On August 16, 1598, there occurred a total eclipse of the Moon, observed by Kepler,[136] in which during totality a part of the Moon was visible and the rest invisible. He says, that while one-half of the disc was seen with great difficulty the other half was discernible by a deep red light of such brilliancy that at first he was doubtful whether our satellite was immersed in the Earth’s shadow at all. This is an instance of the simultaneous operation of those causes (whatever they may be) which result in a totally-eclipsed Moon being sometimes wholly invisible and sometimes entirely visible as a copper-coloured disc. An eclipse of the Moon which happened on the morning of July 6, 1610, may be mentioned as having been the first to be viewed through a telescope. The eclipse was only a large partial one. The following record of the fact is due to Tycho Brahe.[137] “The beginning of the eclipse of the Moon as observed through the Roman telescope, appeared like a dark thread in contact with the shadow”—a description which cannot be said to be unduly explicit. In 1620, on June 15, there was a total eclipse of the Moon, when during the total phase “the Moon was seen with great difficulty. It shone, moreover, like the thinnest nebula, far fainter than the Milky Way, without any copper tinge. About the middle of the second hour nothing at all could be seen of the Moon with the naked eye, and through the telescope so doubtfully was anything seen that no one could tell whether the Moon was not something else.” It is expressly stated, however, that the sky was quite clear. Kepler also observed this eclipse, and says that the Moon quite disappeared, though stars of the 4th and 5th magnitudes were plainly visible.[138] In this same year 1620, there was on December 9 another total eclipse, when “the Moon altogether disappeared so that nothing could be seen of it, though the stars shone brightly all around: she continued lost and invisible for a quarter of an hour more or less.” This observation seems to have been made at Ingolstadt. Wendelinus mentions the eclipse of April 14, 1623, in connection with the question of the visibility of the Moon when totally eclipsed. He says, “but sometimes it so far retains the light derived from the Sun that you would doubt whether any part of it were eclipsed.” This eclipse was observed by Gassendi, and if the above record is correct, it is the more remarkable seeing that the eclipse was not total, only 11/12ths of the Moon’s diameter being obscured.