Sterrekunde

Wat beteken halfverlig?

Wat beteken halfverlig?


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Aristarchus het die relatiewe afstand van die son en die maan beraam deur die hoek tussen die son en die maan waar te neem (α in die diagram) wanneer die maan presies half verlig is. Hoek β moet 90 ° wees sodat die maan half verlig kan wees. Deur die hoek α waar te neem, kon hy dan die skaal van die driehoek en dus die relatiewe lengtes van die sye instel. (Groottes en afstande is nie volgens skaal nie.)

Beteken halfverlig presies 45 grade?


Half verlig beteken dat die Maan in 'n kwartfase is, hetsy die eerste kwartaal of die derde kwartaal.

Die oorspronklike vraag vra: "Beteken halfverlig presies 45 grade?". Ek neem aan dit is die vraag of die hoek $ alpha $ is 45 grade. Die antwoord is nee. Die hoek $ alpha $ word gevind uit trigonometrie te wees $ cos ( alpha) = EM / ES $ waar EM die afstand van die aarde na die maan is en ES die afstand van die aarde na die son. EM / ES is ongeveer 1/390 (= 238000 myl / 93 miljoen myl), so $ alpha $ is 89,85 grade.

Aristarchus probeer die omgekeerde berekening doen om die afstande te vind. As die hoek $ alpha $ akkuraat gemeet kan word, kan die relatiewe afstande EM / ES met dieselfde formule bereken word. Die probleem is die verskil tussen 89,85 grade (die son is 390 keer verder as die maan) en 90 grade (die son is oneindig verder as die maan) is 'n baie klein hoek en moeilik om presies te meet. As die son baie nader was, dan $ alpha $ 'n kleiner waarde sou wees, en die fout in die gemete hoek van $ alpha $ sou die waarde van EM / ES beperk tot 'n meer betekenisvolle omvang as "oneindigheid".


Gibbous

Die maan straal nie sy eie lig uit nie, maar skyn eerder deur sonlig te weerkaats. Afhangend van die relatiewe posisies van die Aarde, Son en Maan, lyk verskillende hoeveelhede van die maanoppervlak verlig. A Gibbous Maan kom enkele dae aan weerskante van 'n volmaan voor.

gibberig fase
Voer u soekterme in:
gibberig fase gĭb'əs [sleutel]: sien fase, in sterrekunde.

Gibbous
A gibberig maan is wanneer meer as die helfte van die maan sigbaar is. Baie boere plant en snoei in die fases van die maan. Die was gibberig maan word beskou as die beste tyd om gewasse te plant wat vrugte of groente bogrond produseer, soos boontjies, spanspekke, stampmielies, ertjies, soetrissies en tamaties.

Maan - as ons ongeveer driekwart van die maan se skyf kan sien
Halfmaan - (ook genoem kwartmaan) wanneer ons die helfte van die maanskyf kan sien (dit is 'n kwart van die hele maanoppervlak).

maan - 'n Maan wat tussen 'n volmaan en 'n halfmaan is.
Globulêre tros - digte trosse sterre gebind deur swaartekrag. Baie bolvormige trosse omring sterrestelsels, insluitend ons eie Melkwegstelsel.
Groot rooi kol - 'n Groot, rooierige storm in die atmosfeer van Jupiter wat soos 'n ovaal gevorm is.

fases van die maan, met die eerste wat die groeiende maan tussen die eerste kwartaal en die volmaan voorstel, en die tweede wanneer dit beskryf hoe die maan kleiner word namate dit van die volmaan af krimp tot die laaste kwartaal.

die fase van die maan tussen eerste kwartaal en laaste kwartaal, wanneer die maan meer as die helfte verlig lyk.
bolvormige tros 'n ongeveer sferiese gemeente van honderdduisende sterre. Die meeste bolvormige trosse bestaan ​​uit ou sterre en bestaan ​​in 'n sterrestelsel.

'n fase van die maan waarin meer as die helfte van die kant wat ons sien, verlig word.
Halfmaan .

: Word gebruik om 'n planeet of maan wat meer as 50 persent verlig is, te beskryf.
Asterisme: 'n opvallende of opvallende patroon van sterre binne 'n groter konstellasie.

'N Fase van die Maan, Mercurius, Venus, ens. Tussen half en vol.
GLOBULARRE KLUSTER.

: Wanneer die maan of ander liggaam meer as die helfte, maar nie volledig, verlig word nie (van gibbus, Latyn vir "bult").

fase vind net voor en na volmaan plaas
Globular Cluster - 'n dig gepakte, bolvormige groep van duisende tot miljoene ou sterre.

. Die fase van die Maan of 'n planeet wanneer dit tussen die helfte en ten volle verlig is.

) met die oostelike rand in die skadu. Die hoeveelheid sigbare verligte gebied neem toe van die een dag na die volgende, wat bedoel word met "was".

Die fase van die maan tussen eerste kwartaal en vol.
Wintersonstilstand
Die oomblik wanneer die Son sy grootste afstand suid van die hemelse ewenaar bereik, op ongeveer 22 Desember.

tussen die eerste en die laaste kwartaal.
& # 9733 Globular star cluster 'n Stampvol, bolvormige groepering van tot 'n miljoen ouer sterre.

Maan verskyn hoër in die middel van die winter - 4 Februarie in die Noordelike Halfrond / 7 Augustus in die Suidelike Halfrond, as in die middel van die somer - 7 Augustus in die Noordelike Halfrond / 4 Februarie in die Suidelike Halfrond.

fases is fases tussen kwart- en volle fases. Grootste verlenging verwys na die grootste skeiding van die planeet van die son in ons lug, na die Ooste of na die Weste.

Maan beswyk Antares in Japan en Hawaii
13 April
Neptunus is 1,2 noordwes van Mars.

