[{"data":1,"prerenderedAt":1090},["ShallowReactive",2],{"questions:phases-of-the-moon":3},{"bank":4,"contentHash":1079,"dependencyHashes":1080,"releaseId":1089},{"schemaVersion":5,"conceptId":6,"revision":5,"title":7,"intro":8,"sections":9,"questions":46,"sourceIds":1067,"reviewStatus":1075,"authoring":1076},1,"phases-of-the-moon","Phases of the Moon: question bank","Seventy-plus questions across nine sections, from naming a crescent to deriving the Saros cycle. Every numeric answer is computed and checked in numbers.py before being written here.",[10,14,18,22,26,30,34,38,42],{"id":11,"title":12,"description":13},"phase-names","Names and shapes of the phases","The eight named phases, waxing vs waning, crescent vs gibbous, and the terminator.",{"id":15,"title":16,"description":17},"shapes-visibility","What you actually see","Half always lit, which side is bright, and the daytime Moon.",{"id":19,"title":20,"description":21},"elongation-math","Elongation and illuminated fraction","The Sun-Earth-Moon angle and the formula for how much of the disc is lit.",{"id":23,"title":24,"description":25},"rise-set-times","Moonrise, moonset and the daily lag","When each phase rises and sets, and why moonrise slides later each day.",{"id":27,"title":28,"description":29},"synodic-sidereal","Synodic vs sidereal months","Why the 29.53-day cycle of phases differs from the Moon's 27.32-day true orbit.",{"id":31,"title":32,"description":33},"indian-calendar","Tithi, paksha and adhik maas","The Indian lunar calendar's vocabulary and arithmetic.",{"id":35,"title":36,"description":37},"eclipses-shadow-myth","Eclipses are not the same as phases","Why phases are not Earth's shadow, and the tilt that makes eclipses rare.",{"id":39,"title":40,"description":41},"tidal-locking-libration","Tidal locking, the far side and libration","Why we see one face, what libration reveals, and the slow recession.",{"id":43,"title":44,"description":45},"missions-deep-time","Chandrayaan-3, the south pole and deep time","Real missions, the lunar day, and the Moon's distant past and future.",[47,72,90,106,123,137,156,173,192,211,228,247,262,279,293,311,323,330,340,349,357,369,379,389,399,419,430,447,462,479,495,505,515,526,543,553,562,571,580,598,608,617,625,634,644,654,663,672,681,692,701,718,736,753,770,778,795,805,814,822,839,857,874,882,899,908,925,943,953,970,987,996,1013,1031,1049],{"id":48,"section":11,"level":49,"prompt":50,"check":51,"hints":67,"solution":69,"skills":70},"phases-of-the-moon.q001","foundation","Which of these correctly lists all eight phases of the Moon, in order, starting from new moon?",{"kind":52,"options":53,"correct":66},"choice",[54,57,60,63],{"id":55,"label":56},"a","New, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, last quarter, waning crescent",{"id":58,"label":59},"b","New, first quarter, waxing crescent, full, last quarter, waning crescent, waxing gibbous, waning gibbous",{"id":61,"label":62},"c","Full, waxing gibbous, first quarter, waxing crescent, new, waning crescent, last quarter, waning gibbous",{"id":64,"label":65},"d","New, crescent, quarter, gibbous, full, gibbous, quarter, crescent, new, repeating twice a month",[55],[68],"Split the month into two halves: growing (waxing) and shrinking (waning).","The correct order is new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, last quarter, waning crescent, then back to new. The disc grows (waxes) through the first half and shrinks (wanes) through the second.",[11,71],"sequence",{"id":73,"section":11,"level":49,"prompt":74,"check":75,"hints":86,"solution":87,"skills":88},"phases-of-the-moon.q002","What does it mean for the Moon to be 'waxing'?",{"kind":52,"options":76,"correct":85},[77,79,81,83],{"id":55,"label":78},"The lit fraction is growing, night by night",{"id":58,"label":80},"The lit fraction is shrinking, night by night",{"id":61,"label":82},"The Moon is getting physically bigger",{"id":64,"label":84},"The Moon is moving closer to Earth",[55],[],"Waxing means growing: the fraction of the disc that looks lit increases from one night to the next. The Moon itself never changes size.",[89],"vocabulary",{"id":91,"section":11,"level":49,"prompt":92,"check":93,"hints":103,"solution":104,"skills":105},"phases-of-the-moon.q003","What does it mean for the Moon to be 'waning'?",{"kind":52,"options":94,"correct":102},[95,97,98,100],{"id":55,"label":96},"The lit fraction is growing",{"id":58,"label":80},{"id":61,"label":99},"The Moon is disappearing forever",{"id":64,"label":101},"The Moon is spinning faster",[58],[],"Waning means shrinking: the lit fraction visible from Earth decreases each night, from full moon back down to new moon.",[89],{"id":107,"section":11,"level":49,"prompt":108,"check":109,"hints":120,"solution":121,"skills":122},"phases-of-the-moon.q004","A Moon that is less than half lit is called a:",{"kind":52,"options":110,"correct":119},[111,113,115,117],{"id":55,"label":112},"Gibbous",{"id":58,"label":114},"Crescent",{"id":61,"label":116},"Quarter",{"id":64,"label":118},"Full",[58],[],"A crescent is any phase with less than half the disc lit — a thin sliver near new moon, growing (waxing crescent) or shrinking (waning crescent).",[89],{"id":124,"section":11,"level":49,"prompt":125,"check":126,"hints":134,"solution":135,"skills":136},"phases-of-the-moon.q005","A Moon that is more than half lit, but not full, is called a:",{"kind":52,"options":127,"correct":133},[128,129,130,131],{"id":55,"label":114},{"id":58,"label":116},{"id":61,"label":112},{"id":64,"label":132},"New",[61],[],"Gibbous describes any phase between half-lit and fully-lit: more than 50% of the disc is bright, but a dark sliver remains.",[89],{"id":138,"section":11,"level":49,"prompt":139,"check":140,"hints":151,"solution":153,"skills":154},"phases-of-the-moon.q006","At first quarter, what fraction of the visible disc is lit?",{"kind":52,"options":141,"correct":150},[142,144,146,148],{"id":55,"label":143},"About 25%",{"id":58,"label":145},"Exactly 50%",{"id":61,"label":147},"About 75%",{"id":64,"label":149},"100%",[58],[152],"'Quarter' here refers to a quarter of the monthly cycle, not a quarter of the disc.","Despite the name 'quarter' referring to a quarter of the way through the cycle (not a quarter of the disc), the Moon appears exactly half-lit at first and last