NCERT Solutions Class 8 Science Chapter 11: Keeping Time with the Skies (Hinglish)

Grade 8 ki science textbook Curiosity ke Chapter 11, Keeping Time with the Skies, ke Probe and ponder, chapter ke andar ke sawaal, Activities 11.1 se 11.4, Keep the curiosity alive ke saare baarah sawaal aur Discover, design, and debate projects ke jawaab. Page numbers 2026-27 reprint ke hisaab se hain (pages 170–189). Chhote notes: Chapter 11 ke notes.

Probe and ponder (page 170)

Kya aapne din mein chaand dekha hai? Kyon dikhta hai? Haan. Chaand har din lagbhag aadha samay ufaq ke upar rehta hai, aur kyonki wo roz lagbhag 50 minute der se ugta hai, us samay ka kuch hissa aksar din ki roshni mein padta hai. Uski dhoop wali satah itni chamakti hai ki neele aasmaan mein dikh jaaye, sivaay Amavasya ke aas-paas, jab wo Suraj ke bahut paas hota hai.

Chaand par rehna ho, to din, maheena aur saal ka kya matlab hoga? Chaand ka hamesha wahi hissa Dharti ki or rehta hai, yaani chaand apni dhuri par utne hi samay mein ek baar ghoomta hai jitne mein wo Dharti ka chakkar lagaata hai. Isliye chaand par ek din, ek suryoday se agle tak, lagbhag 29.5 Dharti-din ka hoga, ek maheene jitna. Hamari or wale hisse se Dharti aasmaan mein lagbhag ek jagah tiki dikhegi aur uski apni kalaayein hongi. Saal phir bhi Suraj ka ek chakkar hoga, lagbhag 365 Dharti-din.

Agar Dharti ke do chaand hote? Alag-alag chakron wali kalaaon ke do set hote, isliye kuch raaton mein alag aakaar ke do chaand dikhte, ya ek ugta to doosra doobta. Grahan zyada hote, aur chaand par aadhaarit calendar banaana bahut mushkil hota.

Ghadi ya calendar ke bina samay kaise naapein? Suraj ki oonchaai aur parchhaai ki lambaai se (dhoop-ghadi), chaand ki kalaaon se, suryaast par ugne wale taaron se, aur rituon ke chakra se, jaise phoolte paudhe ya pravaasi pakshi; ya jal-ghadi, ret-ghadi aur jalti mombatti se.

Chaand ki kalaayein (pages 171–177)

Activity 11.1: chaand ki diary ka vishleshan. Chaand har din alag dikhta hai: Purnima se uska chamakta hissa lagbhag do hafte ghatta hai aur phir badhta hai. Wo har din nahi dikhta; Amavasya ke aas-paas wo Suraj ke itna paas hota hai ki dikhta nahi. Wo roz ek hi samay par ek hi jagah nahi hota: suryoday par har agli subah wo Suraj ke paas dikhta hai, aur Amavasya ke baad suryaast par har agli shaam Suraj se door.

Jab chaand Suraj ke paas dikhta hai to dikhne wala roshan hissa kyon ghatta hai? Jab chaand hamare aasmaan mein Suraj ke paas hota hai, to wo lagbhag Dharti aur Suraj ke beech hota hai. Tab uska roshan aadha zyaadatar humse door ki or hota hai, aur hum uski sirf patli kinaari crescent ke roop mein dekhte hain; Amavasya par bilkul nahi.

Activity 11.2: gend aur lamp. E par, jab gend lamp ki or hai, aapki or wala hissa roshan nahi hota, Amavasya jaisa. Ghadi ki sui ki ulti disha mein ghoomne par roshan hisse ka aakaar badalta hai: crescent, aadha, gibbous aur A par poora, phir waapas. Roshan aur andhere hisse ke beech ki rekha ghumaavdaar dikhti hai, sivaay aadhe ke, jab wo seedhi dikhti hai; ye Fig. 11.4c aur asli chaand se mel khaata hai.

Calendar aur tyohaar (pages 178–184)

Activity 11.3: din ki lambaai. Book ke readings se din 24 ghante 00 minute aur 23 ghante 59 minute ke the, ausat 23 ghante 59.5 minute, jo lagbhag 24 ghante hai. Yahi ausat mean solar day hai.

