[{"data":1,"prerenderedAt":1205},["ShallowReactive",2],{"questions:eclipses":3},{"bank":4,"contentHash":1192,"dependencyHashes":1193,"releaseId":1204},{"schemaVersion":5,"conceptId":6,"revision":5,"title":7,"intro":8,"sections":9,"questions":42,"sourceIds":1178,"reviewStatus":1188,"authoring":1189},1,"eclipses","Eclipses: question bank","Seventy-plus questions across eight sections: shadow geometry and eye safety, solar vs lunar eclipses, why they are rare, the 400× coincidence, totality, the Saros cycle and history, India and evidence, and eclipses beyond Earth. Every numeric answer was computed in Python.",[10,14,18,22,26,30,34,38],{"id":11,"title":12,"description":13},"shadows-safety","Shadows, umbra and penumbra, and eye safety","What a shadow is made of, the safe and unsafe ways to view the Sun, and the geometry behind pinhole projection.",{"id":15,"title":16,"description":17},"solar-vs-lunar","Solar vs lunar eclipses","Whose shadow falls on what, telling the two apart, and how long each kind of eclipse lasts.",{"id":19,"title":20,"description":21},"why-not-monthly","Why not every month","The Moon's 5.1° tilt, the two nodes, and why eclipses arrive in seasons rather than every month.",{"id":23,"title":24,"description":25},"coincidence-and-types","The 400× coincidence and eclipse types","Angular sizes, and what decides whether an eclipse is total, annular or partial.",{"id":27,"title":28,"description":29},"totality-and-viewing","Totality and how to watch it","The corona, Baily's beads, path width and speed, and the one safe moment to look with bare eyes.",{"id":31,"title":32,"description":33},"saros-and-history","The Saros cycle and eclipse history","Aryabhata and Brahmagupta, the Saros and exeligmos, and the 1868 and 1919 eclipses.",{"id":35,"title":36,"description":37},"india-culture-evidence","India, culture and evidence","Eclipse traditions treated respectfully, tested against evidence, and three real upcoming eclipses.",{"id":39,"title":40,"description":41},"beyond-earth","Eclipses and transits beyond Earth","Other planets' moons, Mercury and Venus transits, exoplanets, and artificial eclipses.",[43,69,88,107,123,137,156,175,188,197,217,236,255,270,290,309,327,346,358,370,388,407,426,445,464,473,492,504,515,533,552,571,590,600,609,619,637,655,674,693,711,722,740,750,768,786,806,825,845,865,885,895,905,923,942,960,978,997,1016,1034,1052,1072,1090,1110,1120,1130,1149,1159],{"id":44,"section":11,"level":45,"prompt":46,"check":47,"hints":63,"solution":65,"skills":66},"eclipses.q001","foundation","What is the **umbra** part of a shadow?",{"kind":48,"options":49,"correct":62},"choice",[50,53,56,59],{"id":51,"label":52},"a","The fully dark middle, where the light source is completely hidden",{"id":54,"label":55},"b","The grey fringe where part of the light source still shows",{"id":57,"label":58},"c","The brightest part of a shadow",{"id":60,"label":61},"d","A shadow that only forms at night",[51],[64],"Latin *umbra* means shadow.","The umbra is the fully dark core of a shadow: from inside it, the light source is completely blocked. The grey fringe around it, where part of the source still peeks past the edge, is the penumbra.",[67,68],"umbra","definitions",{"id":70,"section":11,"level":45,"prompt":71,"check":72,"hints":83,"solution":85,"skills":86},"eclipses.q002","Why can never look at the Sun without a certified filter, even during a deep partial eclipse?",{"kind":48,"options":73,"correct":82},[74,76,78,80],{"id":51,"label":75},"Because the Sun's surface is still blazingly bright even when mostly covered",{"id":54,"label":77},"Because eclipses attract more ultraviolet light than usual",{"id":57,"label":79},"Because the Moon reflects harmful rays",{"id":60,"label":81},"It is only a superstition, not a real risk",[51],[84],"Think about how much of the Sun's surface is still shining, not how dim the sky looks.","Even when 90% of the Sun's disc is covered, the remaining sliver of surface is exactly as bright per square metre as always — thousands of times brighter than is safe to view. **Never look at the Sun, even partially eclipsed, without a certified ISO 12312-2 filter.**",[87],"eye-safety",{"id":89,"section":11,"level":45,"prompt":90,"check":91,"hints":102,"solution":104,"skills":105},"eclipses.q003","Which of these is a genuinely safe way to watch a partial solar eclipse?",{"kind":48,"options":92,"correct":101},[93,95,97,99],{"id":51,"label":94},"Sunglasses, even several pairs stacked",{"id":54,"label":96},"A pinhole in a card, projecting an image onto paper",{"id":57,"label":98},"Looking through a phone camera",{"id":60,"label":100},"A quick glance, since it only takes a second",[54],[103],"Safe methods either carry a certification mark or work by projection, not by looking directly at the Sun.","A pinhole projection is completely safe because you never look at the Sun itself — you look at an image of it cast onto paper, with your back to the Sun. Sunglasses, phone cameras and quick glances are all unsafe.",[87,106],"pinhole",{"id":108,"section":11,"level":45,"prompt":109,"check":110,"hints":119,"solution":121,"skills":122},"eclipses.q004","True or false: sunglasses, even several pairs worn together, are safe for viewing a partial solar eclipse.",{"kind":48,"options":111,"correct":118},[112,115],{"id":113,"label":114},"t","True",{"id":116,"label":117},"f","False",[116],[120],"Certified eclipse filters pass about 0.003% of the light. How much do sunglasses pass?","**False.** Sunglasses pass about 10% of sunlight — over 3,000 times more than a certified ISO 12312-2 eclipse filter, which passes only about 0.003%. Stacking pairs does not fix this.",[87],{"id":124,"section":11,"level":125,"prompt":126,"check":127,"hints":131,"solution":134,"skills":135},"eclipses.q005","core","Certified eclipse glasses (ISO 12312-2) transmit about 0.0032% of visible light. Roughly how many times dimmer is that than looking at the Sun with bare eyes? Round to the nearest 1,000.",{"kind":128,"answer":129,"tolerance":130},"number",31000,1000,[132,133],"Divide 100 by the transmission percentage.","100 ÷ 0.0032 = ?","100 ÷ 0.0032 ≈ 31,250, which rounds to about **31,000**. This factor is why the glasses are certified specifically for solar viewing, unlike ordinary sunglasses.",[87,136],"calculation",{"id":138,"section":11,"level":125,"prompt":139,"check":140,"hints":151,"solution":153,"skills":154},"eclipses.q006","Why is looking at the Sun through binoculars dangerous even while wearing certified eclipse glasses over your eyes?",{"kind":48,"options":141,"correct":150},[142,144,146,148],{"id":51,"label":143},"The binoculars gather and concentrate the sunlight before it reaches the filter, which can melt or crack it",{"id":54,"label":145},"Binoculars make the glasses fall off",{"id":57,"label":147},"It is not dangerous, this is a safe combination",{"id":60,"label":149},"Binoculars block too much light, making nothing visible",[51],[152],"Any solar filter for an instrument must go on the far end (the front), not at your eye.","Binoculars and telescopes concentrate sunlight by gathering it over a wide lens and focusing it to a point — enough to melt an eyepiece filter in an instant, causing sudden, severe eye damage. A solar filter must be fitted over the **front**, large end of any optical instrument, never at the eyepiece.",[87,155],"optics",{"id":157,"section":11,"level":125,"prompt":158,"check":159,"hints":170,"solution":172,"skills":173},"eclipses.q007","Why is retinal damage from looking at the Sun especially dangerous, compared with, say, touching something hot?",{"kind":48,"options":160,"correct":169},[161,163,165,167],{"id":51,"label":162},"It