The sun rises every day. So does the moon. We know the solar eclipse occurs when the moon comes between the sun and the earth. Why doesn't it happen every day?
A more acurate, non-Kepler version is here. I'm sorry for my poor English, if you call it English.
The usual chart about the solar eclipse explains how it occurs very well. It gives us good visual definitions of two kinds of shadows, umbra and penumbra. The umbra is the region where the light is completely blocked by the astromonial body (the moon in this case). An observer in the umbra can see a total eclipse. The penumbra is the region in which only a part of the light is obscured and a partial eclipse is observed.
However, it might give us a wrong impression on the frequency of the solar eclipse.
Firstly, if the earth is fixed (does not rotate), the moon goes around the earth once a day, just as we observe it with a pre-Copernican mind. But if both the earth and the sun are fixed, as in the 2D chart above, it takes about 30 days for the moon to make a circle around the earth. That's why we call it month. The arrangement of sun-moon-earth occurs only once a month, not once a day.
Secondly, the sizes and distances of the three objects are deceptively distorted in the chart. If proportionally drawn, the coin-size sun on the front page of a broad sheet newspaper would need the period-size moon on page 4. The shadow made by the distant sun is minuscule.
Finally, the space is 3 dimentional. In most cases, the razar-thin shadow of the moon travels well above the north pole or below the south pole of the dot-size earth.
The interactive chart on top of this document are drawn proportionally to the actual size. The yellow sharp cone shows its umbra. The white grid indicates earth's equator plane. You can zoom in to the earth or zoom out to see the whole solar system. Remember, your slow drag/touch makes the viewpoint move faster than light.
Positions of all planets are calculated on the fly using Kepler's laws of planetary motion. The lunar orbit, which is gravitationally affected by not only the earth but also the sun or even the jupiter, is hard to calculate by the Kelper's laws. In this graphics it is calculated from the formula of the Hydrographic and Oceanographic Department, Japan Coast Guard.
In this interactive graphics, the total solar eclipse does not occur in August, 2017. I am still unsure if the calculation is right. But even if it is right, the lunar position will have 1000km margin of error. It is very small in the vast space but too large to predict the position of the shadow on the surface of our planet. I will try to predict it by using NASA's JPL database.
textures: the earth: Natural Earth, the moon: solarsystemscope