Page 14 - Curriculum Visions Dynamic Book

 Stages in an eclipse of the Sun.
southern region in March.
Sun, Moon, and eclipse
By coincidence, the apparent size of the Sun and the Moon
are the same. As a result, when the Moon moves in front of the Sun, the silhouette of the Moon almost exactly covers the disk of the Sun, producing an eclipse.
The Sun’s size
The Sun is 1,392,000 km across (109 times the diameter of the Earth) and has a mass that is 330,000 times that of the Earth and 743 times the mass of all of the planets combined (see page 49).
The huge mass of the Sun generates an amazing gravitational field that, among other things, holds all of the planets in order. Over time—like a celestial brake—the Sun’s gravity will slow down the rate at which the planets spin. In four billion years, for example, the Earth will only spin on its axis once every 30 days.
The Sun has a reasonably constant size. That is not true for all stars; for example, Betelgeuse changes size from between 430 to 625 times the diameter of the Sun in just under 6 years.
celestial Relating to the sky above, the “heavens.”
eclipse The time when light is cut off by a body coming between the observer and the source of the illumination (for example, eclipse of the Sun), or when the body the observer is on comes between the source of illumination and another body (for example, eclipse of the Moon).
gravitational field The region surrounding a body in which that body’s gravitational force can be felt.
For more on eclipses see Volume 3: Earth and Moon.
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