Astronomy in a nutshell, the chief facts and principles explained in popular language for the general reader and for schools . so poorly illuminated by thesun, that the telescope reveals very littledetail on their surfaces. Their density issomewhat less than that of Jupiter. Uranushas four satellites, Ariel, Umbriel, Titania, andOberon, situated at the respective distancesof 120,000, 167,000, 273,000, and 365,000miles. Neptune has one, nameless, satellite,at a distance of 225,000 miles. The most remarkable thing about thesetwo planets is that their axes of rotation,as compared with those of al
Astronomy in a nutshell, the chief facts and principles explained in popular language for the general reader and for schools . so poorly illuminated by thesun, that the telescope reveals very littledetail on their surfaces. Their density issomewhat less than that of Jupiter. Uranushas four satellites, Ariel, Umbriel, Titania, andOberon, situated at the respective distancesof 120,000, 167,000, 273,000, and 365,000miles. Neptune has one, nameless, satellite,at a distance of 225,000 miles. The most remarkable thing about thesetwo planets is that their axes of rotation,as compared with those of all the otherplanets, are tipped over into a differentplane, so that they rotate in a retrogradeor backward direction, and their satellites,in like manner, revolve from east to axis of Uranus is not far from uprightto the plane of the ecliptic, so that the motionof its satellites carries them alternately farnorthward and far southward of that plane,but the axis of Neptune is tipped so far overthat the retrograde, or east to west, motionis very pronounced. Neptune is celebratedfor having been discovered by means of. Photographs of Mars Made at the Yerkes Observatory by E. E. Barnard, with the forty-inchrefractor, September 28, 1909. Comets 201 mathematical calculations, based on its dis-turbing attraction on Uranus. These cal-culations showed where it ought to be ata certain time, and when telescopes werepointed at the indicated spot the planet wasfound. Similar disturbances of the motionsof Neptune lead some astronomers to thinkthat there is another, yet undiscovered,planet still more distant. 7. Comets. Comets are the most ex-traordinary in appearance of all celestialobjects visible to the naked eye. Greatcomets have been regarded with terror andsuperstitious dread in all ages of the world,wherever ignorance of their nature hasprevailed. They have been taken for prog-nosticators of wars, famines, plagues, thedeath of rulers, the outbreak of revolutions,and the subversio
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