Show I 1 I 1 LECTURES ON ASTRONOMY 1 BY ORSON PRATT LECTURE NINTH mars the next planet in the order of distance after I 1 venus is the earth but as this planet has already received a lengthy description we will pass on to the next in order namely mars the planet mars I 1 revolves in an all orbit of wiles miles from the I 1 run eun consequently its orbit is of miles i exterior to the orbit of the earth mars is in I 1 diameter its apparent diameter vari varis varies e s according to the position which it occupies in its orbit when in conjunction with the sun or in aline a line drawn from the earth through tile the sun and extended to the orbit of mars it is of miles farther from the earth than when in opposition or in that part of its orbit situated in a line drawn from the sun through the earth the surface ot of mars in I 1 1 tion appears about 25 times larger than when in conjunction the orbit of mars is of miles in circumference cumle cum ference rence through this distance it moves in in about days its average rate of velocity is about miles every hour this is about miles mile 0 s slower lower every hour than what the earth moves mars rotates upon an axis from west to east cast in 24 14 hours and 37 minutes its axis axia being inclined from the perpendicular to the theolane plane of its ils orbit 30 deg IS 18 min this is nearly 7 deg greater inclination than the earths axis has consequently its seasons will be somewhat more rigorous or intense than ours each of the seasons will also be nearly double the length of ours the inclination of the orbit of mars to the ecliptic is I 1 deg 51 min 62 a sec ec hence it will never be seen to exceed four times the apparent diameter of the sun from the ecliptic the period of mars or the time which it occupies in going from opposition round to the same point again is about 2 years and 50 days about 36 days before mars attains to its opposition it will begin to retrograde and continue apparently to move contrary to theonder the order of the signs for far about 36 days after the opposition the arc of is equal to about 16 deg 12 min all the superior planets or those bodies which are more distant from the sun than the earth when at and near their oppositions have apparently retrograde movements the greater the distance of the body from the earth the less will be the are arc of and the longer the period of its apparent description and the more frequently will such the eccentricity of the orbit of mars is miles consequently it is nearly miles nearer the sun run at ita its perihelion than at its aphelion from the telescopic appearances of mars it is probable that thai its surface consists of land and water it is also very evident that it is surrounded by a very dense and extensive atmosphere in which numerous clouds float as in tile the atmosphere of the earth it is further evident that snows are congealed in the atmosphere of mars mara and precipitated upon its surface in tile polar re regions giens which is indicated by the brightness of those regions after living exposed to their long winter of six six months the brightness of these spots is gradually diminished by a long exposure to the summer rays of the sun the quantity of light on that planet received from the sun is n not 0 t quite one half as much as we enjoy the mass or tile the quantity of matter contained in mars is times less lesa than the quantity contained in the sun the density of mars is about 19 SO of the density of the earth that is about 4 34 3 4 I 1 times as dense as water it would take about 7 globes like mars to weigh as much as he earth I 1 pound of matter on the earths surface will weigh about 12 pound on the surface of mars man tillie the asteroids the asteroids iare are small planetary bodies revolving around the sun between the orbits of mars and jupiter none of these bodies were discovered the present cerit century tiry the great distance between the orbits of mars and jupiter compared with the distances between tile other planet planetary iry orbits gave rise rise to the idea that there should be a plank planet situated S in this great interval prof bode had detected a law relating to the distances of planetary orbits from each other As you jou recede from the su sun n each planetary orbit is ia found to be nearly one half the distance from froin the orbit of mercury which the next succeeding one has thus the interval between the orbits of venus and mercury is one half the interval between those of the earth and mercury mercur and the interval between the orbits of the earth and mercury is about one half the interval between those of mars and mercury the interval between the orbits of jupiter and mercury is about one half the interval between those of saturn and 1 ATer cury v and BO soon on but when this law was applied to the interval between mars and jupiter it was found to fail in order that the law might hold god it was calculated that a planet ought to be situated from mars about one third the distance between that planet and jupiter astronomers were so thoroughly convicted of the existence of such a body that they actually called a convention in the year 1800 and resolved resolve d to carefully search for the suspected new world A zone of the heavens extending several degrees on each side of the ecliptic was divided