None of us can feel it, but Britain rises and falls by centimeters every 12 hours and 25 minutes as a great bulge of ocean water washes around the country.
Jonathan Amos reports at BBC
Lunar Tides
The Moon’s gravity imparts tremendous energy to the Earth, raising tides throughout the global oceans. What happens to all this energy? This question has been pondered by scientists for over 200 years, and has consequences ranging from the history of the moon to the mixing of the oceans. The Moon’s gravity tugs at the Earth, causing ocean water to slosh back and forth in predictable waves called tides. We can visibly observe some of that energy dissipate at the beach, with waves rolling across coastal shallows and shoals. Most of the energy dissipates due to friction between the water and the shallow floor beneath it. This image showing tidal energy dissipation is courtesy of the Scientific Visualization Studio at the Goddard Space Flight Center. Can you possibly imagine the amount of energy required to lift such a huge column of ocean water by a few centimeters? And knowing that our body is 75% water, this tidal energy of the Moon would surely have a strong impact on us. It does affect our mind and body. We have known that insanity is at its peak during the full moon and mad people completely lose it. It is then that they pray to the god (as Guru, the kind teacher) for restoring mental balance.
The tides at a given place in the Earth’s oceans occur about an hour later each day. Since the Moon passes overhead about an hour later each day, it was long suspected that the Moon was associated with tides. Newton’s Law of Gravitation provided a quantitative understanding of that association.
Differential Forces
Consider a water molecule in the ocean. It is attracted gravitationally by the Earth, but it also experiences a much smaller gravitational attraction from the Moon (much smaller because the Moon is much further away and much less massive than the Earth). But this gravitational attraction of the Moon is not limited to the water molecules; in fact, the Moon exerts a gravitational force on every object on and in the Earth. Tides occur because the Earth is a body of finite extent and these forces are not uniform: some parts of the Earth are closer to the Moon than other parts, and since the gravitational force drops off as the inverse square distance, those parts experience a larger gravitational tug from the Moon than parts that are further away.
In this situation, which is illustrated schematically in the adjacent figure, we say that differential forces act on the body (the Earth in this example). The effect of differential forces on a body is to distort the body. The body of the Earth is rather rigid, so such distortion effects are small (but finite). However, the fluid in the Earth’s oceans is much more easily deformed and this leads to significant tidal effects.
A Simple Tidal Model
We may illustrate the basic idea with a simple model of a planet completely covered by an ocean of uniform depth, with negligible friction between the ocean and the underlying planet, as illustrated in the adjacent figure. The gravitational attraction of the Moon produces two tidal bulges on opposite sides of the Earth.
Without getting too much into the technical details, there are two bulges because of the differential gravitational forces. The liquid at point A is closer to the Moon and experiences a larger gravitational force than the Earth at point B or the ocean at point C. Because it experiences a larger attraction, it is pulled away from the Earth, toward the Moon, thus producing the bulge on the right side. Loosely, we may think of the bulge on the left side as arising because the Earth is pulled away from the water on that side because the gravitational force exerted by the Moon at point B is larger than that exerted at point C. Then, as our idealized Earth rotates under these bulges, a given point on the surface will experience two high and two low tides for each rotation of the planet.
Kendra
The concept of Kendra was derived from these lunar tides and whenever we talk of the Moon, the significator of the mind and consciousness, it is always these kendra that come into focus. Since the ‘bulge’ is always with the Moon, the exact longitude of the Moon in the chart is the ‘high-water’ point. The word Kendra means ‘the center’ of affairs and refers to the ‘four pillars’ which are at the first, fourth, seventh and tenth houses (signs) from the Moon.
Water is life-saving and the high bulge indicates the signs which are life saving or life-giving. These are the first and seventh houses from the Moon. In contrast, the low bulge indicates life-losing or suffering and expenditure of life force. These are the fourth and tenth houses from the Moon.
