[{"data":1,"prerenderedAt":870},["ShallowReactive",2],{"layer:phases-of-the-moon:investigate":3},{"layer":4,"contentHash":851,"dependencyHashes":852,"approval":863,"releaseId":869},{"schemaVersion":5,"conceptId":6,"locale":7,"depth":8,"revision":5,"title":9,"subtitle":10,"summary":11,"objectives":12,"estimatedMinutes":18,"plate":19,"blocks":40,"sourceIds":846,"reviewStatus":847,"authoring":848},1,"phases-of-the-moon","en","investigate","Put the Moon on trial","Eight investigations, from an orange and a lamp to a month-long diary","Stop reading and start checking. Build a working model of the phases with a ball and a lamp, keep a month-long moon diary, measure the fifty-minute daily lag against your own rooftop, hunt earthshine, and predict a festival moonrise well enough to announce it.",[13,14,15,16,17],"Build and run a physical model of the phases, and say exactly where it breaks down.","Keep a month-long moon diary and read the pattern hidden in its gaps.","Measure the daily delay in moonrise and explain why individual nights scatter around the average.","Design an observation that distinguishes the shadow explanation from the viewing-angle explanation.","Predict the moonrise time and lit fraction for a festival date, and compare with a published almanac.",45,{"title":20,"rows":21},"Lesson plate",[22,25,28,31,34,37],{"label":23,"value":24},"Depth","Investigate",{"label":26,"value":27},"Reading time","about 45 minutes",{"label":29,"value":30},"Prior knowledge","Understand: elongation and rise times",{"label":32,"value":33},"Chapters","9",{"label":35,"value":36},"Labs","Unlabelled phase drill, evidence sort, observation match",{"label":38,"value":39},"Field work","One month, two minutes a night",[41,45,51,76,82,85,118,136,141,145,150,153,201,206,223,234,239,242,275,288,293,298,301,306,322,337,353,357,362,366,369,382,415,420,423,436,441,466,471,474,495,508,512,517,522,525,542,555,559,563,568,571,637,642,667,671,674,680,684,818,836],{"id":42,"type":43,"markdown":44},"intro-investigate","prose","Everything you have read so far is a claim. Claims are cheap. This layer is about **checking them**.\n\nThe Moon is the single best object in the sky for a young investigator. It is bright enough to see from a city balcony, big enough that you need no equipment, and slow enough that one observation a day is plenty — but fast enough that a month of watching gives you a complete data set.\n\nOver the next nine chapters you will run seven investigations. Some take ten seconds with a ball and a lamp. One takes a month. Each one ends with a prediction you write down **before** you look, because a prediction you make afterwards is not a prediction.\n\nKeep a notebook. Date every entry. Write down what you saw, including the nights when you saw nothing.",{"id":46,"type":47,"variant":48,"title":49,"markdown":50},"intro-rules","callout","try_it","Three rules for honest observing","**1. Write the prediction down first.** Not in your head. On paper, with the date. Memory quietly rewrites itself to match whatever happened.\n\n**2. Record what you saw, not what you expected.** If the Moon looks wrong, that is the most interesting entry in your notebook. Draw it exactly.\n\n**3. Record the failures.** \"Cloudy, nothing visible\" and \"looked for 20 minutes, could not find it\" are real data. A diary with gaps you have explained is far more useful than one with gaps you have quietly filled in.",{"id":52,"type":53,"tone":54,"items":55},"intro-toolkit","spec","neutral",[56,60,64,68,72],{"label":57,"big":58,"value":59},"Equipment needed","Almost none","A notebook, a pencil, an orange or ball, and a lamp. No telescope required for any investigation here.",{"label":61,"big":62,"value":63},"Longest investigation","1 month","The moon diary (Investigation 3), which cannot be rushed or compressed.",{"label":65,"big":66,"value":67},"Shortest investigation","10 seconds","The ball-and-lamp model (Investigation 1), reproducing all eight phases in one slow turn.",{"label":69,"big":70,"value":71},"Best single number to remember","≈49 min\u002Fday","The average daily delay in moonrise, central to Investigations 2, 4 and 8.",{"label":73,"big":74,"value":75},"Safety note","Adult company at night","Balconies, terraces and rooftops after dark should always involve a parent or guardian nearby.",{"id":77,"type":78,"title":79,"eyebrow":80,"navLabel":81},"ch1","chapter","Investigation 1: build the model","Chapter 01","1 Ball and lamp",{"id":83,"type":43,"markdown":84},"ch1-model","Before you test the sky, test the *explanation*. If the phases really come from a half-lit ball seen at different angles, then a half-lit ball seen at different angles should reproduce every phase exactly — including the ones people find surprising.\n\n**What you need:** a ball (an orange, a tennis ball, a ball of dough), a single bare lamp, and a room you can make dark.\n\n**Set up:** lamp on a table at about head height, everything else switched off. Stand about two metres away. Hold the ball at arm's length in front of your face.",{"id":86,"type":87,"title":88,"items":89},"ch1-model-steps","steps","Running the whole month in thirty seconds",[90,94,98,102,106,110,114],{"title":91,"tag":92,"text":93},"Start facing the lamp","new moon","Hold the ball up between your eyes and the lamp, slightly above your head so it is not in your own shadow. The ball looks dark with a glowing rim. That is new moon.",{"title":95,"tag":96,"text":97},"Turn 45° to your left","waxing crescent","Keep the ball at arm's length, turning your whole body. A bright crescent appears on the right-hand edge. Compare it with the table: it should be about 15% lit.",{"title":99,"tag":100,"text":101},"Turn to 90°","first quarter","The lamp is now off to your right. Exactly half the ball is bright, with a straight dividing line. Check: is the bright half the right half?",{"title":103,"tag":104,"text":105},"Turn to 135°","waxing gibbous","A fat lopsided shape with a dark crescent on the left, about 85% lit.",{"title":107,"tag":108,"text":109},"Turn until the lamp is behind you","full moon","The whole face is lit. Hold the ball high so your head does not cast a shadow on it — if it does, you have just made a lunar eclipse.",{"title":111,"tag":112,"text":113},"Keep turning the same way","waning half","Gibbous, then quarter, then crescent — but now bright on the *left*. You are running the second fortnight.",{"title":115,"tag":116,"text":117},"Arrive back at the lamp","new moon again","One full lap of your body equals one synodic month. Count how many degrees you turned: 360.",{"id":119,"type":120,"prompt":121,"options":122,"explanation":135},"predict-model-shadow","prediction","In the ball-and-lamp model, your head plays the part of Earth. What does your head's shadow represent?",[123,126,129,132],{"id":124,"label":125},"a","The phases of the Moon",{"id":127,"label":128},"b","A lunar eclipse — and it only happens at the full-moon position",{"id":130,"label":131},"c","Night on Earth",{"id":133,"label":134},"d","Nothing; it is just a nuisance","**b**, and it is the most useful accident in the whole demonstration.\n\nYour head's shadow can only fall on the ball when the lamp is directly behind you — that is, at the **full moon** position. At every other angle, your shadow points off into empty space and the ball is lit normally while still showing a partial phase.