CONJUNCTION, in astronomy, is one of the aspects (q. sr.) of the planets. Two heavenly bodies are in C. when they have the same longitude—that is, when the same perpendicular to the ecliptic passes through both. If they have, at the same time, the same latitude--that is, if they are both equally far n. or s. of the ecliptic—they appear from the earth to be in the same spot of the heavens, and to cover one another The sun and moon are in C. at the period of new moon. In the case of the inferior planets, Mercury and Venus, there is an inferior C. when the planet is between the earth and the sun, and a superior when the sun is between the earth and the planet. In general, a heavenly body is in C. with the sun when it is on the same side of the earth and in a line with him; and it is in opposition to the sun when it is on the oppo site side of the earth, the earth being in a line between it and the sun. Planets are
invisible when in C. with the sun, except in rare cases when an inferior planet passes over the sun's disk, and may be seen as a speck on his surface. Conjunctions are either geocentric or heliocentric, according as they are actually witnessed from the earth, or as they would he witnessed if observed from the sun. In observing a C. from the earth's surface, it is usual to reduce the observation to what it would be if made from the earth's center. By this means, the exact times of C. are more accurately fixed, and the' observations of one astronomer made available to every other, wherever he may be on the earth's surface. Grand conjunctions are those where several stars or planets are found together. The Chinese history records one in the reign of the emperor Tehuen hiu (2-514-243G B. c. ), which astronomers calculate to have actually taken place.