What is the tidal effect?
The Earth and the Sun both exert a pull on the Moon. However, the Moon’s power the tides is more than twice that of the Sun, since the Moon is much closer to the Earth than the Sun and force of gravity is inversely proportional to the square of distance.
Does the tidal effect apply to solid bodies like the Moon?
If the Moon were compared of liquid or gas, it would tend to bulge out in the direction of such pull. This is called the tidal effect.
However, since the Moon is solid, the tidal effect does not result in any noticeable distortion of its shape, but nevertheless the imbalance of forces created by the tidal effect does distort the Moon’s shape slightly.
Why does high tide occur twice each day instead of once?
One high tide caused by the bulge produced in the ocean as the Moon pulls the ocean towards it.
Another high tide is created in the ocean due to the slight shift in the solid portions of the Erath towards the Moon, caused by the pull of the Moon. Strictly speaking, this type of tide is not due to the sea ‘rising’ but the land ‘sinking’. The second type of high tide occurs on the side of the Earth facing away from the Moon.
Why the tide does appear to move from east to west?
On account of the Earth’s spinning motion form west to east, the tide appears to move from east to west.
What is the main result of the tidal effect on the Earth-Moon System?
The mutual tidal effects between the Earth and the Moon result in the showing down of the spinning motion of the Earth and the Moon, as the tides act as a brake on the spinning heavenly bodies, Millions of years ago, both the Earth and the Moon were spinning much faster than they do now. In fact, the Moon has completely ceased to rotate relative to the Earth and the other side of the Moon is permanently hidden from observers on Earth.
What is the rate at which the Earth’s rotation is slowing down?
About one second in 50,000 years.
Does the Moon move with constant velocity at all times?
No. the velocity of the Moon is appreciably greater near perigee than near apogee. The Moon speeds up and slows down regularly during each orbit.
Does the slowing down of the Earth’s spinning rate, due to tidal forces, have any other effect on the Earth Moon System?
Yes. The distance between the Earth and the Moon is slowly increasing. The Moon is moving away from the Earth at a rate of about 3 centimeters per year.
Will the Moon continue to move away from the Earth indefinitely?
At some stage in the future, the Earth would slow down its rotation relative to the Moon to such an extent that it would present only one face to the Moon, just as the Moon now presents only open face to the Earth. When such an event occurs, all tidal effects would cease except for tidal effects caused by the Sun. when it is at a distance of about 545,000 km compared to the present distance of about 382,000 km the Moon will stop moving away from the Earth and will instead start moving towards the Earth.
In the far future, when the Moon starts moving towards the Earth, to what extent would it move closer to the Earth?
As the Moon approaches very close to the Earth, the Earth’s gravity would stretch and distort the Moon. Finally, at a critical distance from Earth the distorting forces developed in the Moon would be sufficient to shatter the Moon into millions of pieces which would orbit the Earth in the form of a ring. The ring around the planet Saturn is believed to have been formed in this manner.
Does the tidal effect apply to the Earth also?
Yes. The Earth is pulled by the Moon and the Sun. however, since there is a large body of water on the Earth, the Earth actually distorts and changes shape, resulting in the water levels of the oceans periodically rising and receding. These are known as ocean tides.
Just as tidal effects occur on Earth in the oceans; do they occur in the atmosphere also?
Yes. The tidal effect applies to the atmosphere also since the atmosphere is really a gaseous ocean.
What is secular acceleration?
Besides the regular speeding up and slowing down of the Moon during each orbit, there is also a gradual slowing down of the average speed of the Moon over a very long period. This is due to a combination of the tidal effects and also because of the slight orbital changes caused by the pulls of the planets Venus and Mars. The effect is very small and is noticeable only over a period of hundreds of years.
How can secular acceleration be studied?
Modern astronomers study secular acceleration by going through the records of total solar eclipses left by ancient astronomers. This is because a total solar eclipse can only happen at New Moon, and hence such ancient records are a reliable guide to the behavior of the Moon in the past.