• 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 month. 

Earth in the Solar System [5-8]

• 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 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 today. 
• 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 ever since. 
• 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.