quarter.",[89,155],"misconception",{"id":157,"section":11,"level":49,"prompt":158,"check":159,"hints":170,"solution":171,"skills":172},"phases-of-the-moon.q007","What is the terminator, as astronomers use the word for the Moon?",{"kind":52,"options":160,"correct":169},[161,163,165,167],{"id":55,"label":162},"A satellite that destroys other satellites",{"id":58,"label":164},"The line dividing the lit half of the Moon from the dark half",{"id":61,"label":166},"The edge of a crater",{"id":64,"label":168},"The point where the Moon's orbit crosses Earth's orbit",[58],[],"The terminator is the boundary between lit and unlit ground on the Moon. Along it, the Sun sits low in the lunar sky, throwing long shadows that make craters and mountains stand out sharply.",[89],{"id":174,"section":11,"level":175,"prompt":176,"check":177,"hints":188,"solution":189,"skills":190},"phases-of-the-moon.q008","core","Why do craters and mountains show up most clearly near the terminator, rather than at full moon?",{"kind":52,"options":178,"correct":187},[179,181,183,185],{"id":55,"label":180},"The Moon is closer to Earth at that time",{"id":58,"label":182},"The Sun is low in the lunar sky there, so features cast long shadows",{"id":61,"label":184},"The terminator is a physical wall",{"id":64,"label":186},"Full moon light is a different colour",[58],[],"Near the terminator, sunlight strikes the surface at a shallow angle, so bumps and crater rims throw long shadows that reveal their shape. At full moon, the Sun is nearly overhead everywhere visible, shadows vanish, and the disc looks comparatively flat.",[191],"reasoning",{"id":193,"section":15,"level":49,"prompt":194,"check":195,"hints":206,"solution":208,"skills":209},"phases-of-the-moon.q009","How much of the Moon's surface is lit by the Sun at any given moment (ignoring eclipses)?",{"kind":52,"options":196,"correct":205},[197,199,201,203],{"id":55,"label":198},"It varies through the month, from 0% to 100%",{"id":58,"label":200},"Always exactly half, 50%",{"id":61,"label":202},"Always 59%",{"id":64,"label":204},"It depends on the season on Earth",[58],[207],"Sun, Earth and Moon: only the geometry between them, not the amount of sunlit surface, changes.","Exactly half of any ball lit by a distant light source is lit at any instant — this never changes. What changes through the month is how much of that lit half faces Earth.",[155,210],"core-idea",{"id":212,"section":15,"level":49,"prompt":213,"check":214,"hints":225,"solution":226,"skills":227},"phases-of-the-moon.q010","What actually changes to produce the phases, if half the Moon is always lit?",{"kind":52,"options":215,"correct":224},[216,218,220,222],{"id":55,"label":217},"How much of the lit half faces Earth",{"id":58,"label":219},"The brightness of the Sun",{"id":61,"label":221},"The size of the Moon",{"id":64,"label":223},"Earth's shadow covering different amounts of the Moon",[55],[],"As the Moon orbits, the angle between Sun, Moon and Earth changes, so a different-sized slice of the permanently-lit half faces our direction. That changing view, not a changing light source, is the whole cause of phases.",[210],{"id":229,"section":15,"level":49,"prompt":230,"check":231,"hints":242,"solution":244,"skills":245},"phases-of-the-moon.q011","In the sky over India, a waxing crescent Moon is bright on which side?",{"kind":52,"options":232,"correct":241},[233,235,237,239],{"id":55,"label":234},"The right",{"id":58,"label":236},"The left",{"id":61,"label":238},"The top",{"id":64,"label":240},"The bottom",[55],[243],"Remember: waxing = right (growing towards full), waning = left.","From most of India, a waxing (growing) crescent shows its bright edge on the right, like a backwards C. A waning crescent is bright on the left.",[246],"observation",{"id":248,"section":15,"level":49,"prompt":249,"check":250,"hints":259,"solution":260,"skills":261},"phases-of-the-moon.q012","In the sky over India, a waning crescent Moon is bright on which side?",{"kind":52,"options":251,"correct":258},[252,253,254,256],{"id":55,"label":234},{"id":58,"label":236},{"id":61,"label":255},"Both sides equally",{"id":64,"label":257},"Neither; it is invisible",[58],[],"A waning (shrinking) crescent shows its bright edge on the left as seen from most of India, the mirror image of a waxing crescent.",[246],{"id":263,"section":15,"level":175,"prompt":264,"check":265,"hints":276,"solution":277,"skills":278},"phases-of-the-moon.q013","You see a Moon that is exactly half-lit, bright on the right side. Which phase is it?",{"kind":52,"options":266,"correct":275},[267,269,271,273],{"id":55,"label":268},"First quarter",{"id":58,"label":270},"Last quarter",{"id":61,"label":272},"Full moon",{"id":64,"label":274},"New moon",[55],[],"Bright-on-the-right and exactly half-lit is first quarter, seen about a week after new moon, high in the sky in the evening.",[246],{"id":280,"section":15,"level":175,"prompt":281,"check":282,"hints":290,"solution":291,"skills":292},"phases-of-the-moon.q014","You see a Moon that is exactly half-lit, bright on the left side. Which phase is it?",{"kind":52,"options":283,"correct":289},[284,285,286,288],{"id":55,"label":268},{"id":58,"label":270},{"id":61,"label":287},"Waxing gibbous",{"id":64,"label":274},[58],[],"Bright-on-the-left and exactly half-lit is last quarter, typically seen in the pre-dawn sky, about three weeks after new moon.",[246],{"id":294,"section":15,"level":175,"prompt":295,"check":296,"hints":307,"solution":309,"skills":310},"phases-of-the-moon.q015","Why is the Moon sometimes clearly visible in a daytime sky?",{"kind":52,"options":297,"correct":306},[298,300,302,304],{"id":55,"label":299},"It is a common myth; the Moon is never visible in daylight",{"id":58,"label":301},"The Moon is above the horizon during the day for roughly half of every month, and it reflects enough sunlight to be seen against a blue sky",{"id":61,"label":303},"The Moon only appears in daylight during an eclipse",{"id":64,"label":305},"Daytime moons are a different, smaller object",[58],[308],"Full moon rises at sunset, so it is essentially never visible in a daytime sky; but many other phases are, in the hours after sunrise or before sunset.","The Moon spends about half of each month above the horizon during at least part of the daytime. Whenever it is high enough and not too close to the Sun's glare, it reflects enough sunlight to stand out against blue