Important and interesting as these discoveries were, they were thrown into the shade by those to which he was led during an accurate examination of the planets with a more powerful telescope. On the 7th of January, 1610, at one o'clock in the morning, when he directed this telescope to Jupiter, he observed three stars near the body of the planet; two being to the east and one to the west of him. They were all in a straight line, and parallel to the ecliptic, and appeared brighter than other stars of the same magnitude. Believing them to be fixed stars, he paid no great attention to their distances from Jupiter and from one another. On the 8th of January, however, when, from some cause or other[9], he had been led to observe the stars again, he found a very different arrangement of them: all the three were on the west side of Jupiter, _nearer one another than before_, and almost at equal distances. Though he had not turned his attention to the extraordinary fact of the mutual approach of the stars, yet he began to consider how Jupiter could be found to the east of the three stars, when only the day before he had been to the west of two of them. The only explanation which he could give of this fact was, that the motion of Jupiter was _direct_ contrary to astronomical calculations; and that he had got before these two stars by his own motion. In this dilemma between the testimony of his senses and the results of calculation, he waited for the following night with the utmost anxiety: but his hopes were disappointed; for the heavens were wholly veiled in clouds. On the tenth, two only of the stars appeared, and both on the east of the planet. As it was obviously impossible that Jupiter could have advanced from west to east on the 8th of January, and from east to west on the 10th, Galileo was forced to conclude that the phenomenon which he had observed, arose from the motion of the stars, and he set himself to observe diligently their change of place. On the 11th, there were still only two stars; and both to the east of Jupiter; but the more eastern star was now _twice as large as the other one_, though on the preceding night they had been perfectly equal. This fact threw a new light upon Galileo's difficulties, and he immediately drew the conclusion, which he considered to be indubitable--"that there were in the heavens three stars which revolved round Jupiter, in the same manner as Venus and Mercury revolve round the sun." On the 12th of January, he again observed them in new positions, and of different magnitudes; and, on the 13th, he discovered a fourth star, which completed the four secondary planets with which Jupiter is surrounded.