The Sun, the Moon and the Earth Class 7 Geography Notes Maharashtra State Board
The Moon’s Motions:
Like the Earth, the moon also has axial and orbital motions. The moon while rotating around itself, revolves around the earth and the earth revolves around the sun. As a result, though the moon does not revolve around the sun independently, indirectly, it makes revolutions around the sun. The time it takes to make one revolution around the earth and one rotation around itself is the same. That is why, we constantly see the same side of the moon.
The moon’s orbit of the revolution is also elliptical as that of the Earth. Hence the distance of the moon from the Earth is not the same everywhere along its orbit while revolving. When it is the closest to the earth it is said to be in perigee and when it is at the farthest the position is called apogee.
You have studied the phases of the moon. You know how it waxes from the new moon day to the full moon day and how it wanes from the full moon to the new moon day.
See the figure which shows the different phases of the moon. It shows the relative position of the moon on both the quarters, the full moon, and the new moon days concerning the earth and the sun.
We see the phases of the moon in the sky from the Earth. They are the illuminated portions of the moon. They become visible due to the sunlight reflected from the moon. While revolving around the earth, the moon is on the opposite side of the sun on a full moon day, whereas on a new moon day, it is positioned between the sun and the earth. On the first and the third quarter days, the moon, the earth, and the sun make an angle of 90°. At these positions, we see half the portion of the illuminated moon. Hence in the sky, it appears semicircular.
The orbital path of the Earth and that of the moon are not in the same plane. The moon’s revolutionary orbit makes an angle of about 5° with that of the Earth. As a result, the moon intersects the plane of the earth’s orbit twice during one revolution. On each new moon day, the lines joining the earth the sun and the moon make an angle of 0° whereas on each full moon day, this angle is of 180°. Even so, the sun, the earth, and the moon may not be in one straight line in the same plane on every new moon or full moon day. Hence, eclipses do not occur on each new moon or full moon day. However, sometimes, on a new moon day or a full moon day, the three fall in one line and are in the same plane. Eclipses occur on such occasions. Eclipses may be solar or lunar.
If the moon is between the sun and the earth, the shadow of the moon falls on the earth. At such a time these three celestial objects are on the same plane and fall in one line. Hence the place on the earth where the moon’s shadow falls experiences a solar eclipse. This shadow is of two types. The central portion of the shadow is darker and the periphery is light. In the area of dark shadow on the earth, the sun becomes completely invisible. This condition is known as total solar eclipse. However, during the same period, at the places where the shadow is lighter, the sun disc appears partially covered. This condition is described as a partial solar eclipse. A total solar eclipse is seen in a very limited region of the earth.
Sometimes the moon is in an apogee position. This means it is at its farthest from the earth. As a result, the deep shadow of the moon is cast into space and does not reach the Earth. From a very small region of the earth, only an illuminated edge of the sun disc is seen in the form of a ring. This is called an annular eclipse. An annular eclipse is a rare phenomenon.
A lunar eclipse occurs when the moon enters the shadow of the earth while revolving around it. At this time, it is necessary that the earth is between the sun and the moon, and all three of them are in the same plane. On a full moon day, the moon’s path of revolution passes through the thick shadow of the earth. If the moon is hidden within the shadow, we see a total lunar eclipse and if only a part of the moon is in the shadow, we see a partial lunar eclipse.
Characteristics of Solar Eclipse
- A solar eclipse occurs on a new moon day, but not on every new moon day.
- If and only if the sun, the moon, and the earth are in the same plane and fall in one line, solar eclipses occur.
- The maximum duration of a total solar eclipse is 7 minutes and 20 seconds (440 seconds).
Characteristics of Lunar Eclipse
- A lunar eclipse occurs on a full moon day, but not on every full moon day.
- A lunar eclipse occurs if and only if the sun, the moon, and the earth are in the same plane and fall in one line.
- The maximum duration of a total lunar eclipse is 107 minutes.
Eclipse – An Astronomical Event:
A solar eclipse or lunar eclipse is just an astronomical event. There is nothing ‘auspicious’ or ‘inauspicious’ about these events. It is just a result of the sun, the earth, and the moon being in specific positions. There is a lot of curiosity about eclipses because an eclipse is not a regular occurrence. For scientists working in the field of astronomy, eclipses particularly total or annular solar eclipses present great opportunities for study. Scientists from all over the world make it a point to visit the locations where such events are going to occur. They carry out elaborate studies of eclipse conditions.
While observing a solar eclipse, it is necessary to view the sun disc through dark glasses or special goggles made for that purpose, otherwise, the intense light of the sun can be harmful to the naked eye. During the period of a solar eclipse, a large number of birds and animals get confused due to the untimely darkness that sets in. As this is an event that does not suit their biological clock, their response to the event is also unusual. Try to observe the responses of the birds and animals at the time of such events and record your observations. Like eclipses, some other specific conditions occur concerning the sun or the moon. These are called occultation and transit respectively. Occultation occurs concerning the moon whereas the transit is associated with the sun.
This is a typical event occurring in space. The moon revolves around the Earth. While doing so, it obscures a star or a planet and that celestial body appears to hide behind the moon. This is called occultation. The total solar eclipse is a kind of occultation. During this, the sun’s disc gets hidden completely because of the moon.
If an inner planet like Mercury or Venus comes in between the line of the Earth and the sun, a transit occurs. At that time, a small dot appears to move across the sun disc. Transit is a type of solar eclipse.
Good Maharashtra State Board Class 7 Geography Notes The Sun, the Moon, and the Earth can simplify complex concepts and make studying more efficient.