Nova Persei has always stood where it does now.

The name "new star" is unfortunate as it starts the inquirer on a false track. The object in Perseus is, in all probability, an old star with a new and temporary brilliancy. The star has always existed in its present place in the heavens. Its temporary brilliancy makes it new.

In November, a star of the sort was observed by Tycho Brahe. It was, at first, equal to Jupiter in brightness. For a few days it increased so as to rival Venus, and was visible in the daytime. After some three weeks it began to fade, and by March of 1574 it was no longer visible to the naked eye. In the situation described by Tycho there is now a very faint star visible only in telescopes. To Tycho and his contemporaries this object was a "new" star. They had only catalogued a few of the many stars visible to the naked eye. In a place where there was no star laid down in their catalogues an object suddenly appeared, waxed brilliant, and disappeared utterly.

Many stars of the kind have appeared since Tycho's day. In all likelihood every such appearance was due to a change in the light of a previously existing small star. Such objects do not disappear utterly. They remain in their former situations with greatly diminished light. They have gone through a cycle of brilliancy from feeble light to feeble light again. A sudden change of the sort suggests a sudden catastrophe. What is the cause of this catastrophe? This is the crux of the whole matter. To understand the question, let us take the history of the new star of 1892 as an example.

Dr. Anderson of Edinburgh, an amateur astronomer, was observing the heavens during January, 1892, with a small hand telescope. Comparing the stars in the sky with the dots on his star map, he noticed that an object in the sky was not represented in the map. Astronomers all over the world were notified, and the star was thoroughly observed, especially at the Lick observatory. During the month of February the star slowly declined, with some variations in brightness, from the fifth to the sixth magnitude. During April it declined rapidly from sixth to twelfth magnitude. At the beginning of the month it was just visible to the naked eye; at the end a six-inch telescope would just show it. During May the star's brightness fell to the sixteenth magnitude; it was but just visible in the thirty-six-inch telescope of the observatory. In four months the brilliancy had fallen off more than ten thousand times. Daylight then interfered with the observations until the middle of August, when, to the surprise of the observers, the star was found to have increased in brightness to tenth magnitude, and to have become nebula.

A star is an object like our sun; it is a body with a nucleus, which may be solid or liquid or gas under great pressure, surrounded by a gaseous atmosphere. A nebula is a body uniformly gaseous. The spectra of stars and of nebulæ are characteristically different. A new chapter in the evolution of Nova Aurigæ had begun.

It was at first a star. The nebular hypothesis of LaPlace declares that stars are the results of the evolution from nebulæ. A catastrophe in its history occurred. The star at first increased in brilliancy, then declined almost to extinction. Its last observed stage was nebulous. But the nebulous stage is the starting-point for an evolution upward from nebula to star. Part of the cycle has been observed. In all likelihood, the remaining portion will be traced out in ages to come, and the nebula of 1893 may be known to the astronomers of millions of years in the future as once more a star.

In our ordinary observations of the heavens we see objects in all stages of evolution—here a brilliant, highly heated star; there a fainter one; there again a nebula. It is for the eye of reason to deduce the cycle through which such objects must pass in æons of time. New stars exhibit these changes in the short lifetime of a man.

But what was the nature of the catastrophe which determined such immense changes as these? It was marked to the eye by tremendous changes of brilliancy. Changes of brightness signify changes of temperature. We must conclude that the new star was suddenly raised in temperature. From glowing feebly it began to glow intensely. So far all is plain. Let us consider for a moment what the effect of high temperature is.

No two bodies are more different than the earth and the sun. The earth is surrounded by a cooled crust; the condition of its surface and of its atmosphere is stable; everything is in a condition of equilibrium. The sun is a fiery mass, surrounded by fierce flames of incandescent hydrogen, in whose atmosphere fiery clouds of vaporized iron, gold, silver, and the like are flung to and fro by hurricanes of inconceivable violence. Yet it is a commonplace of science that if the earth were to be raised to the temperature of the sun the two bodies would be alike in everything but size. Every element present in the sun is present on the earth. The enormous difference between the earth and the sun is a matter of temperature and of nothing else.

A rise in temperature would change the earth into a dim star; if the were sufficient, it would change into a brilliant star—as brilliant as you please. Deprive a star of its heat, lower its temperature sufficiently, and it would become a cool body like the earth.

Recent work in spectroscopy has proved that there are many "dark" stars in the sky. If it were not for their effect on neighboring lucid stars we should never dream of their existence. Dark stars revolve with bright components in the systems of Sirius, Procyon, Algol, and many others; and dark stars are moving through space with velocities of scores of miles per second, just as bright stars move.

