diameter through it, and such an Eclipse, (being both total, and central,) is of the longest duration, namely, three hours, 57 minutes and 6 seconds from the beginning to the end, if the Moon be at her greatest distance from the earth; and 3 hours, 37 minutes and 26 seconds, if she be at her least distance. The reason of this difference is, that when the Moon is farthest from the earth, her motions are retarded, but when nearest to the earth, her motions are accelerated. Interrogations for Section Twelfth. Are the rays of light proceeding from the Sun, frequently intercepted? By what are they intercepted? What is understood by the penumbra? What is an Eclipse of the Sun ? At what stage of the Moon does an Eclipse of the Sun happen? How near to either of the nodes must the Sun be to suffer an Eclipse? Does the Moon's orbit differ from the ecliptic? What are the Moon's nodes ? Why cannot the Sun be eclipsed unless he be within 17 degrees of the node? How often is the Moon in the ecliptic? Which is called the ascending node? Which is called the descending node ? What is an Eclipse of the Moon? At what stage of the Moon does this happen? How near must the Sun be to either of the nodes, so that the Moon can suffer an Eclipse? What causes it? Should the same distance from either node at the time of full Moon exceed twelve degrees, could the shadow of the earth touch the surface of the Moon? As the Moon passes between the Sun and the earth at every new Moon, why is not the Sun eclipsed at every new Moon ? Why is not the Moon eclipsed at every full ? What is the farthest point of each orbit from the earth's centre called? What the nearest point? How many times a year does the Sun generally pass by the nodes ? In what time do the nodes pass through all the signs of the ecliptic? How many lunations after the Sun, Moon and nodes have been in conjunction, before they return nearly to the same state again? What is a periodical return of an Eclipse? Are the motions of the Sun, Moon and nodes the same in every part of their orbits ? How can the mean time of these conjunctions be reduced to the truc? How many are the greatest number of Eclipses that can possibly happen in one year How many the least? What the most usual number? ? Which is the most frequent, those of the Sun or Moon ? What is the reason? Are there more visible Eclipses of the Moon than of the Sun ? What is the reason? What is a total Eclipse of the Sun ? How long can the Moon hide the whole face of the Sun from our view? In what part of her orbit must the Moon be to cause a total Eclipse? What is an annular Eclipse? How many miles in diameter would the shadow of the Moon be on the earth, in an Eclipse when total darkness continues four minutes? When the Moon changes exactly in the node, what is the form of the shadow, and where does it strike the earth? When does an Eclipse begin? When does it end? When does it begin and end at any particular place? When the Moon changes 17 degrees short of her descending node, where will her shadow touch the earth? If as far short of her ascending node, where on the earth will her shadow fall? Why in total Eclipses of the Moon is she not invisible, if she be a dark opaque body? Is it possible for the Moon to be visibly eclipsed while the Sun is in sight? When the Moon is full, within six degrees of either node, will she be totally eclipsed? When she passes by the node in the earth's shadow, how much of the Moon will be eclipsed? What is the longest time that the Moon can suffer an Eclipse? What the shortest if she be at her least distance? What is the time of the longest duration of an Eclipse of the Sun ? What the shortest, if the Eclipse be central? |