A Step Further — Phases Are Not Caused by Earth's Shadow — "Keeping Time with the Skies"

1. 13 marks

   Correct this statement: 'The Moon's phases happen because Earth's shadow falls on the Moon.'

   Hint. The chapter states this misconception and its correction explicitly, in its own 'A step further' box.

   ✦ This is incorrect. The chapter states directly: 'The Moon phases do not happen due to Earth's shadow. It is an incorrect explanation for the Moon's phases that Earth's shadow falls on it.' Phases occur because of the changing relative orientation of the Sun, Moon and Earth as the Moon orbits Earth — how much of the Moon's permanently-illuminated half faces Earth keeps changing, which is a completely different mechanism from a shadow falling on it.

2. 23 marks

   What actually causes a lunar eclipse, and on which phase of the Moon can it occur?

   Hint. This is the one event where Earth's shadow genuinely IS involved.

   ✦ A lunar eclipse happens when Earth's shadow falls on the Moon, and it can only happen on a full Moon day — since only then is the Moon positioned on the far side of Earth from the Sun, in line for Earth's shadow to reach it.

3. 32 marks

   What causes a solar eclipse, and on which phase of the Moon can it occur?

   Hint. This time it's the Moon's shadow, and the Moon needs to be positioned between the Sun and Earth.

   ✦ A solar eclipse happens when the Moon comes between the Sun and Earth and its shadow falls on Earth, blocking the Sun from view — it can only happen on a new Moon day, since that is the only time the Moon sits directly between Earth and the Sun.

4. 43 marks

   If a lunar eclipse needs a full Moon and a solar eclipse needs a new Moon — both of which occur every month — why don't eclipses happen every single month?

   Hint. The chapter names one specific geometric reason the three bodies don't line up perfectly every month.

   ✦ The Moon's orbit is slightly tilted with respect to Earth's orbit around the Sun, so the Sun, Earth and Moon are not perfectly aligned at every full or new Moon — only when a full or new Moon happens to coincide with the Moon crossing the plane of Earth's orbit does an eclipse actually occur, which is why eclipses are occasional rather than monthly.

5. 53 marks

   Explain, using Fig. 11.6, why the Moon rises about 50 minutes later each day.

   Hint. Earth completes one rotation in 24 hours, but where has the Moon itself moved to in that same time?

   ✦ In the roughly 24 hours it takes Earth to complete one rotation and bring an observer back to the same facing direction, the Moon has itself moved a little further along in its own orbit around Earth. So Earth needs to rotate a bit more than a full turn — about 50 minutes' worth — before the Moon lines up in the sky at nearly the same spot again, which is why moonrise (and the Moon's overhead position) drifts later by roughly 50 minutes every day.

Solutions written by the tuition.in editorial team and checked against NCERT Curiosity — Textbook of Science for Grade 8, Chapter 11 (hecu111.pdf), Reprint 2026-27, pages 170-189. Questions are referenced from the NCERT textbook for identification.