During the last eight months the astronomer, whether professional or amateur, has very often found himself confronted by such questions as these: What is it? Where is it? Is it really new? Has it never been seen before ? How do they know it is new ? How long will it last? Can I see it? How can I find it? How can I tell it? All very natural questions and some of them easy to answer, while others are at present beyond the range of human knowledge.

It seems very strange to the casual observer, who sees the sky studded with apparently countless stars, that the presence of an additional one should attract such instant notice. He perhaps does not realize that although the stars appear to him countless, and scattered over the sky without any semblance of order, there are really only about two thousand visible at once to the ordinary eye, that not more than three hundred of these are at all conspicuous, and that the astronomer, from long acquaintance, is as familiar with their aspects as with the streets of his native town, so that the appearance of any object of considerable brightness lends an unfamiliar look to that part of the heavens, and at once attracts his notice.

Any one with a little practice may gain a sufficient familiarity with the principal groupings to readily identify a new comet or an inconspicuous planet by its appearance where he knows no star is ordinarily seen.

For instance, almost every one is so well acquainted with the group of bright stars called the Dipper that the appearance among the four stars which make up its "bowl" of a star at all approaching any one of the group in brightness, would be at once noticed as something unusual.

The New Star is a 6tar which suddenly appeared in the middle of a large triangle formed by some of the brighter stars of the constellation Perseus. One of the points of this triangle is formed by the star Algol, one of the longest known and most remarkable of the variable stars. Its exact position is shown by a small circle on the accompanying chart (Fig. 1), which is a copy of one issued by Father Hagen of the Georgetown Observatory, for the convenience of those desiring to observe the star. By holding the chart horizontally, with its top to the left, one will have a good representation of the appearance of the constellation at dark at this season of the year, but he will need a good field-glass to see the New Star.

It was discovered on the evening of Feb. 21, 1901, by the Rev. T. D. Anderson of Edinburg, one of the best known among amateur astronomers, who had already, in 1892, distinguished himself by the discovery of a new star in Auriga, and who has a greater number of discoveries of variable stars to his credit during the last ten years than any other single observer. When first seen, the star's brightness was estimated as 2.7 magnitude; it was evidently brightening rapidly, for on the 22d it had reached the 0.9 magnitude; that is to say, it was twice as bright as on the evening before. The cable message announcing its discovery reached the Harvard College Observatory early in the evening of the 22d, and the observers at once set to work upon the star. Owing to unfavorable weather, observations were made under difficulties, but good estimates, both visual and photometric, were obtained by members of the staff. In the meantime an examination was made of all the photographs of the region taken earlier in the month, resulting in the certainty that as late as the 19th no star so bright as the eleventh magnitude was there. This means that the star had made its upward rush from invisibility in a moderate telescope to a place among the brightest in the heavens in less than three days.

On the 23d the Harvard observations showed the star to have increased to the 0.37 magnitude.

On the evening of the 23d the news had been spread, and other observatories and observers everywhere, both in this country and in Europe, had taken up the work upon the star.

My own observations began on the evening of the 24th, when I found the. star brighter than any other star in the sky, Sirius only excepted. I estimated its magnitude at -0.08, twenty-five times brighter than at Anderson's first observation. On the 25th it had begun to fade fast.

A host of observers were by this time watching the Nova Persei star. It continued to decrease rapidly, until in the middle of March it had reached the fourth magnitude, or a hundred times fainter than when at its brightest. After passing the fourth magnitude, its decrease became slower, and when it had passed too low in he northwest and was los in the wilight, about the end of April, it was still of the sixth magnitude, being decidedly slower to wane than most stars of its class.

(1900.0) 3h 24.4. + 43' 34'.

The New Star In Perseus 78

Fig. 1

Observations were resumed early in October, when it was found at about the seventh magnitude; at my last observation, Dec. 12, it was 7.2 magnitude.

The accompanying diagram (Fig. 2) shows graphically the course of the star's light-changes: the dates run horizontally, from left to right, and the course of its variation in brightness is shown by the heavy line, the high magnitudes being at the top and the faint ones below, as shown in the margin. The star's fluctuations are shown in this way very clearly. This is the common astronomical way of showing such changes. It is called the star's " light-curve."

The most remarkable feature of the star's variation is the series of minor fluctuations, beginning with the commencement of the decrease of light, and continuing to a date later than the beginning of May.

The New Star In Perseus 79

Fig. 2.

The period of these fluctuations was at first less than a day, and the light-range in the neighborhood of half a magnitude, and they increased in both particulars, until at the beginning of May the period was about five days and the light-range about two magnitudes, which is more than double the light-range of any of the ordinary short-period variable stars of similar period.

In the month of August, MM. Flammarion and An-toniadi, at the Observatory of Juvisy, in France, found, on some negatives taken on the 19th of the month, what appeared to be an aureole, or halo, of considerable dimensions surrounding the star and concentric with it; this appeared on at least two negatives, of which copies were immediately sent to a number of the observatories of Europe, with an announcement of the discovery; Wolf, at Konigstuhl, and Kostinsky, of Pul-kova, at once suspected the appearance to be instrumental in its character, and a series of experiments was at once instituted by each of these gentlemen, with the result of independently proving that the appearance was purely photographic, and due to an excess in the star's light of the rays, for which the lense was not corrected.

The star is surrounded by, or projected on, a considerable area of scattered and wispy nebulosity. Changes in this have been announced, but are taken at the observatories with a good deal of reserve, as possibly instrumental in their origin.

The star is now visible only with the aid of a field-glass or small telescope. The small chart (Fig. 3) copied from the Bonn Durchmusterung shows its relation to the neighboring telescopic stars, and corresponds to the dotted square on the first chart, being three degrees square. The Nova is represented by the small circle.

These stars have been appearing from time to time, during the memory of man. By such an occurrence Hipparchus was led to form the first catalogue of the stars of which we have knowledge. In 1572 the attention of Tycho Brahe, who afterward became a great astronomer, was first called to the study of the heavens by the appearance of such a star in the constellation Cassiopea. Lesser outbursts, says Professor Wilson, may have been frequent, and the fact, to which Professor Pickering calls attention in Circular No. 56 of Harvard College Observatory, that eight new stars have been discovered in the last fourteen years, since photographic processes have been so generally applied to astronomical research, points to this conclusion.

"What is it?" "What is the cause of it?" We simply do not know. Men have theorized; but in the absence of any tangible and certainly ascertained fact about these bodies, all theories have more or less the character of better or worse guesses. What little information we have as to the constitution and actions of these stars comes from the spectroscope only, and are rendered more or less enigmatical by our total ignorance of the conditions of pressure, etc., there existing.

The following, quoted from the article on the New Star by Professor Wilson, in the April number of Popular Astronomy for the current year, are the four best known and most plausible theories which have been advanced respecting this class of stars up to the present time. The theories are very clearly stated in the article, but the language in which they are expressed is too technical to be in place in a paper of this character, so they are only given in abstract.

They are: The meeting of two swarms of meteorites moving in opposite directions; the tidal disturbances in the atmospheres of the component stars of a binary system having an orbit of great eccentricity; an outbreak caused by the shrinkage of a cooling body; the passage of a dark body through a cloud of meteorites. Of these, the second seems to me the most likely, as being the simplest and least out of the ordinary course, in that we have not to suppose a special set of conditions for the case, but are dealing with what must actually and frequently occur in the universe.

The New Star In Perseus 80

Fig. 3.

The star is now waning very slowly, if at all, and its future behavior is very hard to forecast. In the meantime it is being watched at every observatory in the world, public and private alike, and scarcely a day passes without an observation of it being secured.