Observatory Talking Points

This exhibit shows twelve of the twenty-four standard time zones around the world. Because the Sun cannot shine on the entire earth at once, but appears to travel across the sky as seen from the earth, different parts of the world have different times. The clock in the center which has the conventional twelve-hour dial gives Indianapolis tire. At present we are on Eastern Standard. The clocks around the outside circle, instead of having conventional twelve-hour dials, have twenty-four-hour dials. The twenty-four-hour dial is used to eliminate the necessity of having special indicators to show a.m. and p.m. at various points in the world. A twenty-four-hour dial has a minute hand just the same as the minute hand on the conventional clock. The hours, however, are closer together and the hand goes around once in a day instead of twice.

Note the clock at the extreme right. It is labeled for the Fiji Islands. You will notice that the hour hand says 8 o’clock. At 3 in the afternoon here in Indianapolis, it is 8 in the morning in the Fiji Islands. There is no ambiguity since the hours are counted from midnight through 24. Melbourne, Australia, farther to the west of the Fiji Islands, shows 6 a.m.; Manilla, 4; India, 2; and Archangel, 0. These are all in the morning. Zero is midnight, the beginning of the day. Perhaps you have noticed that the hour hands of all five of these clocks lie in a sector of the face that is green. This indicates that the time is not only a.m. but is actually tomorrow morning. The day is just beginning. While it is just past midnight in Archangel, in Moscow it is 11 a.m. though no clock is show for Moscow. Notice the last clock Cairo, Egypt. The hour hand points to 22, This is p.m.; and when the hour hand is in the left part of the dial, 12 must be sub­tracted. Twelve form 22 is 10 so it is 10 p.m. in Egypt, 20 o’clock or 8 p.m. in London; 18 o’clock or 6 p.m. in Greenland; 4 p.m. in Buenos Aires; 2 p.m. in Mexico City; noon in San Francisco; and 10 o’ clock this morning in the Pacific Ocean. You will note that the 3 clocks for Mexico City, San Francisco, and Honolulu have brown sectors. After midnight tonight, all the hour hands which are in the green sectors will move into the white indicating that we have over-taken the eastern three-quarters of the earth and we will have tomorrow’s date. Mexico City, San Francisco and Honolulu will lag belling and at that time we will say it is yesterday in these places to the west of us. You probably have noticed the asterisk, Honolulu, Rangoon, and Calcutta are among several places on the surface of the earth which do not adhere to the standard time convention but keep time by a local meridian. Behind you on the wall is a digital Geochrone, showing Standard Time Zones of the World, showing how time is based on the prime meridian of Greenwich all over the earth. On this map you can find a number of places which do not adhere to the standard time convention.

The clocks are manufactured by the International Business Machine Company which accounts for the letters IBM on the dial. The time for setting is obtained by a radio from station WV operated by the United States Bureau of Standards and timed by the United States Naval Observatory. The radio is kept in the office but can be brought down here to the clock room when we wish to set these clocks if for some reason they should get off time.

Signs of the Zodiac

Lobby Floor

The zodiac is inlaid in a 14-foot circle using nine colors of Terrazzo and the 12 signs of the zodiac.  Starting at the east side of the room going counter-clockwise the first sign is that of Aries, the ram. On the twenty-first of March the sun crosses the celestial equator going from the southern to the northern half of the sky and spring begins. On this date the day and the night are each 12 hours long. Following Aries is Taurus, the bull. The sun enters this sign on about the twenty-first of and Gemini or the twins in May. On the 22nd of June the sun is at its northern-most point as seen from the earth. We are on the side of the earth’s orbit such that the northern hemisphere is tilted toward the sun. The 22nd of June is the longest day of the year in the northern hemisphere–the beginning of summer; and the sun enters the sign of Cancer, the crab. The two other signs of summer are Leo, the lion, and Virgo the virgin. On the 22nd of September the sun crosses from the northern to the southern half of the sky and on the northern hemisphere fall begins.  The sign for the beginning of fall is Libra, the scale pans or the balance, followed by the scorpion, Scorpio, and Sagittarius, the archer. On the twenty-first of  December the sun is at its southern in the sky – as sen on Earth. The earth is on the side of its orbit that tips the southern hemisphere to the sun. Winter begins at the northern hemisphere and we have the shortest day in the year. The signs of winter are Capricornus, the sea-goat; Aquarius the water boy; and Pisces, the fishes.

These signs are very ancient. They were put in the sky thousands of years ago. Never refer to them as constellations. Although there are constellations of the same names, they no longer correspond. Due to the precessional motion of the Earth’s axis, when the sun enters the sign of Aries it’s actually entering the constellation of the fishes. The distinction between sign and constellation is very important. The symbols on the inner circle are the shorthand notations for the various signs. The one for Aries, for example, is a conventional, face of the ram; the one for Aquarius is an ancient symbol for water which is the ancestor of our letter m.

Planet Symbols on the Railing

The eleven symbols in the railing are in order the short­hand notations for the Sun; Mercury, which is a conventional Caduceus which is similar to a doctors’ insignia; and Venus, whose symbol is the same as the female sign in biology.  The fourth one is the Earth, a circle with a cross, which is the same as a surveyor’s  bench mark symbol.  The  crescent Moon obvious. The next symbol one is Mars,, and again from biology, the male symbol.