heals faster than a burn",{"id":54,"label":164},"The retina has no pain nerves, so the damage is painless and often unnoticed until hours later",{"id":57,"label":166},"It only affects one eye",{"id":60,"label":168},"It causes an immediate, obvious headache",[54],[171],"Think about what warning signs your body gives you.","The retina cannot feel pain, so sunlight focused onto it by your eye's own lens can damage light-sensing cells with **no warning at all** — the person feels nothing while it happens, and often only notices a blurred or blank patch of vision hours later, sometimes the next day.",[87,174],"misconception",{"id":176,"section":11,"level":177,"prompt":178,"check":179,"hints":183,"solution":185,"skills":186},"eclipses.q008","stretch","A 4 cm ball is held 20 cm from a small point lamp, with a screen 60 cm from the lamp. How wide, in cm, is the shadow on the screen?",{"kind":128,"answer":180,"tolerance":181,"unit":182},12,0,"cm",[184],"Shadow width = ball width × screen distance ÷ ball distance.","Shadow width = 4 × 60 ÷ 20 = **12 cm**. This is the same similar-triangles rule that governs the length of the Moon's own shadow cone.",[187,136],"shadow-geometry",{"id":189,"section":11,"level":177,"prompt":190,"check":191,"hints":193,"solution":195,"skills":196},"eclipses.q009","In the same set-up, the ball is moved to 40 cm from the lamp (screen still at 60 cm). How wide is the shadow now, in cm?",{"kind":128,"answer":192,"tolerance":181,"unit":182},6,[194],"4 × 60 ÷ 40 = ?","Shadow width = 4 × 60 ÷ 40 = **6 cm** — half the earlier width, because the ball's distance from the lamp doubled while the screen stayed put.",[187,136],{"id":198,"section":11,"level":199,"prompt":200,"check":201,"hints":212,"solution":214,"skills":215},"eclipses.q010","challenge","A pinhole camera makes an image of the Sun about 9.3 mm across for every metre of distance between the pinhole and the screen. Why is this rate roughly constant regardless of how big or small the pinhole's hole itself is (as long as it stays small and clean)?",{"kind":48,"options":202,"correct":211},[203,205,207,209],{"id":51,"label":204},"The image size is set by the Sun's fixed angular width and the screen distance, not by the hole's size",{"id":54,"label":206},"Bigger holes always make bigger images, so the rate actually changes with hole size",{"id":57,"label":208},"It is a coincidence with no underlying reason",{"id":60,"label":210},"The rate only holds for holes exactly 1 mm wide",[51],[213],"A pinhole image is a projection: its size is set by an angle, not by the size of the hole.","A pinhole image's size is set by simple projection geometry: image size ≈ distance × tan(angular width). Since the Sun's angular width (about 0.53°) does not change, the image grows in direct proportion to the screen distance, at a fixed rate of about 9.3 mm per metre — completely independent of the pinhole's own diameter, as long as the hole stays small enough to act as a single point (a bigger hole just blurs the same-sized image, it does not enlarge it).",[106,216],"reasoning",{"id":218,"section":15,"level":45,"prompt":219,"check":220,"hints":231,"solution":233,"skills":234},"eclipses.q011","In a solar eclipse, whose shadow falls on what?",{"kind":48,"options":221,"correct":230},[222,224,226,228],{"id":51,"label":223},"The Moon's shadow falls on Earth",{"id":54,"label":225},"Earth's shadow falls on the Moon",{"id":57,"label":227},"The Sun's shadow falls on Earth",{"id":60,"label":229},"Earth's shadow falls on the Sun",[51],[232],"An eclipse is named after the thing that goes dark for you.","In a **solar** eclipse, the Moon passes between Earth and the Sun and its shadow falls on Earth, hiding the Sun from view. In a lunar eclipse, it is the other way round: Earth's shadow falls on the Moon.",[235,68],"solar-eclipse",{"id":237,"section":15,"level":45,"prompt":238,"check":239,"hints":250,"solution":252,"skills":253},"eclipses.q012","At which Moon phase must a solar eclipse always happen?",{"kind":48,"options":240,"correct":249},[241,243,245,247],{"id":51,"label":242},"Full moon",{"id":54,"label":244},"First quarter",{"id":57,"label":246},"New moon",{"id":60,"label":248},"Any phase at all",[57],[251],"The Moon must be between Earth and the Sun.","A solar eclipse can only happen at **new moon**, when the Moon sits between Earth and the Sun. This is necessary but not sufficient — the Moon must also be near a node.",[254],"moon-phase",{"id":256,"section":15,"level":45,"prompt":257,"check":258,"hints":266,"solution":268,"skills":269},"eclipses.q013","At which Moon phase must a lunar eclipse always happen?",{"kind":48,"options":259,"correct":265},[260,261,262,264],{"id":51,"label":246},{"id":54,"label":242},{"id":57,"label":263},"Last quarter",{"id":60,"label":248},[54],[267],"Earth must be between the Sun and the Moon.","A lunar eclipse can only happen at **full moon**, when Earth sits between the Sun and the Moon, so Earth's shadow can fall on the Moon.",[254],{"id":271,"section":15,"level":45,"prompt":272,"check":273,"hints":284,"solution":286,"skills":287},"eclipses.q014","Why does an eclipsed Moon turn red instead of simply going black?",{"kind":48,"options":274,"correct":283},[275,277,279,281],{"id":51,"label":276},"It reflects light from Mars",{"id":54,"label":278},"Sunlight bent through Earth's atmosphere reaches it, and that light has lost most of its blue",{"id":57,"label":280},"The Moon glows with its own heat",{"id":60,"label":282},"It is an optical illusion caused by the dark sky",[54],[285],"Think about what colour the sky is at sunset, and why.","Earth's atmosphere bends (refracts) sunlight around the edge of Earth and into its shadow. Along that long, slanting path, blue light is scattered away — the same reason sunsets are red — so only reddish light reaches the eclipsed Moon.",[288,289],"lunar-eclipse","colour",{"id":291,"section":15,"level":125,"prompt":292,"check":293,"hints":304,"solution":306,"skills":307},"eclipses.q015","A photo taken at 9 p.m. shows a reddish Moon with a dark curved bite out of one side, with stars visible nearby. What kind of eclipse is this?",{"kind":48,"options":294,"correct":303},[295,297,299,301],{"id":51,"label":296},"A total solar eclipse",{"id":54,"label":298},"A partial lunar eclipse",{"id":57,"label":300},"An annular solar eclipse",{"id":60,"label":302},"A penumbral solar eclipse",[54],[305],"It is night-time, and the Moon itself has changed colour and shape.","This is a **partial lunar eclipse**. Night-time and stars rule out any solar eclipse; the reddish colour and curved dark bite are the signature of Earth's round shadow partly covering the Moon.",[308,288],"identify",{"id":310,"section":15,"level":125,"prompt":311,"check":312,"hints":323,"solution":325,"skills":326},"eclipses.q016","Which of these is true about how much of Earth can see a given total lunar eclipse, compared with a given total solar eclipse?",{"kind":48,"options":313,"correct":322},[314,316,318,320],{"id":51,"label":315},"Only a narrow ~160 km strip can see either kind",{"id":54,"label":317},"About half of Earth (the whole night side) can see the lunar eclipse; only a ~160 km strip sees solar totality",{"id":57,"label":319},"The whole planet can see both at once",{"id":60,"label":321},"Neither is visible from more than one country",[54],[324],"Ask what changes in each case: a small patch of Earth's surface, or the Moon itself.","A lunar eclipse changes the Moon itself, so anyone who can see the Moon — roughly half the planet, the whole night side — sees it. A solar eclipse's totality is a tiny, fast-moving shadow spot on Earth's surface, typically only about 160 km