is found associated in a manner which I cannot look upon as accidental with a set of small-magnitude stars, and notably with the trapezium which surrounds that very remarkable black gap within the nebula. The fact that the nebula shares the proper motion of the trapezium appears inexplicable if the nebula is really far out in space beyond the trapezium. A very small proper motion of the trapezium would long since have destroyed the remarkable agreement in the position of the dark gap and the trapezium which has been noticed for so many years.

But whether belonging to our system or far beyond it, the great nebula must have enormous dimensions. A vast gaseous system it is, sustained by what arrangements or forces we cannot tell, nor can we know what purposes it subserves. Mr. Huggins' discovery that comets have gaseous nuclei, may suggest the speculation that in the Orion nebula we see a vast system of comets travelling in extensive orbits around nuclear stars, and so slowly as to exhibit for long intervals of time an unchanged figure. "But of such speculations" we may say with Sir J. Herschel "there is no end."

To return to our telescopic observations:--The trapezium affords a useful test for the light-gathering power of the telescope. Large instruments exhibit nine stars. But our observer may be well satisfied with his instrument and his eye-sight if he can see five with a 3-1/2-inch aperture. A good 3-inch glass shows four distinctly. But with smaller apertures only three are visible.

The whole neighbourhood of the great nebula will well repay research. The observer may sweep over it carefully on any dark night with profit. Above the nebula is the star-cluster 362 H. The star below the nebula is involved in a strong nebulosity. And in searching over this region we meet with delicate double, triple, and multiple stars, which make the survey interesting with almost any power that may be applied.

Above the nebula is the star , a multiple star. To an observer with a good 3-1/2-inch glass appears as an octuple star. It is well seen, however, as a fine multiple star with a smaller aperture. Some of the stars of this group appear to be variable.

The star Orionis is an unequal, easy double, the components being separated by nearly seven seconds. The primary is orange, the smaller star smalt-blue .

The middle star of the belt has a distant blue companion. This star, like , is nebulous. In fact, the whole region within the triangle formed by stars , and is full of nebulous double and multiple stars, whose aggregation in this region I do not consider wholly accidental.

We have not explored half the wealth of Orion, but leave much for future observation. We must turn, however, to other constellations.

Below Orion is Lepus, the Hare, a small constellation containing some remarkable doubles. Among these we may note , a white star with a scarlet companion; , a yellow and garnet double; and , a double star, white and pale violet, with a distant red companion. The star Leporis is a rather close double, white with a small green companion. The intensely red star R Leporis will be found in the position indicated in the map.

Still keeping within the boundary of our map, we may next turn to the fine cluster 2 H in Monoceros. This cluster is visible to the naked eye, and will be easily found. The nebula 2 H is a remarkable one with a powerful telescope.

The star 11 Monocerotis is a fine triple star described by the elder Herschel as one of the finest sights in the heavens. Our observer, however, will see it as a double . Monocerotis is an easy double, yellow and lavender.

We may now leave the region covered by the map and take a survey of the heavens for some objects well seen at this season.

Towards the south-east, high up above the horizon, we see the twin-stars Castor and Pollux. The upper is Castor, the finest double star visible in the northern heavens. The components are nearly equal and rather more than 5" apart . Both are white according to the best observers, but the smaller is thought by some to be slightly greenish.

Pollux is a coarse but fine triple star . The components orange, grey, and lilac.

There are many other fine objects in Gemini, but we pass to Cancer.

The star Cancri is a wide double, the colours orange and blue.

Procyon, the first-magnitude star between Praesepe and Sirius, is finely coloured--yellow with a distant orange companion, which appears to be variable.

Below the Twins, almost in a line with them, is the star Hydrae, called Al Fard, or "the Solitary One." It is a 2nd magnitude variable. I mention it, however, not on its own account, but as a guide to the fine double Hydrae. This star is the middle one of a group of three, lying between Pollux and Al Fard rather nearer the latter. The components of Hydrae are separated by about 3-1/2" . The primary is of the fourth, the companion of the eighth magnitude; the former is yellow, the latter a ruddy purple. The period of Hydrae is about 450 years.

The constellation Leo Minor, now due east and about midway between the horizon and the zenith, is well worth sweeping over. It contains several fine fields.

Let us next turn to the western heavens. Here there are some noteworthy objects.

To begin with, there are the Pleiades, showing to the naked eye only six or seven stars. In the telescope the Pleiades appear as shown in Plate 3.

The Hyades also show some fine fields with low powers.