Venus, op 5 Desember in die nabye infrarooi deur Damian Peach met behulp van die 1-meter Chilescope. Hier is flou wolkbandjies sigbaar, maar moenie verwag dat dit visueel in u omvang sal verskyn nie. Suid is op.

beteken 'begrens deur konvekse kurwes' en beskryf die voorkoms van 'n liggaam as meer as die helfte, maar minder as al sy verligte sy sigbaar is.

Maan gloei bo die Internasionale Ruimtestasie in hierdie uitsig vanaf die ruimtetuig Atlantis. 'N Bemanningslid het die foto geskiet toe Atlantis die stasie op 19 Julie verlaat het. [NASA]
- Vorige
Volgende -
.

: meer as die helfte van die maan lyk verlig, met al hoe minder verlig op opeenvolgende dae.

: net na Volmaan
Afnemende sekelmaan: net voor Nuwemaan
Moonrise, Maansondergang.
U sien nie alle maanfases te alle tye nie.

fase verminder, sal die maan die 270 posisie bereik, regs na regs. Dit is 'derde' of 'laaste kwartaal'. Dit word gevolg deur 'n dunner sekelmaan en 'n terugkeer na nuwe maan. Van vol tot nuut het die Maan "afgeneem" en gelei deur die Son. Die fasesiklus duur 29,53 dae.

Maan soos vanaf die aarde waargeneem
Die Maan is die grootste natuurlike satelliet van die Aarde en die naaste grootste hemelse voorwerp. Die waarneming van die maan kan bereik word deur verskillende instrumente te gebruik wat wissel van die blote oog tot groot teleskope.

Maan oor die Sydney Tower (hoogste gebou in Sydney).
Hieronder: foto's van en binne die Queen Victoria-gebou in Sydney op ons laaste volle dag in Australië. "Die mooiste winkelsentrum ter wêreld." .

Die fase neem steeds toe, met die maan wat later en later op die dag styg en na plaaslike middernag sigbaar is. Full The Moon stem weer ooreen met die son en die aarde, maar hierdie keer is ons planeet tussen ons ster en ons satelliet. Die volmaan kom met sonsondergang op en sak onder sonop.

'N Paar dae later word die maan 'n

Maan is net 'n maan meer as 'n kwart, maar nie vol nie.

Tussen volle en kwartmaan word gesê dat die fase is

. As minder as die helfte van die maan deur sonlig verlig word, is die fase halfmaan. As die maan in die rigting van die son is en die kant na die aarde sy donker of skaduwee helfte is, word gesê dat die maan nuut is.

maan - die fases tussen halfmaan en volmaan.
Groot rooi kol - Die groot rooi storm wat soos 'n tornado op Jupiter rondloop.
Hooglande - Plekke op die maan wat bokant die vlak is wat deur vloeiende lawa glad gemaak is.
Ligjaar - die afstand wat die lig in een jaar aflê.

'N Byvoeglike naamwoord wat op die Maan of Venus toegepas word wanneer dit meer as halfvol is (maar nie vol is nie). [H76]
Giga-.

Begrens deur konvekse kurwes. Die term word veral gebruik met verwysing na die maan as dit tussen die eerste kwartaal en die volle of tussen die volle en die laaste kwartaal is, of na ander hemelliggame wanneer hulle 'n soortgelyke voorkoms het. Sien fases van die maan. Gibbs vrye energie = Gibbs funksie.

Tussen die eerste kwartaal en die laaste kwartaal, as meer as die helfte van die kant van die maan in sonlig in die gesig staar, word gesê dat die maan '

. "Van die laaste kwartaal tot die eerste kwartaal, as meer as die helfte van die kant van die maan wat in die gesig staar in skaduwee is, word gesê dat die maan 'n" sekelmaan is.

Aarde met SW Noord-Amerika sigbaar 127k gif
Aarde deur Meteosat 4 satelliet (IR-filter) 688k jpg
Weer-beeld van Noord-Amerika (B&W) 396k gif
gedeelte van die aarde van Clementine 82k gif
Ruimtestasie Mir over the Earth 111k gif
Galileo-beeld van Antarktika geneem met die eerste pas van 140k gif.

moon sal sekerlik hierdie jaar se produksie belemmer. Dit lyk asof hierdie flou meteore uitstraal van naby die ster Skat of Delta in die sterrebeeld Waterman die waterdraer. Die maksimum uurlikse tarief kan 15 tot 20 meteore in 'n donker lug bereik.

Hier is die volgorde van die fases - nuut (as u die maan nie kan sien nie - dis alles donker), wassingelmaan, eerste kwartaal (as u die regte helfte van die verligting sien sien), was

, Derde kwartaal - ook die laaste kwartaal genoem (as u die linkerkant sien verlig),.

Die geringde planeet sal op 28 Junie, kort na sonsondergang, naby die waks sigbaar wees

Maan. Die maan sal 88% verlig wees, met 'n skeiding van Saturnus van ongeveer 10 wanneer albei die volgende oggend omstreeks 01:30 GMT plaasvind.

deel ("ou maan").
Maan, Maanfase, Nuwe Maan.

Gedurende die volgende week gaan die maan aan en word dit deur die

fase (paneel 3) totdat, 2 weke na nuwemaan, die volmaan (paneel 4) sigbaar is.

Die "fases" van die maan is: nuwe maan, sekelmaan, eerste kwartaal, was

, Laaste kwartaal, Crescent, New Moon ..
'N Maansverduistering vind plaas wanneer die aarde tussen die son en die maan is.

Pamela: Reg, so as die Maan om die posisie van ware volmaan wentel, neem dit ons 'n rukkie om vas te trek dat dit nou die

Toe die Italiaanse fisikus Galileo Galilei die planeet die eerste keer in die vroeë 17de eeu waargeneem het, het hy gevind dat dit fases soos die maan vertoon, wat wissel van halfmaan tot

is die stadium tussen die volmaan en die derde kwartaal. Die derde kwartfase is wanneer die helfte van die verligte maan vanaf die aarde sigbaar is. Die hoeveelheid as die verligte skyf afneem, nog in 'n stadium wat bekend staan ​​as die kwynende halfmaan totdat geen van die skyf verlig word nie.