wide.",[288,235],{"id":328,"section":15,"level":125,"prompt":329,"check":330,"hints":341,"solution":343,"skills":344},"eclipses.q017","Which statement about eclipse duration is correct?",{"kind":48,"options":331,"correct":340},[332,334,336,338],{"id":51,"label":333},"Solar totality can last up to about 7 minutes 32 seconds; lunar totality up to about 1 hour 40 minutes",{"id":54,"label":335},"Both last about the same time, a few minutes",{"id":57,"label":337},"Lunar totality is always shorter than solar totality",{"id":60,"label":339},"Solar totality can last several hours",[51],[342],"The Moon's own shadow at Earth is tiny; Earth's shadow at the Moon is much bigger.","Solar totality is capped at about **7 min 32 s**, because the Moon's shadow spot on Earth is narrow and moves fast. Lunar totality can last up to about **1 h 40 min**, because Earth's shadow at the Moon's distance is far wider than the Moon itself.",[345],"duration",{"id":347,"section":15,"level":177,"prompt":348,"check":349,"hints":353,"solution":356,"skills":357},"eclipses.q018","Earth's umbra at the Moon's distance is about 9,196 km across, and the Moon is 3,475 km wide, moving at about 3,408 km\u002Fh relative to the shadow. About how many hours can the Moon spend fully inside the umbra, at most? Round to 1 decimal place.",{"kind":128,"answer":350,"tolerance":351,"unit":352},1.7,0.1,"hours",[354,355],"The Moon's centre must cross (umbra width − Moon's own width).","(9,196 − 3,475) ÷ 3,408 = ?","(9,196 − 3,475) ÷ 3,408 ≈ **1.7 hours** (about 1 h 41 min), matching the topic's stated maximum of roughly 1 h 47 min once small corrections for the atmosphere are included.",[136,288],{"id":359,"section":15,"level":177,"prompt":360,"check":361,"hints":365,"solution":367,"skills":368},"eclipses.q019","The Moon's shadow moves through space at about 3,679 km\u002Fh, and Earth's equator spins eastward at about 1,674 km\u002Fh in the same direction. What is the slowest the shadow can cross the ground near the equator?",{"kind":128,"answer":362,"tolerance":363,"unit":364},2005,20,"km\u002Fh",[366],"Since both move the same way, subtract the smaller from the larger.","3,679 − 1,674 ≈ **2,005 km\u002Fh**. This is the minimum; away from the equator, or at an angle, the shadow can move much faster.",[136,369],"shadow-speed",{"id":371,"section":15,"level":199,"prompt":372,"check":373,"hints":384,"solution":386,"skills":387},"eclipses.q020","Why is a solar eclipse dangerous to view directly for its entire partial phase, while a lunar eclipse is safe to view throughout, in terms of what you are actually looking at in each case?",{"kind":48,"options":374,"correct":383},[375,377,379,381],{"id":51,"label":376},"In a solar eclipse you look at the Sun's own bright surface; in a lunar eclipse you look at the Moon, only reflecting much dimmer light",{"id":54,"label":378},"Solar eclipses are simply rarer, which makes them more dangerous",{"id":57,"label":380},"Lunar eclipses are further away, so they are automatically safer",{"id":60,"label":382},"There is no real difference in danger between the two",[51],[385],"What is the light source in each case: the Sun itself, or moonlight?","In a solar eclipse, you are looking directly at the **Sun's own blazing surface**, and any part of it still visible is dangerously bright, however small. In a lunar eclipse you are looking at the **Moon**, which only reflects sunlight and, even eclipsed, remains fainter than a full moon (about 10,000× fainter) — never anywhere near a light source you need to protect your eyes from.",[87,216],{"id":389,"section":19,"level":45,"prompt":390,"check":391,"hints":402,"solution":404,"skills":405},"eclipses.q021","Why isn't there a solar eclipse at every new moon?",{"kind":48,"options":392,"correct":401},[393,395,397,399],{"id":51,"label":394},"The Moon's orbit is tilted, so it usually passes above or below the Sun",{"id":54,"label":396},"The Moon is sometimes too small",{"id":57,"label":398},"Clouds usually block it",{"id":60,"label":400},"New moon does not happen every month",[51],[403],"Picture the Moon's path as a slightly tilted ring around Earth.","The Moon's orbit is tilted by about **5.1°** compared with Earth's orbital plane, so most new moons find the Moon too far above or below the Sun–Earth line for its shadow to reach Earth.",[406,216],"tilt",{"id":408,"section":19,"level":45,"prompt":409,"check":410,"hints":421,"solution":423,"skills":424},"eclipses.q022","What are the two **nodes** of the Moon's orbit?",{"kind":48,"options":411,"correct":420},[412,414,416,418],{"id":51,"label":413},"The Moon's nearest and furthest points from Earth",{"id":54,"label":415},"The two points where the Moon's tilted path crosses Earth's orbital plane",{"id":57,"label":417},"The two poles of the Moon",{"id":60,"label":419},"The times of sunrise and sunset",[54],[422],"A tilted circle crossing a flat plane crosses it in exactly two places.","The **nodes** are the two points where the Moon's tilted orbit crosses the flat plane of Earth's orbit around the Sun. Eclipses can only happen when the Moon is near a node.",[425,68],"nodes",{"id":427,"section":19,"level":45,"prompt":428,"check":429,"hints":440,"solution":442,"skills":443},"eclipses.q023","Roughly how many eclipses of any kind (solar and lunar together) happen in a typical year?",{"kind":48,"options":430,"correct":439},[431,433,435,437],{"id":51,"label":432},"0 to 1",{"id":54,"label":434},"4 to 7",{"id":57,"label":436},"24",{"id":60,"label":438},"100 or more",[54],[441],"It is more than a couple but far fewer than one a month.","A typical year has **4 to 7** eclipses of all kinds, with 2 to 5 of those being solar eclipses.",[444],"frequency",{"id":446,"section":19,"level":125,"prompt":447,"check":448,"hints":459,"solution":461,"skills":462},"eclipses.q024","If the Moon's orbit had **no tilt at all**, roughly how many solar eclipses would happen in a year?",{"kind":48,"options":449,"correct":458},[450,452,454,456],{"id":51,"label":451},"0",{"id":54,"label":453},"4 to 7, same as now",{"id":57,"label":455},"About 12, one every new moon",{"id":60,"label":457},"Exactly 2",[57],[460],"With zero tilt, is the Moon ever off the Sun-Earth line at new moon?","With no tilt, the Moon would be exactly on the Sun-Earth line at **every** new moon, giving about **12** solar eclipses a year (and 12 lunar eclipses too).",[406,463],"prediction",{"id":465,"section":19,"level":125,"prompt":466,"check":467,"hints":469,"solution":471,"skills":472},"eclipses.q025","The Moon's orbital tilt is 5.145°, and the Sun's own apparent width is about 0.53°. About how many times bigger is the tilt than the Sun's width? Round to the nearest whole number.",{"kind":128,"answer":468,"tolerance":5},10,[470],"5.145 ÷ 0.53 = ?","5.145 ÷ 0.53 ≈ **9.7**, which rounds to about **10**. The tilt is nearly ten times the size of the very target the Moon has to hit, which is why most months miss entirely.",[136,406],{"id":474,"section":19,"level":125,"prompt":475,"check":476,"hints":487,"solution":489,"skills":490},"eclipses.q026","An eclipse season lasts about 32 days, and a synodic month (new moon to new moon) is 29.53 days. What must follow?",{"kind":48,"options":477,"correct":486},[478,480,482,484],{"id":51,"label":479},"Some eclipse seasons could have no solar eclipse at all",{"id":54,"label":481},"At least one new moon must fall inside every eclipse season, guaranteeing at least one solar eclipse per season",{"id":57,"label":483},"There are exactly two solar eclipses every year, no more",{"id":60,"label":485},"Eclipse seasons happen every single month",[54],[488],"Compare the season's length with the gap between new