We cannot even begin to imagine the size of the universe. Objects in the universe are separated by huge stretches of essentially empty space.  Scientists wonder if the universe is infinite, which means that there would be no limit to its size.  Our powerful telescopes have found no end to the stars, or the huge flocks of stars that we call galaxies.

     In space, distances are measured in light years -- the distance that light in space can travel in a year. Light travels at 186,000 miles a second. It takes light a little over 8 minutes to reach us from our sun. It takes light from our sun more than four years to reach the nearest star, Proxima Centauri.

     Scientists think that the universe is governed by the same natural laws everywhere. There is gravity everywhere, and it works in the same way. The structure of the atoms of elements is the same everywhere. Light travels at the same speed under the same conditions everywhere. This means that your world, no matter where it is located, will obey the same laws of physics and chemistry as the earth.

     One of the questions that interests me is whether, just as there are physical and chemical laws, there are also universal biological laws. We cannot know this by studying a single planet, but we can think about it.

Now, let's start thinking about how your planet took form.

     Though stars, planets, comets, and moons engage our attention, the universe is mostly empty. In the spaces between the stars, you might be able to find one tiny hydrogen atom in a cubic yard of the vacuum. It is difficult to imagine such an absence of matter -- here on earth we have air, that fills emptiness as we commonly think of it.

    However, the vacuum of space does have matter in it. Gravity causes the material objects in space to attract each other. The more massive the lump of matter, the more pull it exerts on anything around it. As little clumps of space dust collect, they exert more gravitational force on everything near them. In time, huge clouds of dust can accumulate. As gravity pulls the atoms more closely together, the dust heats up. Eventually a huge mass of hot matter can become a star, surrounded by a swirling, flattened disk of dust that may have smaller lumps of matter accumulating in it. These smaller lumps may become planets and their satellites. They, too, may be hot for a time.

     The relationship of the planet to its sun determines such characteristics as temperature, year length, and gravitational forces. We can calculate how much solar energy the planet receives. Newtonian physics has provided formulas that allow us to work out these relationships. We can do at least rough calculations that will help us to describe these relationships realistically.

     For more information, check Lesson 1 of your Science Notes or visit some of the helpful web sites out on the web. Or you may Return to Lesson 1 and check on the assignments.