Is the Earth a spheroid or an ellipsoid?

Neither. It's an ovoid. That is, very slightly egg-shaped. Let me explain.

Thousands of years ago the ancient Persians thought the Earth was a stone tablet held in the beak of an eagle perched on the shoulders of a giant kneeling on the back of an elephant standing on a turtle swimming through the sea of eternity. Wow! Heavy stuff! The egg-heads later decided it must be an egg because all life came from it.

Then some free-thinker dared to suggest that it must be flat because no one had slid off the egg's curved surface yet (well, it made sense).

It wasn't long before those pesky Greeks came along and stuck their noses in by declaring that the Earth was a sphere. No one believed them. Then around 240 BC Eratosthenes, a Greek working in Alexandria, went to the bottom of a well, probably after a heavy night on the grapes. The next day he noticed that the sun was directly overhead at noon when it should have been 7° from the zenith. Being a maths freak he made some quick calculations and found to his horror that his results did not agree with what Euclid had been telling people many years earlier. He concluded that the Earth was indeed a sphere and proceeded to calculate its diameter and circumference. He came quite close, much closer than that Columbus guy who got lost somewhere between east and west.

Eratosthenes must have seen a few stars as well when he fell into the hole but we have no record of him making any other celestial observations.

By the 16th century people were convinced that the Greeks were nuts and the Earth was actually an oblate spheroid, or an ellipsoid. The French didn't agree. They went one better. They suspected the earth was an egg (again?) and in 1736 the French Academy of Sciences sent two expeditions, one to Lapland and one to Ecuador, to settle the question of the Earth's shape once and for all. Their findings were close, but not exactly conclusive.

We now know from the latest scientific evidence and NASA's satellite data that the Earth is indeed an ovoid, give or take a few bumps. So back to the egg. After all those years and a few billion dollars down the gurgler we have discovered what the ancients already knew 6000 years ago.

The Earth is slightly flattened at the poles.  Its equatorial diameter is 45 km (28 miles) longer than its polar diameter. But wait, that's not all. As well as being generally ovoid, the Earth also has a vertical pear-shaped asymmetry, the north pole being 48 m (148 ft)  further from the equatorial plane than the south pole.

The "pointy end of the egg ", so to speak, is at about 37° west longitude (400 km off the eastern tip of Brazil) where the equator's longer axis is 159 m (522 ft) greater than its short axis. The "fat" end is just north of east Papua New Guinea.

These variations may seem trivial but they are significant enough to be considered a necessary part of precise calculations in cartography and new-fangled position finding electronics.

Many scientists still disagree about the true shape of the Earth but recent evidence and the perturbations of satellite orbits prove beyond a doubt that the Earth is indeed an ovoid.

However, the earth's shape is being continually evaluated and the figures I have given above may already be obsolete. Perhaps in a few hundred years some deeper thinker will come up with proof  that the Earth is actually a peanut.

Atoms do not naturally destruct. They continuously recycle through time and the universe. Our bodies (and all other things) are made up of atoms or sub-atomic particles that have existed for billions of years and will continue to exist for billions more. They are continuously assembling and disassembling to form the molecules of which everything in the universe is made. When a molecule disintegrates its atoms go on to make something else.

Many billions of atoms pass through our bodies every 6 months or so. In fact as many as 90% of our atomically structured molecules are replaced during this period.

Our bodies are made up of indestructible atoms that were once part of other persons and objects. There are atoms in our bodies that have probably passed through Caligula, Macbeth, Shakespeare, and Napoleon, to name a few.

We mustn't get too excited though; it's still a bit early for us to have inherited anything from Marilyn Monroe.

If you are an amateur astronomer or a navigator, have you ever needed to make celestial observations using a sextant, from your own back yard or any other location where a reference horizon is not visible?

Not a problem. Do what I do. Ask the wife for her largest oven tray. No! No! Don't tell her why you want it. Lay it on a flat surface and pour in some dark viscous fluid. Engine sump oil will do fine. The angular altitude of the celestial object you are observing will be half the angle between the object and its reflection in the fluid.

Is gravity a force? I am sure the malcontent would insist "There is no gravity. The Earth SUCKS". Most people would say that gravity is a force of attraction. With apologies to Newton this is not strictly correct either. Einstein gave him a bit of a nudge with his General Theory of Relativity.

According to the theory, gravity is not a force. It is the geometric consequence of the curvature of space-time warped by mass and energy in its vicinity.

Space and time are joined together in an interdependent combination in which time becomes the "fourth dimension". We refer to this union as a space-time, ie a four-dimensional non-Euclidean continuum that is warped by the presence of large masses. Moving objects in this continuum follow geodesic orbits that are paths curved toward the mass causing the greatest distortion. This apparent attraction toward the mass is what we call 'gravity', still simply referred to as a "force".
(Come to think of it, no one has worked out yet why the objects begin to move in the first place.)

The American physicist John Wheeler put it very succinctly when he said, "Matter tells space how to curve, and space tells matter how to move" (I believe space-time would have been a more suitable expression).

There is a lot more to it than that, of course. This is a complex subject not easy to explain properly in a few short sentences and without resorting to some horrendous mathematics. Einstein moved in the most complex areas of physics, indeed all science. To even begin to understand his theories requires a total suspension of disbelief and an acceptance of some bizarre and often disturbing truths.

There are many theories attempting to explain the nature of gravity but most of them eventually come back to different interpretations of the universe, time, multi-dimensions and the continuum.
Many questions remain unanswered, for instance why are atoms mostly empty space and what causes the strange behaviors observed in quantum mechanics.

This site is for entertainment and social interest and it is not an appropriate place to get into a heavy discussion of Einstein's or anyone else's theories. I hope to launch a site in the near future dealing wholly with the General Theory of Relativity.

I am currently writing a book titled "The nature of the Cosmos"  in which I will be discussing in detail the make-up of the universe, relativity, gravity, and space-time continuum.

Meanwhile, site visitors wanting to know more about these topics might find interest in the following related subjects: general relativity, string theory, quantum theory, Lorenz transformations, Minkowski space and Reimannian geometry. More information can be found at http://people.hofstra.edu/faculty/Stefan_Waner/diff_geom/tc.html