It is that point where the moon passes the plane | earth. e earth's orbit from north to south. Do the nodes change their position as regards a fixed point in the s? They have a retrograde motion of about 19 degrees year. When is the moon in north latitude in the heavens? When it is north of the earth's orbit or ecliptic. When is the moon in south latitude in the heavens ? When it is south of the earth's orbit or ecliptic. What is the greatest latitude of the moon? 5 degrees north or south of the earth's orbit or ic. What is the greatest declination of the moon, or its distance north h of the equinoctial or equator? About 28 degrees. LESSON XXXVIII. Q. Which are the superior planets? A. Mars, "the Asteroids," Jupiter, Saturn, Uranus a Neptune. Q. Why are they called superior planets? A. Because their orbits are greater than the orbit the earth. HELIOCENTRIC AND GEOCENTRIO LATITUDE AND LONGITUDE. Q. What is the Heliocentric latitude and longitude of a planet? A. It is its latitude and longitude, as seen from sun. (See Diagram.) Q. What is the Geocentric latitude and longitude of a planet? A. It is its latitude and longitude as seen from earth. It will be seen by inspecting the diagram upon the opposite pa that there are two small circles introduced into the diagram, the wh How near one of the nodes must the moon be at new moon to circle which represents the moon's orbit, and the shaded circle wh an eclipse of the sun? Within seventeen degrees. (16° 59′′.) How near one of the nodes must the moon be at full moon to an eclipse of the moon? About 12 degrees. (11° 25′ 4′′.) If the moon is exactly in one of her nodes at new or full moon, ind of an eclipse will it cause It will cause a great eclipse of the sun or moon. What is the extent of the solar ecliptic limit in which an eclipse sun can take place? Thirty-four degrees, seventeen degrees on each of either node. What is the extent of the lunar ecliptic limit in which an eclipse moon can take place? Twenty-four degrees, twelve on each side of r node. INFERIOR AND SUPERIOR CONJUNCTION. How many kinds of conjunction are there? When is a planet in inferior conjunction with the sun? lies in the plane of the earth's orbit or ecliptic; this shaded circle introduced into the diagram only to show the two points where moon's orbit intersects the plane of the earth's orbit or ecliptic; th two points are called the moon's nodes; the point where the m passes from the south to the north side, or above the earth's orbit called the ascending node; and the opposite point, or where the m descends below the earth's orbit, is called the descending node; line passing through the centre of the earth from one node to the oth is called the "line of the nodes." It will be seen also that one half the moon's orbit is above the plane of the earth's orbit, and the ot half below it. The planets Mercury and Venus are called inferior planets, beca their orbits are within that of the earth, and of course nearer to the s The other primary planets, Mars, Asteroids, Jupiter, Uranus a Neptune, are called superior planets for the same reason that th orbits are greater, or outside that of the earth. It will be seen by inspecting the diagram upon the opposite pa that the planets, seen by two observers at the same time, one upon sun and the other upon the earth, would not appear to be exactly 1. same point of the heavens. The heliocentric longitude of a pla is where it would appear to be if seen from the sun, and the geocent longitude of a planet is its longitude as seen from the earth. SON XL. ILLUSTRATED ASTRONOMY. R OF ECLIPSES IN A YEAR. on of the moon and her ascending node, the nodes have a retrograde motion of about nineteen degrees in a year, it is only 177 days from the conjunction of one node to the conjunction of the other, therefore, in whatever time of the year we have eclipses of the sun or moon at either node, we may be sure that in 177 days, we shall have eclipses about the other node. If we suppose the moon at new moon to be 17 degrees from her ascending node on the first day of January, there would be a small eclipse of the sun, and at the next full moon, January 15th, there would be a total eclipse of the moon; as the moon would be only about 2 degrees from the descending node; at the next new moon, January 29th, the moon would then be about 12 degrees upon the other side of the ascending node, which would cause another small eclipse of the sun,-hence we would have two small eclipses of the sun at the ascending node, and one great eclipse of the moon at the descending node, from January 1st to January 29th. (See Diagram.) At every subsequent new moon, the moon would be so high that the shadow would pass above the north pole, and at every full moon, the moon would pass below the earth's shadow, until June 26th, when the moon's descending node would come around to the sun, e would be of the moon, January (see Diagram;) at this time the moon would be about 7 degrees from node. clipse take place? At her descending node; this would cause another eclipse of the sun. the next full moon, July 11th, there would be another total eclipse of the moon; again, at the next new moon, July 25th, the moon would would be of the sun, January still be within 17 degrees of her descending node, which would produce ending node. another small eclipse of the sun. ? From July 25th, there would be no eclipses of the sun or moon, as would be of the sun, June 26th, shadow of the moon would pass below the south pole, and at every full at every subsequent new moon, the moon would be so low that the ng node. moon the moon would pass above the earth's shadow, until December 20th, when the ascending node would come around again to the sun, and ould be of the moon, July 11th, degrees of her ascending node; we would, therefore, have another at the 12th new moon in the year, the moon would again be within 17 small eclipse of the sun, which would be the seventh and last eclipse during the year. It will be seen from the above, that we should have would be of the sun, July 25th, five eclipses of the sun, and two total eclipses of the moon, during the ng node. ast eclipse? year, which is the greatest number that can possibly take place in a year. Seven eclipses in a year do not occur twice in a hundred years, although perhaps we may have seven eclipses in one year's e would be of the sun, Decem- time, for several times during a century. To have seven eclipses dur ascending node. >ses in this case from January 29th to is so high at new moon that its e north pole, and at full moon, the earth's shadow. es in this case from July 25th to Decem- n of the moon and her ascending node, n, or only two eclipses in a year? n number of eclipses in a year? r of Eclipses in a Year. year from the time of one node ing the same year, it is necessary that the moon and nodes be in a particular position on the first day of January. After the sun, moon and nodes have been once in a line of conjunction; they return nearly to the same position again in 223 lunations or 18 years 11 days 7 hours 43 minutes 20 seconds, when four leap years are included, or one day less, when five leap years are included; consequently, if to the mean time of any eclipse of the sun or moon, we add 18 years 11 days 7 hours 43 minutes 20 seconds, we shall have the mean time of the return of the same eclipse for a long period of time. This period was first discovered by the Chaldeans, by a long series of observations, extending through many centuries, and by it they were able to foretell, with considerable exactness, the appearance of an eclipse, varying at most but a few hours. Every eclipse within this period of 18 years, belongs to a separate series of eclipses, that is, there is but one eclipse during the 18 years, which belongs to the same series. If any series of eclipses commence at the ascending node, the shadow of the moon just touches the earth at the north pole; at the. next return in 18 years, the shadow will pass across the earth a little more to the south, and at each return, the shadow will continue to pass more to the south until it will have appeared about 77 times, which will take about 1,388 years, when it will pass off the earth at the south pole, and at the expiration of 12,492 years, the same eclipses will commence again to go through a similar course. Those eclipses of the sun which come in at the descending node, the shadow of the moon first touch the earth at the south pole, and at each return passes more rin, and finally leaves the earth at the north pole, after having apreared the usual number of times. The velocity of the moon's shadow across the earth in an eclipse of the sun is about 1,850 mues an hour, or about four times the velocity of a cannon ball. The moon when totally eclipsed, is generally visible if it is above the horizon, and the sky is clear: it generally appears of a faint dusky red, or copper color, this is caused by the rays of the sun, which pass through to " the atmosphere of the |