Gedurende die week na die eerste kwartaalfase sien ons meer en meer van die Maan se verligte halfrond (posisie D), 'n fase wat waksing (of groei) genoem word.

(van die Latynse gibbus, wat boggel beteken).

Ongelukkig vir waarnemers wat hierdie jaar 'n donker lug wil hê, die Waning

maan sal 'n moeilike kykervaring skep as gevolg van die helder maanlig wat die helderste Lyrids wegspoel.

Die eerste verskietende sterre van 2015 behoort aan die Quadrantids, 'n stort wat in die nag van 3/4 Januarie 'n hoogtepunt bereik. Ondanks die inmenging van 'n

Maan, verwag 'n paar helder, soms blou en geelkleurige meteore wat gloeiende paadjies kan verlaat.
Nuus
Dawn begin finale benadering tot die dwergplaneet Ceres.

Die maandelikse siklus van die maan (ons sal nie die woord hier met hoofletters gebruik nie) moes vroeë mense verduister het - "was & # 34 van dun sekel (" nuwe maan ") tot halfmaan, dan na 'n"

"maan en 'n volle een, en daarna weer" afneem "na 'n sekelmaan. Die siklus, wat ongeveer 29 duur.

Dit is onafhanklik van enige fase wat mag voorkom as Mars 'n

fase, dan lyk dit asof die CM nie in die middel is nie. Die CM is die areografiese lengte in graden, gesien vanaf die aarde op 'n gegewe Universele Tyd (U.T.). Dit kan bereken word deur 0,24 / min., Of 14,6 / uur, by te voeg tot die daaglikse CM-waarde vir 0h U.T.

As die maan kleiner as 'n kwart verskyn, noem ons dit 'n sekelmaan. As die maan groter as 'n kwart verskyn, noem ons dit

. As die maan groter word (fases nuut tot vol) word dit aan die was. meer
Die Aarde se Maan.

"Waks" beteken groei en "kwyn" beteken krimp. Een gepaste definisie van "

Die stort bereik gewoonlik 'n hoogtepunt van 21 en 22 April, hoewel sommige meteore sigbaar is van 16 tot 25 April

maan kan vanjaar 'n probleem wees, en baie van die flouer meteore in sy glans wegsteek. Dit sal voor sonsopkoms sak en 'n kort venster van donker lug bied.

Volgens die geosentriese model van die heelal moes dit onmoontlik gewees het, aangesien Venus se baan dit nader aan die aarde as die son geplaas het - waar dit slegs halfmaan en nuwe fases kon vertoon. Die waarnemings van Galileo dat dit egter deur die sekel gaan,

As dit nou sou gaan, sou dit die land verlig met die stralende krag van a

Maan. Wat 'n wonder sou dit wees as ons uit die tyd kon stap en kyk hoe die toekoms van Orion versnel, terwyl die een na die ander van hierdie massiewe sterre opduik, wat verwoesting en nuwe sterre-lewe agterlaat.

Die maan verlig te veel van die lug as dit is

, kwart of vol, en voorkom dat ons flouer sterrevoorwerpe sien.
As u gemaklik binne wil bly, kan u die webwerf van die Kanadese Ruimteagentskap besoek om die Noorderlig aanlyn te bewonder.


Halflewe

Halflewe:
A halflewe is die tydsinterval wat nodig is vir die helfte van die atoomkerne van 'n radioaktiewe monster om te verval (spontaan verander in ander kernspesies deur deeltjies en energie uit te gee), of, gelykstaande,.

Protosteller halflewe: nuwe metodologie en beramings
L. E. Kristensen1 en M. M. Dunham2,3.

Halflewe: Die hoeveelheid tyd wat nodig is om die helfte van die massa van 'n radioaktiewe isotoop te verval.
Heliosentriese afstand: Die afstand vanaf die son.
Helium: 'n Element met atoomgetal 2-simbool: He. Dit is die tweede mees algemene element in die son en die buitenste planete, maar skaars op die rotsagtige planete.

Die tyd wat nodig is om die helfte van die atome in 'n radioaktiewe monster te verval.
Halo.

:
'N Maatstaf van die snelheid van radioaktiewe verval van onstabiele, radioaktiewe atome. Dit is die tyd wat die helfte van die kerne in 'n radioaktiewe monster neem om te disintegreer of te verval. Halfwaardetydperke kan wissel van 'n sekonde tot miljarde jare, afhangende van die stof.
Hawking-straling:.

is die tyd wat die helfte van die atome van die radionuklied verval. Vir die geval van eenverval kernreaksies:.

van 'n radio-isotoop is die tyd wat dit neem voordat die helfte van die radio-isotoop verval.

van 'n hoeveelheid waarvan die waarde mettertyd afneem, is die interval wat benodig word om die hoeveelheid te verval tot die helfte van sy aanvanklike waarde. Die konsep het ontstaan ​​in die beskrywing van hoe lank dit atome neem om radioaktiewe verval te ondergaan, maar is ook van toepassing in 'n wye verskeidenheid ander situasies.
is byna 300 dae.

(simbool ti) Tyd geneem tydens 'n eksponensiële vervalproses, soos radioaktiwiteit, voordat die helfte van die beskikbare reaksies plaasgevind het. Halfleeftye kan wissel van klein fraksies van 'n sekonde tot miljarde jare.

7.3 Datering van planetêre oppervlaktes
Halley3.2 Newton's Great Synthesis, 13.3 Die "Langharige" komete, 13.3 Die "Langharige" komete
halo25.1 Die argitektuur van die sterrestelsel, 25.1 die argitektuur van die sterrestelsel.