Zyaadatar Bharatiya tyohaar har saal alag taareekh par kyon padte hain? Kai tyohaar chandra ya chandra-saur calendar se chalte hain, jinke maheene chaand ke hisaab se hain aur saur Gregorian calendar ke maheenon se mel nahi khaate. Chandra varsh saur varsh se lagbhag 11 din chhota hai, isliye ye tyohaar har saal alag Gregorian taareekh par padte hain.

Kritrim upgrah (pages 185–186)

Shaam ko dikhne wale ‘chalte taare’ kya hain? Kya unki gati aavarti hai? Ye kritrim upgrah hain, jo upar abhi bhi Suraj ki roshni mein hote hain jabki zameen par andhera hota hai. Unki gati aavarti hai: zyaadatar lagbhag 100 minute mein Dharti ka ek chakkar lagaate hain, baar-baar.

Activity 11.4: upgrah dekhna. Suryoday se theek pehle ya suryaast ke baad, kisi bade ke saath khule aasmaan wali jagah jaaiye. Tezi se aasmaan paar karta roshni ka bindu, sthir ya timtimaata, upgrah hai. Apps aur websites batati hain ki upgrah aapki jagah ke upar se kab guzrenge.

Keep the curiosity alive (pages 187–188)

1. True ya False. (i) True: hum chaand ka sirf wo hissa dekhte hain jo hamari or Suraj ki roshni lautaata hai. (ii) False: kalaayein is baat se hoti hain ki chaand ke dhoop wale aadhe ka kitna hissa hum dekh paate hain; jab Dharti ki chhaaya chaand par padti hai to chandra grahan hota hai. (iii) True. (iv) False: chaand aksar din mein bhi dikhta hai.

2. Amol ka janamdin. Nahi. Purnima lagbhag har 29.5 din mein aati hai, isliye 12 Purnima lagbhag 354 din leti hain, saal se 11 din kam. Agle saal Purnima 6 May se lagbhag 11 din pehle aa jaati hai, aur janamdin par chaand ghat raha hota hai. Purnima lagbhag usi taareekh par kai saalon baad hi lautti hai, lagbhag 19 saal baad.

3. Fig. 11.10 mein do galtiyaan. Chaand ke andhere hisse ke andar taare banaaye gaye hain, par roshni na hone par bhi chaand apne peechhe ke taare chhupa leta hai. Aur chaand ko baadal ke aage dikhaaya gaya hai, jabki baadal sirf kuch kilometre upar hain aur chaand lagbhag 3,84,000 km door; baadal chaand ko chhupa sakta hai, ulta kabhi nahi.

4. Chhah tasveerein. (i) Amavasya ke teen din baad: D (patla crescent). Purnima: E. Purnima ke teen din baad: A (gibbous). Purnima ke ek hafte baad: C (aadha). Amavasya ka din: B. (ii) F kabhi kala ke roop mein nahi dikhta: asli kala mein roshan aur andhere hisse ki seema vyaas (diameter) ke ek sire se doosre sire tak jaati hai, par F mein gol ‘kaatne’ jaisa nishaan hai, jo grahan ka aakaar hai. B, yaani Amavasya, bhi aasmaan mein kabhi nahi dikhta. Tasveerein sirf aakaar parakhti hain; Bharat se dekhne par ghatta chaand asal mein apni baayin (poorvi) or chamakta hai.

5. Malini ka chaand. (i) Malini ne aadha chaand dekha, jiska chamakta aadha doobte Suraj ki taraf, yaani paschim ki or tha (dakshin ki or munh karne par daayin taraf). (ii) Ye badhta chaand hai: suryaast par aasmaan mein ooncha chaand Amavasya ke lagbhag ek hafte baad, Shukla Paksha mein hota hai.

6. Ravi aur Kaushalya. Kaushalya sach bol rahi hain. Suryaast ke samay poorab mein ugta chaand Suraj ke saamne hota hai, isliye wo Purnima ka chaand hi hoga, crescent nahi; suryaast par crescent paschim mein neeche, Suraj ke paas hota hai, isliye Ravi galat hain. Purnima se kuch din pehle badhta gibbous chaand dopahar mein ugta hai aur poorvi aasmaan mein dikhta hai, jaisa Kaushalya ne kaha.

7. Dheema chaand. Kam baar. Agar chaand dheere ghoome, to har chandra maas lamba ho jaata hai, isliye 12 chandra maas saur varsh ki lambaai ke kareeb aa jaate hain. Saalaana lagbhag 11 din ka antar ghat jaata hai, use ek maheena banne mein zyada samay lagta hai, aur atirikt maheene ki zaroorat kam baar padti hai.