moons.","Because the eclipse season (about 32 days) is **longer** than one synodic month (29.53 days), a new moon cannot possibly \"skip over\" it — at least one must fall inside, guaranteeing at least one solar eclipse in every season, and so at least two a year.",[216,491],"eclipse-season",{"id":493,"section":19,"level":177,"prompt":494,"check":495,"hints":499,"solution":502,"skills":503},"eclipses.q027","At the Moon's average distance (384,400 km), a 5.145° tilt puts the Moon how far above or below the Sun-Earth line, in km? Round to the nearest 1,000 km.",{"kind":128,"answer":496,"tolerance":497,"unit":498},34600,500,"km",[500,501],"distance × tan(tilt) = ?","384,400 × tan(5.145°) ≈ ?","384,400 × tan(5.145°) ≈ **34,600 km** — about 2.7 Earth-diameters off target, which is why most new moons produce no eclipse at all.",[136,406],{"id":505,"section":19,"level":177,"prompt":506,"check":507,"hints":510,"solution":512,"skills":513},"eclipses.q028","The line of nodes regresses (slides backwards) at about 19.34° per year, completing a full circuit in about how many years? Round to 1 decimal place.",{"kind":128,"answer":508,"tolerance":351,"unit":509},18.6,"years",[511],"360 ÷ 19.34 = ?","360 ÷ 19.34 ≈ **18.6 years**. This is why eclipse seasons drift steadily earlier through the calendar year rather than staying fixed to particular months.",[514,136],"node-regression",{"id":516,"section":19,"level":199,"prompt":517,"check":518,"hints":529,"solution":531,"skills":532},"eclipses.q029","Phase (new\u002Ffull moon) repeats every month; being near a node happens in two short seasons a year. Why does an eclipse needing BOTH at once, rather than either alone, make eclipses rare?",{"kind":48,"options":519,"correct":528},[520,522,524,526],{"id":51,"label":521},"Because neither condition alone is rare, but both being true at the same moment restricts eclipses to a few short seasons a year",{"id":54,"label":523},"Because the phase condition alone already makes eclipses rare",{"id":57,"label":525},"Because the node condition alone already guarantees an eclipse every time",{"id":60,"label":527},"The two conditions are actually the same thing, so this makes no difference",[51],[530],"Phase repeats every month; being near a node happens roughly twice a year. What has to line up?","New or full moon happens every month, and the Moon passes near a node roughly twice a year (in each of two eclipse seasons). Neither condition alone is rare. What is rare is **both being true at the same time**: the right phase has to fall inside the narrow window when the Sun is also near a node, which restricts eclipses to a few short seasons rather than every month.",[216,425],{"id":534,"section":23,"level":45,"prompt":535,"check":536,"hints":547,"solution":549,"skills":550},"eclipses.q030","The Sun is about how many times wider than the Moon?",{"kind":48,"options":537,"correct":546},[538,540,542,544],{"id":51,"label":539},"About 4 times",{"id":54,"label":541},"About 40 times",{"id":57,"label":543},"About 400 times",{"id":60,"label":545},"About 4,000 times",[57],[548],"The famous coincidence in this topic uses this number twice.","The Sun is about **400 times** wider than the Moon (401 times, precisely) — and also about 400 times further away, which is why they look almost the same size in our sky.",[551],"the-400-coincidence",{"id":553,"section":23,"level":45,"prompt":554,"check":555,"hints":566,"solution":568,"skills":569},"eclipses.q031","What makes an eclipse **annular** rather than total?",{"kind":48,"options":556,"correct":565},[557,559,561,563],{"id":51,"label":558},"The Moon is near the far end of its orbit and looks too small to fully cover the Sun",{"id":54,"label":560},"Thin cloud lets a ring of light through",{"id":57,"label":562},"It happens at full moon",{"id":60,"label":564},"The Sun is unusually large that day",[51],[567],"Think about the Moon's changing distance.","Near **apogee** (its furthest point), the Moon looks smaller than the Sun, so it cannot cover it fully — a bright ring, or \"ring of fire\", is left showing all the way round.",[570],"annular",{"id":572,"section":23,"level":125,"prompt":573,"check":574,"hints":585,"solution":587,"skills":588},"eclipses.q032","The Moon's apparent width ranges from 29.5′ (apogee) to 32.9′ (perigee); the Sun's ranges from 31.5′ to 32.5′. Which combination gives a **total** eclipse?",{"kind":48,"options":575,"correct":584},[576,578,580,582],{"id":51,"label":577},"Moon at apogee, Sun at its largest",{"id":54,"label":579},"Moon at perigee, Sun at its smallest",{"id":57,"label":581},"Moon at apogee, Sun at its smallest",{"id":60,"label":583},"Any combination gives total",[54],[586],"Total needs the Moon to look bigger than the Sun.","Moon at perigee (32.9′) against the Sun at its smallest (31.5′) gives the deepest, longest possible total eclipse, since the Moon comfortably outsizes the Sun.",[589],"angular-size",{"id":591,"section":23,"level":125,"prompt":592,"check":593,"hints":596,"solution":598,"skills":599},"eclipses.q033","In the deepest annular eclipse, the Moon covers about 90.5% of the Sun's **diameter**. About what percentage of the Sun's **area** is left shining? Round to the nearest whole per cent.",{"kind":128,"answer":594,"tolerance":5,"unit":595},18,"%",[597],"Area scales as the square of the diameter. Find the area covered first, then subtract from 100%.","Area covered ≈ 0.905² ≈ 0.819, or about 82%. Area left shining ≈ 100 − 82 = **18%** (18.1% precisely), which is why an annular eclipse never gets properly dark.",[136,570],{"id":601,"section":23,"level":125,"prompt":602,"check":603,"hints":605,"solution":607,"skills":608},"eclipses.q034","A partial eclipse covers 99% of the Sun's diameter as seen from your town. About what percentage of its area is still shining?",{"kind":128,"answer":604,"tolerance":5,"unit":595},2,[606],"1 − 0.99² = ?","1 − 0.99² = 1 − 0.9801 = 0.0199, about **2%**. Still thousands of times brighter than is safe to view, and your pupils are wide open because the sky looks dim — a genuinely dangerous moment.",[136,87],{"id":610,"section":23,"level":177,"prompt":611,"check":612,"hints":615,"solution":617,"skills":618},"eclipses.q035","The Sun is 1,392,700 km across and the Moon is 3,475 km across. What is the Sun-to-Moon ratio by size, to 1 decimal place?",{"kind":128,"answer":613,"tolerance":614},400.8,0.2,[616],"Divide the Sun's diameter by the Moon's diameter.","Size ratio: 1,392,700 ÷ 3,475 ≈ **400.8**. Distance ratio: 149,597,871 ÷ 384,400 ≈ **389.2**. The two ratios are within about 3% of each other, which is why the Sun and Moon look almost exactly the same size in our sky — the coincidence behind total eclipses.",[136,551],{"id":620,"section":23,"level":177,"prompt":621,"check":622,"hints":633,"solution":635,"skills":636},"eclipses.q036","The Moon's umbra cone is about 374,180 km long; the Moon's average distance from Earth's surface is about 378,029 km. Is an *average* solar eclipse total, annular, or does it depend on other factors too?",{"kind":48,"options":623,"correct":632},[624,626,628,630],{"id":51,"label":625},"Always total, since the cone is long enough",{"id":54,"label":627},"Annular, since the cone falls about 3,850 km short of the surface on average",{"id":57,"label":629},"Always partial",{"id":60,"label":631},"There is no such thing as an average eclipse",[54],[634],"Compare the cone's length with the distance it needs to reach.","374,180 km falls short of 378,029 km by about 3,850 km, so on **average** the umbra does not reach the ground at all — an average solar eclipse is **annular**. Only when the Moon is nearer than usual (near perigee) does the umbra overshoot