In enige verskynsel word die tyd waartydens die hoofveranderlike met die helfte van die oorspronklike waarde verander, losweg gebruik om die kenmerkende tydskaal van 'n verskynsel aan te dui. In radioaktiewe verval, die tyd vir die helfte van die atome in 'n stelsel om te disintegreer.
Halley se komeet.

van die -stabiele kern, en f staan ​​vir 'n integraal wat afhang van die -verval-energie en die tipe oorgang. [H76]
Faber-Jackson verhouding.

van 2,62 miljoen jaar, relatief kort in vergelyking met die ouderdom van ons sonnestelsel, sou enige radioaktiewe yster-60 wat ontstaan ​​het vanaf die geboorte van die sonnestelsel, lankal in stabiele elemente verval het en dus nie meer op die aarde gevind word nie. ' .

die tyd wat nodig is vir die helfte van 'n radioaktiewe materiaal om tot 'n meer stabiele materiaal te verval (dit is NIE die helfte van die ouderdom van die rots nie!). heliosentries (heelal): model van die heelal met die son in die middel en alle ander voorwerpe wat daar rondom beweeg.

) waarop die verbrokkeling plaasvind, dan volg die ouderdom van die rots direk.

Ons gebruik die radioaktiewe materiaal

is die tyd wat dit neem voordat 1/2 van die radioaktiewe materiaal verval, dikwels in 'n nie-radioaktiewe vorm. Jodium 129 verval byvoorbeeld in Xenon 129 met 'n halfleeftyd van 17 miljoen jaar.

Pamela: Presies, so hier gebruik ons ​​nog steeds uraan, in hierdie geval kyk ons ​​na uraan-238, wat 'n

Die ander is dat tritium self radioaktief is, met 'n

van 12,32 jaar. Behalwe dat dit 'n radiologiese gevaar inhou in geval van lekkasie, beteken dit dat tritium nie vir lang tydperke gestoor kan word nie, aangesien dit uiteindelik sal verval.

Vir elke tydperk gelyk aan a

, bepaal 'n muntstuk of 'n gegewe atoom verval (sirkel word blou), of in die onstabiele toestand bly (sirkel bly geel). In die onderstaande diagram het ons die toestand van 64 atome gemeet, meer as tien halfleeftye.

Dit is radioaktief en verval met 'n

van 2,6 miljoen jaar. Omdat ons planeet 4,5 miljard jaar oud is, mag geen oorspronklike yster-60 op die aarde gelaat word nie, tensy dit uit die ruimte kom.

Maar Rb-87 verval in Sr-87 met 'n

van 47 miljard jaar. En daar is nog 'n isotoop van strontium, Sr-86, wat deur geen rubidiumverval geproduseer word nie. Die isotoop Sr-87 word radiogenies genoem, omdat dit deur radioaktiewe verval geproduseer kan word, terwyl Sr-86 nie-radiogenies is.

"Die verval van hierdie nikkel het 'n

van ongeveer 20 dae en sy produkte is wat die helder supernova wat ons op 'n afstand sien, dryf. Wat ook belangrik is, is hoe vinnig hierdie uitgestote materiaal beweeg, wat ook die helderheid en afname van die supernova beïnvloed.

van 2,6 miljoen jaar, wat beteken dat dit na 15 miljoen jaar heeltemal verval, dus enige monsters wat hier op Aarde gevind is, moes van elders neergelê word, aangesien daar geen manier was dat enige yster-60 kon oorleef van die vorming van die planeet 4,6 miljard jaar gelede nie. . En deposito's is gevind.

van 2,19 mikrosekondes. ('N Mikrosekonde is 'n miljoenste sekonde.) Daar is ook ontdek dat 'n pion 'n boodskapperdeeltjie is. Soos u binnekort sal sien, hang die vier kragte wat ons vroeër bespreek het, alles af van die sogenaamde boodskapperdeeltjies wat dra? die krag tussen interaksies.

Deeltjiebestraling
Radioaktief, Radioaktiewe verval,

Wat is 'n molekule?
Hulpmiddels vir wiskunde en wetenskap.

87.7 jaar, wat saam met die agteruitgang van die termokoppels wat die hitte gelei, beteken dat die kragopwekkers teen 2025 nie krag aan al die instrumente aan boord sal kan lewer nie.

Protonbederf: Die protonbederf is 'n hipotetiese verval waarin 'n proton in ligter deeltjies soos positron en muon verval. Maar daar is geen eksperimentele bewyse daarvan nie. Die teoretiese

'N Radioaktiewe isotoop van koolstof wat in die boonste atmosfeer geproduseer word en in lewende plante en diere voorkom, wat gebruik kan word in koolstof-14-datering omdat dit tot stikstof (14N) en 'n beta-straal met 'n

swak krag Die kernmag betrokke by radioaktiewe verval. Die swak krag word gekenmerk deur die stadige tempo van sekere kernreaksies, soos die verval van die neutron, wat met a voorkom

Na hierdie tyd was die heelal nie meer warm of dig genoeg om protone of neutrone te skep nie, dus is die verhouding gevries. Gratis neutrone ondergaan egter beta-verval, wat neutrone in protone omskakel met a

Hierdie radioaktiewe, onstabiele vorm van berillium ontbind in 1,6 miljoen jaar, 'n tydperk wat dit genoem word

. Dit beteken dat enige berillium-10 wat in die maangrond voorkom, daar lank na die skepping van die maan neergesit moes word, en baie daarvan is afkomstig van die sonwinde, het Caffee gesê.

Radioaktiewe datering - Die proses waardeur monsters met die radioaktiewe dateer kan word

verskillende elemente bevat.
Radiokoolstofdatering - 'n tegniek wat die verhouding isotope in 'n monster gebruik om die ouderdom daarvan te bepaal.


Sterrekunde

Die ware bedreiging wat hierdie mega-konstellasies vir die sterrekundegemeenskap inhou, begin nou eers begryp word.

