and Changes in the Earth and Sky [K-4]
The sun, moon, stars, clouds,
birds, and airplanes all have properties, locations, and movements that
can be observed and described.
The sun provides the light and
heat necessary to maintain the temperature of the earth.
Objects in the sky have patterns
of movement. The sun, for example, appears to move across the sky in the
same way every day, but its path changes slowly over the seasons. The moon
moves across the sky on a daily basis much like the sun. The observable
shape of the moon changes fromday to day in a cycle that lasts about a
Earth in the Solar System
The earth is the third planet
from the sun in a system that includes the moon, the sun, eight other planets
and their moons, and smaller objects, such as asteroids and comets. The
sun, an average star, is the central and largest body in the solar system.
Most objects in the solar systems
are in regular and predicatable motion. those motions explain such phenomena
as the day, the year, phases of the moon, and eclipses.
Gravity is the force that keeps
planets in orbit aroundthe sun and governs the rest of the motion in the
solar system. Gravity alone holds us to the earth's surface and explains
the phenomena of the tides.
The sun is the major source
of energy for phenomena on the earth's surface, such as growth of plants,
winds, ocean currents, and the water cycle.
Seasons result from variations
in the amount of the suns's energy hitting the surface, due to the tilt
of the earth's rotatoin on its axis and the length of the day.
The Origin and
Evolution of the Earth and Universe [9-12]
The sun, the earth, and the rest
of the solar system formed from a nebular cloud of dust and gas 4.6 billion
years ago. The early earth was very different from the planet we live on
The origin of the universe remains
one of the greatest questions in science. The "big bang" theory places
the origin between 10 and 20 billion years ago, when the universe began
in a hot dense state; according to this theory, the universe has been expanding
Early in the history of the universe,
matter, primarily the light atoms hydrogen and helium, clumped together
by gravitational attraction to form countless trillions of stars. Billions
of galaxies, each of which is a gravitationally bound cluster of billions
of stars, now form most of the visible mass in the universe.
Stars produce energy from nuclear
reactions, primarily the fusion of hydrogen to form helium. These and other
processes in stars have led to the formation of all the other elements.