sky, just fainter than at night.",[155],{"id":312,"section":15,"level":175,"prompt":313,"check":314,"hints":319,"solution":320,"skills":321},"phases-of-the-moon.q016","A full moon is, by definition, what percentage of its disc lit?",{"kind":315,"answer":316,"tolerance":317,"unit":318},"number",100,0,"%",[],"By definition, full moon is the moment the near side faces the Sun almost directly, so essentially the entire visible disc is lit: 100%.",[322],"definitions",{"id":324,"section":15,"level":175,"prompt":325,"check":326,"hints":327,"solution":328,"skills":329},"phases-of-the-moon.q017","A new moon is, by definition, what percentage of its disc lit (as seen from Earth)?",{"kind":315,"answer":317,"tolerance":317,"unit":318},[],"At new moon, the Moon sits almost between Earth and the Sun, so its near side (the side facing Earth) is the *unlit* far-from-Sun side: essentially 0% appears lit, and the Moon is invisible against the daytime sky.",[322],{"id":331,"section":19,"level":175,"prompt":332,"check":333,"hints":337,"solution":338,"skills":339},"phases-of-the-moon.q018","What is the name for the angle between the Sun and the Moon, as measured from Earth?",{"kind":334,"accept":335},"text",[336],"elongation",[],"This Sun-Earth-Moon angle is called elongation. It is 0° at new moon (Moon and Sun in the same direction), 90° at first quarter, 180° at full moon (opposite the Sun), and 270° at last quarter.",[89],{"id":341,"section":19,"level":175,"prompt":342,"check":343,"hints":346,"solution":347,"skills":348},"phases-of-the-moon.q019","What is the elongation, in degrees, at first quarter?",{"kind":315,"answer":344,"tolerance":317,"unit":345},90,"degrees",[],"First quarter occurs a quarter of the way through the cycle in angle terms: elongation = 90°, which is also why the Moon then appears exactly half-lit.",[322],{"id":350,"section":19,"level":175,"prompt":351,"check":352,"hints":354,"solution":355,"skills":356},"phases-of-the-moon.q020","What is the elongation, in degrees, at full moon?",{"kind":315,"answer":353,"tolerance":317,"unit":345},180,[],"At full moon the Moon is opposite the Sun in the sky, an elongation of 180°.",[322],{"id":358,"section":19,"level":359,"prompt":360,"check":361,"hints":363,"solution":365,"skills":366},"phases-of-the-moon.q021","stretch","Using the formula illuminated fraction = (1 − cos(elongation)) ÷ 2, what fraction of the disc is lit at an elongation of 60°? Give your answer as a percentage, to the nearest whole number.",{"kind":315,"answer":362,"tolerance":5,"unit":318},25,[364],"cos 60° = 0.5 exactly.","(1 − cos 60°) ÷ 2 = (1 − 0.5) ÷ 2 = 0.25, so **25%**. This is less than half, correctly matching a crescent phase (elongation under 90°).",[367,368],"formula","calculation",{"id":370,"section":19,"level":359,"prompt":371,"check":372,"hints":375,"solution":377,"skills":378},"phases-of-the-moon.q022","Using illuminated fraction = (1 − cos(elongation)) ÷ 2, what fraction of the disc is lit at an elongation of 135° (waxing gibbous)? Give your answer as a percentage to one decimal place.",{"kind":315,"answer":373,"tolerance":374,"unit":318},85.4,0.2,[376],"135° is past 90°, so its cosine is negative, which makes the top of the fraction bigger than 1.","cos 135° ≈ -0.7071. (1 − (-0.7071)) ÷ 2 ≈ **85.4%**, matching the table value for waxing gibbous.",[367,368],{"id":380,"section":19,"level":359,"prompt":381,"check":382,"hints":385,"solution":387,"skills":388},"phases-of-the-moon.q023","A Moon is 3.69 days after new moon. Using day = synodic month × elongation ÷ 360 (synodic month = 29.53 days), what elongation, in degrees, does this correspond to? Round to the nearest 5 degrees.",{"kind":315,"answer":383,"tolerance":384,"unit":345},45,3,[386],"Rearrange day = synodic × elongation ÷ 360 to solve for elongation.","Rearranging: elongation = day × 360 ÷ synodic month = 3.69 × 360 ÷ 29.53 ≈ **45°**, the waxing crescent phase.",[367,368],{"id":390,"section":19,"level":359,"prompt":391,"check":392,"hints":396,"solution":397,"skills":398},"phases-of-the-moon.q024","Using day = synodic month × elongation ÷ 360, how many days after new moon does an elongation of 270° (last quarter) occur? Use synodic month = 29.53 days, and round to two decimal places.",{"kind":315,"answer":393,"tolerance":394,"unit":395},22.15,0.05,"days",[],"day = 29.53 × 270 ÷ 360 = **22.15 days**, about three weeks after new moon.",[367,368],{"id":400,"section":19,"level":401,"prompt":402,"check":403,"hints":414,"solution":416,"skills":417},"phases-of-the-moon.q025","challenge","Two Moons are at elongation 60° and elongation 300°. What do these two phases have in common?",{"kind":52,"options":404,"correct":413},[405,407,409,411],{"id":55,"label":406},"Nothing; they look completely different",{"id":58,"label":408},"They have exactly the same illuminated fraction, but one is waxing and the other waning",{"id":61,"label":410},"They are both full moons",{"id":64,"label":412},"They occur on the same night",[58],[415],"cos(θ) = cos(360° − θ) for any angle θ.","Illuminated fraction depends on (1 − cos(elongation)) ÷ 2, and cos(60°) = cos(300°) (cosine is symmetric about 0°\u002F360°), so both give the same fraction lit. One (60°) is before full moon and waxing; the other (300°) is after full moon and waning — mirror-image crescents\u002Fgibbous shapes.",[418,191],"symmetry",{"id":420,"section":19,"level":401,"prompt":421,"check":422,"hints":425,"solution":427,"skills":428},"phases-of-the-moon.q026","At what elongation, to the nearest degree, is exactly a quarter (25%) of the Moon's disc lit? Use (1 − cos(elongation)) ÷ 2 = 0.25 and solve for elongation between 0° and 180°.",{"kind":315,"answer":423,"tolerance":424,"unit":345},60,2,[426],"Rearrange to isolate cos(elongation), then use the fact that cos 60° = 0.5.","Set (1 − cos θ) ÷ 2 = 0.25, so 1 − cos θ = 0.5, so cos θ = 0.5, so θ = 60°. (A second solution, 300°, also gives 25% but on the waning side — see the previous question.)",[367,429],"algebra",{"id":431,"section":23,"level":175,"prompt":432,"check":433,"hints":444,"solution":445,"skills":446},"phases-of-the-moon.q027","At what time does a full moon typically rise?",{"kind":52,"options":434,"correct":443},[435,437,439,441],{"id":55,"label":436},"At sunrise",{"id":58,"label":438},"At noon",{"id":61,"label":440},"At sunset",{"id":64,"label":442},"At midnight",[61],[],"Full