\n\nThat is a working proof of the main point of this topic, done with an orange. **Phases happen at every angle. Shadows only happen at one.** They cannot be the same thing.\n\nTry deliberately eclipsing the ball, then move it slightly up or down. The eclipse ends; the full-moon phase does not. In the real sky, the Moon's tilted orbit does exactly that \"slightly up or down\" at almost every full moon.",{"id":137,"type":47,"variant":138,"title":139,"markdown":140},"ch1-model-limit","model_limit","Where the orange model breaks down","The model gets the geometry of phases exactly right, and that is a lot. But be honest about what it cannot show:\n\n- **Scale.** Your ball is at arm's length; the Moon is 30 Earth-diameters away. That is why a real eclipse is a rare near-miss rather than something that happens whenever you lift the ball.\n- **The 5.1° tilt** of the Moon's orbit, which is the actual reason eclipses are rare. Your arm has no tilt.\n- **Rotation.** The ball is not spinning once per lap, so it cannot show you why the same face points at Earth. Add that by marking one spot on the ball with a sticker and keeping the sticker towards your face.\n- **Brightness.** A lamp two metres away lights an orange far more evenly than the Sun lights the Moon — but not by enough to matter for this test.",{"id":142,"type":47,"variant":48,"title":143,"markdown":144},"ch1-variant-globe","A two-person variant worth trying","If you have a helper, this works even better as a two-person demonstration. One person stands still holding the lamp (or a bright torch) at chest height; the other slowly walks a full circle around a small ball fixed on a stick planted between them, calling out the phase they see at each stop. Swap roles afterwards. Seeing the *same* physical setup from two different vantage points — the \"Earth\" holder and the walking \"Moon\" — makes it obvious that the phase depends only on the angle between the three bodies, never on who is doing the looking.",{"id":146,"type":78,"title":147,"eyebrow":148,"navLabel":149},"ch2","Investigation 2: predict before you look","Chapter 02","2 Predict first",{"id":151,"type":43,"markdown":152},"ch2-predict","Here is a test you can run tonight, with no equipment at all.\n\nFind out today's phase — from a calendar, a newspaper, a panchang, or a phone. Do **not** look at the sky yet.\n\nNow, using only the rules you have learned, predict three things and write them down:\n\n1. **Shape.** How much of the disc will be lit, and which edge will be bright?\n2. **Time.** Roughly when will the Moon rise and set? (Hours behind the Sun = elongation ÷ 15.)\n3. **Place.** At 8 pm tonight, where will it be — east, south, west, and low or high?\n\nThen go out and check. Be strict with yourself: \"roughly right\" counts as right only if you said \"roughly\" in advance.",{"id":154,"type":155,"caption":156,"columns":157,"rows":162},"ch2-predict-table","table","Your prediction sheet: fill in the last column from the sky",[158,159,160,161],"Phase (from the calendar)","Predicted shape","Predicted rise time","Where at 8 pm",[163,168,173,178,183,188,193,197],[164,165,166,167],"New moon","Invisible","06:00 (with the Sun)","Not visible — already set",[169,170,171,172],"Waxing crescent","15% lit, bright on the right","09:00","Low in the west, setting soon",[174,175,176,177],"First quarter","50% lit, bright on the right","12:00","High in the south-west",[179,180,181,182],"Waxing gibbous","85% lit, dark sliver on the left","15:00","High in the south-east, climbing",[184,185,186,187],"Full moon","100% lit","18:00 (at sunset)","Low in the east, just risen",[189,190,191,192],"Waning gibbous","85% lit, dark sliver on the right","21:00","Not yet risen",[194,195,196,192],"Last quarter","50% lit, bright on the left","00:00 (midnight)",[198,199,200,192],"Waning crescent","15% lit, bright on the left","03:00",{"id":202,"type":47,"variant":203,"title":204,"markdown":205},"ch2-when-wrong","careful","When your prediction misses — and it will","Real moonrise can differ from the simple table by **up to about an hour and a half**, and the difference is not a mistake on your part. Three real causes:\n\n- **Your latitude.** The table assumes sunrise at 6 am. In Srinagar in December the Sun rises after 7:20, and everything shifts.\n- **The Moon's orbit is not a circle.** It speeds up when closer to Earth and slows down when further, so it does not gain elongation at a perfectly steady rate.\n- **The tilt of the Moon's path** against the horizon changes through the year. In autumn the Moon's nightly delay can shrink to under 30 minutes; in spring it can stretch past 70.\n\nA miss of an hour is normal physics. A miss of six hours means you have identified the wrong phase — go back and check which edge was bright.",{"id":207,"type":208,"component":209,"componentVersion":5,"config":210,"objective":216,"textAlternative":217,"help":218},"lab-moon-predict","interactive","moon-phase",{"startDay":211,"views":212,"showNames":214,"showTithi":214,"quizRounds":215},3.7,[213],"from-earth",false,10,"Practise naming a phase from the shape alone, with no labels, before you try it on the real sky.","This lab shows only the sky view: a Moon disc with part of it lit, and **no phase name printed**. A slider moves the day through the month.\n\nIt opens at **day 3.7**, a waxing crescent about 15% lit with the bright edge on the right.\n\nTen quiz rounds then show a randomly chosen Moon and ask two things: what is this phase called, and is it waxing or waning? The two clues you have are how much of the disc is bright (less than half is a crescent, more than half is gibbous) and which edge is bright (right means waxing from India, left means waning).\n\nA good score here is the difference between recognising a phase in a picture and recognising it on a balcony at 8 pm, which is the skill you actually want.",{"simplerExplanation":219,"hints":220},"No names, no help. Look at the shape, decide the phase, then check.",[221,222],"Ask two questions in order: more or less than half? Then which edge is bright?","If it is exactly half, look at which side — right means first quarter, left means last quarter.",{"id":224,"type":225,"title":226,"problem":227,"steps":228,"help":232},"we-predict-future-date","worked_example","Predicting a phase several days ahead","Today is 5 days after new moon (a waxing crescent). Predict, in one sentence each, what the Moon will look like 10 days from now and 20 days from now, using the phase table.",[229,230,231],"10 days from now is day 5 + 10 = 15, one day past full moon (14.77), so expect a fat **waning gibbous**, close to 100% lit.","20 days from now is day 5 + 20 = 25, close to the waning crescent day (25.84), so expect a thin **waning crescent**, bright on the left, low in the pre-dawn sky.","Check both against a full lap: a synodic month is about 29.5 days, so day 25 is still comfortably inside the same month as day 5 — no need to wrap around to a second cycle yet.",{"simplerExplanation":233},"Just add the number of days to today's day-of-month number, then look up which phase that day number is closest to in the table.",{"id":235,"type":78,"title":236,"eyebrow":237,"navLabel":238},"ch3","Investigation 3: the month-long moon diary","Chapter 03","3 The moon diary",{"id":240,"type":43,"markdown":241},"ch3-diary-method","This is the central investigation of the topic, and the only one that cannot be rushed. It takes a month, two minutes a night.