The question where we are seems to be a simple question to a practical mind. At the most it is answered by giving
the coordinates of the point. But it is not that simple. It is not very easy to give the exact coordinates of the point in a sphereical coordinate system having the Sun at
The World makes 3 periodical motions we barely feel: Rotating around the Sun, spinning, precession movement.
And the Sun moves around the center of Milky Way. And the Universe, at least our part of the Universe expands. Due to the
dark matter it may be. As we feel looking at the image right of this division, our sensory organs deceive us. We could say the better if we
have understood what we are. But having some predictions with us that appear to be at least partly true, we need to investigete, reinvastigate.
THE MOTION AROUND THE SUN
The basic geometry of the Earth around the Sun is repeated in the figure.
The diameter of the Sun is about 100 times of the Earth.
The shape of Earth’s orbit is an ellipse an eccentricity of less than 0.02. The distance between the foci is 4.8
The speed of our orbit is 108,000 km/h (30 km/s). The planet travels 940 million km during one orbit. The Earth
completes one orbit every 365.25 mean solar days.
We have already seen Kepler's first law, the orbits are ellipses. The second law states that a line joining a
planet and the Sun sweeps out equal areas during equal intervals of time.
The number of Kepler's laws is actually 3; third states the square of the orbital period of a planet is proportional
to the cube (3rd power) of the mean distance from the Sun .
The Earth rotates around once in 24 hours - that's a rate of 1000 miles (at the equator, 0° latitude, at surface)
per hour! The linear velocity at the equator 1/67 (approximately 1.5 %) of the velocity due to orbiting around the sun.
The angle between the tangent to the orbit's plane and the axis of rotation is about 23.5 °.
We do not know much about the changes these quantities have shown within 4.5 billion years, from the day of formation
till today. We do not even exactly know if the Earth is formed within and with the Solar System*.
It is a real pity that for some 30 thousand years we thought we were standing still and the whole Universe was spinning
around us. A good proof of the ability of our sensory organs.
The Earth is not a perfect sphere; it is slightly oblate.
The bulge in the middle along the equator is due to its rotation and the fact that it is not completely rigid. The
equatorial diameter is 43 Km (0.34%) greater than the polar diameter.
Sun and Moon have non-uniform gravitational forces on the Earth, pulling harder on the near side of the bulge than
on the far side. They try to make it perpendicular to the plane of orbit (Earth's, around Sun).
This is torque-induced precession (gyroscopic precession), the phenomenon in which the axis of a spinning object
(e.g. the Earth) "wobbles" when a torque is applied to it.
This of course means we have to expect winters in August in northern hemisphere after about 13 thousand years.
THE MOTION of the SUN, TOWARDS VEGA and AROUND the GALAXY
Sun and the Earth are moving at about 43,000 miles per hour (70,000 km/hr, roughly 43 times the Earth's linear
surface velocity at the equator) roughly in the direction of the bright star Vega in the constellation of Lyra .
They together move around the center of Milky Way and the speed is an astounding 483,000 miles per hour (792,000 km/hr).
A tour around the Galaxy takes about 225 million years. This means about 20 tours since the date of Earth's formation.
Solar system "bounces" up and down through the plane of the galaxy every 35 to 40 million years. As it passes through the densest part of the plane,
gravitational forces from the surrounding giant gas and dust clouds dislodge comets from their paths increasing the chances of a comet collision tenfold. The comets plunge
into the solar system, some of them colliding with the earth.
Before we conduct a detailed study of our position, we want to add two images shown left. The upper image is a sketch.
Both images are clickable
We have put the sketch because the page emphasizes we are a part of the Orion Spur and Sirius is always in our vicinity.
Later on we will try to make use of these data.
We have put the figure left-below because the reference emphasizes the dangers in our neighborhood and neighborhoods to
be. We seem to be lucky having an almost excellent umbrella like our athmosphere.
It is to be noted that different sources give different values for the period of our voyage up and down the galactic
plane. The given numbers change from 35 to 70 million years.
A real concern should be the probability of entrance of these cosmic radiation (protons, neutrinos etc.) into the Earth
triggering extra nuclear reactions. A further reference
emphasizes the connection between cosmic rays and the cilimate (life).
* "We found that Earth, the moon, as well as Martian and other meteorites which are samples of asteroids, have a lower concentration of the O-16 than does the sun," said Kevin
McKeegan, a Genesis co-investigator from UCLA, and the lead author of one of two Science papers published this week. "The implication is that we did not form out of the same
solar nebula materials that created the sun -- just how and why remains to be discovered."