Путешествие на Луну
Reply from the Observatory of Cambridge
—Iftheshotshouldpreservecontinuouslyitsinitialvelocityof12,000yardspersecond,itwouldrequirelittlemorethanninehourstoreachitsdestination;but,inasmuchasthatinitialvelocitywillbecontinuallydecreasing,itwilloccupy300,000seconds,thatis83hrs.20m.inreachingthepointwheretheattractionoftheearthandmoonwillbeinequilibrio.Fromthispointitwillfallintothemoonin50,000seconds,or13hrs.53m.20sec.Itwillbedesirable,therefore,todischargeit97hrs.13m.20sec.beforethearrivalofthemoonatthepointaimedat.
Regardingquestionfour,"Atwhatprecisemomentwillthemoonpresentherselfinthemostfavorableposition,etc.?"
Answer.—Afterwhathasbeensaidabove,itwillbenecessary,firstofall,tochoosetheperiodwhenthemoonwillbeinperigee,andalsothemomentwhenshewillbecrossingthezenith,whichlattereventwillfurtherdiminishtheentiredistancebyalengthequaltotheradiusoftheearth,i.e.3,919miles;theresultofwhichwillbethatthefinalpassageremainingtobeaccomplishedwillbe214,976miles.Butalthoughthemoonpassesherperigeeeverymonth,shedoesnotreachthezenithalwaysatexactlythesamemoment.Shedoesnotappearunderthesetwoconditionssimultaneously,exceptatlongintervalsoftime.Itwillbenecessary,therefore,towaitforthemomentwhenherpassageinperigeeshallcoincidewiththatinthezenith.Now,byafortunatecircumstance,onthe4thofDecemberintheensuingyearthemoonwillpresentthesetwoconditions.