\n\n**Method.** Every day, at a fixed time if you can (8 pm is a good choice), go to the same spot and record:\n\n- **Date and time**, to the minute.\n- **A drawing.** Always start by drawing a faint full circle, then shade in the part that is actually glowing. Never draw only the bright shape.\n- **Direction and height.** East, south-east, south, south-west or west; and low, halfway, or near overhead. A clenched fist held at arm's length covers about 10° of sky — use fists above the horizon as a measure.\n- **Whether you saw it at all.** \"Not visible, clear sky, looked 8:00-8:15\" is valuable data. It usually means the Moon had not risen yet, which is itself a measurement.\n\n**Stretch version.** Also note the exact clock time you first see the Moon clear the same rooftop or tree each evening. That single number is the basis of Investigation 4.",{"id":243,"type":155,"caption":244,"columns":245,"rows":251},"ch3-diary-template","A diary page, with two rows filled in as an example",[246,247,248,249,250],"Date","Time","Drawing described","Where in the sky","Notes",[252,258,263,267,269,272],[253,254,255,256,257],"Day 1","19:10","Very thin sliver, bright on the right, about one-tenth lit","West, one fist above the rooftops","Found it only because I knew where to look. Gone by 19:45.",[259,254,260,261,262],"Day 2","Thicker sliver, bright on the right, about one-fifth lit","West, two fists up","Noticeably higher and fatter than yesterday. Faint grey glow filling the dark part.",[264,265,265,265,266],"Day 3","—","your turn",[268,265,265,265,266],"Day 4",[270,265,265,265,271],"...","keep going",[273,265,265,265,274],"Day 29","back to a sliver",{"id":276,"type":120,"prompt":277,"options":278,"explanation":287},"predict-diary-outcome","Before you begin a month of diary entries, predict: on how many of the 29 nights will you be able to see the Moon at 8 pm sharp, assuming perfectly clear skies every night?",[279,281,283,285],{"id":124,"label":280},"All 29 — the Moon is up every night",{"id":127,"label":282},"About 15 — roughly half",{"id":130,"label":284},"About 22",{"id":133,"label":286},"About 7","**c, about 22 nights**, and working out why is a good exercise.\n\nAt 8 pm the Moon is above the horizon whenever it has risen and not yet set. Moonrise slides from about 6 am at new moon, through noon at first quarter, 6 pm at full moon, midnight at last quarter, and back round.\n\nRoughly, the Moon is up at 8 pm from a day or two after new moon (when it sets around 8 pm) all the way to last quarter (when it rises around midnight) — but in the last week, moonrise is after 8 pm, so you miss it. That is about seven or eight nights lost out of 29.\n\nOption **a** catches most people out. \"The Moon is out at night\" is one of those things everybody believes and nobody has checked. Your diary will disprove it within a fortnight.",{"id":289,"type":47,"variant":290,"title":291,"markdown":292},"ch3-diary-gaps","observation","The gaps in your diary are the discovery","When you lay out your finished diary, the missing nights will form a **block**, not a scatter. They will all be clustered in the last week of the lunar month.\n\nThat pattern is not about weather or laziness. It is the direct fingerprint of the Moon rising almost an hour later every day. By the end of the cycle, 8 pm is simply before moonrise.\n\nWhich means you have measured something real without even trying: **the Moon's rising time drifts steadily later through the month**. That is the subject of the next investigation.",{"id":294,"type":78,"title":295,"eyebrow":296,"navLabel":297},"ch4","Investigation 4: measuring the daily lag","Chapter 04","4 The 50-minute lag",{"id":299,"type":43,"markdown":300},"ch4-lag","Claim to be tested: **the Moon rises about fifty minutes later each day.**\n\nThis one you can measure yourself, to a precision that would have impressed an astronomer three hundred years ago.\n\n**Method.** Choose a fixed landmark on your eastern horizon: a rooftop edge, the top of a water tank, a particular tree. Stand in exactly the same spot each time — mark it with chalk. Then, on several evenings in a row, note the **exact clock time** at which the Moon's upper edge clears that landmark.\n\nThe best fortnight for this is from full moon onwards, when moonrise happens at a sociable hour and slides later each night.\n\n**Result.** Subtract each night's time from the next. You should get a set of numbers clustering around **50 minutes**.",{"id":302,"type":47,"variant":303,"title":304,"markdown":305},"ch4-why-landmark","nuance","Why a fixed landmark matters more than it seems","Judging 'the Moon has risen' by eye, with no landmark, is surprisingly unreliable, because the Moon looks huge and obvious near the horizon (the Moon illusion, met again in Deepen) and it is easy to notice it a few minutes late or early depending on cloud, haze, or simply where you happened to be looking. A fixed chalk mark and a fixed landmark turn a vague impression into a repeatable, comparable measurement — the same discipline a real observatory uses, just with humbler tools.",{"id":307,"type":308,"items":309},"ch4-lag-formulas","formulas",[310,313,316,319],{"expression":311,"caption":312},"13.18° − 0.9856° = 12.19°","How far the Moon gains on the Sun each day: its own motion minus the Sun's apparent motion.",{"expression":314,"caption":315},"12.19° ÷ 15°\u002Fh = 0.813 h","Turn that gain into time: the sky rotates 15° every hour.",{"expression":317,"caption":318},"0.813 h x 60 = 48.8 min","The average daily delay in moonrise: about 49 minutes.",{"expression":320,"caption":321},"24 h ÷ 29.53 d = 48.8 min","The same answer a different way: one whole day of delay, spread over one lunar month.",{"id":323,"type":225,"title":324,"problem":325,"steps":326,"help":334},"we-lag","Predicting tomorrow's moonrise from tonight's","Tonight the Moon rose at 19:24. Predict tomorrow's moonrise. Then predict moonrise one week from tonight.",[327,328,329,330,331,332,333],"The average daily delay is about 49 minutes.","Tomorrow: 19:24 + 49 minutes = **20:13**.","One week is 7 days, so the total delay is 7 x 48.8 = 341 minutes.","341 minutes is 5 hours and 41 minutes.","19:24 + 5 h 41 min = **01:05**, that is, just after midnight on the following night.","Sanity check: seven days is about a quarter of a lunar month, so the Moon should slip about a quarter of 24 hours, which is 6 hours. Our 5 h 41 min is close to that. ✓","Real answer: expect to be off by up to an hour, because the daily delay is not constant — see the careful note below.",{"simplerExplanation":335,"anotherExample":336},"Add about 50 minutes for each day that passes. Seven days is roughly 6 hours later.","If a full moon rises at 18:10 tonight, the waning gibbous three nights later rises at roughly 18:10 + 147 minutes = 20:37.",{"id":338,"type":339,"itemId":340,"prompt":341,"check":342,"hints":347,"feedback":350},"practice-lag","practice","phases-of-the-moon.investigate-lag-4days","The Moon rises at 18:30 tonight. Using an average delay of 49 minutes per day, how many minutes later will it rise **four** days from now? Give your answer in minutes.",{"kind":343,"answer":344,"tolerance":345,"unit":346},"number",195,4,"minutes",[348,349],"Multiply the daily delay by the number of days: 49 x 4.","You are asked for the delay itself, not the clock time.",{"correct":351,"incorrect":352},"Right: 4 x 48.8 = about **195 minutes**, which is 3 hours and 15 minutes. Moonrise would be around 21:45.","The delay builds up day by day. Four days at about 49 minutes each gives roughly 195 minutes in total.",{"id":354,"type":47,"variant":303,"title":355,"markdown":356},"ch4-lag-varies","Why your measurements will scatter (and that is correct)","Your numbers will not all be 49. You may get 38 one night and 64 another. Nothing has gone wrong. The daily delay genuinely varies, for two real reasons:\n\n**The Moon's orbit is an ellipse.