into 24 equal parts and a n d parceled out to ns as many observers each of I 1 whom was required to thoroughly examine the portion I 1 assigned to him this plan was successful piazzi on the evening of the first day of the year J 1801 discovered the planet ceres after ascertaining t its distance from the sun it was found to occupy the position between the orbits of mars mare and jupiter I 1 require I 1 by bodes law of planetary distances this discovery wits was with joy joi by the whole astronomical world the great chain in the solar system was filled the discrepancy in bodes law vanished and the harmony in the whole planetary system seemed to be completed but scarcely had astronomers time to congratulate one another in relation to this great discovery when they were startled at the announcement onno 0 of f dr olbers of bremen who had on an the evening of the of march 1802 discovered another planet hiving having its mean distance and periodic time almost identical with thit that of ceres here was an anoula anoma ly presented in in the solar system two planets having about the same distances and periods and whose elliptic orbits actually intersected each oth er that is is each planet in in different points of its path w was as alternately nearer ind and then further f from rom the sun than the other this new planet was called pallas dr dir olbers conjectured that these two minute bodies might be fragments of acme same greater planet which by some unknown cause had been burst asunder or broken in pieces if such a catastrophe ever happened it must have taken place atone of the points of the intersections of their orbits i the force necessary necess arV to burst a planet and project the fragments in different ferek dif directions so as to pursue I 1 elliptic orbits or of vinous various degrees of ela centricity I 1 can be calculated c the larger fragments borsuch of such a planet would deviate from the original path less than the smaller ones however great the inclinations of their orbits or however eccentric the eglip 1 i ses yet they would all intersect each other at the point where the explosion happe happened ned i j IT under rider the influence of this bold hy hypothesis po thesis as i i tron omers pointed their telescopes to the opposite opp ansite co constellations cetus and vir virgo 9 0 where the nodes of the two orbits lie as the most likely place to discover other fra fragments and on the ad of septem I 1 her 1804 mr harding of lilienthal discovered the planet juno near oneff one of the points of the intersection 8 e tion of the other two orbits dr olbers finding hs his theory assuming the air air of f reality continued his researches with still greater zeal and on the of march 1807 he discover ed the fourth of these supposed fragments in in the constellation virgo not far fa r from tha th point of the intersection of the th other three orbits this planet was named vesta the researches continued for nearly 40 years and no other fragments were dis dij covered and it began to be supposed that all the mall r bodies revolving in in this region wery aate ted but on the esth of december 1845 professor hencke of dreisen discovered another asteroid ait eroid I 1 which was called astria A astrea and on july 1847 the same observer detected another which wits was called hebe this great success in in disco discovering vering A new div worlds in in the of pur own on system excited I 1 other astronomers asti monomers to commence a diligent resea research feli for these supposed fragmentary bodies mr hind of london on the of august 1847 discover ed a seventh which was called iris and on the of october the same year he discovered the eighth which is ia called flora and on the of april 1848 mr graham of ireland discovered the ninth asteroid which is called metis thus within the short period of less than 2 21 12 1 2 years five new asteroids were detected and added to the group of worlds revolving between the orbits of mars and jupiter I 1 all of these bodies are extremely small vesta which is probably one of the largest is believed I 1 to be only miles in diameter junos diameter is is stated to be only about 79 miles and ceres miles it is e extremely difficult to measure these minute worlds at so great a distance and consequently consear these approximations may be f far ar from the truth juno is supposed to have a rotation rot ution upon an axis axis in in about 27 hours but this is uncertain the rotation of the other asteroids has not as yet teen been detected tile the distances from the sun and the periodic times of these nine bodies have already been calculated the mean distances at which they revolve around the sun is nearly the same and they per perform form their rev revolutions solutions in nearly the same periods 0 the orbits of the older planets are inclined at a very small angle to the ecliptic but the orbits orbit of a several everal of the new planets are inclined at a considerable angle to the ecliptic that j f pallas being affe e greatest greatest Trea grea test tesi amounting to 34 deg 37 min inin see sec the eccentricity of some of these orbits is much greater grealer than that of the old planets pl aneti juno pallas 1 iris hebe and nd astrea have tile greatest eccentricities C ties amounting to nearly one quarter of their mean