Notes Class 7 Chapter 2 Geography Maharashtra Board

Notes For All Chapters – Geography Class 7

The Sun, the Moon and the Earth

1. The Sun, the Earth, and the Moon System

• The sun is the center of the solar system and provides heat and light to the planets.
• The earth revolves around the sun and rotates on its axis, causing day and night.
• The moon is the earth’s only natural satellite and revolves around the earth while rotating on its axis.

Movements of the Earth and the Moon

1. Rotation of the Earth – The earth rotates on its axis, causing day and night.
2. Revolution of the Earth – The earth revolves around the sun in an elliptical orbit, causing different seasons.
3. Revolution of the Moon – The moon revolves around the earth in an elliptical orbit, taking about 27.3 days to complete one revolution.

2. The Moon’s Orbit and Phases

• The moon does not emit light but reflects the sun’s light.
• It goes through different phases during its revolution around the earth.
• The phases of the moon occur because of the relative positions of the sun, the moon, and the earth.

Phases of the Moon

1. New Moon – The moon is between the sun and the earth; the side facing us is completely dark.
2. Waxing Crescent – A small portion of the moon is visible.
3. First Quarter – Half of the moon is visible.
4. Waxing Gibbous – More than half of the moon is visible.
5. Full Moon – The earth is between the sun and the moon, and the entire moon is visible.
6. Waning Gibbous – The visible part of the moon starts decreasing.
7. Last Quarter – Again, half of the moon is visible.
8. Waning Crescent – Only a small portion of the moon is visible before the cycle repeats.

3. Eclipses

An eclipse occurs when one celestial body moves into the shadow of another.

Types of Eclipses

Solar Eclipse (Sun → Moon → Earth)

• Occurs on a new moon day when the moon comes between the sun and the earth.
• The moon blocks sunlight, casting a shadow on the earth.

Types of Solar Eclipse:

• Total Solar Eclipse – The moon completely covers the sun.
• Partial Solar Eclipse – Only a part of the sun is blocked.
• Annular Solar Eclipse – The moon appears smaller than the sun, leaving a ring-like shape visible.

Lunar Eclipse (Sun → Earth → Moon)

• Occurs on a full moon day when the earth comes between the sun and the moon.
• The earth’s shadow falls on the moon, causing it to darken.

Types of Lunar Eclipse:

• Total Lunar Eclipse – The entire moon is covered by the earth’s shadow.
• Partial Lunar Eclipse – Only part of the moon enters the earth’s shadow.

4. Why Do Eclipses Not Occur Every Month?

• The moon’s orbit is inclined at 5° to the earth’s orbit.
• Eclipses occur only when the sun, the earth, and the moon align at nodal points.
• This alignment happens only a few times a year, leading to eclipses.

5. Apogee and Perigee of the Moon

• The moon’s orbit is elliptical, meaning its distance from the earth varies.
• Perigee – The moon is closest to the earth.
• Apogee – The moon is farthest from the earth.
• When a solar eclipse occurs at perigee, it is more likely to be a total solar eclipse because the moon appears larger.
• When a solar eclipse occurs at apogee, it is usually an annular eclipse because the moon appears smaller.

6. Observing a Solar Eclipse Safely

• Looking directly at a solar eclipse can damage eyesight.
• Use solar filters, eclipse glasses, or a pinhole projector to observe safely.
• Do not use regular sunglasses or unfiltered telescopes.

7. Superstitions Related to Eclipses and How to Eradicate Them

• Many cultures have superstitions about eclipses, believing they bring bad luck.
• Ways to eliminate superstitions:
  • Spread scientific awareness about eclipses.
  • Encourage people to observe eclipses safely to understand them.
  • Use media and schools to teach the science behind eclipses.
  • Promote astronomical studies to increase knowledge.

8. Important Facts to Remember

• A solar eclipse occurs only on a new moon day and a lunar eclipse occurs only on a full moon day.
• The maximum duration of a total solar eclipse is about 7.5 minutes, while a total lunar eclipse can last 107 minutes.
• The moon’s orbit intersects the earth’s orbit twice in one revolution.
• Total and annular solar eclipses depend on the moon’s distance from the earth (perigee or apogee).

Conclusion

This chapter explains the relationship between the sun, the earth, and the moon. It highlights the causes of eclipses, the phases of the moon, and the importance of understanding celestial events scientifically. By learning about these natural phenomena, we can move past superstitions and appreciate the beauty of astronomy.