** When the Moon is nearer Earth it moves faster along its path and gains more elongation per day; when further, less.\n\n**The angle of the Moon's path to your horizon changes through the year.** This is the bigger effect. In autumn, the Moon's path lies at a shallow angle to the eastern horizon for northern observers, and successive moonrises can be only 25 to 35 minutes apart. That is the origin of the **Harvest Moon**: several evenings running with a bright Moon rising close to sunset, which once gave farmers extra light to finish the harvest.\n\n**49 minutes is the average over a whole month, not a promise about tonight.** Average your own measurements over a fortnight and you should land close to it.",{"id":358,"type":78,"title":359,"eyebrow":360,"navLabel":361},"ch5","Investigation 5: is it really the same face?","Chapter 05","5 The same face?",{"id":363,"type":47,"variant":290,"title":364,"markdown":365},"ch5-what-youll-need","What you'll need for this one","A pencil, paper, and access to the Moon on at least three different nights within about two weeks. Binoculars help but are not required: the largest dark patches (the maria) are visible to the naked eye from a dark-enough spot.",{"id":367,"type":43,"markdown":368},"ch5-same-face","Claim to be tested: **the Moon always shows us the same face.**\n\nThis is easy to check and surprisingly satisfying, because you are testing a statement about something 384,400 km away using nothing but a pencil.\n\n**Method.** On three or four nights spread across a fortnight — say a waxing crescent, first quarter, gibbous and full — draw the dark patches you can see on the bright part. Do not try to be artistic. Just get the *positions* right relative to the edge of the disc.\n\n**What to expect.** The lit region grows from night to night, revealing more patches. But the patches you drew before **do not move, do not change their spacing, and do not rotate away**. The big dark oval you drew near the top edge on night four is still near the top edge on night fourteen.\n\nCompare with what you would see if the Moon did not keep one face towards us: fresh terrain every night, with old features sliding off the edge.",{"id":370,"type":120,"prompt":371,"options":372,"explanation":381},"predict-crater-drift","You draw a distinctive dark patch near the centre of the Moon at first quarter. Two weeks later, at full moon, where will it be?",[373,375,377,379],{"id":124,"label":374},"Gone — it will have rotated round to the far side",{"id":127,"label":376},"Still near the centre, in essentially the same place",{"id":130,"label":378},"Moved to the edge of the disc",{"id":133,"label":380},"Upside down","**b.** It will be in essentially the same place, because the Moon spins exactly once per orbit.\n\nTwo details make this more interesting than a flat \"no change\":\n\n**The patch will look different**, even though it has not moved. At first quarter it was near the terminator with long shadows; at full moon the Sun is overhead there and it looks flat and washed out. Same feature, different lighting.\n\n**It will have wobbled slightly.** The Moon rocks gently back and forth — an effect called **libration** — by up to about 8° in one direction and 7° in the other. Over a month that wobble lets us peek a little way round each edge in turn. If you draw very carefully, over several months, you can actually detect it. That is an Extend-level observation, and it is how we get to see 59% of the Moon rather than 50%.",{"id":383,"type":208,"component":384,"componentVersion":5,"config":385,"objective":413,"textAlternative":414},"lab-match-evidence","match-pairs",{"prompt":386,"mode":387,"pairs":388},"Match each observation you can make from the ground to the claim it tests.","connect",[389,392,395,398,401,404,407,410],{"a":390,"b":391},"A half-lit Moon at 90° from the Sun","Phases are not Earth's shadow",{"a":393,"b":394},"Moonrise 50 minutes later each night","The Moon moves eastward around Earth",{"a":396,"b":397},"Dark patches never move or rotate away","The Moon spins once per orbit",{"a":399,"b":400},"Grey glow on the unlit crescent","Earth reflects sunlight onto the Moon",{"a":402,"b":403},"Craters vanish at full moon","Surface detail needs low, shadow-casting light",{"a":405,"b":406},"Full moon rises exactly at sunset","The Moon is opposite the Sun when it is full",{"a":408,"b":409},"Same phase reported from Delhi and London","The phase depends on geometry, not on where you stand",{"a":411,"b":412},"Eclipses happen only a few times a year","The Moon's orbit is tilted to Earth's","Connect each naked-eye observation to the specific claim about the Moon that it puts to the test.","Eight observations on the left are joined to the eight claims they test on the right.\n\n\"A half-lit Moon at 90° from the Sun\" tests \"phases are not Earth's shadow\", because a shadow could only fall at 180°. \"Moonrise 50 minutes later each night\" tests \"the Moon moves eastward around Earth\". \"Dark patches never move or rotate away\" tests \"the Moon spins once per orbit\". \"Grey glow on the unlit crescent\" tests \"Earth reflects sunlight onto the Moon\". \"Craters vanish at full moon\" tests \"surface detail needs low, shadow-casting light\". \"Full moon rises exactly at sunset\" tests \"the Moon is opposite the Sun when it is full\". \"Same phase reported from Delhi and London\" tests \"the phase depends on geometry, not on where you stand\". \"Eclipses happen only a few times a year\" tests \"the Moon's orbit is tilted to Earth's\".\n\nEvery one of these is checkable by an ordinary person with no equipment beyond a notebook — which is the real point of the exercise.",{"id":416,"type":78,"title":417,"eyebrow":418,"navLabel":419},"ch6","Investigation 6: hunt for earthshine","Chapter 06","6 Earthshine hunt",{"id":421,"type":43,"markdown":422},"ch6-earthshine-method","Claim to be tested: **the unlit part of a crescent Moon is faintly lit by light bounced off Earth.**\n\n**When:** two to five days after new moon, looking west about an hour after sunset. Or two to five days before new moon, looking east about an hour before sunrise.\n\n**Method:**\n1. Wait until the twilight has properly faded. Too early and the sky itself is brighter than the earthshine.\n2. Get the bright crescent out of your direct line of sight — hide it behind a finger, a lamp-post or the edge of a roof. Glare is what defeats most people.\n3. Give your eyes two or three minutes to adapt. Do not look at a phone screen during this.