Die nuwe LEO-satelliete beïnvloed nie elke sterrekundige program op dieselfde manier nie.

Daar is geen tegniese of regulatoriese struikelblok om 'n konstellasie van ultra-helder satelliete te loods wat baie of die meeste sterrekundige programme onmoontlik kan maak nie.

Die span het die instrument gebruik om 50 nuwe potensiële planete te bevestig, 'n eerste vir kunsmatige intelligensie soos toegepas op sterrekunde.

Die tegnologie het ons werk makliker en doeltreffender gemaak, wat 'n fundamentele verskuiwing in die manier waarop sterrekunde gedoen is, aangedui het.

Die outeurs het gesorg dat die moontlikheid van ander polarisasiebronne, wat altyd in die sterrekunde kommerwekkend is, uit die weg geruim word.

Moslems het baie ontdekkings in wiskunde, chemie, fisika, medisyne, sterrekunde en sielkunde gedoen.

Byna alles wat ons tot dusver van donker materie weet, kom van die sterrekunde.

Een van die groot uitdagings in die sterrekunde is om vas te stel wanneer die eerste sterrestelsels gevorm het, en hoe dit daar uitsien.

Kosmiese straalwaarnemings is uitdagender as baie ander vorme van sterrekunde.

'N Geleerde professor het verklaar dat niemand wat astronomie ken nie,' Maan 'met' Omnibus 'kan korreleer nie.

In die eerste plek kom die sterrekunde, insluitend die verskynsels wat in die hemel vertoon word, buite die perke van die aarde se atmosfeer.

Die wetenskap het begin met sterrekunde, en die eerste instrumente wat mense vir die doel van ondersoek uitgedink het, was astronomies.

Soos in die hoofstuk oor sterrekunde gesê, kom die driehoekige vorm in die landmassas van die planeet Mars voor.

Hy het tot laat in die nag gepraat oor sterrekunde en die nuutste ontdekkings daarvan.


Fases van die maan

In hierdie episode van Crash Course Astronomy lei Phil u deur die oorsaak en name van die maanfases.

PHIL PLAIT: Behalwe die son, is die maan die duidelikste voorwerp in die lug. Helder, silwerig, met prikkelende kenmerke op sy gesig, was dit die teiken van verbeelding, poësie, wetenskap en selfs af en toe 'n vuurpyl.

PHIL: As u selfs die mees vlugtige aandag daaraan skenk, sal u sien dat dit elke dag verander. Soms is dit bedags, soms snags, en die vorm verander altyd. Wat veroorsaak hierdie gedrag?

Die maan is basies 'n reuse bal rots wat 3 500 kilometer dwars in die ruimte hang. Die oppervlak daarvan is eintlik redelik donker, met ongeveer dieselfde weerkaatsing as 'n bord of asfalt. Dit lyk egter vir ons helder, want dit sit in volle sonlig. Die son verlig dit, en dit weerkaats die lig na ons hier op aarde. En omdat dit 'n bol is en om die aarde wentel, verander die manier waarop ons dit deur die son sien verlig. Dit is wat sy fases veroorsaak: meetkunde.

Die belangrikste ding om dit alles te onthou, is: omdat die maan 'n bal is en in die ruimte, word die helfte daarvan altyd deur die son verlig. Dit geld ook vir die aarde en elke sferiese voorwerp in die ruimte. Half na die son, half gesigte weg. Ons noem die deel wat na die son kyk, die daglig, of die helder kant en die helfte na die nag of die donker kant.

Die fase van die maan verwys na die vorm wat die maan vir ons lyk, hoeveel daarvan ons vanaf die aarde sien verlig. Die sleutel tot dit alles is hierdie lyn, wat die verligte dagkant van die onverligte nagkant verdeel. Ons noem die lyn die terminator. As u die maan in die gesig staar met die son agter u, sien u die helfte van die maan wat volledig deur sonlig verlig word en dit vol lyk. As u na die kant toe gaan, sien u die helfte van die verligte kant en die helfte van die donker kant, en ons sê die maan is halfvol. As die son aan die ander kant van die maan is, kyk u na die helfte wat nie verlig is nie, en dit lyk donker.

Nou, let op, ek het niks behalwe ons standpunt hier beweeg nie. Die maan is dus altyd half verlig en half donker. Onthou dat. Die fase van die maan wat ons sien hang af van watter rigting die sonlig dit tref, en die hoek wat ons vanaf die aarde sien.

Die maan wentel ongeveer een keer per maand om die aarde. In werklikheid is dit waar die woord 'maand' vandaan kom: 'maand' en 'maan' is kognate, woorde wat soortgelyke etimologiese geskiedenis het. En in die meeste tale, insluitend Engels, is die twee woorde baie dieselfde. Die tydsduur wat ons die maand noem, is afgelei van die tydsduur van die maan om deur al sy fases te gaan: 29 en 'n half dae.

Om die fases te beskryf, begin ons dus aan die begin: nuwemaan. Nuwemaan gebeur as die son, maan en die aarde min of meer in 'n lyn is. Die baan van die maan word eintlik 'n bietjie na die aarde gekantel, so die nuwe maan gebeur soms as die maan "onder" die son is, of "daarbo". Maar op 'n stadium in sy baan, op 'n stadium in die maand, lyk dit asof dit so na aan die son is as wat dit kan. Hoe lyk dit vanaf die aarde? Die maan is tussen die aarde en die son, dus vanuit ons perspektief sien ons net die donker helfte, die onbeligte helfte, van die maan. Die ander kant, die ander kant, van die maan is verlig, maar ons kan dit nie sien nie. Dit is dus sinvol om dit die begin van die maan se siklus te noem, vandaar die term nuwemaan.

