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What causes solar and lunar eclipses?

Class 7 ScienceNCERT chapter: Earth, Moon, and the Sunइसे हिंदी में पढ़ें

Exam-ready answer

Eclipses happen when the Sun, Earth and Moon come in a straight line. In a solar eclipse, the Moon comes between the Sun and the Earth, and its shadow falls on the Earth. In a lunar eclipse, the Earth comes between the Sun and the Moon, and the Earth's shadow falls on the Moon.

Explanation

Light travels in a straight line, so an opaque object in its path casts a shadow. The Earth and the Moon are both opaque and both cast long shadows in space. An eclipse happens when one of them moves into the other's shadow. For this, the Sun, Earth and Moon must be in a straight line.

A solar eclipse can happen only on a new moon day, when the Moon is between the Sun and the Earth. The Moon blocks the Sun for people standing in its shadow. If the Sun is fully hidden, it is a total solar eclipse; if only part is hidden, it is a partial solar eclipse. We must never look at the Sun directly, even during an eclipse, as it can damage the eyes.

A lunar eclipse can happen only on a full moon night, when the Earth is between the Sun and the Moon. The Earth's shadow falls on the Moon and darkens it, and it is safe to watch with bare eyes. Eclipses do not happen every month because the Moon's path around the Earth is slightly tilted, so the three bodies are usually not exactly in line.

Points to remember

  1. Eclipse: an event in which one celestial body comes into the shadow of another.
  2. Solar eclipse: Sun – Moon – Earth in a line; the Moon's shadow falls on the Earth; occurs only on a new moon day.
  3. Lunar eclipse: Sun – Earth – Moon in a line; the Earth's shadow falls on the Moon; occurs only on a full moon night.
  4. Eclipses can be total or partial depending on how much is covered.
  5. Eclipses are not monthly because the Moon's orbit is slightly tilted to the Earth's orbit.

Exam tip

Draw two simple diagrams showing the order of Sun, Moon and Earth for each eclipse, shade the shadow region, and write 'new moon' or 'full moon' below each.

Questions students also ask

Why should we not look directly at a solar eclipse?
Even when most of the Sun is covered, the visible part is extremely bright and can permanently damage the eyes. A solar eclipse should be seen only with proper solar filters or by pinhole projection.
Why does a lunar eclipse not happen every full moon?
The Moon's path around the Earth is slightly tilted compared to the Earth's path around the Sun. On most full moon nights, the Moon passes just above or below the Earth's shadow, so no eclipse occurs.
Who can see a lunar eclipse?
A lunar eclipse can be seen from every place on Earth where it is night and the Moon is above the horizon at that time. A solar eclipse, in contrast, is seen only from the small area where the Moon's shadow falls.

Chapter labels help you find the topic in your textbook. Check your own edition: chapter names and order can change. These are Know.it explanations, not official NCERT solutions.