\n4. Look at where the rest of the disc should be.\n\n**Success looks like:** a complete dim circle, blue-grey, with the brilliant crescent on one edge. Once you have seen it you will never miss it again.",{"id":424,"type":120,"prompt":425,"options":426,"explanation":435},"predict-earthshine-when","On which night would earthshine be **hardest** to see?",[427,429,431,433],{"id":124,"label":428},"Two days after new moon",{"id":127,"label":430},"Four days after new moon",{"id":130,"label":432},"Two days before full moon",{"id":133,"label":434},"Three days before new moon","**c, two days before full moon** — and for two reasons that stack up.\n\n**Reason one: there is almost no earthshine to see.** Earth and Moon show each other opposite phases. When our Moon is nearly full, the Moon's sky holds a nearly *new* Earth: a dark disc with a thin bright rim, sending almost nothing our way.\n\n**Reason two: there is almost no unlit Moon left.** At two days before full, over 95% of the disc is in dazzling direct sunlight. The tiny remaining sliver of night side is swamped by glare.\n\nOptions a, b and d are all good earthshine nights. b is the classic: bright enough Earthlight, a thin enough crescent, and the Moon high enough above the murk near the horizon.",{"id":437,"type":47,"variant":438,"title":439,"markdown":440},"ch6-earthshine-science","example","Earthshine is still a research tool","This is not just a pretty sight. Measuring how bright earthshine is tells you how much sunlight Earth is currently reflecting back into space — Earth's **albedo** — averaged over a whole hemisphere at once.\n\nObservatories have tracked earthshine for decades for exactly this reason. Clouds and ice reflect strongly; dark oceans and forests reflect weakly. A change in Earth's albedo over years is a change in how much solar energy our planet keeps.\n\nSo an observation that Leonardo da Vinci explained around 1510, which you can make from a terrace with your own eyes, is also a genuine climate measurement. Good science is often like that: the same phenomenon at different levels of care.",{"id":442,"type":155,"caption":443,"columns":444,"rows":448},"ch6-earthshine-log","A sample earthshine observing log",[445,446,447,250],"Attempt","Days from new moon","Result",[449,454,458,462],[450,451,452,453],"1","2","Not seen","Too much twilight glow still in the sky; tried too early after sunset",[451,455,456,457],"3","Faint success","Blocked the crescent behind a water tank; waited five minutes for eyes to adjust",[455,459,460,461],"4","Clear success","Best result: dim grey disc clearly outlined, crescent bright on the edge",[459,463,464,465],"5","Fainter success","Crescent now thicker; earthshine noticeably harder to see against the brighter glare",{"id":467,"type":78,"title":468,"eyebrow":469,"navLabel":470},"ch7","Investigation 7: does everyone see the same Moon?","Chapter 07","7 Same Moon?",{"id":472,"type":43,"markdown":473},"ch7-same-moon","Claim to be tested: **everyone on Earth sees the same phase at the same time; only the orientation and the clock differ.**\n\n**Method.** You need one contact somewhere far away — a cousin in another country, a pen-friend, a school exchange partner. If you have none, use two cities' published moonrise times and phase images.\n\nAgree an exact moment — say 18:00 Indian Standard Time on a given date — and both describe the Moon as it appears at that instant, if it is visible.\n\n**Record:** the fraction lit, which edge is bright, the height above the horizon, and the local time.",{"id":475,"type":155,"caption":476,"columns":477,"rows":482},"ch7-three-cities","What three observers see at the same instant during a waxing crescent",[478,479,480,481],"Observer","Local time","Fraction lit","Appearance",[483,488,491],[484,485,486,487],"Delhi, India (28°N)","18:00","15%","Bright edge on the right, tipped like a tilted D, low in the west",[489,485,486,490],"Kochi, India (10°N)","Same fraction lit, but the horns point almost straight up: a bowl",[492,493,486,494],"Melbourne, Australia (38°S)","23:30","Bright edge on the left; in fact already set, so not visible at that moment",{"id":496,"type":120,"prompt":497,"options":498,"explanation":507},"predict-same-phase","Your cousin in Melbourne photographs the Moon on the same date as you do in Delhi. Her crescent is bright on the left; yours is bright on the right. What should you conclude?",[499,501,503,505],{"id":124,"label":500},"One of you has mixed up the date",{"id":127,"label":502},"The southern hemisphere is a fortnight behind",{"id":130,"label":504},"It is the same phase, seen from a viewpoint that is effectively upside down",{"id":133,"label":506},"The Moon changed phase during the day","**c.** You and she are standing on opposite sides of a ball, so \"up\" for her is roughly \"down\" for you. The same crescent is simply rotated by about 180°.\n\nYou can check this without leaving the room: print her photo, turn it upside down, and hold it next to yours. They will match.\n\nOption **b** is the trap, and it is a nice one to think about: it would require the Sun-Earth-Moon geometry to be different for different countries, which is impossible — there is only one Moon and one Sun, and the angle between them does not care where you are standing on Earth.\n\nThe one genuine difference is **the calendar date**. The instant of full moon might fall at 23:40 on the 5th in Delhi and at 02:10 on the 6th in Tokyo. Same instant; different date on the wall.",{"id":509,"type":47,"variant":203,"title":510,"markdown":511},"ch7-time-zones","Compare instants, not dates","If you and a distant friend compare notes, agree on an exact instant in a single time zone, otherwise you will confuse a genuine result with a bookkeeping mistake.\n\n\"Monday evening\" is not a shared moment. Delhi is 5 hours 30 minutes ahead of London and 4 hours 30 minutes behind Sydney. The Moon will have moved several degrees between your two observations, and near a quarter phase that is enough to change the shape visibly.",{"id":513,"type":47,"variant":514,"title":515,"markdown":516},"ch7-misconception-harvest","misconception","“The Harvest Moon is physically bigger and more orange”","It is not physically bigger, and its colour comes from the same low-altitude reddening that affects any rising Moon or Sun, not from anything unique to autumn. What is genuinely special about the Harvest Moon is purely a **timing** effect: around the September equinox in the northern hemisphere, the Moon's path meets the evening horizon at an unusually shallow angle, so its normal ~50-minute daily rise-delay shrinks to as little as 25-30 minutes for several nights running. That gives several evenings in a row with a bright, low, moon rising soon after sunset — a real and useful investigation-worthy fact, but a geometry-and-timing story, not a change in the Moon itself.",{"id":518,"type":78,"title":519,"eyebrow":520,"navLabel":521},"ch8","Investigation 8: predict a festival moonrise","Chapter 08","8 Karva Chauth",{"id":523,"type":43,"markdown":524},"ch8-kc","Here is a prediction with a real audience. On **Karva Chauth**, women who have fasted all day break the fast when they see the Moon — so the whole household wants to know when the Moon will rise, and nobody wants to be wrong.