Familiar talks on astronomy, with chapters on geography and navigaton . believed as desperately loud. In this day I presume a whistle can be heardquite five miles, through a telephone. MERCURY. Let us commence with Mercury, the nearestplanet to the sun. Its diameter is about 3,000 miles, and its meandistance from the sun about 56,000,000 miles;it turns upon its axis once in 24 hrs., 5 min.,1and it makes one revolution about the sun in 88days. Its day, then, is about the length of ours,and its year is about one fourth as long as volume is one nineteenth that of the earth. In the diagra
Familiar talks on astronomy, with chapters on geography and navigaton . believed as desperately loud. In this day I presume a whistle can be heardquite five miles, through a telephone. MERCURY. Let us commence with Mercury, the nearestplanet to the sun. Its diameter is about 3,000 miles, and its meandistance from the sun about 56,000,000 miles;it turns upon its axis once in 24 hrs., 5 min.,1and it makes one revolution about the sun in 88days. Its day, then, is about the length of ours,and its year is about one fourth as long as volume is one nineteenth that of the earth. In the diagram (Fig. 7) let S be the sun, E the earth, and M, IVf, M, M,. be Mercury in four different positions in its orbit. Since the earth and Mercury move around the sun with 1 See note, page 137. The Planet Mercury. 119 different velocities, they will have all possiblerelative positions with respect to each other; sowe may, for the purpose of illustration, supposethe earth to be at rest in its orbit. Let EErepresent the orbit of the earth, and M, M, M,the orbit of Fig. 7. We see from this diagram that Mercury cannever be in opposition to the sun; that is, seenin a line directly opposite the sun. Hence itcan never be on the meridian at midnight, norcan it be above the horizon at It cango, indeed, but twenty-nine degrees from thesun, and consequently it is rarely to be seen 1 Pope says: And Venus sets ere Mercury can rise —which is an absurdity. 120 Familiar Talks on Astronomy, etc, with the naked eye. It is generally so near thesun that the suns light overpowers it. When Mercury is at M, it is between theearth and sun, and is said to be in inferior con-junction. When it is at M, the sun is betweenit and the earth, and it is said to be in superiorconjunction. When in either of these two posi-tions it must rise and set with the sun, and it isnot visible. You see this at once; since it is ina line with the sun, it must rise and set with it. The positions M, M, repre
Size: 1640px × 1524px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, bookidfamiliartalk, bookyear1889