the surface and give totality.",[187,216],{"id":638,"section":23,"level":199,"prompt":639,"check":640,"hints":651,"solution":653,"skills":654},"eclipses.q037","A total eclipse needs the Moon's disc to be bigger than the Sun's; an annular eclipse needs it smaller. Using the ranges Moon 29.5′-32.9′ and Sun 31.5′-32.5′, why are annular eclipses, in fact, a little more common than total ones?",{"kind":48,"options":641,"correct":650},[642,644,646,648],{"id":51,"label":643},"The ranges overlap, but the Moon's average apparent size is slightly below the Sun's, so it is smaller than the Sun slightly more often than bigger",{"id":54,"label":645},"Annular eclipses are not actually more common; this is a myth",{"id":57,"label":647},"The Sun's size never changes, so only the Moon's distance matters, favouring total eclipses",{"id":60,"label":649},"Annular eclipses need less precise alignment, so they happen more often",[51],[652],"Which is bigger on average: the Moon's typical apparent size, or the Sun's?","The two ranges overlap (29.5′-32.9′ for the Moon against 31.5′-32.5′ for the Sun), so depending on where each body is in its orbit, the Moon can be bigger (giving total) or smaller (giving annular) than the Sun. Because the Moon's **average** apparent size (about 31.1′) is slightly below the Sun's average (about 32.0′), the Moon is smaller than the Sun slightly more often than it is bigger, which is why annular eclipses are, in fact, a little more common than total ones over the long run.",[216,551],{"id":656,"section":27,"level":45,"prompt":657,"check":658,"hints":669,"solution":671,"skills":672},"eclipses.q038","What is the **corona**, and when can you normally see it?",{"kind":48,"options":659,"correct":668},[660,662,664,666],{"id":51,"label":661},"The Sun's faint outer atmosphere, visible only during totality",{"id":54,"label":663},"A ring of clouds around the Moon",{"id":57,"label":665},"The bright edge of the Sun, visible every sunny day",{"id":60,"label":667},"A halo caused by ice crystals",[51],[670],"It is far too faint to see against the Sun's normal disc.","The **corona** is the Sun's faint, pearly outer atmosphere, about a millionth as bright as the Sun's disc. It is only visible when the disc itself is completely hidden — during totality.",[673,68],"corona",{"id":675,"section":27,"level":45,"prompt":676,"check":677,"hints":688,"solution":690,"skills":691},"eclipses.q039","What are **Baily's beads**?",{"kind":48,"options":678,"correct":687},[679,681,683,685],{"id":51,"label":680},"Stars visible only during totality",{"id":54,"label":682},"Points of sunlight shining through valleys on the Moon's ragged edge, just before or after totality",{"id":57,"label":684},"Small meteors seen during an eclipse",{"id":60,"label":686},"Beads worn by ancient eclipse-watchers",[54],[689],"Think about the Moon's edge not being perfectly smooth.","**Baily's beads** are bright points of sunlight shining through valleys on the Moon's mountainous edge, appearing for a few seconds just before totality begins and just after it ends.",[692,68],"totality",{"id":694,"section":27,"level":125,"prompt":695,"check":696,"hints":707,"solution":709,"skills":710},"eclipses.q040","Roughly how much does the temperature typically drop during totality?",{"kind":48,"options":697,"correct":706},[698,700,702,704],{"id":51,"label":699},"About 5°C, with 10-15°C possible in deserts",{"id":54,"label":701},"About 50°C",{"id":57,"label":703},"It never changes",{"id":60,"label":705},"It rises, because of the corona's heat",[51],[708],"It is a noticeable but not extreme change.","Temperatures typically drop by around **5°C** during totality, with drops of 10-15°C measured in especially dry, clear places such as deserts.",[692],{"id":712,"section":27,"level":125,"prompt":713,"check":714,"hints":718,"solution":720,"skills":721},"eclipses.q041","The path of totality is typically about 160 km wide. If the shadow crosses the ground at about 2,000 km\u002Fh, roughly how many minutes does it take to sweep across that width?",{"kind":128,"answer":715,"tolerance":716,"unit":717},4.8,0.3,"minutes",[719],"Time = distance ÷ speed. Convert speed to km per minute first.","2,000 km\u002Fh ≈ 33.3 km\u002Fmin. 160 ÷ 33.3 ≈ **4.8 minutes**. Any one point on the ground is inside the path for less time than this, since totality only lasts while you are near the path's centre.",[136,369],{"id":723,"section":27,"level":125,"prompt":724,"check":725,"hints":736,"solution":738,"skills":739},"eclipses.q042","What is the single moment during a solar eclipse when it is safe to look with bare eyes?",{"kind":48,"options":726,"correct":735},[727,729,731,733],{"id":51,"label":728},"Whenever more than 90% is covered",{"id":54,"label":730},"During totality of a total eclipse, inside the path of totality, only",{"id":57,"label":732},"During any annular eclipse",{"id":60,"label":734},"There is never a safe moment for bare eyes",[54],[737],"It is a very specific, narrow exception.","Bare eyes are safe **only** during totality of a **total** eclipse, when the Sun's disc is completely hidden, and only for people standing inside the path of totality. Filters must go back on the instant any bright sliver reappears.",[87,692],{"id":741,"section":27,"level":177,"prompt":742,"check":743,"hints":746,"solution":748,"skills":749},"eclipses.q043","The corona's temperature is between about 1 and 3 million °C, while the Sun's visible surface (the photosphere) is about 5,500°C. About how many times hotter is the corona than the surface, at its hottest?",{"kind":128,"answer":744,"tolerance":745},545,30,[747],"3,000,000 ÷ 5,500 = ?","3,000,000 ÷ 5,500 ≈ **545**. This is one of the Sun's genuine mysteries: the corona is hundreds of times hotter than the surface beneath it, and scientists are still working out exactly why.",[673,136],{"id":751,"section":27,"level":177,"prompt":752,"check":753,"hints":764,"solution":766,"skills":767},"eclipses.q044","Why does a solar eclipse's path of totality only ever cross a narrow strip of Earth, while the partial phase is visible across a much wider region?",{"kind":48,"options":754,"correct":763},[755,757,759,761],{"id":51,"label":756},"The Moon's umbra (full shadow) is narrow, but its penumbra (partial shadow) is thousands of kilometres wide",{"id":54,"label":758},"Clouds only block totality, not partial views",{"id":57,"label":760},"The Moon moves faster during totality",{"id":60,"label":762},"It is a limitation of cameras, not of the shadow itself",[51],[765],"Recall the two parts of a shadow.","The Moon's **umbra**, where the Sun is fully covered, is a narrow cone that lands as a spot only about 160 km wide. Its much wider **penumbra**, where only part of the Sun is covered, spans thousands of kilometres, which is why partial views are common but totality is rare.",[187,216],{"id":769,"section":27,"level":199,"prompt":770,"check":771,"hints":782,"solution":784,"skills":785},"eclipses.q045","A traveller wants the **longest possible** totality. Which combination of Moon and Earth positions should they aim for, and why?",{"kind":48,"options":772,"correct":781},[773,775,777,779],{"id":51,"label":774},"Moon near perigee (looks biggest) and Sun near its smallest apparent size, around early July, giving the deepest possible coverage",{"id":54,"label":776},"Moon near apogee and Sun near its largest apparent size, for maximum contrast",{"id":57,"label":778},"It does not matter; totality length never varies",{"id":60,"label":780},"Moon near perigee and Sun near its largest size, in January",[51],[783],"Longest totality needs the biggest possible Moon and the smallest possible Sun.","They should