distance the hypothesis which considers these bodies as the fragments of a planet which has been is sustained a ined b by a co considerable amount of evid evidence evidente enre arising from Y the le anomalies and apparent irregularities observed in this system of bodies the inclination of the orbits their eccentricities the position of the nodes and aphelia and many other othar peculiarities seem to indicate that these bodies have diverged from one common node and therefore that they were originally one single planet when however r we shall have arrived to a knowledge of the great laws that operated in the construction of the fhe solar system we shall then perhaps perli aps see that the apparent anomalies and irregularities of the tero idal system are among the possible results of the workings of the grand mechanical laws of the universe ordained by the great architect of nature to display in endless variety his wis wisdom doin power and 9 goodness fodness ness tile the next planet beyond pallas is jupiter this is tile the largest planet in the system its distance from the sun is of mile and the circumference of its orbit is 31 1 of miles it completes one revolution in 12 1 2 ditri its average velocity is nearly miles every hour lour A faint idea of the great distance around the circumference 0 of f this planet s orbit may he be acquired by supposing a rail car to travel without intermission at tile the rate of miles per day with such a velocity it would require over years to perform the grand grana jour ney when jupiter is nearest to the earth at the time of its opposition to the sun its distance is of miles from us A steam carriage moving at the rate of 20 miles per hour lour would require about 2300 years to pass over that thai distance even light itself though it darts 1 1000 miles every second would require 34 minutes and 43 seconds 10 lo come from the nearest point of jupiter T s orbit to us when jupiter is in conjunction with the sun it is of miles from us light will pass over this distance in 51 minutes and 13 leonds if tile the light of jupiter were to be extinguished at the moment of its conjunction with the sun we should not be aware of the fact until aim after the son on junction whereas if its likht light were to be extinguished at the moment of its opposition we should bt be aware of it in after or in other words let two planets be situated in Ju orbit one in conjunction and the other in opposition with the sun and let the light of both planets be extinguished at the he same instant we should continue to see the planet in conjunction and after the one in opposition had disappeared this can be demonstrated by calculating cau lating the exact moment of the eclipses of Ju moons in con conjunction june I 1 and opposition and it will be found invariably that the eclipses will happen 16 1612 12 1 2 minutes later when in e conjunction junction on than when in opposition and as jupiter is of miles further farther off when in conjunction than in opposition it follows that it must take light 16 1612 1 2 minutes to traverse that distance it was in this manner that the velocity of I 1 light was first discovered tile the diameter of jupiter is miles and its circumference is over miles it has been found to revolve around its axis in the short space of 9 hours and 56 minutes this is determined by telescopic observations of certain permanent spots upon its disc which are seen to be cabied across the same f from east to west re remaining visible 4 hours and 58 minutes and then d disappearing appearing is for the same length of time the equatorial regions of jupiter mu must st move with a velocity of over miles ev ery hour this is very nearly equal to its velocity in its orbit As that hemisphere of jupiter which is turned from tile the sun rotates in the same direction as the orbit a ual al in motion 0 ti 0 n the velocity from we west t to to e east ast at the time of their midnight will be g greatly reat accelerated amounting to miles a minute as is sun rotates in a direction from east to west contrary to the orbi motion the velocity from west to east arising from rom the orbit motion will at the time of their noon be greatly diminished amounting to no more than 50 miles a minute the inhabitants of jupiter therefore will be carried from west to east miles a minute swifter at th P ir midnight than at their noon from noon till midi midnight tight which is a period of only about 5 hours tile the velocity will in increase C r e a se at an all average rate of about 3 miles a minute or 36 16 rods per second the decrease from midnight to noon will be in the same proportion year on is our years during tins this time jupiter makes revolutions upon its axis consequently there are days dayi of about 10 hours long in in one of Jupi jupiter iter s years the rapid rotation of 0 this planet will have the effect to make all bodies for many degrees each side of its equator lighter than what they would be if there then i were no rotation gravity at the surface of this ibis planet is is more than 3 times as great as at the surface of the earth this is is owing to the bulk ana ana quantity of matter in in jupiter its quantity of matter is is times dimes as much as is is contained in in the earth while its bulk is is 1323 times greater A body I 1 weighing one |