Spring and Neap Tides
When the sun and moon are aligned, there are exceptionally strong gravitational forces, causing very high and very low tides which are called spring tides, though they have nothing to do with the season. When the sun and moon are not aligned, the gravitational forces cancel each other out, and the tides are not as dramatically high and low. These are called neap tides.
One thing is clear now – the Sun also has an impact on these tides, which means the Sun also has ‘Kendra’ houses called ‘Sūrya kendra’ and the signs in the 1st (Sun longitude) and 7th house (180° from Sun) will have the ‘solar bulge on tide’ whereas the 4th and 10th houses (90° from Sun) will have low tides. The impact of the Sun is much lower than that of the Moon, which makes the Moon the temporary boss and it rules the mind which is the boss of the mind-body-soul jīvātmā system. We now have two bulges – one is the bigger lunar bulge and other is the smaller solar-bulge in the ocean waters.
Spring Tides
When the moon is full or new, the gravitational pull of the moon and sun are combined spring tides occur. Basically, the lunar-bulge is now in alignment with the solar-bulge. This causes the overall bulge in the ocean water to be very high. At these times, the high tides are very high and the low tides are very low. This is known as a spring high tide. Spring tides are especially strong tides (they do not have anything to do with the season Spring). They occur when the Earth, the Sun, and the Moon are in a line. The gravitational forces of the Moon and the Sun both contribute to the tides. Spring tides occur at the full moon (pūrṇimā) and the new moon (amāvāsya).
Neap Tides
During the moon’s quarter phases the sun and moon work at right angles, causing the bulges to cancel each other. The result is a smaller difference between high and low tides and is known as a neap tide. Neap tides are especially weak tides. They occur when the gravitational forces of the Moon and the Sun are perpendicular to one another (with respect to the Earth). Neap tides occur during quarter moons called aṣṭamī (8th tithī).
Graha Kendra
In this manner the seven planets from Sun to Saturn, called the naked-eye planets, exert a gravtitational force on the earth which has some effect on the tides. Of these the impact of Sun and Moon are the strongest. Indicentally, these two planets are also the luminaries (planets with high light). Therefore they symbolise the play of emotions and information in the mind. Full moon or new moon symbolises high emotions while the quarter moons aṣṭamī (8th tithī) shows the best balance of emotion and higher logic. Yet there is a difference between the full moon and the new moon in that the quantity of moonlight is different – full moon (pūrṇimā) has full light showing complete exposure and driving away of darkness while the new moon (amāvāsya) has no moonlight showing the victory of the dark forces which promise material wealth and slavery of mankind.
Proxigean Spring Tide
The Proxigean Spring Tide is a rare, unusually high tide.
This very high tide occurs when the moon is both unusually close to the Earth (at its closest perigee, called the proxigee) and in the New Moon phase (when the Moon is between the Sun and the Earth). The proxigean spring tide occurs at most once every 1.5 years. Now this period of 1½ years or 18 months is the period taken by the nodes (Rāhu and Ketu) to transit a sign as their zodiac transit (360°) is the Saros cycle[1] of about 18 years.
Navagraha
We have now determined that there are nine factors or variables which can affect the mind-body system and these are called the navagraha. These include the seven naked-eye planets from Sun to Saturn and the nodes Rāhu and Ketu.
The word graha is derived from grahaṇa which means to capture or seize. These graha have the power of seizing the body and mind through forces of which one is the gravitational force which is studied from ‘kendra houses’. The influence of the kendra houses is called kendra dṛṣṭi – aspect of quadrants. The Maharṣi have provided equations to determine the overall influence of the dṛṣṭi (or effect of all forces including the gravitational force). Yet we must bear in mind that the kendra (gravity) is fundamental and its impact is very strong. Everything works around it or works to alter and influence it.
[1] The periodicity and recurrence of eclipses is governed by the Saros cycle, a period of approximately 6585.3 days (18 years 11 days 8 hours). Later we learn that this is called Rahu Dasha!
