Nova Aqullae.—Many will remember the night of June 9th, 1918, when Mr. G. V. Hudson, of Karori, noticed an unfamiliar point of light in the constellation Aquila. His telephone message to the Dominion Astronomer enabled enthusiasts to leave their beds and rush to the local observatories. The light that was gathered in by our telescopes carried messages that were far more marvellous than we realized at the time. All that we could do was to record the rapid changes in brightness that were taking place, to fix the position of the Nova with regard to surrounding stars by taking a few photographs, and to endeavour to identify a few of the bright lines with dark companions which were revealed when a small spectroscope was applied to the telescope. We have since learnt that the explosion, which we watched that night, had taken place 1,200 years before. During the whole of those twelve centuries the light had been speeding towards us, and spreading out equally in all other directions at a speed of about 186,300 miles per second. Photographic records show that before the explosion there was an eleventh magnitude star apparently in the place of the Nova. The brightness increased with such startling suddenness that in three days it attained a magnitude, -1.4, thus outshining every star in the sky except Sirius. Now that its approximate distance has been found, we can page 30 page 31 look at this in another way. It means that, before the explosion, it was shining with four times the intensity of our Sun. In three days its intrinsic luminosity rose to 400,000 times that of the Sun. Then in the next 18 days it lost 98 per cent. of its maximum brightness, or 392,000 times that of the Sun. In eight months it became invisible to the naked eye. Spectrograms, taken during its vivid stage, show that ionized gases were rushing out from the scene of the explosion at a speed of more than a thousand miles a second. After six months a faint gaseous shell became visible. When photographed by Dr. Hubble on April 25th, 1927, this shell had grown to 18 seconds in diameter.