moon means the Moon is opposite the Sun in the sky (elongation 180°), so it rises in the east just as the Sun sets in the west, and sets at sunrise the next morning.",[210],{"id":448,"section":23,"level":175,"prompt":449,"check":450,"hints":459,"solution":460,"skills":461},"phases-of-the-moon.q028","At what time does a new moon typically rise?",{"kind":52,"options":451,"correct":458},[452,454,455,456],{"id":55,"label":453},"At sunrise, with the Sun",{"id":58,"label":440},{"id":61,"label":442},{"id":64,"label":457},"It never rises",[55],[],"New moon has the Moon very close to the Sun in the sky (elongation ≈ 0°), so it rises and sets at almost the same time as the Sun — which is also why it is invisible, lost in the Sun's glare.",[210],{"id":463,"section":23,"level":175,"prompt":464,"check":465,"hints":476,"solution":477,"skills":478},"phases-of-the-moon.q029","At what time does a first-quarter moon typically rise?",{"kind":52,"options":466,"correct":475},[467,469,471,473],{"id":55,"label":468},"Around 06:00, at sunrise",{"id":58,"label":470},"Around midday, 12:00",{"id":61,"label":472},"Around 18:00, at sunset",{"id":64,"label":474},"Around midnight",[58],[],"First quarter is 90° behind the Sun in elongation, which corresponds to about 6 hours behind sunrise: around midday. It is then high in the sky in the evening.",[368],{"id":480,"section":23,"level":175,"prompt":481,"check":482,"hints":492,"solution":493,"skills":494},"phases-of-the-moon.q030","At what time does a last-quarter moon typically rise?",{"kind":52,"options":483,"correct":491},[484,486,488,490],{"id":55,"label":485},"Around 06:00",{"id":58,"label":487},"Around midday",{"id":61,"label":489},"Around 18:00",{"id":64,"label":474},[64],[],"Last quarter is 270° of elongation, three-quarters of the way round, corresponding to about 18 hours behind sunrise: around midnight.",[368],{"id":496,"section":23,"level":359,"prompt":497,"check":498,"hints":501,"solution":503,"skills":504},"phases-of-the-moon.q031","If sunrise is at 06:00, and every 15° of elongation delays moonrise by 1 hour, at what clock time (24-hour, e.g. 14.5 for 14:30) would a Moon at elongation 105° rise?",{"kind":315,"answer":499,"tolerance":394,"unit":500},13,"hours (24h)",[502],"Divide the elongation by 15 to get hours of delay, then add to 06:00.","Extra delay = 105 ÷ 15 = 7 hours. Moonrise = 06:00 + 7 h = **13:00**.",[367,368],{"id":506,"section":23,"level":359,"prompt":507,"check":508,"hints":511,"solution":513,"skills":514},"phases-of-the-moon.q032","On average, moonrise happens how many minutes later each day than the day before? Round to the nearest whole minute.",{"kind":315,"answer":509,"tolerance":424,"unit":510},49,"minutes",[512],"Divide the Moon's daily gain in degrees by 15 to convert to hours, then to minutes.","The Moon gains about 12.19° per day on the Sun, which translates (at 15°\u002Fhour) to about **49 minutes** later each day, on average.",[368],{"id":516,"section":23,"level":359,"prompt":517,"check":518,"hints":521,"solution":523,"skills":524},"phases-of-the-moon.q033","A full moon rises at 18:10 tonight. Using an average delay of 49 minutes per day, at approximately what time (in decimal hours, e.g. 19.5 for 19:30) will it rise 3 nights later?",{"kind":315,"answer":519,"tolerance":520,"unit":500},20.60481654293272,0.15,[522],"Convert 18:10 to decimal hours first (18 + 10\u002F60), then add the total delay in hours.","3 nights × 48.8 minutes ≈ 146 minutes ≈ 2.44 hours later. 18:10 + about 2.4 h ≈ **20:36**.",[368,525],"word-problem",{"id":527,"section":23,"level":401,"prompt":528,"check":529,"hints":540,"solution":541,"skills":542},"phases-of-the-moon.q034","Why can real moonrise times differ from the simple 'add 50 minutes a day' rule by up to an hour or more on some nights?",{"kind":52,"options":530,"correct":539},[531,533,535,537],{"id":55,"label":532},"The rule is simply wrong and should never be used",{"id":58,"label":534},"The Moon's elliptical orbit changes its speed, and the angle of its path to the horizon changes with the season, both of which make the daily delay vary",{"id":61,"label":536},"Time zones change every night",{"id":64,"label":538},"The Moon sometimes skips a night entirely",[58],[],"The 50-minute figure is a monthly average. On any given night, the Moon's real orbital speed (faster near perigee, slower near apogee) and the changing angle between the Moon's path and the horizon both push the real delay above or below that average — sometimes by a large amount, as in the Harvest Moon effect.",[191],{"id":544,"section":23,"level":401,"prompt":545,"check":546,"hints":548,"solution":550,"skills":551},"phases-of-the-moon.q035","Karva Chauth's Moon sits at roughly 222° elongation. Using (1 − cos(elongation)) ÷ 2, what percentage of its disc is lit? Round to the nearest whole percent.",{"kind":315,"answer":547,"tolerance":5,"unit":318},87,[549],"222° is past 180°, so the cosine is negative.","cos 222° ≈ -0.743. (1 − (-0.743)) ÷ 2 ≈ **87%**, a fat waning gibbous.",[367,368,552],"festival",{"id":554,"section":27,"level":175,"prompt":555,"check":556,"hints":559,"solution":560,"skills":561},"phases-of-the-moon.q036","What is the name for the 27.32-day period in which the Moon completes one true orbit of Earth relative to the distant stars?",{"kind":334,"accept":557},[558],"sidereal month",[],"This is the sidereal month: how long the Moon takes to return to the same position against the fixed stars, measured relative to the stars rather than to the Sun.",[89],{"id":563,"section":27,"level":175,"prompt":564,"check":565,"hints":568,"solution":569,"skills":570},"phases-of-the-moon.q037","What is the name for the 29.53-day period from one new moon to the next?",{"kind":334,"accept":566},[567],"synodic month",[],"This is the synodic month: the cycle of phases, driven by the changing angle between Sun, Earth and Moon, not by the Moon's raw orbital period.",[89],{"id":572,"section":27,"level":359,"prompt":573,"check":574,"hints":577,"solution":578,"skills":579},"phases-of-the-moon.q038","The sidereal month is 27.32 days and the synodic month is 29.53 days. By how many days do they differ, to two decimal places?",{"kind":315,"answer":575,"tolerance":576,"unit":395},2.21,0.02,[],"29.53 − 27.32 = **2.21 days**, a little over two days.",[368],{"id":581,"section":27,"level":359,"prompt":582,"check":583,"hints":594,"solution":596,"skills":597},"phases-of-the-moon.q039","Why