aim for an eclipse where the Moon is near **perigee** (its closest point, making it look as large as possible) and the Sun is near its **smallest** apparent size, which happens in early **July** when Earth is furthest from the Sun (aphelion). Together, a bigger Moon and a smaller Sun give the deepest possible coverage and the longest possible totality — approaching the theoretical maximum of 7 minutes 32 seconds.",[216,692],{"id":787,"section":31,"level":45,"prompt":788,"check":789,"hints":800,"solution":802,"skills":803},"eclipses.q046","Who first explained eclipses as shadows rather than a demon swallowing the Sun or Moon, in the Aryabhatiya (499 CE)?",{"kind":48,"options":790,"correct":799},[791,793,795,797],{"id":51,"label":792},"Aryabhata",{"id":54,"label":794},"Brahmagupta",{"id":57,"label":796},"Newton",{"id":60,"label":798},"Eddington",[51],[801],"This astronomer's book title is also his own name.","**Aryabhata**, writing the *Aryabhatiya* in 499 CE at the age of 23, stated that eclipses are caused by shadows — the Moon entering Earth's shadow, and the Moon's own shadow falling on Earth — rather than by Rahu, a demon in the older account.",[804,805],"aryabhata","history",{"id":807,"section":31,"level":45,"prompt":808,"check":809,"hints":820,"solution":822,"skills":823},"eclipses.q047","What is the **Saros**, in simple terms?",{"kind":48,"options":810,"correct":819},[811,813,815,817],{"id":51,"label":812},"A period of about 18 years after which similar eclipses tend to repeat",{"id":54,"label":814},"The name of an ancient Indian eclipse god",{"id":57,"label":816},"A unit of angular measurement",{"id":60,"label":818},"The distance between the Earth and the Moon",[51],[821],"It was discovered by pattern-spotting in old records.","The **Saros** is a period of about 18 years and 11 days, after which the Sun, Earth and Moon return to a very similar arrangement, so a similar eclipse tends to recur. It was noticed by Babylonian astronomers from centuries of records.",[824,68],"saros",{"id":826,"section":31,"level":125,"prompt":827,"check":828,"hints":839,"solution":841,"skills":842},"eclipses.q048","In classical Indian astronomy, what are the names given to the two nodes of the Moon's orbit?",{"kind":48,"options":829,"correct":838},[830,832,834,836],{"id":51,"label":831},"Rahu and Ketu",{"id":54,"label":833},"Surya and Chandra",{"id":57,"label":835},"Agni and Vayu",{"id":60,"label":837},"Indra and Varuna",[51],[840],"These two names come from a story about a demon's severed head and body.","The two nodes are called **Rahu** and **Ketu** in classical Indian astronomy — the ascending and descending nodes, described in the older story as a demon's head and body chasing the Sun and Moon.",[843,844],"rahu-ketu","india",{"id":846,"section":31,"level":125,"prompt":847,"check":848,"hints":859,"solution":861,"skills":862},"eclipses.q049","What did the 1868 total solar eclipse, observed from Guntur, India, lead to the discovery of?",{"kind":48,"options":849,"correct":858},[850,852,854,856],{"id":51,"label":851},"The planet Neptune",{"id":54,"label":853},"A new element, later named helium",{"id":57,"label":855},"The rings of Saturn",{"id":60,"label":857},"Gravity",[54],[860],"The discovery used a spectroscope, which reads light like a fingerprint.","During the 1868 eclipse, Jules Janssen (at Guntur) found an unidentified yellow spectral line in the Sun's prominences. It matched no known element and was named **helium**, after the Greek word for the Sun — isolated on Earth only 27 years later, in 1895.",[863,864,805],"1868","helium",{"id":866,"section":31,"level":125,"prompt":867,"check":868,"hints":879,"solution":881,"skills":882},"eclipses.q050","What did the 1919 solar eclipse expeditions (Príncipe and Sobral) test?",{"kind":48,"options":869,"correct":878},[870,872,874,876],{"id":51,"label":871},"Whether the Moon has water",{"id":54,"label":873},"Einstein's prediction that gravity bends starlight",{"id":57,"label":875},"The existence of the corona",{"id":60,"label":877},"Whether eclipses could be predicted at all",[54],[880],"Totality was needed to see faint stars very close to the Sun's position.","The 1919 expeditions measured the bending of starlight passing close to the Sun during totality, testing Einstein's general relativity. The measured deflection matched Einstein's predicted 1.75 arcseconds far better than the smaller Newtonian prediction of 0.87 arcseconds.",[883,884,805],"1919","einstein",{"id":886,"section":31,"level":177,"prompt":887,"check":888,"hints":891,"solution":893,"skills":894},"eclipses.q051","One Saros is about 6,585.32 days. Expressed as 18 years plus a leftover, roughly how many days is the leftover (using 4 leap days across the span)? Round to 1 decimal place.",{"kind":128,"answer":889,"tolerance":614,"unit":890},11.3,"days",[892],"18 × 365 = 6,570. Add the leap days, then subtract from 6,585.32.","18 × 365 + 4 = 6,574 days. 6,585.32 − 6,574 = **11.3 days**. That leftover, about a third of a day, is why the next eclipse in the same Saros series lands roughly a third of the way around the world to the west.",[824,136],{"id":896,"section":31,"level":177,"prompt":897,"check":898,"hints":900,"solution":902,"skills":903},"eclipses.q052","Three Saros cycles make up the exeligmos, which restores an eclipse to nearly the same longitude. About how many years is that?",{"kind":128,"answer":899,"tolerance":5,"unit":509},54,[901],"Multiply one Saros (about 18.03 years) by 3.","3 × 18.03 ≈ **54 years** (with an extra roughly 34 days). Because the leftover time in each Saros is close to a third of a day, three Saros cycles bring the eclipse back to nearly its starting longitude.",[824,904],"exeligmos",{"id":906,"section":31,"level":199,"prompt":907,"check":908,"hints":919,"solution":921,"skills":922},"eclipses.q053","Brahmagupta's Brahmasphutasiddhanta (628 CE) computed eclipses accurately using node-based geometry, yet also defended the traditional Rahu account; his later Khandakhadyaka (665 CE) drops that defence. What does this illustrate?",{"kind":48,"options":909,"correct":918},[910,912,914,916],{"id":51,"label":911},"A scientist can hold accurate mathematics alongside a traditional belief at first, and drop the belief only later, as understanding changes gradually",{"id":54,"label":913},"Brahmagupta never actually understood the correct geometry",{"id":57,"label":915},"The Rahu account and the node geometry are exactly the same thing with no difference",{"id":60,"label":917},"Scientific understanding always changes instantly, in a single moment",[51],[920],"Compare his early and later books.","It shows that adopting an accurate mathematical model does not automatically or instantly erase every older belief — Brahmagupta could compute eclipses correctly using the nodes while still defending the Rahu tradition in his earlier book, and only dropped that defence in a later, more purely practical work. Understanding can shift gradually, even within one career, rather than as a single sudden switch.",[216,805],{"id":924,"section":35,"level":45,"prompt":925,"check":926,"hints":937,"solution":939,"skills":940},"eclipses.q054","Many families in India traditionally avoid cooking or eating during an eclipse. What does the evidence show about this practice's stated reason (that eclipse light harms food)?",{"kind":48,"options":927,"correct":936},[928,930,932,934],{"id":51,"label":929},"It is fully confirmed by careful measurement",{"id":54,"label":931},"Careful comparisons find no measurable effect on food from eclipse light itself",{"id":57,"label":933},"It has never been checked",{"id":60,"label":935},"Food only spoils faster