Universe Today
Definition:
Origin of the Universe:
Evolution of the Universe:
Structure of the Universe:
Fate of the Universe:
History of Study:
Celestial bodies do not all revolve around a single point
The center of Earth is the center of the lunar sphere—the orbit of the moon around Earth; all the spheres rotate around the Sun, which is near the center of the Universe
The distance between Earth and the Sun is an insignificant fraction of the distance from Earth and Sun to the stars, so parallax is not observed in the stars
The stars are immovable – their apparent daily motion is caused by the daily rotation of Earth
Earth is moved in a sphere around the Sun, causing the apparent annual migration of the Sun
Earth has more than one motion
Earth’s orbital motion around the Sun causes the seeming reverse in direction of the motions of the planets.
When viewed in an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by an external force.
The vector sum of the external forces (F) on an object is equal to the mass (m) of that object multiplied by the acceleration vector (a) of the object. In mathematical form, this is expressed as: F=ma
When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.
