The Birmingham age-herald., 1922-05-07


 terestins during the next few
 months, This month eur interest will
 be centered ip the two planets which
 are closer to the sun than the earth and for that reason called inferior
 planets, Mercury and Venus. These
 planets are never seen far from the
 sun in the sky. Venus. not more than 47 degrees from the sun, and Mer-
 cury. not more than 2s degrees away. They are usually so close to the sun
 that we cannot see them because of
 the suns glare. When they are near
 their greatest distances from the
 sun we can see them in the evening; or morning twilight. Mercury being
 nearer to the sun and less brilliant
 than Venus Is seen less frequently.
 There are many who have never seen it to know 1t. The present month
 provides very favorable opportunity for those who wish to know this hashful planet. It Is at it's greatest distance east of the sun on May 23
 It's position at that time Is marked on figure 1. The map represents the appearance of the sky about 7:30
 on May %. It's position at that time is marked on figure l. The map rep
 resents the appearance of the sky
 about 7:30 on May 23. If one looks at this time Mercury can be seen very easily in the position indicated.
 But there need be no uncertainty, for just above Mercury lies Venus.
 the brightest of all heavenly bodies
 except the sun and moon. This planet cannot be mistaken. As indicated,
 Mercury is brighter than any other
 object in that part of the sky except Capella at A, which is but little
 brighter There is no difficulty in
 seeing the planet if one looks in the
 right place at the right time.
 Both Mercury and Venus change their positions rapidly. One need not
 wait until May 23 to see these plan
 cts Venus can be seen at any time during the month and Mercury for while before the 23d and a few days
 after that time. Many will be in-
 terested in seeing Mercury early and following It in it's motions. In figure
 2 I have represented the motions of the sun and these planets and the po- sitions of few of the bright stars. Capella. as stated, is the star marked in figure l, the twins, Castor and poilux, are marked B and C. Procyon is at D and Betelgeuse at F. .Mer- cury passed the sun and became an evening star April 24. The positions
 marked 1. g. 3, etc, apply for the
  June 5, 10, f3. IS. The sun and Venus
 move eastward at nearly uniform rate, but Venus moves faster and each day is little farther from the
 sun. At first Mercury moves rapidly and is farther from the sun each day until position 6, May 23 when it Is farthest east of the sun or at It's
 greatest eastern elongation, as as- tronomers call it. Mercury then con- l ,at
 fast as the sun, until June 5. posi- tion Q, when 1t ceases it's direct or
 eastward motion and begins it's west
 ward or "retrograde" motion. At this
 time. June 5. Mercury is said to be stationary" With the sun moving
 eastward and Mercury moving west
 ward they soon pass in position 12
 on June IS. This is called inferior conjunction. After that time Mercury is west of the sun and is morning star. The diagram shows why we see
 planet much longer before it's greatest elongation than after. At first Mercury gains rapidly on Venus, but it does not quite overtake it. The closet approach is on May 20. when it is a little over degrees from Venus, position g. They remain near each other for a while and then separate rapidly. Venus continues it's at which time 1t will be south of
 Antares in Scorpio, a little beyond
 the southeastern boundary of figure | 1. In the interval it moves halfway around the sky.
 What is the law or principle un- deriving these curious motions? This question was asked as soon
 as such motions were observed. A l careful record of the facts of ob-
 servation was necessary. before the explanation was possible. The cause
 Is thoroughly understood. This cause
 Is explained in Figure 3. Mercury
 moves around the sun in an orbi. which is nearly circular. but with the sun out of the center. Venus and the earth move in nearly cir cular paths with the sun at the cen ter. 1t Is the fact that We make our observations from the moving earth that complicates the apparent | motions. The real motions are rather simple. Each planet is in the posi- tions shown by corresponding figures, the dates and figures corresponding with those used in Figure 2. On April 24, at O, Mercury was at su- perior conjunction on the opposite 1 side of sun from the earth. By May l it has moved to position ] to the east of the sun. but the earth has | also moved. The diagram shows the relative positions. Mercury ap- | pears further from the sun in the l successive positions until position (, | in which the line from the earth 10 | Mercury is tangent to the orbit of Mercury In this position we have | the line to Mercury making the !, greatest angle with the line from l the earth to the sum that is we see ! Mercury as far from the sun in the | sky as possible. After this time it 1 draws closer to the sun until 1t is in the same direction as the sun it l inferior conjunction in position i2, ] on June IS.
 I have also shown the motion of Mercury with respect to Venus. The direction of Mercury approaches that | of Venus until May 20 position E. after which the planets separate. The 1 to one of the fixed stars, Pollux. The l stars are so far away that they ap- l pear in the same--that is, in parallel directions wherever the earth may | be. At first both planets are in directions very different from that If 1 Pollux. Their eastward motions ! carry them closer to it. On June s, position g. Mercury is closest to Pol lux. Venus continues to approach Pollux. On June l3. position H.. it | lies in the same direction as Pollux and passes It. They are not quite in | the same position as shown in Fig ure 2, as neither Pollux nor Venus lies exactly in the plane of the tt,f