6i6 SCIENCE PROGRESS 



The fact that new stars, which in our stellar universe are 

 confined to its luminous backbone, the Milky Way, are also 

 found in spiral nebulae, among other reasons, suggests that the 

 latter may be distant replicas of our stellar system. If so, 

 considering that according to modern methods of celestial 

 photography it would be possible to get a record of about 

 three-quarters of a million of such spirals, a magnificent picture 

 is unfolded before the imagination of the immense depths of 

 space, emblematical of the attributes of Power and of Wisdom, 

 of Immensity and of Omnipresence, of the Adorable Creator. 



Incidentally a comparison of the luminosities of the novae 

 of our Milky Way, and of those of the spiral nebulae, enables 

 us to get some idea of the distance of the spirals. We may 

 reasonably suppose that the two sets of novae, the Milky Way 

 family, and that of the spiral nebulae attain in general the 

 same absolute magnitude, or luminous power, when they are 

 at their greatest brilliancy. If their apparent magnitudes, or 

 intensities of illumination, be considered, the new stars of the 

 Milky Way, discovered in the last quarter of a century, attained 

 a maximum brilliancy about eight times as great as those of 

 the spiral nebulae. This means that they appeared to the eye 

 to be sixteen hundred times as bright. But, by a well-known 

 law of photometry, the apparent brightness, or intensity of 

 illumination of two objects, is inversely as the square of their 

 distances. From which it follows that the new stars immersed 

 in the spiral nebulae are forty times as far away as those 

 peopling the clouds of our own Milky Way. The spiral nebulae 

 containing them are therefore at least 1 20,000 light-years away, 

 and may be as distant as 800,000 light-years. A light-year is 

 the distance travelled in a year by a light beam, the velocity 

 of which is 186,000 miles a second. 



To return to the enumeration of the new stars recently 

 discovered. A systematic search on the plates of the Harvard 

 College Observatory has revealed six others, two of which. 

 Nova Lyrae and Nova Ophiuchi, the third recorded in this 

 constellation, appeared in the year 1919. For 1920 we have 

 to record the naked-eye new star, Nova Cygni, also number 

 three in the constellation, discovered by that veteran and 

 indefatigable observer of meteors, Mr. Denning, on August 20, 

 when it had a magnitude of 3' 7. It rose to r8 on August 24, 

 since when it has steadily declined in apparent luminosity, 

 until at the beginning of November it had fallen to about the 

 tenth magnitude. 



A light-curve is a graph which connects dates, yearly, 

 monthly, or daily, or indeed in general intervals of time, with 

 the apparent magnitude, or intensity of illumination, of a star 

 that varies in brightness. If we compare the light-curves of 