The others in order are Jupiter, like a number “4″;  Saturn, something like a letter “h“;  Uranus, a figure like the Sun but with an  upward pointing arrow; Neptune’s trident; and the superposed letters P and L for Pluto.   The letters are partially in honor of the philanthropist that funded the search for Pluto, Percival Lowell.  The symbols are repeated once and the twenty-third and twenty-fourth places are occupied by the sun and the earth once more.

The telescope is a 38-inch Cassegrain reflector. This means that the principal mirror that is at the lower end of the tube is 38 inches in diameter. This mirror is ground to an accuracy of one-quarter wavelength of light in the form of a parabola which is the same curve that is used in making head lamp and search light reflectors. It has the property that light falling upon it in parallel rays is all reflected to a single point in front of the mirror called the focus. Astronomical mirrors are coated with aluminum in a coating one molecule thick on the front surface so that the sight does not pass thought the glass. In this telescope, before the light reaches the focus, it is intercepted by a secondary mirror is convex rather than concave and slows down the convergence of the light rays so that a longer, slimmer cone of light converges to a focus back of the main mirror, passing through a 9-inch hole in the main primary mirror, and the eyepiece focuses the image. This secondary mirror is 13-inches in diameter. This arrangement is called a Cassegrain reflector. The telescope is mounted in a U-shaped yoke. The axis which is in a horizontal position when the telescope isn’t in use and pointed in an east-west direction is called the declination axis It is about this axis that the telescope can be turned north and south. The u-shaped yoke is welded to the end of the inclined polar axis. This axis is parallel to the axis of rotation of the earth. This type of mounting is called equatorial. It has the definite advantage that the stars and the other celestial objects can be followed by means of a single motion about the polar axis. Objects rising in the east climb in the sky and move west­ward at the same time. If the telescope were mounted on a altitude/vertical and azimuth/horizontal axis, two variable motions would be necessary to follow a rising star. The equatorial mounting follows the star with one uniform motion. When 1^st built the telescope was driven by means of a 1/75 horse-power Bodine motor that was housed inside the hollow pier.  This old motor is on display in the NW corner of the dome.  The motor operates a gear box which supplies power through an inclined shaft and bevel gear to a worm gear on the north side below the right ascen­sion plate. A large tangent screw in a circular black housing is clamped to the polar axis and drives the telescope westward just rapidly enough, (once around in 23 hours and 56 minutes) to compensate for the rotation of the earth. The position of the telescope with respect to our horizon is indicated on the hour circle between the two bearings on the polar axis, Right ascension in the sky is set on the large plate above the tangent screw. This coordinate corresponds in the sky to longitude on the earth and enables us to ‘set the telescope accurately on any object in the heavens (in conjunction, of  Mounted above the main tube are three small telescopes– a three-inch refractor which is used as a finder for objects bright enough, and a  long-focus, 6-inch refractor which was formerly mounted on-the Irvington campus and later on the roof of Jordon Hall. It is used as a guide telescope for photographic or other work. The third telescope is a short-focus 6-inch reflector with a Newtonian mounting. It is called a “richest field” telescope because it is designed to see the maximum number of stars in any given cluster or region of the sky.

The moving parts of the telescope weight between 11/2 and 2 tons. The telescope is mounted on 33 cubic yards of concrete in the form of a pedestal beneath it and separated from the build­ing. This pedestal sits upon a concrete slab approximately 30 x 6 feet and two feet thick. This slab rests on four legs. The four chimneys or boxes which house these concrete legs can be seen in the lobby. (They are below the cabinets in the dome.) No part of the telescope mounting touches the building at any place. Vibrations of the building do hot hinder the telescope

The telescope is the largest in the state of Indiana. There are approximately on dozen larger in the United States. (Do not make the statement that is the largest available for the public or any other comparative statement which can be challenged by a visitor who knows better or thinks that he knows better, which is just as bad.) Small adjustments after the telescope is set upon an object are accomplished by means of two slow motion motors, one slowing or speeding the right ascension motion is alongside of the equatorial drive inside the pier. It is the motor on the west which drives a differential gear inside the gear box and slows down or speeds up the westward motion of the telescope for fine ad­justment. Adjustments north and south are accomplished by means of a reversible motor housed on the east arm of the u-shaped yoke just above the right ascension plate. This motor has a long screw which drives an arm attached to the clamp on the east end of the declination axis. The clamps are electro­magnetic (or if you prefer, solenoidal). In demonstrating the telescope do not clamp and unclamp these solenoid clamps. They have a certain life expectancy and should never be used unless for actual observation purposes. The same is true of the drive rotors. In leaving the telescope, leave it exactly on the meridian so that east and west hour circle readings are 0, and at 40⁰ north declination. Be sure that the motors and lights are turned off and t at the stage is pushed far enough back, so that no damage can be done to the telescope if

it should be moved. The stage should be left with brakes up and the casters in contact with the floor. However, never use the stage for the public unless all four brakes are set down. This is very important because the casters are not heavy enough to bear the load of the stage and visitors as well. After you have the telescope sets or before if you prefer, but before allowing visitors to come up the steps, lock the stage in position. Never leave the telescope alone for any length of time. It may turn and hit against the railing on the stage and do serious damage. In changing eye pieces never hand an eye piece to anyone. If you take the eye piece out of the telescope go down t e ladder and put it in the cabinet. If you get it from the cabinet, go up the ladder and put it in the telescope. Never pass the eye piece from one person to another. Many accidents have occurred this way. This rule should never be violated.