\n\nKarva Chauth falls on **chaturthi of krishna paksha**: the fourth tithi after Purnima. In elongation terms the Moon has swung past full and is now between 216° and 228°, so we can take about **222°** for the middle of that tithi.\n\nEverything else follows from the rules you already have.",{"id":526,"type":225,"title":527,"problem":528,"steps":529,"help":537},"we-karva-chauth","Predicting the Karva Chauth moonrise","Karva Chauth is the fourth tithi of krishna paksha, at an elongation of about 222°. Work out how much of the Moon will be lit and roughly what time it will rise, assuming a 6 pm sunset.",[530,531,532,533,534,535,536],"**Elongation.** Krishna paksha chaturthi runs from 216° to 228° of elongation. Take the middle: **222°**.","**Day of the month.** day = 29.53 x 222 ÷ 360 = **18.21 days** after new moon — that is 3.45 days after full moon.","**Fraction lit.** (1 − cos 222°) ÷ 2 = **0.872**, about **87%**. A fat waning gibbous, bright enough to cast a shadow.","**Hours behind the Sun.** 222 ÷ 15 = **14.8 hours**.","**Moonrise.** Sunrise at 06:00 plus 14.8 hours gives **20:48** — a little before 9 pm.","**Cross-check the other way.** Full moon rises at sunset, 18:00. Karva Chauth is 3.45 days later, and each day costs about 49 minutes, so the delay is 3.45 x 48.8 = 168 minutes, that is 2 h 48 min. 18:00 + 2 h 48 min = **20:48**. The two methods agree. ✓","**Reality check before you announce it.** Real published moonrise for a city can differ from this by up to an hour and a half, because of latitude, season and the Moon's elliptical orbit. Use the calculation to know *roughly* when to start looking, and a published local time for the actual announcement.",{"simplerExplanation":538,"hints":539},"Karva Chauth's Moon is about three and a half days past full, so it rises about three hours after sunset, and it is a fat gibbous about 87% lit.",[540,541],"Full moon rises at sunset. Every day after that, moonrise slips about 50 minutes later.","Three and a half days x 50 minutes is roughly 175 minutes, just under three hours.",{"id":543,"type":339,"itemId":544,"prompt":545,"check":546,"hints":549,"feedback":552},"practice-kc-fraction","phases-of-the-moon.investigate-kc-lit","On Karva Chauth the Moon is at about 222° elongation. To the nearest whole per cent, how much of its disc is lit? Use lit fraction = (1 − cos e) ÷ 2.",{"kind":343,"answer":547,"tolerance":5,"unit":548},87,"%",[550,551],"cos 222° is about -0.743 — note the minus sign.","Subtracting a negative number makes the top of the fraction bigger than 1.",{"correct":553,"incorrect":554},"Correct: (1 − (-0.743)) ÷ 2 = 0.872, so about **87%**. A fat waning gibbous, unmistakable once it clears the rooftops.","The angle is past 180°, so the cosine is negative: about -0.743. Then (1 − (-0.743)) ÷ 2 = 0.872, which is 87%.",{"id":556,"type":47,"variant":48,"title":557,"markdown":558},"ch8-kc-observe","Turn it into a household experiment","A week before Karva Chauth, write your predicted moonrise time on a piece of paper and stick it on the fridge. Next to it, write the time from a published almanac or a panchang.\n\nOn the night, have someone note the exact minute the Moon's edge clears the rooftop.\n\nThree numbers to compare: yours, the almanac's, and reality. The almanac should win — it accounts for your latitude, the Moon's elliptical orbit and refraction near the horizon. But if your simple calculation lands within an hour, you have done real celestial mechanics with a pencil.",{"id":560,"type":561,"prompt":562},"reflect-kc-other-festivals","reflection","The same method (find the elongation, find the day of the month, work out the rise time) can predict roughly when the crescent Moon needed for Eid will first become visible after new moon, or when Sharad Purnima's especially bright full moon will rise. Pick a lunar festival from your own community's calendar and describe, step by step, how you would predict it using nothing but the rules in this layer.",{"id":564,"type":78,"title":565,"eyebrow":566,"navLabel":567},"ch9","Weighing the evidence","Chapter 09","9 Weighing evidence",{"id":569,"type":43,"markdown":570},"ch9-evidence","Science is not only collecting observations. It is asking which explanation each observation supports — and, harder, which it rules **out**.\n\nPut the shadow hypothesis on trial. The claim: *\"The phases of the Moon are caused by Earth's shadow falling on it.\"*\n\nA good test is one where the two explanations predict **different** things. Sort the evidence below and see what survives.",{"id":572,"type":208,"component":573,"componentVersion":5,"config":574,"objective":635,"textAlternative":636},"lab-sort-evidence","sort-game",{"prompt":575,"bins":576,"seconds":585,"items":586},"Does each observation support the shadow explanation of phases, or rule it out?",[577,580,582],{"id":578,"label":579},"rules-out","Rules out the shadow idea",{"id":54,"label":581},"Neither: both explanations fit",{"id":583,"label":584},"eclipse","Evidence about eclipses, not phases",0,[587,591,595,599,603,607,611,615,619,623,627,631],{"id":588,"label":589,"bin":578,"why":590},"e1","The Moon is half lit when it is 90° away from the Sun in the sky","Earth's shadow points straight away from the Sun, so at 90° it is nowhere near the Moon. Yet we see a clean half-lit disc.",{"id":592,"label":593,"bin":578,"why":594},"e2","The shape changes smoothly every single night","A shadow crossing would be an occasional event lasting hours, not a smooth fortnight-long change.",{"id":596,"label":597,"bin":578,"why":598},"e3","The curved edge of a gibbous Moon bulges the opposite way to a crescent's","One round shadow cannot produce both curvatures. A sphere lit from the side can.",{"id":600,"label":601,"bin":54,"why":602},"e4","The dark part of the Moon is completely black","Both explanations predict a dark region, so this observation does not separate them. Earthshine is a better test.",{"id":604,"label":605,"bin":54,"why":606},"e5","The Moon is round","True but useless here: both explanations assume a round Moon.",{"id":608,"label":609,"bin":583,"why":610},"e6","Once or twice a year the full moon turns coppery red for a couple of hours","This is a genuine lunar eclipse: Earth's shadow really does fall on the Moon, and sunlight bent through our atmosphere reddens it.",{"id":612,"label":613,"bin":583,"why":614},"e7","That reddening only ever happens at full moon","Confirms that Earth's shadow can only reach the Moon at full moon — the fact that destroys the shadow explanation of the other phases.",{"id":616,"label":617,"bin":578,"why":618},"e8","An orange held near a lamp shows every phase with no shadow involved","A working model producing all eight phases with nothing casting a shadow on the ball.",{"id":620,"label":621,"bin":578,"why":622},"e9","A crescent Moon is visible in the evening but never at dawn","A shadow explanation says nothing about time of day. The viewing-angle explanation predicts it exactly.",{"id":624,"label":625,"bin":583,"why":626},"e10","Eclipses happen only a few times a year, not monthly","Because the Moon's orbit is tilted 5.1°, so it usually misses the shadow entirely — while phases carry on regardless.",{"id":628,"label":629,"bin":578,"why":630},"e11","Astronauts photographed a crescent Earth from lunar orbit","Earth shows phases too, for the same reason, and nothing was casting a shadow on Earth in those photographs.",{"id":632,"label":633,"bin":578,"why":634},"e12","The Moon is visible in the daytime for about half of each month","Only makes sense if the Moon's position relative to the Sun keeps changing, which is also what produces the phases.","Sort a dozen observations by whether they rule out the shadow explanation of phases, are neutral, or belong to eclipses.","Twelve observations are sorted into three bins.