Dink nou vir 'n oomblik hieroor. Omdat die maan naby die son in die lug is, beweeg dit saam met die son oor die lug. Dit is bedags daar bo! U kan dit slegs sien vanaf die deel van die aarde wat aangesteek is, dit is dag. Dit is 'n baie algemene misvatting dat die maan net snags op is. Maar dit is letterlik net so gereeld bedags. Met nuwemaan bly die maan naby die son, sodat dit met sonsopkoms opkom en met sonsondergang sak. Dit maak dit uiters moeilik om te sien. Dit sit immers langs die helderste voorwerp in die lug, en net 'n klein bietjie daarvan word vanuit ons perspektief verlig. Maar nie vir lank nie. Omdat die maan om die aarde wentel, beweeg dit na 'n paar dae 'n bietjie na die ooste. Nou sien ons dit in 'n effense hoek, en ons kan 'n bietjie van die verligte helfte van die maan aan sy kant na die son sien.

Die terminator, die dag / naglyn, lyk geboë rondom die maan, dus wat ons sien, is 'n dun, verligte sekelmaan. Op hierdie punt is die sekel nog baie dun, met die horings van die sekel wat van die son af wys. Let daarop dat die maan nog redelik naby die son in die lug is, net 'n bietjie oos, en miskien 'n uur of twee na sonsopkoms opkom. Maar dit beteken dat dit die hele dag op is en dan ondergaan nadat die son dit gedoen het. Dit is die beste tyd om die sekelmaan te sien, wanneer die son reeds onder is en die lug begin donker word. Die maan sal laag wees oor die westelike horison en dit sal binnekort sak nadat die son dit gedoen het.

Kom ons wag 'n paar dae. Oké. Nou het die maan 'n bietjie meer in sy wentelbaan om die aarde beweeg en is dit verder van die son in die lug. Ons sien 'n bietjie meer van die verligte deel, en die sekel is wyer. Aangesien dit al hoe dikker word, sê ons dit is 'n "wasende halfmaan" wat maanwas beteken om te groei of groter te word. Dit is ook nou ver van die son af, dus is dit makliker om dit raak te sien, selfs gedurende die dag voor sononder.

Sewe of so dae na nuwemaan bereik ons ​​ons eerste mylpaal: die maan is nou 'n kwart van sy pad om sy baan. Dit is 90 grade weg van die son in die lug, wat beteken dat ons reguit na die terminator, die maan se dag / naglyn, kyk. Dit sny reg in die middel van die sigbare gesig van die maan af, sodat dit half verlig is, met die sonkant van die maan sigbaar en die ander kant donker.

Verwarrend, hierdie fase word behoorlik as 'eerste kwart' benoem omdat die maan 'n kwart van die pad deur sy siklus is. 'N Kwart van sy pad deur die aarde, al lyk dit halfvol. Dit is dus nie regtig die halfvolmaan nie — sterrekundiges verkies 'eerste kwartaal', dus as u alle sterrekunde wil laat klink, moet u dit so noem.

Maar die tyd stap aan. Die maan gaan voort met sy swaartekragdans met die aarde en swaai om sy baan. Nou, meer as halfvol, sê ons die vorm is "gibbous", wat geswel of konveks beteken. Aangesien dit wyer word, is dit eintlik die wasende maag van die maan. Dit styg laatmiddag op en is die grootste deel van die nag.

Ons volgende groot stap kom twee weke na nuwemaan, wanneer dit halfpad deur sy baan beweeg word. Dit is nou oorkant die son in die lug, 180 grade rondom. Die aarde is tussen die maan en die son, dus kyk ons ​​na die helmaan van die maan. Dit is die volmaan. Aangesien dit oorkant die son staan, kom dit teen sonsondergang op en sak met sonsopkoms onder, dit lê die hele nag op en skyn op die aarde. Maar wag weer 'n paar dae en dinge verander. As die maan vol is, is dit 180 grade om die lug van die son af. As dit dan in 'n sirkel om die aarde bly beweeg, begin die afstand tussen hom en die son nou afneem, al gaan dit in dieselfde rigting voort. Soos voorheen styg dit en sak later, maar nou styg dit na sononder en sak na sonop. As u soggens vroeg opstaan ​​terwyl die son net in die ooste opkom, sien u die amper-maar-nie-volmaan wat in die weste sak.

Nie net dit nie, maar ons gaan weer deur al die fases gaan, maar in omgekeerde volgorde.

'N Paar dae na volmaan krimp die verligte kant. Dit is in die kwynende of krimpende, gibberige fase. Dan, drie weke of so na die nuwe maan en 'n week na die volle, is die maan weer half verlig, en die terminator verdeel die maan se gesig in twee ewe helftes. Dit is die "derde kwart" maan, want die maan is 'n driekwart pad deur sy siklus. Dit lyk baie soos die eerste kwartaal, maar die kant wat aangesteek is, is nou donker, en andersom. Dit is 270 grade om die lug van die son af. Dit styg om middernag en sit om 12:00.

'N Paar dae later en die maan is weer 'n halfmaan en word dunner. Dit is nou 'n "kwynende sekel". Dit styg net 'n paar uur voor sonsopkoms en sak 'n paar uur voor sononder.

Dan is ons uiteindelik weer waar ons begin het. Een maand na nuwemaan het die maan 360 grade om die lug gereis en is dit weer so naby aan die son as wat dit kan kom. Dit is nuwemaan en die siklus begin weer, soos dit vir ewig gedoen het.

'N Interessante ding gebeur as u u perspektief van die aarde na die maan skuif. Die fases van die maan wat ons vanaf die aarde sien, hang af van die hoek van die maan en die son in die lug. Maar op die maan is die hoeke presies 180 grade omgekeer. Wanneer die nuwe maan tussen die aarde en die son is, is die aarde oorkant die son, gesien vanaf die maan. Dit is vol aarde! Al die ander fases is ook teenoorgestelde, dus as ons 'n volmaan sien, sal 'n maanbewoner 'n nuwe aarde sien, ensovoorts.

