Basic Astronomy

Basic Astronomy

What makes the planets move the way they do?

To begin with, there is some misunderstanding as to just what is meant by the term universe. Often popular writers use it to mean the particular group of stars to which our Sun belongs. As the astronomer uses the term, however, it is considered to mean the sum total of all the stars and other cosmic bodies.

Scientists do not know as yet how the universe originated and developed. The most useful idea about it so far is that set forth by Albert Friedmann in 1922. He based his ideas on Einstein’s relativity theory. According to Dr. Friedmann, everything in the universe was at one time packed together into a tiny point. This means all energy as well as matter – remember that the one can be converted into the other as is demonstrated by atomic power plants. Well, since all the energy and all of the matter in existence were confined in such a small space, the pressures were tremendous. The result was an enormous explosion.

Stars and galaxies… Could it be, intelligent life is awaiting for us somewhere in the Universe. Illustration: Elena (Megan Jorgensen)

After this explosion, every particle in the universe began to move away from every other particle. This is the theory of the expanding universe. American astronomer Edwin Hubble found good evidence that it is the truest picture of the cosmos that we have.

If you want to know how every particle in the universe can move away from every other particle, consider the example of a child’s balloon. If you make a series of ink dots at random on the balloon’s surface and then blow it up, you will find that the distances between every given spot and all of the other spots increase.

When the primordial universe exploded, its particles were those of atom of hydrogen gas and dust. Some quantities of this condensed into stars, and groups of stars began to congregate as galaxies. Not all of them did, however, and there are still great clouds of dust and hydrogen in the universe.

Those astronomers who go along with this theory believe that the universe will keep expanding until some definite time far off in the future. Then the particles will begin to come together again. The universe will shrink once more into an infinitesimal point, the internal pressures will increase, and there will be another explosion.

Thus, over countless years, the universe will alternately shrink and expand. It is interesting to compare this theory with the ancient Hindu concept in which the god Brahma breathes the entire cosmos in and out, each breath lasting billions of years.

It is possible for astronomers to observe the rate at which the universe is expanding. Once they learned that rate, it was only a matter of working backwards to find the time when it had started. That was approximately 15 billion years ago.

We know that light travels at a certain speed, actually 186 thousand miles per second. If the universe is fifteen billion years old, than no light can reach us that comes from a distance farther than that which light can travel in that time. That distance, by the way, is 90 sextillion miles, – a figure we can represent by 90 with 21 zeroes following it.

Now, if astronomers can locate objects in the universe that are 90 sextillion miles away, then their light must have started out from them 15 billion years ago. But 15 billion years is the age of the universe. So the light from those objects must have begun its trip at the time the universe was formed.

In 1963, astronomers first discovered those bodies. They not only give off the light, but radio waves as well. The interesting question is, since their light comes from the most distant possible point in the universe, when we look at them, are we seeing the light that was given off at the time the universe was created? And what are they like now?

The groups of stars that formed when the universe began to expand are known as galaxies. The galaxy in which our Sun is located is popularly called the Milky Way. It looks like a bright band of millions of stars that sweeps across the sky. Actually, it has been estimated that it is made up of over 200 billion separate stars.

We see the Milky Way as a band because of the way that we are positioned in it. It is really shaped like a Fourth of July pinwheel. The Earth is so situated that we look across the narrow edge of the pinwheel. In our galaxy, our Sun is a rather small and aging star.

Astronomers know that by the kind of light that it gives off. If it were younger, the light would be bluer. The Sun, when it set, will appear as a blue ball instead of a red one.

The next star to our Sun is Alpha Centauri. It is about 26 trillion miles away. The light that arrives here from Alpha Centauri started out over four years ago. There is some evidence that there are planets circling this star.

Our Sun does not remain still in the galaxy. It moves at a constant rate towards a point in the constellation of Hercules, dragging the solar system of planets along with it. It is at this point that the galaxy becomes to students of astrology. Professor Giorgio Piccardi of the University of Florence in Italy showed that forces which apparently originate in the galaxy are capable of altering the rate of chemical reactions, some of which involve compounds analogous to those found in human issues. This has suggested that the forces which make astrology “work” may not originate in the solar system at all, but at some point in the Milky Way or even beyond.

At this point we have moved from the universe and into the galaxy. We will now go from the galaxy down into the solar system proper.

Astronomers estimate that the solar system is 4, 5 billion years old. When the explosion occurred, the universe was filled with clouds of gas and dust. Gravity drew the particles of these together causing huge incandescent bodies – the stars – to condense out of the contracting clouds. One of those bodies was our Sun. Out of the remains of the cloud from which the Sun was formed, the planets appeared. Probably they were originally rings of dust that rotated around the Sun’s equator. Eventually the condensed into spheres of more or less solid matter.

The planets are arranged roughly on a plane that extends from the Sun’s equator. They move a little above and below that plane at different times. The distance they are above and below the plane is known as planet’s latitude. The plane itself is known as the ecliptic.

The Sun has no declination. The reason is that declination is measured from the Earth, and, from that viewpoint, the ecliptic passes through both the Earth’s and the Sun’s centers.

Now, though the ecliptic passes through the Earth’s center, it does not coincide with the Earth’s equator. The Earth is tilted off-center on its axis by about 23 degrees. Because the ecliptic and the equator do not coincide, from our point of view the Sun appears to go below the equator in winter and return above in in the summer.

The times at which it crosses the equator are known as the autumnal equinox – and the vernal equinox.

The Earth turns on its axis at a regular rate, on revolution per day. For convenience geographers divided the Earth into 360 divisions along the equator. Those are called degrees of longitude pass by given point in 24 hours. This is at the rate of 15 degrees per hour or one degree every four minutes.

The particular degree on which you are situated is called your meridian. It is also the highest point that the Sun will reach any day. This is the location of the medium coeli (M.C) or Midheaven. The meridian passes through the zenith or the point in the sky directly over your head. The zenith is always the same number of degrees above the equator which gives them their ship’s latitude.

Another method of measuring positions in the sky is by their hour angle. We saw that the Earth moved at the rate of one degree every four minutes. For us, that means that the heavenly bodies seem to move over our heads at the same rate. We can locate a body by saying how long it will take to reach our meridian or by how long it has been since it passed our meridian.

For instance, let us say that a body is located 15 degrees to the east of our meridian. We know that at the rate of four minutes for each degree, it will take 4 times 15 minutes or one hour to come to our meridian. Thus we say that the body has an hour angle of one hour east. If it had passed the meridian and was 15 degrees away, we would say it was one hour west.