during lunar eclipses",[54],[938],"Eclipse light is just reduced ordinary sunlight — nothing new is produced.","Careful, repeated comparisons find **no measurable effect** of eclipse light on food safety — an eclipse simply reduces the amount of ordinary sunlight reaching the ground, and produces no new kind of radiation.",[941,844],"evidence",{"id":943,"section":35,"level":125,"prompt":944,"check":945,"hints":956,"solution":958,"skills":959},"eclipses.q055","What is the one **real, measured** risk connected to solar eclipse superstitions, even though the traditional explanation given is usually different?",{"kind":48,"options":946,"correct":955},[947,949,951,953],{"id":51,"label":948},"A rise in eye injuries from people looking at the Sun unsafely",{"id":54,"label":950},"Food poisoning",{"id":57,"label":952},"An increase in traffic accidents",{"id":60,"label":954},"A rise in birth complications",[51],[957],"Think about what people might be tempted to do during an eclipse, not what the eclipse itself does.","Public-health records genuinely show a spike in **eye injuries** around solar eclipses, from people looking at the Sun without protection — the one real risk, even though many traditional customs focus on food or pregnancy instead.",[941,87],{"id":961,"section":35,"level":125,"prompt":962,"check":963,"hints":974,"solution":976,"skills":977},"eclipses.q056","A single hospital reports slightly more birth complications on the day of an eclipse than usual. What is the scientifically careful conclusion?",{"kind":48,"options":964,"correct":973},[965,967,969,971],{"id":51,"label":966},"This single result proves eclipses are harmful",{"id":54,"label":968},"Small day-to-day differences happen by chance alone in small samples; check many hospitals and years before concluding anything",{"id":57,"label":970},"The hospital's records must be wrong",{"id":60,"label":972},"This proves the opposite: eclipses have no effect at all",[54],[975],"A single day's small medical count naturally bounces up and down.","A single day's numbers at one hospital tell you very little — such small counts vary randomly by chance alone. A careful conclusion needs data pooled from **many** eclipses, hospitals and years, looking for a consistent, repeatable pattern.",[941,216],{"id":979,"section":35,"level":125,"prompt":980,"check":981,"hints":992,"solution":994,"skills":995},"eclipses.q057","Which of these three real, upcoming eclipses will be a total lunar eclipse fully visible across India?",{"kind":48,"options":982,"correct":991},[983,985,987,989],{"id":51,"label":984},"31 December 2028",{"id":54,"label":986},"21 May 2031",{"id":57,"label":988},"20 March 2034",{"id":60,"label":990},"None of these",[51],[993],"Lunar eclipses are visible from the whole night side of Earth at once.","**31 December 2028** is a total lunar eclipse, fully visible across the whole of India. 21 May 2031 is an annular solar eclipse crossing Kerala and nearby regions, and 20 March 2034 is a total solar eclipse crossing northern India.",[996],"real-dates",{"id":998,"section":35,"level":177,"prompt":999,"check":1000,"hints":1011,"solution":1013,"skills":1014},"eclipses.q058","Why are \"an eclipse superstition is common in India\" and \"eclipses have a real geometric and physical explanation\" not actually in conflict with each other?",{"kind":48,"options":1001,"correct":1010},[1002,1004,1006,1008],{"id":51,"label":1003},"A sincerely held cultural belief and a separate, correct physical explanation can both be true — they answer meaning and mechanism",{"id":54,"label":1005},"They are in conflict; only one can be true",{"id":57,"label":1007},"The physical explanation replaces the cultural belief entirely, with nothing left to it",{"id":60,"label":1009},"Cultural beliefs are always scientifically accurate",[51],[1012],"One statement is about culture and meaning; the other is about physical cause and effect.","A cultural or traditional belief can be widely and sincerely held, carrying real meaning and history for a family or community, while a separate, independently checkable physical explanation also correctly describes the mechanism behind the event. They are not competing answers to the same question — one is about shared meaning and story, the other about cause and effect — so respecting one does not require denying the other, though it is still worth knowing what the evidence actually shows.",[216,1015],"sensitivity",{"id":1017,"section":35,"level":177,"prompt":1018,"check":1019,"hints":1030,"solution":1032,"skills":1033},"eclipses.q059","The 21 May 2031 annular eclipse's path crosses Kerala, northern Sri Lanka, and the Andaman & Nicobar Islands. A family in Delhi, well outside this path, wants to view the eclipse safely. What should they expect to see, and what equipment do they need?",{"kind":48,"options":1020,"correct":1029},[1021,1023,1025,1027],{"id":51,"label":1022},"A ring of fire, needing no equipment",{"id":54,"label":1024},"A partial eclipse, needing certified filters or projection throughout",{"id":57,"label":1026},"Nothing at all is visible from Delhi",{"id":60,"label":1028},"A total eclipse, safe to view briefly with bare eyes",[54],[1031],"Outside the central path, only the wider penumbra reaches you.","Delhi, outside the narrow annular path, would see a **partial** eclipse — the Sun's disc partly covered but never a full ring. Certified ISO 12312-2 filters or projection are needed for the entire event, since the Sun's surface is never fully hidden.",[996,87],{"id":1035,"section":35,"level":199,"prompt":1036,"check":1037,"hints":1048,"solution":1050,"skills":1051},"eclipses.q060","A friend argues that because millions of people have followed eclipse customs for centuries without apparent harm, the customs must be based on correct science. What is the flaw in this reasoning?",{"kind":48,"options":1038,"correct":1047},[1039,1041,1043,1045],{"id":51,"label":1040},"Harmless long use does not test the custom's stated reason; that needs a controlled comparison against people who did not follow it",{"id":54,"label":1042},"There is no flaw; the friend is correct",{"id":57,"label":1044},"Millions of people can never be mistaken about anything",{"id":60,"label":1046},"The custom must be false simply because it is old",[51],[1049],"Long, harmless use of a tradition does not by itself test any specific causal claim it makes.","Long, apparently harmless use of a tradition shows only that following it has not obviously hurt anyone — it does not, by itself, test whether the tradition's *stated reason* is correct, because there is no comparison group. To actually test the claim, you would need a **controlled comparison**: people who followed the custom and people who did not, under otherwise identical conditions, to see whether any real difference in outcomes appears. Without that comparison, harmlessness is not evidence that the stated mechanism is real.",[216,941],{"id":1053,"section":39,"level":45,"prompt":1054,"check":1055,"hints":1066,"solution":1068,"skills":1069},"eclipses.q061","Why can Mars's moon Phobos never cause a total eclipse of the Sun, seen from Mars?",{"kind":48,"options":1056,"correct":1065},[1057,1059,1061,1063],{"id":51,"label":1058},"It is too far from Mars",{"id":54,"label":1060},"Its angular size is smaller than the Sun's, as seen from Mars",{"id":57,"label":1062},"Mars has no atmosphere",{"id":60,"label":1064},"Phobos orbits backwards",[54],[1067],"The same rule as everywhere else: compare angular sizes.","Phobos looks only about 61% as wide as the Sun from Mars's surface, so it can only ever produce a **transit** — a small dark dot crossing the Sun — never a full