Astronomy Author:Alexander Bain Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: stars on the meridian at 1G hours 15 minutes on the same clock ; the sidereal reckoning of hours being carried on to 24, instead of making two half days of 12 ho... more »urs each. 100. Confusion sometimes arises from the use of the words latitude and longitude in celestial measurements, since they do not mark the same quantities in the celestial sphere that they do in the sphere of the earth. Latitude on the earth means distance from the earth's equator; latitude in the heavens does not mean distance from the celestial equator, which is the earth's equator extended to the sky: this distance is expressed by declination; and celestial latitude means distance from the ecliptic, which runs in a different direction from the equator of heavens and earth. So longitude on the earth is paralleled by right ascension in the heavens. 101. The reason of this discrepancy is, that the celestial equator is not the most permanent circle of the heavens; it has not the fixed position that the terrestrial equator maintains in the earth; on the contrary, it shifts its place in the course of ages, and divides the starry sphere differently at different periods. The only circle on the heavens that approaches to the permanency of the earth's equator is the ecliptic, which passes through nearly the same line among the stars at all times; and for this reason the terms latitude and longitude, expressing on the earth invariable measurements, are used to express the least variable of the starry measurements, or measurements by the ecliptic. 102. To avoid the incessant repetition of the term " celestial" before "equator," when speaking of the equator of the heavens, this equator is sometimes called the equinoctial, which, without any second word, distinguishes it from the equator of the earth. GEOMETRICAL AS...« less