Activity 11.1 — A Month of Watching the Moon — "Keeping Time with the Skies"

1. 13 marks

   What columns would you need in a table to properly document the Moon's appearance over a month, following Table 11.1?

   Hint. The book asks for five things to be tracked, starting from the date and building up to comparisons with the previous day.

   ✦ Table 11.1 tracks: the date; when the Moon was seen (sunrise or sunset); a shaded circle showing the bright portion's shape; whether the bright portion increased or decreased compared to the previous day; and whether the Moon appeared closer to or farther from the Sun in the sky than the day before, since it is exactly these day-to-day comparisons that later reveal the waxing/waning pattern.

2. 22 marks

   Why does the activity instruct you to begin the very first observation on the morning after a full Moon day?

   Hint. The chapter says this is 'when it is easiest to spot the Moon in the sky' — link that to where the Moon sits relative to the Sun right after a full Moon.

   ✦ Just after a full Moon, the Moon is still nearly opposite the Sun in the sky, so at sunrise it is high and bright in the western sky — the easiest, most unambiguous starting point to begin a systematic log, rather than trying to first locate a faint crescent near the Sun's glare.

3. 32 marks

   Why does the activity switch from sunrise observations to sunset observations after about 15 days?

   Hint. The Moon keeps shifting closer to the Sun in the sky as it wanes — what eventually happens to a sunrise sighting?

   ✦ As the waning fortnight progresses, the Moon keeps moving closer to the Sun's position in the sky each day, and around the new Moon it becomes impossible to see at sunrise at all (too close to the Sun's glare). The chapter's fix is to switch to sunset observations for the remaining ~15 days, since that is when the newly waxing crescent becomes visible again low in the western sky after sunset.

4. 43 marks

   Predict what the 'size of the bright portion' column in Table 11.1 would show across a full month's entries, day by day.

   Hint. The chapter names this two-week shrinking stretch the waning period and the two-week growing stretch the waxing period — trace both across roughly 29-30 days.

   ✦ Starting from a full Moon (the bright portion at its largest), the entries would show 'Decreased' for about two weeks (the waning period) until the bright portion is no longer visible at new Moon; then the entries would flip to 'Increased' for the next roughly two weeks (the waxing period), because the bright portion regrows back to a full circle, completing the roughly month-long cycle the chapter describes.

5. 52 marks

   The chapter suggests beginning this activity a month or more before this chapter is scheduled to be learnt. Why is that timing advice practical rather than optional?

   Hint. A single observation can't show a cycle — what does the activity actually need to have happened before it can be analysed?

   ✦ The whole point of Activity 11.1 is to capture a complete cycle of change — the Moon shrinking to invisible and regrowing to full — which by the chapter's own account takes about a month to unfold. Starting the log only when the chapter begins would mean there isn't enough real data collected yet to analyse the pattern the lesson is built around, so the observation window has to be opened well in advance.

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.