is the synodic month longer than the sidereal month?",{"kind":52,"options":584,"correct":593},[585,587,589,591],{"id":55,"label":586},"The Moon's orbit is an ellipse",{"id":58,"label":588},"Earth itself keeps moving around the Sun during the month, so the Moon must travel a bit further to catch up with the Sun again",{"id":61,"label":590},"The Moon slows down every month",{"id":64,"label":592},"It is a rounding error in ancient measurements",[58],[595],"This effect exists even for a perfectly circular lunar orbit.","After one true 360° orbit (the sidereal month), the Sun has itself moved on because Earth has travelled around it. The Moon needs a little extra time to 'catch up' to the Sun's new position, which is exactly the synodic month's extra length.",[191,155],{"id":599,"section":27,"level":401,"prompt":600,"check":601,"hints":604,"solution":606,"skills":607},"phases-of-the-moon.q040","The Moon moves about 13.18° per day against the stars, and the Sun's apparent yearly motion is about 0.9856° per day. To the nearest 0.01°, how much does the Moon gain on the Sun each day?",{"kind":315,"answer":602,"tolerance":576,"unit":603},12.19,"degrees\u002Fday",[605],"Subtract the Sun's daily apparent motion from the Moon's daily motion.","13.176 − 0.9856 = **12.19° per day**, which over about 29.5 days adds up to a full 360° lap.",[368],{"id":609,"section":27,"level":401,"prompt":610,"check":611,"hints":613,"solution":614,"skills":615},"phases-of-the-moon.q041","Using a daily gain of 12.191° between the Moon and the Sun, derive the synodic month in days (360° ÷ daily gain). Round to two decimal places.",{"kind":315,"answer":612,"tolerance":576,"unit":395},29.53,[],"360 ÷ 12.191 ≈ **29.53 days**, matching the accepted synodic month value to within a hundredth of a day.",[616,368],"derivation",{"id":618,"section":31,"level":49,"prompt":619,"check":620,"hints":622,"solution":623,"skills":624},"phases-of-the-moon.q042","How many degrees of elongation does one tithi correspond to?",{"kind":315,"answer":621,"tolerance":317,"unit":345},12,[],"A tithi is defined as the time for the Moon to gain 12° of elongation on the Sun. There are 360 ÷ 12 = 30 tithis in a full cycle.",[322],{"id":626,"section":31,"level":49,"prompt":627,"check":628,"hints":631,"solution":632,"skills":633},"phases-of-the-moon.q043","How many tithis make up a full lunar month?",{"kind":315,"answer":629,"tolerance":317,"unit":630},30,"tithis",[],"360° of elongation, divided into 12°-wide tithis, gives 360 ÷ 12 = 30 tithis per lunar month.",[368],{"id":635,"section":31,"level":49,"prompt":636,"check":637,"hints":641,"solution":642,"skills":643},"phases-of-the-moon.q044","What is the Sanskrit\u002FHindi name for the waxing (growing) fortnight of the lunar month?",{"kind":334,"accept":638},[639,640],"shukla paksha","shukla-paksha",[],"Shukla paksha is the bright, waxing half of the lunar month, from Amavasya (new moon) to Purnima (full moon).",[89],{"id":645,"section":31,"level":49,"prompt":646,"check":647,"hints":651,"solution":652,"skills":653},"phases-of-the-moon.q045","What is the Sanskrit\u002FHindi name for the waning (shrinking) fortnight of the lunar month?",{"kind":334,"accept":648},[649,650],"krishna paksha","krishna-paksha",[],"Krishna paksha is the dark, waning half of the lunar month, from Purnima (full moon) back to Amavasya (new moon).",[89],{"id":655,"section":31,"level":49,"prompt":656,"check":657,"hints":660,"solution":661,"skills":662},"phases-of-the-moon.q046","What is the Sanskrit\u002FHindi name for the full moon day?",{"kind":334,"accept":658},[659],"purnima",[],"Purnima is the full moon, the fifteenth tithi, at elongation 180°.",[89],{"id":664,"section":31,"level":49,"prompt":665,"check":666,"hints":669,"solution":670,"skills":671},"phases-of-the-moon.q047","What is the Sanskrit\u002FHindi name for the new moon day?",{"kind":334,"accept":667},[668],"amavasya",[],"Amavasya is the new moon, the thirtieth tithi (sometimes labelled tithi 0), at elongation 0°\u002F360°.",[89],{"id":673,"section":31,"level":175,"prompt":674,"check":675,"hints":678,"solution":679,"skills":680},"phases-of-the-moon.q048","A lunar year of 12 synodic months lasts 354.37 days. A solar (tropical) year lasts 365.24 days. What is the shortfall, in days, to one decimal place?",{"kind":315,"answer":676,"tolerance":677,"unit":395},10.9,0.1,[],"365.24 − 354.37 = **10.9 days**, the yearly backlog that adhik maas exists to repay.",[368],{"id":682,"section":31,"level":175,"prompt":683,"check":684,"hints":689,"solution":690,"skills":691},"phases-of-the-moon.q049","What is the name for the extra 'leap' month inserted into the Hindu lunisolar calendar to keep it aligned with the solar year?",{"kind":334,"accept":685},[686,687,688],"adhik maas","adhik-maas","adhikmaas",[],"This extra month is called adhik maas. It is inserted roughly every 32-33 months, whenever the shortfall between the lunar year and solar year has accumulated to about one full lunar month.",[89],{"id":693,"section":31,"level":359,"prompt":694,"check":695,"hints":698,"solution":699,"skills":700},"phases-of-the-moon.q050","The lunar calendar falls behind the solar year by 10.875 days annually. Roughly how many years pass before that shortfall equals one whole synodic month (29.53 days)? Round to one decimal place.",{"kind":315,"answer":696,"tolerance":677,"unit":697},2.7,"years",[],"29.53 ÷ 10.875 ≈ **2.7 years**, so an adhik maas is needed roughly every 32-33 lunar months.",[368,616],{"id":702,"section":31,"level":359,"prompt":703,"check":704,"hints":715,"solution":716,"skills":717},"phases-of-the-moon.q051","Why does a tithi sometimes last noticeably more or less than its average of about 23.6 hours?",{"kind":52,"options":705,"correct":714},[706,708,710,712],{"id":55,"label":707},"Clocks in ancient India were imprecise",{"id":58,"label":709},"A tithi is defined by a fixed 12° gain in elongation, and the Moon's elliptical orbit makes its speed vary through the month",{"id":61,"label":711},"The Sun sometimes skips a day",{"id":64,"label":713},"It never varies; 23.6 hours is exact every time",[58],[],"Because a tithi is an angle (12° of elongation), not a fixed duration, it takes less real time when the Moon is moving faster (near perigee) and more real time when the Moon is moving