Aldebaran, the principal star of the Hyades, as also of the constellation Taurus, is a noted red star. It is chiefly remarkable for the close spectroscopic analysis to which it has been subjected by Messrs. Huggins and Miller. Unlike Betelgeuse, the spectrum of Aldebaran exhibits the lines corresponding to hydrogen, and no less than eight metals--sodium, magnesium, calcium, iron, bismuth, tellurium, antimony, and mercury, are proved to exist in the constitution of this brilliant red star.

A HALF-HOUR WITH LYRA, HERCULES, CORVUS, CRATER, ETC.

The observations now to be commenced are supposed to take place during the second quarter of the year,--at ten o'clock on the 20th of April, or at nine on the 5th of May, or at eight on the 21st of May, or at seven on the 5th of June, or at hours intermediate to these on intermediate days.

We again look first for the Great Bear, now near the zenith, and thence find the Pole-star. Turning towards the north, we see Cassiopeia between the Pole-star and the horizon. Towards the north-west is the brilliant Capella, and towards the north-east the equally brilliant Vega, beneath which, and somewhat northerly, is the cross in Cygnus. The Milky Way passes from the eastern horizon towards the north , and so round to the western horizon.

In selecting a region for special observation, we shall adopt a different plan from that used in the preceding "half-hour." The region on the equator and towards the south is indeed particularly interesting, since it includes the nebular region in Virgo. Within this space nebulae are clustered more closely than over any corresponding space in the heavens, save only the greater Magellanic cloud. But to the observer with telescopes of moderate power these nebulae present few features of special interest; and there are regions of the sky now well situated for observation, which, at most other epochs are either low down towards the horizon or inconveniently near to the zenith. We shall therefore select one of these, the region included in the second map of Plate 2, and the neighbouring part of the celestial sphere.

At any of the hours above named, the constellation Hercules lies towards the east. A quadrant taken from the zenith to the eastern horizon passes close to the last star of the Great Bear's tail, through , a star in Bootes' head, near Herculis, between the two "Alphas" which mark the heads of Hercules and Ophiuchus, and so past Ophiuchi, a third-magnitude star near the horizon. And here we may turn aside for a moment to notice the remarkable vertical row of six conspicuous stars towards the east-south-east; these are, counting them in order from the horizon, , , and Ophiuchi, , , and Serpentis.

Let the telescope first be directed towards Vega. This orb presents a brilliant appearance in the telescope. Its colour is a bluish-white. In an ordinary telescope Vega appears as a single star, but with a large object-glass two distant small companions are seen. A nine-inch glass shows also two small companions within a few seconds of Vega. In the great Harvard refractor Vega is seen with no less than thirty-five companions. I imagine that all these stars, and others which can be seen in neighbouring fields, indicate the association of Vega with the neighbouring stream of the Milky Way.

Let our observer now direct his telescope to the star Lyrae. Or rather, let him first closely examine this star with the naked eye. The star is easily identified, since it lies to the left of Vega, forming with a small equilateral triangle. A careful scrutiny suffices to indicate a peculiarity in this star. If our observer possesses very good eye-sight, he will distinctly recognise it as a "naked-eye double"; but more probably he will only notice that it appears lengthened in a north and south direction. In the finder the star is easily divided. Applying a low power to the telescope itself, we see Lyrae as a wide double, the line joining the components lying nearly north and south. The southernmost component is called ^, the other ^. Seen as a double, both components appear white.

Now, if the observer's telescope is sufficiently powerful, each of the components may be seen to be itself double. First try ^, the northern pair. The line joining the components is directed as shown in Plate 3. The distance between them is 3"?2, their magnitudes 5 and 6-1/2, and their colours yellow and ruddy. If the observer succeeds in seeing ^ fairly divided, he will probably not fail in detecting the duplicity of ^, though this is a rather closer pair, the distance between the components being only 2"?6. The magnitudes are 5 and 5-1/2, both being white. Between ^ and ^ are three faint stars, possibly forming with the quadruple a single system.

Let us next turn to the third star of the equilateral triangle mentioned above--viz. to the star Lyrae. This is a splendid but easy double. It is figured in Plate 3, but it must be noticed that the figure of and the other nine small figures are not drawn on the same scale as Lyrae. The actual distance between the components of Lyra is 44", or about one-fourth of the distance separating ^ from ^. The components of are very nearly equal in magnitude, in colour topaz and green, the topaz component being estimated as of the fifth magnitude, the green component intermediate between the fifth and sixth magnitudes.

We may now turn to a star not figured in the map, but readily found. It will be noticed that the stars , , , and form, with two small stars towards the left, a somewhat regular hexagonal figure--a hexagon, in fact, having three equal long sides and three nearly equal short sides alternating with the others. The star Lyrae forms the angle next to . It is a wide and unequal double, as figured in Plate 3. The larger component is azure blue; the smaller is violet, and, being only of the ninth magnitude, is somewhat difficult to catch with apertures under 3 inches.