\n\n**Rules out the shadow idea:** a half-lit Moon 90° from the Sun; the shape changing smoothly every night; gibbous and crescent edges curving opposite ways; the orange-and-lamp model producing all eight phases; a crescent visible only in the evening; the Moon being up in daylight for half the month; astronaut photographs of a crescent Earth.\n\n**Neither — both explanations fit:** the dark part being black; the Moon being round. These are true but useless for choosing between the two ideas, and spotting that is a real scientific skill.\n\n**Evidence about eclipses, not phases:** the occasional coppery-red full moon; the fact that it only happens at full moon; and eclipses occurring only a few times a year because of the 5.1° tilt.\n\nThe pattern to take away: the strongest evidence is always the kind where the two explanations predict *different* things.",{"id":638,"type":47,"variant":639,"title":640,"markdown":641},"ch9-neutral-evidence","aha","The most useful bin is the middle one","Most people, asked to defend a belief, gather evidence that fits it. The trouble is that evidence which fits *both* explanations proves nothing at all, however much of it you pile up.\n\n\"The dark part is black\" fits the shadow idea. It also fits the viewing-angle idea. It therefore cannot help you choose, and a hundred more observations like it would not help either.\n\nThe observations that did the work were the ones where the two ideas **disagree**: at 90° elongation, one predicts a fully lit Moon with no shadow anywhere near it, and the other predicts exactly half. The sky says half.\n\nLearning to look for that kind of evidence, rather than the comfortable kind, is most of what being a scientist involves.",{"id":643,"type":644,"title":645,"terms":646},"ch9-glossary-inv","glossary","Field-notebook vocabulary",[647,651,655,659,663],{"term":648,"meaning":649,"example":650},"Hindsight bias","The tendency to remember a past prediction as more accurate than it really was, once the outcome is known.","Writing predictions down before observing is the standard defence against it.",{"term":652,"meaning":653,"example":654},"Naked-eye astronomy","Observing the sky using only the unaided eye, no telescope or binoculars required.","Every investigation in this layer can be done naked-eye.",{"term":656,"meaning":657,"example":658},"Landmark method","Timing an event (such as moonrise) against a fixed reference point on the horizon, such as a rooftop or tree, to get precise, repeatable measurements.","Used to measure the daily lag in Investigation 4.",{"term":660,"meaning":661,"example":662},"Control test","An observation designed so that two rival explanations predict different, checkable outcomes.","A half-lit Moon at 90 degrees elongation is a control test that rules out the shadow explanation.",{"term":664,"meaning":665,"example":666},"Albedo","The fraction of incoming sunlight a surface reflects rather than absorbs.","Earthshine measurements are really a way of measuring Earth's albedo from the Moon's surface.",{"id":668,"type":47,"variant":48,"title":669,"markdown":670},"ch9-field-note","Turn any claim in this topic into your own investigation","The seven investigations here are a starting list, not a complete one. Almost every fact in the earlier layers can be turned into a naked-eye check: does the Moon really look flat and washed-out at full moon compared with a quarter phase? Does a crescent Moon really always appear near the Sun in the sky, never opposite it? Pick a claim you have not yet tested, design one observation that would show it false if it were false, and run it. That instinct — always ask what evidence *would* change your mind — is the whole of Investigation 9's method, applied to a claim of your own choosing.",{"id":672,"type":561,"prompt":673},"reflect-investigate","Look back at your own diary and predictions. Find one night where you were clearly wrong. Write two paragraphs: what you predicted and why it seemed reasonable, and what you now think went wrong. Then say what you would record differently next month to catch that kind of error earlier.",{"id":675,"type":676,"conceptId":677,"relation":678,"explanation":679},"connect-eclipses-inv","connection","eclipses","helps_understand","Several of the observations here are really about eclipses. Sorting phase evidence from eclipse evidence is the first step into that topic.",{"id":681,"type":676,"conceptId":682,"relation":678,"explanation":683},"connect-light-inv","light","Earthshine, the terminator and the flat full moon are all consequences of how light travels and reflects.",{"id":685,"type":686,"title":687,"questions":688},"quiz-investigate","quiz","Check yourself",[689,702,714,727,740,753,766,779,792,805],{"itemId":690,"prompt":691,"options":692,"correct":127,"why":701},"phases-of-the-moon.investigate-q-prediction","Why must a prediction be written down before the observation?",[693,695,697,699],{"id":124,"label":694},"It is a school rule",{"id":127,"label":696},"Memory quietly rewrites itself to match what happened",{"id":130,"label":698},"It makes the Moon easier to see",{"id":133,"label":700},"It is not necessary","Hindsight bias is real and universal. A prediction remembered after the fact almost always turns out to have been 'basically right'. Paper does not do that.",{"itemId":703,"prompt":704,"options":705,"correct":127,"why":713},"phases-of-the-moon.investigate-q-head-shadow","In the ball-and-lamp model, your head's shadow falling on the ball represents:",[706,708,710,712],{"id":124,"label":707},"A new moon",{"id":127,"label":709},"A lunar eclipse",{"id":130,"label":711},"A crescent phase",{"id":133,"label":131},"And crucially it can only happen at the full-moon position, which is exactly why shadows cannot explain phases at every other angle.",{"itemId":715,"prompt":716,"options":717,"correct":127,"why":726},"phases-of-the-moon.investigate-q-gaps","Your 8 pm diary has a block of 'not visible' entries. Where in the month are they?",[718,720,722,724],{"id":124,"label":719},"Scattered at random",{"id":127,"label":721},"Clustered in the last week of the lunar month",{"id":130,"label":723},"All at full moon",{"id":133,"label":725},"Only on cloudy nights","In the last week, moonrise has slipped past 8 pm, so there is simply no Moon above the horizon at your observing time. The gap is data, not failure.",{"itemId":728,"prompt":729,"options":730,"correct":127,"why":739},"phases-of-the-moon.investigate-q-lag","You measure the gap between successive moonrises on five nights and get 41, 47, 52, 58 and 49 minutes. What should you conclude?",[731,733,735,737],{"id":124,"label":732},"Your measurements are unreliable",{"id":127,"label":734},"The delay genuinely varies around an average of about 50 minutes",{"id":130,"label":736},"The Moon