slower (near apogee).",[191],{"id":719,"section":31,"level":401,"prompt":720,"check":721,"hints":732,"solution":733,"skills":734},"phases-of-the-moon.q052","What is the Metonic cycle?",{"kind":52,"options":722,"correct":731},[723,725,727,729],{"id":55,"label":724},"A cycle of 12 lunar months exactly equal to one solar year",{"id":58,"label":726},"The near-coincidence that 235 synodic months and 19 tropical years last almost exactly the same number of days",{"id":61,"label":728},"The 18.6-year cycle of the Moon's orbital nodes",{"id":64,"label":730},"The cycle by which eclipses repeat",[58],[],"The Metonic cycle is the discovery, made independently by several ancient astronomers, that 19 tropical years and 235 synodic months (12 ordinary years plus 7 leap months) come out to almost the same length — used in calendars such as the Hebrew calendar's fixed 19-year, 7-leap-month rule.",[735],"history",{"id":737,"section":35,"level":49,"prompt":738,"check":739,"hints":750,"solution":751,"skills":752},"phases-of-the-moon.q053","What actually causes the Moon's phases?",{"kind":52,"options":740,"correct":749},[741,743,745,747],{"id":55,"label":742},"Earth's shadow falling on different parts of the Moon",{"id":58,"label":744},"The changing angle between Sun, Earth and Moon, which changes how much of the permanently-lit half faces us",{"id":61,"label":746},"Clouds on the Moon",{"id":64,"label":748},"The Moon changing size",[58],[],"Phases come from geometry: as the Moon orbits, a different amount of its permanently sunlit half faces Earth. Earth's shadow is a completely different, much rarer phenomenon: an eclipse.",[155,210],{"id":754,"section":35,"level":49,"prompt":755,"check":756,"hints":767,"solution":768,"skills":769},"phases-of-the-moon.q054","When does Earth's shadow actually fall on the Moon?",{"kind":52,"options":757,"correct":766},[758,760,762,764],{"id":55,"label":759},"Every night",{"id":58,"label":761},"Only during a lunar eclipse, which happens a few times a year at most",{"id":61,"label":763},"Every full moon",{"id":64,"label":765},"Only during a new moon",[58],[],"Earth's shadow only reaches the Moon during a lunar eclipse, a distinct and comparatively rare event — not the ordinary monthly cycle of phases.",[155],{"id":771,"section":35,"level":175,"prompt":772,"check":773,"hints":775,"solution":776,"skills":777},"phases-of-the-moon.q055","By how many degrees is the Moon's orbit tilted relative to Earth's orbit around the Sun? (Round to one decimal place.)",{"kind":315,"answer":774,"tolerance":394,"unit":345},5.1,[],"The Moon's orbital plane is tilted about **5.1°** to Earth's orbital plane (the ecliptic). This tilt is the reason eclipses do not happen every single month.",[322],{"id":779,"section":35,"level":175,"prompt":780,"check":781,"hints":792,"solution":793,"skills":794},"phases-of-the-moon.q056","Why doesn't a lunar eclipse happen at every single full moon?",{"kind":52,"options":782,"correct":791},[783,785,787,789],{"id":55,"label":784},"The Moon is too far away most months",{"id":58,"label":786},"The Moon's orbit is tilted, so most full moons pass above or below Earth's shadow rather than through it",{"id":61,"label":788},"Earth's shadow only exists sometimes",{"id":64,"label":790},"The Sun blocks it",[58],[],"Because the Moon's orbit is tilted about 5.1° to Earth's orbital plane, most full moons occur when the Moon is above or below the flat plane that contains Earth's shadow, missing it entirely. Only when a full moon happens near one of the two points where the two orbital planes cross (the nodes) does the Moon pass through the shadow.",[191],{"id":796,"section":35,"level":359,"prompt":797,"check":798,"hints":802,"solution":803,"skills":804},"phases-of-the-moon.q057","What is the name for the two points where the Moon's tilted orbital plane crosses Earth's orbital plane, and near which eclipses can occur?",{"kind":334,"accept":799},[800,801],"nodes","node",[],"These crossing points are called nodes. An eclipse requires a new or full moon to occur close to one of the two nodes; away from a node, the Moon passes safely above or below the line-up needed for an eclipse.",[89],{"id":806,"section":35,"level":359,"prompt":807,"check":808,"hints":811,"solution":812,"skills":813},"phases-of-the-moon.q058","The Saros cycle is 223 synodic months long. Using a synodic month of 29.5306 days, how many days is one Saros cycle? Round to two decimal places.",{"kind":315,"answer":809,"tolerance":810,"unit":395},6585.32,0.5,[],"223 × 29.5306 = **6585.32 days**, which works out to about 18 years and 11 days.",[368],{"id":815,"section":35,"level":401,"prompt":816,"check":817,"hints":819,"solution":820,"skills":821},"phases-of-the-moon.q059","Using the Saros length of 6585.32 days and a tropical year of 365.242 days, how many years long is one Saros cycle? Round to two decimal places.",{"kind":315,"answer":818,"tolerance":576,"unit":697},18.03,[],"6585.32 ÷ 365.242 ≈ **18.03 years**, or about 18 years and 11 days — the reason similar eclipses recur on a roughly 18-year rhythm.",[368,616],{"id":823,"section":35,"level":401,"prompt":824,"check":825,"hints":836,"solution":837,"skills":838},"phases-of-the-moon.q060","What must be true, geometrically, for a total solar eclipse to occur?",{"kind":52,"options":826,"correct":835},[827,829,831,833],{"id":55,"label":828},"The Moon must be full",{"id":58,"label":830},"The Moon must be new, and close enough to a node that its shadow reaches Earth's surface, with the Moon's angular size at least matching the Sun's",{"id":61,"label":832},"Earth must be at aphelion",{"id":64,"label":834},"It can happen at any new moon, anywhere on Earth",[58],[],"A total solar eclipse needs a new moon (so the Moon is between Earth and the Sun), positioned close enough to a node for the Moon's shadow to actually touch Earth, and the Moon's apparent size (which varies with distance) must be at least as large as the Sun's for that particular alignment.",[191],{"id":840,"section":39,"level":175,"prompt":841,"check":842,"hints":853,"solution":855,"skills":856},"phases-of-the-moon.q061","Why do we always see (almost) the same face of the Moon?",{"kind":52,"options":843,"correct":852},[844,846,848,850],{"id":55,"label":845},"The Moon does not spin at all",{"id":58,"label":847},"The Moon is tidally locked: it spins on its axis in exactly the same