8. 3 saal mein 37 Purnima. Teen saal mein 3 × 12 = 36 calendar maheene hote hain. 37 Purnima ko 36 maheenon mein rakhne par kam se kam ek maheene mein do Purnima padengi. Ye isliye sambhav hai kyonki Purnima lagbhag 29.5 din ke antar par aati hai, jabki zyaadatar maheene 30 ya 31 din ke hote hain.

9. Vaishali ki raat. Purnima. Chaand Suraj ke saamne hota hai, isliye Suraj doobne par ugta hai aur Suraj ugne par doobta hai, aur poori raat aasmaan mein rehta hai.

10. Leap year na hon to. Calendar har saal rituon se lagbhag chauthaai din peechhe chhoot jaata: 4 saal mein ek din, 120 saal mein lagbhag ek maheena. Swatantrata Diwas, jo aaj garam monsoon ke mausam mein aata hai, tab sardi mein chala jaata jab ye khiskaav lagbhag aadha saal, yaani lagbhag 182 din, ho jaata, jismein lagbhag 182 × 4 ≈ 730 saal lagte.

11. Kritrim upgrah kyon bheje jaate hain? Phone, TV aur internet ke signal pahunchaane, raasta dhoondhne, mausam par nazar rakhne, aapda mein madad aur vaigyanik research ke liye, jaise Cartosat se nakshe banaana aur AstroSat se taaron ka adhyayan.

12. Samay ke maap. (i) Din: Dharti ka apni dhuri par ghoomna, jo Suraj ke apni sabse oonchi jagah par lautne mein dikhta hai. (ii) Maheena: chaand ka Dharti ka chakkar, jo kalaaon ke ek chakra mein dikhta hai. (iii) Saal: Dharti ka Suraj ka chakkar, jo rituon ke ek chakra mein dikhta hai.

Discover, design, and debate (pages 188–189)

Crescent Suraj ki or hota hai. Suraj se crescent chaand ki or sabse chhote raaste se ungli le jaane par ungli hamesha pehle roshan kinaari tak pahunchti hai, jo dikhaata hai ki chaand Suraj ki lautaayi roshni se chamakta hai. Crescent ke dono siron ko jodne wali rekha chaand ka vyaas hai.

Indian National Calendar ki alag padne wali taareekhein. Gregorian leap year mein 29 February se 20 April tak ki taareekhein ek din alag padti hain: 10 Phalguna 1 March ki jagah 29 February ko, 1 Chaitra 22 March ki jagah 21 March ko aata hai, aur Chaitra 31 din ka hota hai. 1 Vaisakha (21 April) se taareekhein phir mel khaati hain.

Alag-alag rajyon ke Naye Saal ke tyohaar. Andhra Pradesh aur Telangana: Ugadi (chandra-saur); Karnataka: Ugadi (chandra-saur); Maharashtra: Gudi Padwa (chandra-saur); Gujarat: Bestu Varas, Diwali ke agle din (chandra-saur); Manipur: Sajibu Cheiraoba (chandra-saur); Tamil Nadu: Puthandu (saur); Kerala: Vishu (saur); West Bengal: Poila Baisakh (saur); Assam: Bohag Bihu (saur); Punjab: Vaisakhi (saur); Odisha: Pana Sankranti (saur).

Paanch saal mein Eid-ul-Fitr aur Diwali. Bharat ke zyaadatar hisson mein manaayi gayi taareekhein (kuch jagah ek din ka antar ho sakta hai):

Saal	Eid-ul-Fitr	Diwali
2021	14 May	4 November
2022	3 May	24 October
2023	22 April	12 November
2024	11 April	31 October
2025	31 March	20 October

Eid har saal lagbhag 11 din pehle aati hai, kyonki wo shuddh chandra calendar se chalti hai. Diwali bhi har saal lagbhag 11 din pehle khiskti hai, par 2023 mein lagbhag 19 din aage koodti hai: us saal July aur August mein ek atirikt maheena, Adhik Shravan, tha, jo chandra-saur calendar mein Diwali 2022 aur Diwali 2023 ke beech dikhta hai.

Saal bhar suryoday. Ek hi jagah se har maheene nishaan lagaane par suryoday ki jagah December ke ant se June ke ant tak uttar ki or (poorab ki or munh karne par baayin taraf) khisakti hai, phir December ke ant tak dakshin ki or, aur lagbhag 20 March aur 23 September ko theek poorab mein hoti hai. Yahi Uttarayan aur Dakshinayan hai jo hamare poorvajon ne dekha tha.