The Montgomery advertiser., 1902-07-06
SKIES IN JULY.
MARS AND VENUS IN coNJUNc
 TIDN THIS MONTH.
Position of Other Plans.s-The Ter restrial Atmosphere-Dust Notes
 in Air-Twilights and Refrac- tion-scorpio, ophiuchus.

 in her last quarter on the 18th. On the 4th she will be nearest to, and on the 18th remotest from, the earth. While at
 tho beginning of the month the sun is still near the summer solstice. he will have desce nded nearly 5 degrees at its
 termination. In course of the month the
 rising and setting points of the sun will shift degrees along the horizon toward
 the true east and west points of the same.
 The planet Mercury will remain in Gem
 ini throughout the whole month. On the
 18th 1t will reach its greatest elongatioa
 west. being then 20 degrees S5 seconds dis
 tant from the sun. The reader will re-
 member that this swiftest of all planets
 making a circuit round the sun withins the brief period of three months. aud
 whose synodic period is about one month longer. not infrequently passes within
 month through three consecutive zodia-
 cal consultations. That during July It
 will finger In one constellation only may
 prove somewhat perplexing to some, but 1t must not be forgotten that the appar- ent motion of the planets renders the whole matter plain. Viewed from the sun or distant point on the line drawn | through the sun perpendicular to the plane of the ecliptic, the planets would be seen to travel in their nearly circular orbits with regular motion; but as seen from the earth the apparent motion is much more complicated being made up of their actual motion around the sun coni-. bined with an apparent motion due to the earth's own movement. The apparent motion of a planet as seen from the earth. Is called geocentric motion. and this goc- centric motion is made up of two mo- tione--that of a body moving once year around the circumference of circle equal to the earth's orbit while the Cen- ter of this circle itself goes around the sun upon the real orbit of the planet, and with periodic timc equal to that of the planet. In consequence of this .iooped' motion we have the peculiar back-and-forth movement of the planets among the stars It plainly follows from this that by this retrograde motion of q planet it will often finger In the zodiacal constellation in which it happens to be at the time longer than when its appar- ent motion is direct. The very irregu- larity of these apparent planetary mo- tions suggested to the ancients the name of planet, a Greek word signifying wanderer.
 Venus and Mars will be in Taurus dur ing the greater portion of the month. but toward the end will enter Gemini. They will be near together throughout the whole month and on the last day they will be but little more than l degree distant from each other, thus presenting the ever attractive phenomenon of planetary conjunction. Both will rise be- tween and 8 o'clock and act as morn ing stars Jupiter and Saturn have not
 materially changed their position since last month. the former being in Capri corn and rising about 9 o'clock in the evening. the latter being In Sagittarius S4 t.0xx awlt ltear The subject of the atmosphere sur. rounding the earth Is distinctly an astro- nomIcal one of the highest possible im-. portance and interest. The atmosphere is one of the three divisions that conn pose the structure of the eatxhA That part of the earth which forms the dry
 land and is a vast strong ball is the lith-
 osphere, the liquid layer resting in the
 holIows. of the Atmosphere Is water
 shell, called the hydrosphere, and that
 envelope of gas surrounding the whole to
 a considerable height is known as the att
 mosphere. It was not until the close of
 the eighteenth century that the air ceased
 to be regarded as an element. By exper-
 iments 1t was then found that the atmos-
 phere consists of two gases-nitrogen and
 oxygen--but it was not discovered before
 the year 1894 that it contains still more
 inert gas than nitrogen. which IS called
 argon. This forms one-hundredth of the
 volume of air from which oxygen is re-
 moved. Besides these the atmosphere con
 tains carbonic acid and water vapor,
 both of which play very conspicuous
 part in the economy of nature. There is,
 however, another ingredient of the atmos-
 phere-solid dust-the importance of
 which was not recognize duntil a com
 paratively recent date. Solid dust is al-
 ways present in the atmosphere through
 out It's whole depth. Twenty million me-
 teorites are calculated to reach the earth
 every day and most of these are broken up by the friction of the air, furnishing
 supply of cosmic dust which. being ex-
 ceedingly fine and even invisible. settles
 down very slowly. Terrestrial dust is
 carried into the atmosphere by ascending
 currents of air and Is of many kinds, re-
 sulting from the wearing down of rocks,
 from volcanic explosion, from howers Tn the form of pollen, from minute organ isms, either plants or animals, from burn ing fuel from factories mines, flour mills
 and from the spray of the sea. The
 number of notes Is almost incrediple- Every puff of smoke from cigar con
 tains about 4.000, 100000 separate granules of dust Dust appears to float in the at-
 mosphere and the notes of sunbeam seem to be rising as often as falllng.
 This is however, a result or currents ot air. In still air dust always falls, but
 the large notes fall most rapidly under
 the pull of gravitation and against the resistance of the friction of the air. In ono cubic centimeter of the air of great cities there are hundreds of thousands of
 notes. in the air of small villages there are thousands and there are hundreds even in the open country far from towns and factories These minute notes catch ing and scattering the sunlight are the agents by which the whole atmosphere IS so illuminated that not even the bright
 est of the stars or planets is visible by day. If the air were free from dust we sbould plainly see the sun shining from 2 rerfectlv black star-filled sky. and one s,dc of a house would be daZzliagly illu- roinated the other in shadow of abso- ! lute darkness. ,..,.. a,,o .o the scattering of sunlight by the dust notes of the higher layers. to some exE tent, too. to the true color or oxygen, | The red tints at sunrise and sunset ana the lingering twilight or hlgh latluue' have a similar origin. IWlhsht is P'u- duced when light from the sum- "hlle still below the horizon, strikes on the upner atmosphere too obliquefy for refrac- lion to bend the rays down to the sur face. then the illuminated dust notes Of tbe upper air light up the sky for hours with A soft simmer on lofty m m'n;itains, where the atmosphere contains little water vapor and few dust notes. tfe air is heated so slightly by 'he solar rays passing through that 1t remains tit- | terly cold, authough the suns direct feat |