Suppose that a dark star of this sort were to collide with the earth, or even to meet it in a merely grazing collision. In an instant the earth would be raised in cosmic dignity from a dark star, as it is at present, to an exceedingly brilliant one.

There are strong reasons for believing that the brilliancy of the new star of 1892 was due to the grazing collision of two bodies of the sort, one dark perhaps, the other bright. It is impossible to describe the details of such an impact. The spectroscopic evidence indicates that after the impact the system consisted of three, or it may be four, separate bodies. It is likely that the explanation of the new star of 1901—Nova Persei, to give it its proper name—is to be found in the history of its fellow of 1892.

A star is peacefully shining in its place. Fate brings it in collision with another object of the same sort. The energy of impact is transformed into the energy of heat—from molar it becomes molecular. Every shooting star that we see in our August sky is a tiny model of just such an effect. Its energy of motion is partly transformed into the energy of heat. It blazes forth into a mass of glowing gas and disappears. If the mass were moving outside of the earth's sphere of attraction the residuum of gas would become a tiny nebula. The case of Nova Persei promises to be interesting. It appears that on February 25 its spectrum was continuous. It contained no lines, either bright or dark, such as mark the presence of glowing or absorbing gaseous atmospheres. On February 26 the bright and dark lines had developed, and the spectrum is, in general, like that of its congener of 1892. We have observation, then, of an earlier stage of development in 1901 than we possessed in 1892. It would be easy to speculate on the meaning of this appearance, which is, so far, unique in the history of new stars. It is better, however, to wait until a series of observations has been obtained, and to seek for an interpretation of a longer series of facts. The general explanation will, in all probability, be the same for the two Novæ of 1892 and 1901. The differences will be differences of detail, and cannot fail to be instructive and important.

Edward S. Holden.
In the New York Sun.

The following regarding the new star appeared in The Baltimore Sun, February 26, 1901:—

In speaking of the discovery of a new star in the constellation Perseus by Dr. T. D. Anderson of Edinburgh, Dr. N. E. Dorsey, associate in physics of the Johns Hopkins University, said yesterday to a reporter of The Sun:—

"It is very interesting to note that the most important of new stars recently discovered is Nova Aurigæ, which was discovered in 1892 by Dr. Anderson. An examination of the Harvard plates showed that it was recorded on the plates exposed between December 10, 1891, and January 10, 1892. It was brightest on December 20, when it was of the 4.4 magnitude. By April 1 it had become invisible except through a large telescope, but in August, 1892, it temporarily brightened up again, and through the years 1893 and 1894 it remained between the ten and eleven magnitude. Professor Barnerd's observations with the large Lick telescope showed it in 1895 as a small, bright nebula, with a star-like nucleus.

"A swarm of meteorites swiftly traversing a remote gaseous nebula would account for most of the peculiarities of the spectrum of Nova Aurigæ. But a thoroughly satisfactory explanation of new stars has not yet been suggested.

"Other recently discovered stars are Nova Normæ, discovered in 1893; Nova Carina, in 1895; the Nova Sagittarii, in 1896."

A special dispatch to The Sun from Charlottesville. Va., last night says: "The wonderful new star, which the scientists at the University of Virginia for the present call Nova Persei, was seen a few minutes after 7 p.m. on Friday by Mr. Richard D. Micou of Alexandria, a student in the academic department of that institution. He drew a map of the constellation Perseus, with the position magnitude of the star indicated, and reported the facts, exhibiting the map to Prof. M. W. Humphreys Saturday morning. Whether he was the first to discover it can be determined only after the exact time of its discovery at other places, as Edinburgh and Munich, shall have been reported."

A dispatch from Ithaca, N. Y., quotes Prof. E. A. Fuerties, of Cornell University, as saying: "This new star has undoubtedly appeared to inhabitants of the earth thousands of years ago. This new discovery recalls the famous Tau, or Star of Bethlehem, which guided the Wise Men to the place of the birth of the Saviour, except that, from the published reports of the body, it is even more brilliant than the Biblical star. Astronomers find that there are records of a star similar to Tau in the oldest Chinese reports, made thousands of years before the birth of Christ, and, with all deference to the beautiful story, undoubtedly the Chinese saw the same star that was the guide of the Wise Men. This new star is probably that of Bethlehem, but it is a star whose period of appearance is perhaps many times longer than that of Bethlehem."

Dispatches from Lick Observatory, California, say that the star is easily found in full sunlight with a twelve-inch telescope. It has also been seen at Yale and Harvard in daylight.