Het u al na die dun sekelmaan gekyk en die spookagtige gesig van die res van die onverligte kant gesien? Dit is omdat dit nie regtig onverlig is nie. Die byna volle aarde weerkaats sonlig op die maan en verlig die andersins donker deel. Die aarde is groter en weerkaatsender as die maan, dus is dit eintlik 50 keer helderder as 'n volmaan! Hierdie gloed word Earthshine genoem, 'n term wat ek nogal van hou. Nog digterlik is dit 'die ou maan in die arms van die nuwe maan' genoem, met verwysing na die onverligte deel omring deur die halfmaan se horings. Dit is heerlik, is dit nie?

Die maan is een van die mooiste en verblydendste voorwerpe in die lug om waar te neem. Dit is elke dag anders! Tog is dit ook dieselfde, want ons sien min of meer dieselfde helfte daarvan, dieselfde gesig, die hele tyd. Dit is groot en helder, en die kenmerke op die oppervlak is sigbaar aan die oog (en selfs beter met 'n verkyker of 'n klein teleskoop). Namate die fases onverbiddelik verander, verander die sonlighoek wat die oppervlak tref, nuwe dinge in ons siening. Die bewegings word vertroostend, selfs bekend. Dit is 'n herinnering dat die heelal aanvanklik vreemd en ingewikkeld mag lyk en verbiedend is, maar met verloop van tyd word dit u omgewing as u buite gaan en dit ervaar.

Today you learned why the moon has phases: it's a sphere, and it orbits the Earth, so the angle at which we see its lit side changes. It goes from new, to waxing crescent, to half full, waxing gibbous, full, waning gibbous, half full, waning crescent, and then the cycle starts all over again. This also affects when it rises and sets, and what we see on the surface.


What is the impression under a Bortle 1 sky?

I have never seen a Bortle 1 sky in my life. I have seen several Bortle 3 skies, and Bortle 2 skies a few times (sadly, before I was into astronomy).

What is the impression under a perfect, pristine sky? What does the Milky Way look like? What does the zodiacal light look like? What do stars look like? How much color do you see in the sky? Can you see your surroundings? I have seen reports about people getting lost in the constellations, and not being able to discern even well-known asterism such as the Big Dipper. Note: we talk great skies here, with little atmospheric extinction, perfect seeing, little humidity etc (of course, no moonlight! And preferably, no Venus up. ). I know a a few of you have been fortunate enough to experience such skies. Please share your experiences!

#2 Cali

What does the Milky Way look like?

It looks like a carpet of stars. There are so many stars that it is hard to make out familiar constellations.

#3 sg6

You can see the dipper, it sits outside the band of the Milky Way. It is one of the few that remains "easy".

Cassiopeia, Perseus, Cygnus all get mixed in and are difficult. If I recall half of Lyra is lost but Vega just sits out of the main band.

Cannot see the ground and stumble around cursing.

Useful to learn how to use the Dipper to get to Auriga, Bootes, Leo and Ursa Minor before getting to one.

Biggest problem is cricking your neck, and keeping mouth closed.

As it is dark people don't see you drooling.

Hopefully breathing kicks in automatically after 30-60 seconds.

Just when you start breathing slowly bring the head and neck back to their usual operating position.

Neck is the biggest problem.

#4 InkDark

What does the Milky Way look like?

It looks like a carpet of stars. There are so many stars that it is hard to make out familiar constellations.

(I kid you not.)

- Cal

So true. and M31 just sits there!

. and you can see your shadow on the ground.

#5 Gary Z

I highly recommend that you have a chair to sit down in before you look up. the view is breathtaking for the first time.

#6 Bob4BVM

There are a few places where I go in certain mountain areas of far eastern Oregon to get to Bortle 1.

One is a site at over 9500 feet on a mountain surrounded by desert with the nearest town streetlights over 100 miles away.

I will never forget the first time we were camped there. The stars were so bright & clear that the experience was like you were standing IN the dome of the heavens, not below it, the 3-D feeling was unmistakable. Yes the stars colors were very distinct, adding to the 3-D effect.

I did however find it initially disturbing that there was a huge band of smoky haze that ran from horizon to horizon roughly following the plane of the Milky Way. I was at first offended that smoke would be messing up the great view of our galaxy.

It took a while for it to sink in, but I finally realized. what looked like 'smoke' was the huge outer halo of the galaxy, extending far above and below the bright band of the galaxy, easily tripling its overall width. I did not have a telescope along on that first camping trip to that mountain. None was necessary, it would have diluted the immersive experience of just laying on my back and taking in that enormous river of stars which to its outer limits covered fully half of the visible sky from horizon to horizon.

#7 Migwan

If you have transparency to go with such dark skies, the stars are amazing. Jupiter shows a bit of color and should the moon come up, it'll hurt. So whatever you do, don't stare at it.

#8 vsteblina

There is Bortle 1. and there is Bortle 1 under great observing conditions.

It was August, 1996 and we were camped on the Beaverhead National Forest in Montana. It was around the time of Perseids shower.

I got out my LaFuma recliner, crawled into a sleeping bag and set the alarm for after midnight.

When I awoke, perfectly dark adapted, I might add. I looked towards the northeast and noticed a dim disk that was rather large.

Didn't need a flashlight. It was that bright I could walk over to the star atlas I left on the picnic table.

Never, ever came close to seeing M33 as a disk after that observation. I even did a internet search, astronomical history books, and cultural history for comments about a "dark moon". Nada.

I think the important part was being asleep for several hours and waking up with any artificial light.

I have a observing site in a somewhat dark site that is off-grid. One evening, we were observing while the kids were playing in the house a couple hundred feet away. They put a candle in the window so they could play.

I had to ask the kids to move the candle out of the window and block its light. It was too bright and definitely affected our viewing.

If your at a Bortle 1 site. sleep outside and view the sky before turning on the RED light.

#9 Tannhäuser Gate

Cannot see the ground and stumble around cursing.