eclipse.",[1070,1071],"mars","transit",{"id":1073,"section":39,"level":45,"prompt":1074,"check":1075,"hints":1086,"solution":1088,"skills":1089},"eclipses.q062","What is the key difference between a **transit** and a **total eclipse**?",{"kind":48,"options":1076,"correct":1085},[1077,1079,1081,1083],{"id":51,"label":1078},"A transit only happens at night",{"id":54,"label":1080},"In a transit, the crossing body looks smaller than the light source and only partly dims it; in a total eclipse, it looks bigger and fully covers it",{"id":57,"label":1082},"There is no real difference",{"id":60,"label":1084},"A transit only happens on other planets",[54],[1087],"It comes down to angular size again.","A **transit** happens when the crossing body's angular size is *smaller* than the light source's, so it only dims part of the light (a small dark dot). A **total eclipse** needs the crossing body to look *bigger*, fully covering the source.",[68,1071],{"id":1091,"section":39,"level":125,"prompt":1092,"check":1093,"hints":1104,"solution":1106,"skills":1107},"eclipses.q063","Why does Jupiter's moon Io cause true, sharp total eclipses on Jupiter's clouds, unlike Mars's moons?",{"kind":48,"options":1094,"correct":1103},[1095,1097,1099,1101],{"id":51,"label":1096},"Io is closer to the Sun than Mars is",{"id":54,"label":1098},"Io's angular size, from Jupiter, is nearly five times the Sun's tiny, distant angular width",{"id":57,"label":1100},"Jupiter has no sunlight at all",{"id":60,"label":1102},"It does not; Io only transits, like Phobos",[54],[1105],"Jupiter is much further from the Sun, so the Sun looks much smaller there.","From Jupiter, the Sun looks tiny (about 0.1°) because Jupiter is so far away, while Io is a large, close moon — its angular size is nearly **five times** the Sun's, so it comfortably blacks it out.",[1108,1109],"jupiter","eclipse",{"id":1111,"section":39,"level":125,"prompt":1112,"check":1113,"hints":1116,"solution":1118,"skills":1119},"eclipses.q064","Venus's disc covers about 3.03% of the Sun's width during a transit. About what percentage of the Sun's light does it block?",{"kind":128,"answer":1114,"tolerance":1115,"unit":595},0.09,0.02,[1117],"Light blocked depends on area, so square the width ratio.","0.0303² ≈ 0.00092, about **0.091%** — a tiny but genuinely measurable dip, using exactly the method used to find exoplanets.",[1071,136],{"id":1121,"section":39,"level":125,"prompt":1122,"check":1123,"hints":1125,"solution":1127,"skills":1128},"eclipses.q065","Venus transits come in pairs eight years apart, then a gap of over a century. What is the length of the full repeating cycle?",{"kind":128,"answer":1124,"tolerance":5,"unit":509},243,[1126],"Add the four gaps: 8 + 105.5 + 8 + 121.5.","8 + 105.5 + 8 + 121.5 = **243 years**. The last pair was 2004 and 2012; the next pair will be 2117 and 2125.",[1129,136],"venus",{"id":1131,"section":39,"level":177,"prompt":1132,"check":1133,"hints":1144,"solution":1146,"skills":1147},"eclipses.q066","Earth's transit dip, seen from a distant star system, would be about 0.0084% (from Earth being about 0.917% of the Sun's width). A space telescope can detect dips as small as about 0.001%. Could it detect an Earth-sized planet this way?",{"kind":48,"options":1134,"correct":1143},[1135,1137,1139,1141],{"id":51,"label":1136},"No, the dip is too small",{"id":54,"label":1138},"Yes — 0.0084% is more than 8 times the detection floor of 0.001%",{"id":57,"label":1140},"Only if the planet is closer to its star",{"id":60,"label":1142},"Telescopes cannot measure brightness dips at all",[54],[1145],"Compare 0.0084% with 0.001%.","0.0084% ÷ 0.001% ≈ 8.4, so the dip clears the detection floor comfortably — **yes**, a sufficiently sensitive telescope could detect an Earth-sized planet transiting a Sun-like star this way, which is exactly how many real exoplanets have been found.",[1148,216],"exoplanets",{"id":1150,"section":39,"level":177,"prompt":1151,"check":1152,"hints":1155,"solution":1157,"skills":1158},"eclipses.q067","Phobos's real angular size is about 61.4% of the Sun's, as seen from Mars. If Phobos stayed at the same distance but grew until its angular size exactly matched the Sun's, by about what percentage would its diameter need to increase? Round to the nearest 10%.",{"kind":128,"answer":1153,"tolerance":1154,"unit":595},63,8,[1156],"New size ÷ old size = 1 ÷ 0.614. Convert that scale factor into a percentage increase.","1 ÷ 0.614 ≈ 1.629, so the diameter would need to grow by about **63%** (from 22.5 km to about 36.7 km) to match the Sun's angular size at Phobos's real altitude.",[136,1070],{"id":1160,"section":39,"level":199,"prompt":1161,"check":1162,"hints":1173,"solution":1175,"skills":1176},"eclipses.q068","A coronagraph's small disc, mounted close to its camera, blocks a star's bright disc the same way the Moon blocks the Sun. Using angular size (real size ÷ distance), why can a disc only a few centimetres across do the Moon's job?",{"kind":48,"options":1163,"correct":1172},[1164,1166,1168,1170],{"id":51,"label":1165},"Angular size depends on size ÷ distance, so a tiny disc held very close can match the angular size of a huge but very distant object like the Moon",{"id":54,"label":1167},"The disc must actually be built to the Moon's exact real size, just scaled down",{"id":57,"label":1169},"It cannot; coronagraphs use a completely different method",{"id":60,"label":1171},"The camera's zoom lens does the blocking, not the disc",[51],[1174],"Angular size = size ÷ distance. The Moon is huge but very far; the coronagraph's disc is tiny but very close.","Angular size depends only on the ratio of real size to distance, not on real size alone. The Moon is enormous (3,475 km) but very far away (384,400 km); a coronagraph's disc is tiny (a few centimetres) but held extremely close to the camera. By choosing the right small distance, the disc's angular size — size ÷ distance — can be made to match the Sun's, exactly reproducing the Moon's blocking effect without needing anything remotely moon-sized.",[216,1177],"coronagraph",[1179,1180,1181,1182,1183,1184,1185,1186,1187],"eclipses-nasa-eclipses","eclipses-nasa-safety","eclipses-timeanddate","eclipses-wiki-solar","eclipses-wiki-lunar","eclipses-britannica-kids","eclipses-mactutor-aryabhata","eclipses-mactutor-brahmagupta","eclipses-ncert-curiosity","needs_review",{"generatedBy":1190,"notes":1191},"claude-code","Draft generated locally; pending owner review. Every numeric answer computed in Python and asserted before writing.","9a4e34ed37b12141854e074d49eb14fb27c89faa13420ea0a16dbe05a9b11017",{"logic:questions":1194,"source:eclipses-britannica-kids":1195,"source:eclipses-mactutor-aryabhata":1196,"source:eclipses-mactutor-brahmagupta":1197,"source:eclipses-nasa-eclipses":1198,"source:eclipses-nasa-safety":1199,"source:eclipses-ncert-curiosity":1200,"source:eclipses-timeanddate":1201,"source:eclipses-wiki-lunar":1202,"source:eclipses-wiki-solar":1203},"e7fd7c240a65bea1bff6277f7af7cca65e2c7fcb13c6d756cb943d53f3cbc948","b10d074ebe9d86c884d3f9aab5d21f1e9ba85495f2d6add6a9263b96a9eb0a6a","48492b6b93e53c68ffa8073d6918178c069db9a731071b532c12890222bcca0f","23c06c35aa0b40700c4be3106b23677d0a2a4d8f427f00716b497a361d40245c","c0bbcfd69fe06099e49c296bba2b105973ec1a794b69292fb65b4d81e9a2d672","f585b6bff2c52e5ed1c593b6222bc1e2805b7024b64f26d49271a5f19aa6dff7","c8e27588447f45548af86f4ac4ceb632dd451d78252b13c94d725b85ce34a24d","1508f2bc1fe7211250c3bc94beb9fff17e79cf0168bd0bd30264ee1e68d0086a","a72372b1c84fe7003a52eaf5654f6b88dabc645b405b6df7578cea1bae5d55e2","e32e7e8bfd7f8db32db243544cfc60cb96c0c7f050e964450ae3fc99bb21d344","preview-7e1cbbcc4f",1789899599512]