time it takes to orbit Earth once",{"id":61,"label":849},"The Moon is much bigger on one side",{"id":64,"label":851},"Earth's gravity holds one side still",[58],[854],"The Moon IS spinning — just at exactly the rate that keeps one face pointed our way.","The Moon rotates once on its own axis in the same time it takes to complete one orbit (both about 27.3 days) — a state called tidal locking. Because spin and orbit match, the same hemisphere always faces Earth.",[155,210],{"id":858,"section":39,"level":175,"prompt":859,"check":860,"hints":871,"solution":872,"skills":873},"phases-of-the-moon.q062","What is wrong with calling the far side of the Moon 'the dark side'?",{"kind":52,"options":861,"correct":870},[862,864,866,868],{"id":55,"label":863},"Nothing; it is always dark",{"id":58,"label":865},"Every part of the Moon gets roughly two weeks of sunlight and two weeks of darkness each month, including the far side; it is unseen from Earth, not unlit",{"id":61,"label":867},"The far side is actually brighter than the near side",{"id":64,"label":869},"There is no far side",[58],[],"The far side receives the same roughly fortnight-on, fortnight-off cycle of sunlight as the near side. It only earned the nickname 'dark side' because it was unknown to humans until 1959, not because it lacks sunlight.",[155],{"id":875,"section":39,"level":359,"prompt":876,"check":877,"hints":879,"solution":880,"skills":881},"phases-of-the-moon.q063","Due to libration, what percentage of the Moon's surface becomes visible from Earth at some point over time (never all at once)?",{"kind":315,"answer":878,"tolerance":5,"unit":318},59,[],"Libration in longitude and latitude together let observers see slightly round each edge at different times, raising the total ever-visible fraction to about **59%**, compared with a plain 50% for a non-wobbling Moon.",[322],{"id":883,"section":39,"level":359,"prompt":884,"check":885,"hints":896,"solution":897,"skills":898},"phases-of-the-moon.q064","What causes libration in longitude?",{"kind":52,"options":886,"correct":895},[887,889,891,893],{"id":55,"label":888},"The Moon's orbital speed varies (because its orbit is elliptical) while its spin rate stays constant, so the two drift in and out of step through the month",{"id":58,"label":890},"The Moon's axis is tilted",{"id":61,"label":892},"Earth wobbles on its axis",{"id":64,"label":894},"The Moon's crust is uneven",[55],[],"The Moon's spin rate is constant, but its orbital speed speeds up near perigee and slows down near apogee (an elliptical orbit). The two rates only match exactly on average, so at other points in the month they drift slightly out of step, letting us peek a little round the eastern or western edge.",[191],{"id":900,"section":39,"level":401,"prompt":901,"check":902,"hints":905,"solution":906,"skills":907},"phases-of-the-moon.q065","Laser ranging shows the Moon receding from Earth at about 3.8 cm per year. At that rate, how many centimetres would it recede over an 80-year human lifetime?",{"kind":315,"answer":903,"tolerance":424,"unit":904},304,"cm",[],"3.8 × 80 = **304 cm**, a little over a metre — far too small to notice by eye, but measurable with laser ranging.",[368],{"id":909,"section":39,"level":401,"prompt":910,"check":911,"hints":922,"solution":923,"skills":924},"phases-of-the-moon.q066","What provided the very first direct, ongoing physical measurement of the Moon's recession rate?",{"kind":52,"options":912,"correct":921},[913,915,917,919],{"id":55,"label":914},"Photographs comparing the Moon's size over decades",{"id":58,"label":916},"Laser pulses timed as they bounce off retroreflectors left on the Moon by Apollo astronauts",{"id":61,"label":918},"Radio telescopes listening for a signal from the Moon",{"id":64,"label":920},"Counting craters",[58],[],"Apollo astronauts left small mirror arrays (retroreflectors) on the surface. Timing how long a laser pulse takes to bounce back and forth, repeated over decades, reveals the slow, steady growth in distance directly, to within a few centimetres.",[735],{"id":926,"section":39,"level":401,"prompt":927,"check":928,"hints":939,"solution":940,"skills":941},"phases-of-the-moon.q067","What is the actual physical mechanism causing the Moon to recede from Earth?",{"kind":52,"options":929,"correct":938},[930,932,934,936],{"id":55,"label":931},"The Moon's engines",{"id":58,"label":933},"Earth's spin drags its tidal bulge ahead of the Earth-Moon line, and gravity on that bulge nudges the Moon into a wider orbit",{"id":61,"label":935},"Solar wind pressure",{"id":64,"label":937},"The Moon is losing mass",[58],[],"Earth's 24-hour spin is faster than the Moon's month-long orbit, so friction drags Earth's tidal bulge slightly ahead of the Earth-Moon line. Gravity acting through that misaligned bulge nudges the Moon forward, and a faster-moving satellite settles into a wider orbit — the same mechanism (in reverse roles) that originally locked the Moon's own rotation.",[942],"mechanism",{"id":944,"section":43,"level":175,"prompt":945,"check":946,"hints":949,"solution":950,"skills":951},"phases-of-the-moon.q068","What is the name of the lander that touched down on the Moon during India's Chandrayaan-3 mission?",{"kind":334,"accept":947},[948],"vikram",[],"The lander was named Vikram, after Vikram Sarabhai, the founder of India's space programme. It carried the Pragyan rover.",[952],"mission-facts",{"id":954,"section":43,"level":175,"prompt":955,"check":956,"hints":967,"solution":968,"skills":969},"phases-of-the-moon.q069","On what date did Chandrayaan-3's lander touch down on the Moon?",{"kind":52,"options":957,"correct":966},[958,960,962,964],{"id":55,"label":959},"15 August 2023",{"id":58,"label":961},"23 August 2023",{"id":61,"label":963},"2 September 2023",{"id":64,"label":965},"14 July 2023",[58],[],"Chandrayaan-3 landed on 23 August 2023, an anniversary now marked in India as National Space Day. (14 July 2023 was the launch date, not the landing.)",[952],{"id":971,"section":43,"level":175,"prompt":972,"check":973,"hints":984,"solution":985,"skills":986},"phases-of-the-moon.q070","Why was the lunar south pole chosen as Chandrayaan-3's target region rather than the equator, where earlier missions usually landed?",{"kind":52,"options":974,"correct":983},[975,977,979,981],{"id":55,"label":976},"It was easier to land on",{"id":58,"label":978},"Permanently