For noon to occur the same time daily, the earth needs to do one full rotation daily.For noon to occur approximately at the same time daily, a point on Earth's axis must continually face the direction of orbital motion as opposed to always pointing in the same direction.
Earth's tilt is not what I question however. I question the axis always pointing in the same direction
The front of the axle is always facing the orbital direction of motion.
With the axle always pointing in the same direction, noon in March would be midnight in September.
jacmac wrote:1) Do you agree that the end (either end) of the axis of rotation of the earth always points to the same place in the sky, as defined by the stars. Yes or no ? I think yes.
A "point" on the axle facing the direction of circular or orbital motion.jacmac wrote:2) What is the "front" of the axle of the wheelbarrow?
A solar day is a complete rotation of an object on its axis. A sidereal day is one complete rotation of an object about the center of its orbit. If Earth was the sun, the moon would have a perpetual solar day: its not rotating on its axis. However, it would have one sidereal day.jacmac wrote:Also, check out the difference between the Solar day and the Sidereal day.
A solar day is a complete rotation of an object on its axis. A sidereal day is one complete rotation of an object about the center of its orbit.
Move the flashlight to the edge of the spinning lazy Susan and the light on the fixed ceiling moves.
Earth's rotation observed from the center: sun.jacmac wrote:A solar day is a complete rotation of the earth(on its axis) relative to the sun, high noon to high noon, for example.
Earth's rotation observed from a fixed distance: a star.jacmac wrote:A siderial day is a slightly different complete rotation of the earth(on its axis) relative to the STARS.
http://spaceplace.nasa.gov/seasons/en/ The illustration in the NASA link shows America in direct sunlight (noon) in March and in Earth's shadow (midnight) 180 degrees later in September. If Earth is orbiting the sun and making one complete rotation daily, that is exactly what we should experience: a 12 hour change in time every 6 months or 180 degrees: 6 hours every 90 degrees. However, the sun is overhead at noon every day throughout the year and we don't have to change our clocks.
Dad, an observer at the center of a merry-go-round sees only one side of Junior mounted on the horse. Mom at a fixed distance away, sees all sides of Junior once per orbit. Both see Junior at the same time but from a different perspective.
jtb wrote:Help me out. We don't experience this 180 degree shift in time. The only alternative I can think of is that the sun is actually orbiting Earth.
One rotation/orbit: left side of Earth is facing the sun... for half the day, right side the other half of the day.One rotation/orbit: left side of Earth is facing the sun. 180 degrees, or 6 months later the right side is facing the sun.
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