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Class 8 Science: Keeping Time with the Skies, 8 practice questions with answers

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These are 8 practice questions on Class 8 Science Chapter 11, Keeping Time with the Skies, of the new NCERT textbook, Curiosity. Each has a worked answer and the textbook page it comes from. They cover the phases of the Moon and moonrise, lunar, solar and luni-solar calendars, leap years, the Indian National Calendar, and artificial satellites. Try each one on paper before you open the answer.

These questions are our own, drafted with AI help, and every answer was re-computed and checked against the textbook page it cites, but no practising teacher has reviewed them yet. If you find a mistake, please tell us.

What the chapter says you need

Facts from the NCERT textbook (Curiosity: Textbook of Science for Grade 8, Chapter 11, printed pages 170 to 189):

The Moon and its phases

Question 1. Tonight the Moon rises at 7:10 p.m. At about what time will it rise tomorrow?

Answer: at about 8:00 p.m. The Moon rises about 50 minutes later each day, because while the Earth turns once, the Moon moves a little further along its orbit, and the Earth has to turn a bit more before the Moon comes back to nearly the same place in the sky. 7:10 p.m. + 50 minutes = 8:00 p.m. (Moonrise, pages 173 and 177.)

Question 2. Over several nights, the bright part of the Moon grows from a thin crescent towards a full circle. Is this the waxing or the waning period, and what is it called in India?

Answer: the waxing period, called Shukla Paksha. When the bright part of the Moon increases, after the new Moon, it is the waxing period, generally called Shukla Paksha in India. When the bright part shrinks, after the full Moon, it is the waning period, Krishna Paksha. (Phases of the Moon, pages 172 and 173.)

Calendars

Question 3. A purely lunar calendar has 354 days in a year, while the seasons repeat in about 365 days. By about how many days does such a calendar fall behind the seasons in 3 years?

Answer: about 33 days, more than a month. Each lunar year is about 365 − 354 = 11 days shorter than the cycle of seasons, so in 3 years the gap is about 3 × 11 = 33 days. That is why luni-solar calendars add an extra month, Adhika Maasa, every few years to stay in step with the seasons. (Lunar calendars, page 179; luni-solar calendars, pages 181 and 182.)

Question 4. Which of these years are leap years in the Gregorian calendar: 2028, 2030, 2100, 2400?

Answer: 2028 and 2400. A year divisible by 4 is a leap year: 2028 ÷ 4 = 507, so it is one, but 2030 is not divisible by 4. Century years skip the leap day, so 2100 is not a leap year even though it is divisible by 4, but every 400 years the leap day is added back, and 2400 ÷ 400 = 6, so 2400 is a leap year. (Solar calendars and leap years, page 180.)

Question 5. In a regular year of the Indian National Calendar, how many days are there in the second to sixth months together?

Answer: 155 days. In a regular year, the second to sixth months have 31 days each. That is 5 months × 31 days = 155 days. (The other seven months have 30 days each, and 155 + 7 × 30 = 365.) (The Indian National Calendar, page 182.)

Question 6. A festival on a purely lunar calendar falls on 10 April this year. Near which date will it fall two years later?

Answer: about 19 March. A lunar year of 12 lunar months has 354 days, about 365 − 354 = 11 days fewer than a solar year, and a purely lunar calendar does not correct for this. So the festival comes about 11 days earlier each Gregorian year: in two years, about 2 × 11 = 22 days earlier. 22 days before 10 April is 19 March (10 days back to 31 March, then 12 more). (Lunar calendars, page 179; festivals, page 183.)

Question 7. In a Purnimant calendar, on which day does a month end?

Answer: on the full Moon day. In a Purnimant calendar, a new month starts on the day after the full Moon and ends on the full Moon. In an Amant calendar, it starts on the day after the new Moon and ends on the new Moon. (Amant and Purnimant, page 182.)

Artificial satellites

Question 8. Most artificial satellites take about 100 minutes to go once round the Earth. About how many times does such a satellite go round the Earth in one day?

Answer: about 14 times. One day has 24 × 60 = 1440 minutes, and 1440 ÷ 100 = 14.4, so a satellite completes about 14 orbits in a day. (Artificial satellites, page 185.)

Questions students ask

Do people in different countries see the same phase of the Moon on the same day? Nearly the same phase. The Earth rotates once in a day, which is much shorter than the Moon's revolution of nearly a month, so on a given day people on different parts of the Earth see nearly the same phase. (Page 176.)

What is Adhika Maasa? An extra month that some luni-solar calendars add every few years. Twelve lunar months fall short of the solar year by nearly 11 days, and when the difference grows to nearly a month, the extra month keeps the lunar months in step with the seasons. (Pages 181 and 182.)

Why are there no lunar and solar eclipses every month? Lunar eclipses can happen only on a full Moon day and solar eclipses only on a new Moon day, but not every month, because the Moon's orbit is slightly tilted to the Earth's orbit round the Sun; on most full and new Moon days, the Sun, Earth and Moon are not in line. (Page 177.)

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Sources

All opened and read on 22 October 2026. Page numbers are the printed page numbers of the textbook; printed page = PDF page + 169.

The facts are from the textbook pages above. The questions, worked answers and checks are our own, and every number was re-computed by script. This guide is general information; follow your teacher and the textbook.