is speeding up",{"id":133,"label":738},"You picked the wrong landmark","The average of those five is 49 minutes, right on the expected 49. The scatter is real physics: an elliptical orbit and a changing angle to the horizon.",{"itemId":741,"prompt":742,"options":743,"correct":127,"why":752},"phases-of-the-moon.investigate-q-earthshine-best","When is earthshine easiest to see?",[744,746,748,750],{"id":124,"label":745},"At full moon",{"id":127,"label":747},"A few days either side of new moon",{"id":130,"label":749},"At first quarter",{"id":133,"label":751},"During a lunar eclipse","Two reasons stack: the Moon sees a nearly full Earth then, so Earthlight is strongest, and there is very little glare from the thin sunlit crescent.",{"itemId":754,"prompt":755,"options":756,"correct":127,"why":765},"phases-of-the-moon.investigate-q-patches","You sketch the Moon's dark patches on four nights across a fortnight. What do you find?",[757,759,761,763],{"id":124,"label":758},"They rotate steadily out of view",{"id":127,"label":760},"They stay in the same places, but the lighting on them changes",{"id":130,"label":762},"They change shape",{"id":133,"label":764},"Different patches every night","The Moon spins once per orbit, so the same face stays towards us. What changes is the Sun angle: near the terminator the patches show relief, at full moon they look flat.",{"itemId":767,"prompt":768,"options":769,"correct":130,"why":778},"phases-of-the-moon.investigate-q-melbourne","Your cousin in Melbourne sees a crescent bright on the left on the same date you see one bright on the right. This means:",[770,772,774,776],{"id":124,"label":771},"The southern hemisphere is two weeks behind",{"id":127,"label":773},"One of you is mistaken",{"id":130,"label":775},"It is the same phase seen from an effectively upside-down viewpoint",{"id":133,"label":777},"There are two Moons","Print her photo, rotate it 180°, and it matches yours. The Sun-Earth-Moon angle is the same for everybody on the planet at a given instant.",{"itemId":780,"prompt":781,"options":782,"correct":127,"why":791},"phases-of-the-moon.investigate-q-neutral","Which observation does NOT help decide between 'phases are shadows' and 'phases are a viewing angle'?",[783,785,787,789],{"id":124,"label":784},"The Moon is half lit at 90° elongation",{"id":127,"label":786},"The dark part of the Moon looks black",{"id":130,"label":788},"A gibbous edge curves the opposite way to a crescent edge",{"id":133,"label":790},"A crescent is only ever seen near sunset or sunrise","Both explanations predict a dark region, so it cannot separate them. Useful evidence is evidence where the two ideas disagree.",{"itemId":793,"prompt":794,"options":795,"correct":127,"why":804},"phases-of-the-moon.investigate-q-kc","About what time does the Karva Chauth Moon (elongation roughly 222°) rise, for a 6 pm sunset?",[796,798,800,802],{"id":124,"label":797},"About 6 pm, with the Sun setting",{"id":127,"label":799},"About 9 pm",{"id":130,"label":801},"About midnight",{"id":133,"label":803},"About 3 am","222 ÷ 15 = 14.8 hours behind the Sun, so moonrise is about 06:00 + 14.8 h = 20:48. Cross-check: it is 3.4 days past full, and full moon rises at sunset, so add about 168 minutes to 18:00.",{"itemId":806,"prompt":807,"options":808,"correct":130,"why":817},"phases-of-the-moon.investigate-q-modellimit","What can the orange-and-lamp model NOT show you?",[809,811,813,815],{"id":124,"label":810},"Why phases happen",{"id":127,"label":812},"Why a crescent is bright on one side",{"id":130,"label":814},"Why eclipses are rare, because the model has no tilted orbit",{"id":133,"label":816},"What a gibbous Moon looks like","Your arm sweeps a flat circle. The real Moon's orbit is tilted 5.1° to Earth's, which is why it usually misses the shadow — the model cannot show that.",{"id":819,"type":820,"title":821,"points":822},"cheat-sheet-investigate","summary","Investigator's cheat sheet",[823,824,825,826,827,828,829,830,831,832,833,834,835],"**Write predictions down first**, with the date. A prediction recalled afterwards is not evidence.","**Record the failures.** 'Looked, saw nothing, clear sky' is a measurement, usually of moonrise time.","**The orange-and-lamp model** reproduces all eight phases with nothing casting a shadow — a complete refutation of the shadow idea, done on a kitchen table.","**Your head's shadow in that model is a lunar eclipse**, and it only works at the full-moon position.","**A month-long moon diary** is the central investigation: draw a full circle first, then shade the lit part.","**The gaps in an 8 pm diary cluster in the last week**, because moonrise has slipped past your observing time.","**Measure the daily lag** against a fixed landmark. Expect an average near 49 minutes, with real scatter from 30 to 70.","**The Harvest Moon** is the autumn case where successive moonrises are unusually close together.","**Dark patches never move**, proving synchronous rotation; but the lighting on them changes completely.","**Earthshine is best two to five days either side of new moon.** Hide the bright crescent and let your eyes adapt.","**Everyone sees the same phase**; only orientation, local time and calendar date differ.","**Karva Chauth's Moon** is about 87% lit at roughly 222° elongation, rising near 20:48 for a 6 pm sunset.","**The best evidence is where two explanations disagree.** Evidence that fits both proves nothing, however much you gather.",{"id":837,"type":838,"sourceIds":839},"sources-investigate","sources",[840,841,842,843,844,845],"phases-of-the-moon-nasa-moon-phases","phases-of-the-moon-wikipedia-lunar-phase","phases-of-the-moon-timeanddate-moon","phases-of-the-moon-nasa-svs-libration","phases-of-the-moon-britannica-moon","phases-of-the-moon-nasa-moon-facts",[840,841,842,843,844,845],"needs_review",{"generatedBy":849,"notes":850},"claude-code","Draft generated locally; pending owner review. Daily-lag, Karva Chauth and lit-fraction figures computed in numbers.py.","e9551f8f840eee7172be2089c14af28ee3a61779fca11b3cf1205f933c5d5472",{"component:moon-phase@1":853,"logic:practice":854,"component:match-pairs@1":855,"component:sort-game@1":856,"source:phases-of-the-moon-britannica-moon":857,"source:phases-of-the-moon-nasa-moon-facts":858,"source:phases-of-the-moon-nasa-moon-phases":859,"source:phases-of-the-moon-nasa-svs-libration":860,"source:phases-of-the-moon-timeanddate-moon":861,"source:phases-of-the-moon-wikipedia-lunar-phase":862},"39afeb0bba7518b8118317655457b27214a4a2a315d236762bf1d6a6a40e18f3","3d6b0fe1b15255975a32b0fcd94e8019bc959ad45cbf12e136e86149549c6878","2a8ee4ac87460b4e1175a4bb13c96b03d577db06dde95670eb7fcfe4ad787899","b164f45a2c8ca08f26c450768ff0231e113e9fe45381eddb34dc6d0548596c38","7851afcfed44e83c91e1cd033e5a51b31ed72915a7f12ac117b6c8076cf99a8a","42fce1fa13db44246876ac36bd3506964da8f7fa12ecfcb17813905e4161b696","a204a49fd1f0bcc99b9c71da877e71b83931eba1bf4e931d4af08d83cabb175c","e28faaf9d6da287ce1cdb3b7a69399f9bd6eb3488f41f10fb1ad71da7869c299","bae89711f5182b93b0801064bc61ce6f84a72c54016f6369f629d9fbf2be2d7f","7d0371e53bbaa01b158d9a8d193e8b907f2089d4cb08a73f37d1328b6add3ef9",{"state":864,"reviewer":865,"selfReview":866,"reviewedAt":867,"method":868},"approved","The library owner",true,"2026-09-20T10:18:37.581Z","owner_bulk","preview-7e1cbbcc4f",1789899597273]