Observers on Earth have been examining the skies for thousands of years. Today’s young people are not often challenged to explain the movement of stars, planets, the moon, and the sun. They may not notice any movement of these bodies in just a few minutes or even an hour. Teachers instruct students that our earth rotates on its axis and revolves around our sun using video animations of solar system mechanics. These animations may not support their assertions with extensive experimental evidence.
The best science teaching is a discovery-based approach when possible. Without prior instruction it is doubtful that contemporary observers of the heavens would conclude that diurnal (daily) motion of the sun and stars is not real but instead, apparent. Historically, thousands of brilliant natural philosophers did not grasp this truth. Natural philosophers, renamed “scientists” in 1833 thanks to William Whewell, mostly accepted the heliocentrism of Nicolaus Copernicus. In the centuries prior to Copernicus, very few natural philosophers adhered to the heliocentric (sun-centered) concept that the earth rotates on its axis and revolves around a central sun. They were geocentrists believing earth was central with sun and stars revolving around us.
The centuries since Copernicus’ proposal of heliocentrism did not produce unanimity. In the 17th century brilliant astronomer Galileo was sentenced to house arrest by a church tribunal in the last years of his life. The commonly accepted interpretation that scripture taught a motionless Earth at the center of the universe was a difficult hurdle to overcome. In 1992 under Pope John Paul II the Catholic Church formally absolved Galileo. A church spokesman stated, “We today know that Galileo was right in adopting the Copernican astronomical theory.”
What experimental evidence is involved in proving that the earth rotates on its axis and revolves around the sun? After having taught extensive units on astronomy many years ago, I reviewed the unit notes I retained. We devoted considerable time to the study of experimental evidence and performing classroom demonstrations to reinforce the heliocentric view of astronomy. I have selected two topics supporting belief in Earth’s rotation (Coriolis effect, and the Focault pendulum), and two topics supporting belief in Earth’s revolution (seasonal changes in angles of insolation, and the shift in constellations throughout the year). Following is a brief description of each.
CORIOLIS EFFECT (Indicator of Earth’s rotation): In the northern hemisphere, moving objects are deflected to the right. Southern hemisphere moving objects are deflected to the left. Wind flowing over the earth’s surface is an example. If a low pressure area exists, air tends to flow from high to low pressure, always deflecting to the right. This explains why moving air in a low pressure system such as a nor’easter or hurricane has counterclockwise wind circulation. Rotating playground carousels illustrate the effect. A moving ball rolled across the platform is deflected to the right if the platform is rotating counterclockwise as does Earth in the northern hemisphere and to the left if the platform is rotating clockwise as in the southern hemisphere. Airline pilots must correct for this effect otherwise they will miss the destination they “aim” for. If Earth did not rotate, there would be no such effect. Gustave de Coriolis described this effect in 1835.
FOCAULT PENDULUM (Indicator of Earth’s rotation): Science museums around the world have exhibits of the Focault pendulum. Physicist Leon Focault devised an experiment in Paris in 1851. He suspended a 28kg mass on a 67m long wire. Wikipedia describes an idealized experiment performed at either the north or south pole of the Earth: “…the plane of oscillation of a pendulum remains fixed relative to the distant masses of the universe while the Earth rotates underneath it, taking one sidereal day to complete a rotation.” At Franklin Institute in Philadelphia PA, my classes observed a working Focault pendulum many times.
CHANGING STAR CONSTELLATIONS throughout the year (Indicator of Earth’s revolution around the sun): We invite you to read our past post on The Bible Zodiac. The detail in this post should help you understand the proof for Earth’s revolution around the Sun:
DIFFERING ANGLES OF INSOLATION from season to season (Indicator of Earth’s revolution around the Sun): Insolation refers to the angle at which the rays of sunlight strike the surface of the Earth at noon each day. This angle changes from season to season. Direct (straight overhead) rays arrive at the Tropic of Cancer on June 22 and the Tropic of Capricorn on December 22, six months later. On March 22 and September 22 direct rays fall on the equator. These dates correspond with beginnings of seasons. The angle of insolation varies 47º to produce seasonal cycles depending on the location of earth in its orbit. This results from Earth’s constant 23.5º axis tilt. Our understanding of Earth’s revolution is strengthened by knowledge of these facts.
God has perfected an intricate, orderly Solar System to produce the wondrous cycles we observe. Humanity was slow to understand cause and effect within our system. Proof was difficult to accept because men imposed personal interpretations of reality upon what they observed. The Creator gifts man with ability to observe, analyze, and explain in search of truth concerning our Solar System.