The star ^ Lyrae is orange, ^ blue. In the same field with these are seen many other stars.

The stars ^ and ^ may also be seen in a single field, the distance between them being about half the moon's mean diameter. The former is quadruple, the components being yellow, bluish, pale blue, and blue.

Turn next to the stars and Lyrae, the former a multiple, the latter an unequal double star. It is not, however, in these respects that these stars are chiefly interesting, but for their variability. The variability of has not indeed been fully established, though it is certain that, having once been less bright, is now considerably brighter than . The change, however, may be due to the variation of alone. This star is one of the most remarkable variables known. Its period is 12d. 21h. 53m. 10s. In this time it passes from a maximum brilliancy--that of a star of the 3?4 magnitude--to a minimum lustre equal to that of a star of the 4?3 magnitude, thence to the same maximum brilliancy as before, thence to another minimum of lustre--that of a star of the 4?5 magnitude--and so to its maximum lustre again, when the cycle of changes recommences. These remarkable changes seem to point to the existence of two unequal dark satellites, whose dimensions bear a much greater proportion to those of the bright components of Lyrae than the dimensions of the members of the Solar System bear to those of the sun. In this case, at any rate, the conjecture hazarded about Algol, that the star revolves around a dark central orb, would be insufficient to account for the observed variation.

Nearly midway between and lies the wonderful ring-nebula 57 M, of which an imperfect idea will be conveyed by the last figure of Plate 3. This nebula was discovered in 1772, by Darquier, at Toulouse. It is seen as a ring of light with very moderate telescopic power. In a good 3-1/2-inch telescope the nebula exhibits a mottled appearance and a sparkling light. Larger instruments exhibit a faint light within the ring; and in Lord Rosse's great Telescope "wisps of stars" are seen within, and faint streaks of light stream from the outer border of the ring. This nebula has been subjected to spectrum-analysis by Mr. Huggins. It turns out to be a gaseous nebula! In fact, ring-nebulae--of which only seven have been detected--seem to belong to the same class as the planetary nebulae, all of which exhibit the line-spectrum indicative of gaseity. The brightest of the three lines seen in the spectrum of the ring-nebula in Lyra presents a rather peculiar appearance, "since it consists," says Mr. Huggins, "of two bright dots, corresponding to sections of the ring, and between these there is not darkness, but an excessively faint line joining them. This observation makes it probable that the faint nebulous matter occupying the central portion is similar in constitution to that of the ring."

The constellation Hercules also contains many very interesting objects. Let us first inspect a nebula presenting a remarkable contrast with that just described. I refer to the nebula 13 M, known as Halley's nebula . This nebula is visible to the naked eye, and in a good telescope it is a most wonderful object: "perhaps no one ever saw it for the first time without uttering a shout of wonder." It requires a very powerful telescope completely to resolve this fine nebula, but the outlying streamers may be resolved with a good 3-inch telescope. Sir W. Herschel considered that the number of the stars composing this wonderful object was at least 14,000. The accepted views respecting nebulae would place this and other clusters far beyond the limits of our sidereal system, and would make the component stars not very unequal to our own sun. It seems to me far more probable, on the contrary, that the cluster belongs to our own system, and that its components are very much smaller than the average of separate stars. Perhaps the whole mass of the cluster does not exceed that of an average first-magnitude star.

The nebulae 92 M and 50 H may be found, after a little searching, from the positions indicated in the map. They are both well worthy of study, the former being a very bright globular cluster, the latter a bright and large round nebula. The spectra of these, as of the great cluster, resemble the solar spectrum, being continuous, though, of course, very much fainter.

The star Herculis is a wide and easy double--a beautiful object. The components, situated as shown in Plate 3, are of the fourth and eighth magnitude, and coloured respectively greenish-white and grape-red.

The star Herculis is not shown in the map, but may be very readily found, lying between the two gammas, Herculis and Serpentis , rather nearer the latter. It is a wide double, the components of fifth and seventh magnitude, the larger yellowish-white, the smaller ruddy yellow.

Ras Algethi, or Herculis, is also beyond the limits of the map, but may be easily found by means of Map 2, Frontispiece. It is, properly speaking, a multiple star. Considered as a double, the arrangement of the components is that shown in Plate 3. The larger is of magnitude 3-1/2, the smaller of magnitude 5-1/2; the former orange, the latter emerald. The companion stars are small, and require a good telescope to be well seen. Ras Algethi is a variable, changing from magnitude 3 to magnitude 3-1/2 in a period of 66-1/3 days.

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