shadowed polar craters, caused by the Moon's very small axial tilt, are cold enough to trap water ice, a valuable resource for future missions",{"id":61,"label":980},"It has the most sunlight",{"id":64,"label":982},"It was the closest point to Earth",[58],[],"Because the Moon's axial tilt is so small, some deep polar crater floors never receive direct sunlight and stay extremely cold, trapping water ice that would evaporate anywhere sunlit — a resource future missions want to use for water, oxygen and fuel. The terrain there is also far rougher and harder to land on than the equatorial plains earlier missions favoured.",[191],{"id":988,"section":43,"level":359,"prompt":989,"check":990,"hints":993,"solution":994,"skills":995},"phases-of-the-moon.q071","One full lunar day-night cycle equals one synodic month, 29.53 Earth-days. Roughly how many Earth-days of continuous sunlight (half the cycle) does that give? Round to one decimal place.",{"kind":315,"answer":991,"tolerance":677,"unit":992},14.8,"Earth-days",[],"29.53 ÷ 2 ≈ **14.8 Earth-days** of continuous sunlight, followed by roughly the same length of continuous darkness and extreme cold — which is why Chandrayaan-3's solar-powered lander was designed for one lunar day of operation.",[368],{"id":997,"section":43,"level":359,"prompt":998,"check":999,"hints":1010,"solution":1011,"skills":1012},"phases-of-the-moon.q072","Which mission first returned photographs of the Moon's far side?",{"kind":52,"options":1000,"correct":1009},[1001,1003,1005,1007],{"id":55,"label":1002},"Apollo 11",{"id":58,"label":1004},"Luna 3, in 1959",{"id":61,"label":1006},"Chandrayaan-1",{"id":64,"label":1008},"Chang'e-4",[58],[],"The Soviet probe Luna 3 returned the first, grainy photographs of the far side in 1959. Apollo 8's crew were the first humans to see it directly, in 1968; Chang'e-4 was the first to land there, in 2019.",[735],{"id":1014,"section":43,"level":359,"prompt":1015,"check":1016,"hints":1027,"solution":1028,"skills":1029},"phases-of-the-moon.q073","What evidence, independent of laser ranging, also supports a slowing Earth and a receding Moon?",{"kind":52,"options":1017,"correct":1026},[1018,1020,1022,1024],{"id":55,"label":1019},"Modern satellite photographs",{"id":58,"label":1021},"Daily growth bands in ancient fossil corals, which imply a shorter day hundreds of millions of years ago",{"id":61,"label":1023},"Ancient Egyptian star charts",{"id":64,"label":1025},"The colour of moonlight",[58],[],"Certain fossil corals lay down microscopic daily growth rings within larger yearly bands. Counting the rings per year in very old fossils implies more, shorter days per year long ago — consistent with a faster-spinning early Earth and, by the same physics, a closer Moon.",[1030],"evidence",{"id":1032,"section":43,"level":401,"prompt":1033,"check":1034,"hints":1045,"solution":1046,"skills":1047},"phases-of-the-moon.q074","Roughly why will total solar eclipses eventually stop being possible, many hundreds of millions of years from now?",{"kind":52,"options":1035,"correct":1044},[1036,1038,1040,1042],{"id":55,"label":1037},"The Sun will run out of fuel first",{"id":58,"label":1039},"The receding Moon will eventually look smaller than the Sun even at its closest approach, so it can no longer fully cover the Sun",{"id":61,"label":1041},"Earth's orbit will shrink",{"id":64,"label":1043},"The Moon will stop orbiting Earth",[58],[],"Total eclipses need the Moon to look at least as big as the Sun, which currently just barely happens at the Moon's closest approach (perigee). As the Moon recedes it looks steadily smaller, and eventually even perigee will not be close enough for totality — leaving only annular eclipses (a ring of Sun around the Moon) from then on.",[191,1048],"far-future",{"id":1050,"section":43,"level":401,"prompt":1051,"check":1052,"hints":1063,"solution":1064,"skills":1065},"phases-of-the-moon.q075","How do the Hindu and Islamic lunar calendars differ in the way they handle the roughly 11-day-a-year gap between 12 lunar months and one solar year?",{"kind":52,"options":1053,"correct":1062},[1054,1056,1058,1060],{"id":55,"label":1055},"Both ignore the gap completely",{"id":58,"label":1057},"Hindu calendars insert adhik maas to stay aligned with the seasons; the Islamic calendar makes no correction and drifts over about 33 years",{"id":61,"label":1059},"Both insert an extra month every year",{"id":64,"label":1061},"The Islamic calendar is solar, not lunar",[58],[],"The Hindu lunisolar calendar deliberately inserts an adhik maas roughly every 32-33 months to stay anchored to the same season. The Islamic (Hijri) calendar makes no such adjustment, so a given Islamic month drifts steadily earlier against the solar year, cycling through every season roughly every 33 years.",[1066],"comparison",[1068,1069,1070,1071,1072,1073,1074],"phases-of-the-moon-nasa-moon-phases","phases-of-the-moon-wikipedia-lunar-phase","phases-of-the-moon-wikipedia-hindu-calendar","phases-of-the-moon-wikipedia-saros","phases-of-the-moon-wikipedia-tidal-locking","phases-of-the-moon-isro-chandrayaan3","phases-of-the-moon-nssdc-apollo-llr","needs_review",{"generatedBy":1077,"notes":1078},"claude-code","Draft generated locally; pending owner review. Every numeric answer computed and cross-checked against numbers.py.","4bc7aeecd722042187774f6c57c6805487e120a8982b6f9e0ced39fee24eacd8",{"logic:questions":1081,"source:phases-of-the-moon-isro-chandrayaan3":1082,"source:phases-of-the-moon-nasa-moon-phases":1083,"source:phases-of-the-moon-nssdc-apollo-llr":1084,"source:phases-of-the-moon-wikipedia-hindu-calendar":1085,"source:phases-of-the-moon-wikipedia-lunar-phase":1086,"source:phases-of-the-moon-wikipedia-saros":1087,"source:phases-of-the-moon-wikipedia-tidal-locking":1088},"e7fd7c240a65bea1bff6277f7af7cca65e2c7fcb13c6d756cb943d53f3cbc948","6add9b81691e662b3e30f5adf80290aa1891a8306c87ea2ce4c65fa718077468","a204a49fd1f0bcc99b9c71da877e71b83931eba1bf4e931d4af08d83cabb175c","15d68c7c8e7c5840ddb4a445227372b32238fff4b4f20713e7baaba612edfac4","8e594d900f52500015a6a6a8a85532f2a10b743592b6ba41ad92d43adb5fb040","7d0371e53bbaa01b158d9a8d193e8b907f2089d4cb08a73f37d1328b6add3ef9","edb1d31009cfc4429b26cecbff8aec2839c4ab5df7c9e86c1203f7f2abde1a92","5a0004750c70296311da84b7e5d934630608574f01b5e3f87445136cf54ff892","preview-7e1cbbcc4f",1789899599973]