#10 Rocklobster

So true. and M31 just sits there!


. and you can see your shadow on the ground.

My mind boggles at the thought of the MW being bright enough to cast shadows. Ongelooflik.

I lived in Saudi Arabia till the age of 13 and and spent many nights camping in the desert. I so wish I had paid attention to what the night sky looked like there, but it was sadly before I was heavily into astronomy.

Sent from my N10 using Tapatalk

#11 esd726

#12 Allan Wade

What is impressive is how many objects are visible naked eye. I should do a Messier tour sometime and see how many I can bag. I know that’s something many people have done.

I went around the globular clusters to see how many naked eye ones I could see, and managed 16 over an observing year.

The biggest impression a Bortle 1 sky makes on me is that let down feeling the next time I observe from my bright suburban home.

#13 LDW47

I have never seen a Bortle 1 sky in my life. I have seen several Bortle 3 skies, and Bortle 2 skies a few times (sadly, before I was into astronomy).

What is the impression under a perfect, pristine sky? What does the Milky Way look like? What does the zodiacal light look like? What do stars look like? How much color do you see in the sky? Can you see your surroundings? I have seen reports about people getting lost in the constellations, and not being able to discern even well-known asterism such as the Big Dipper. Note: we talk great skies here, with little atmospheric extinction, perfect seeing, little humidity etc (of course, no moonlight! And preferably, no Venus up. ). I know a a few of you have been fortunate enough to experience such skies. Please share your experiences!

At my remote camp on the Ottawa River up here in northern Canada under Bortle 1, SQM-L 22.05 skies, on the great nites, it is everything you mention except for the color ! When you look at the tops of the 200+ year old pine they shine from the glow of the Milky Way as if there was a / the moon shining ! And to think I and my wife have had 50 years of that, we are truly blessed ! Clear Skies !

#14 Ladyhawke


I have never seen a Bortle 1 sky in my life. I have seen several Bortle 3 skies, and Bortle 2 skies a few times (sadly, before I was into astronomy).

What is the impression under a perfect, pristine sky? What does the Milky Way look like? What does the zodiacal light look like? What do stars look like? How much color do you see in the sky? Can you see your surroundings? I have seen reports about people getting lost in the constellations, and not being able to discern even well-known asterism such as the Big Dipper. Note: we talk great skies here, with little atmospheric extinction, perfect seeing, little humidity etc (of course, no moonlight! And preferably, no Venus up. ). I know a a few of you have been fortunate enough to experience such skies. Please share your experiences!

It looks like this. The most beautiful thing I have ever seen in my life. Cerro Tololo observatory - Chile

#15 LDW47

The most impressive is the Big Dipper hanging over the high pine covered hills to the north with M81-82 waiting to be seen ! The first is at early twilight ! PS: When I post these pics in a reduced size I lose the mass of stars under my Bortle 1 skies, its a shame !

Edited by LDW47, 01 February 2020 - 11:15 AM.

#16 Traveler

At an altitude of 5000m, -15 degrees Celsius and Bortle 1 skies in Nepal, M33 for instance is a big and bright object. When i first saw this, i can not believe it. After this ( i was several times at that area with my wife but without any telescopes) one gets very spoilled. if one can stand the hike, the food, the cold, the bad smells, no shower, the lack of oxygene etc. etc. to get to those places.

#17 MikeBOKC

Looks like this: Okie Tex star party.

Aangehegte kleinkiekies

#18 MEE

Some posts from Cloudynights members describing experiences under Bortle Class 1 skies:


From CN member Wyatt Davis, Texas, May 2019

“You could see the structure across the entire expanse of the Milky Way, and it was lit light blue from within and seemed almost translucent.”

Christopher Beere, Namibia, July 2011

Part of this original thread:

“The main factor that distinguishes these perfect class 1 skies from excellent class 2 skies is the natural sky phenomena. They are very prominent features of the sky. In fact the zodiacal light dominates the sky in the hours before sunrise and the band is visible all the way into the star clouds of Sagittarius setting on the western horizon. I couldnt believe it when i saw it on the first night - it arcs across the entire sky.

Airglow is very bright throughout the night and really prominent on the eastern and southern horizon. Again you cant quite believe your eyes at first its so bright.

You often hear people talk about The Galaxy stretching from horizon to horizon. But ive never seen it anything like this before. The lack of extinction because of the incredible transparency means you can actually see the starclouds glowing on the horizon.”

The zodiacal light and band extend across the entire sky, from one horizon to the other

There is a color difference between the zodiacal light (yellowish) and the band of the Milky Way (blue)


Noodling Google’s Doodle

I like Google. I know, I know, there have been some issues with them, and I understand all that. But the company really does seem to try to make the world a better place as well as it can, and while there have been some stumbles, a lot of what Google does is really wonderful.

I’m also a big fan of small wonders just little things that make life a wee bit more fun. That’s why I like the Google Doodles—drawings or animations they put at the top of their search page, usually related to the day it’s up. For example, today is Earth Day, so they have a terrific little animated cartoon showing the sun and moon moving across the sky over the Earth:

The Doodle is adorable, showing fish swimming, water and air circulating, and even prairie dogs running around (at least, I assume they’re prairie dogs those cute varmints are all over Boulder, so maybe I’m biased). And since it’s a celebration of Earth Day and all the bounty our planet has to offer, it would take an abominably curmudgeonly anal-retentive jerk to notice that perhaps, just kan wees, there might be a few scientific errors in the Doodle.

OK, mea culpa. I can’t help it. I do like this Doodle, but it’s like an itch I have to scratch: There are a few mistakes in it. They aren’t a big deal, but neither is that tiny little itch located just perfectly in the small of your back where you can’t reach it and you have to scramble all over the house looking for something sticking out you can rub up against to scratch it.

So here are some of the scientific boo-boos in the Doodle. And before you send me hate mail, please read the last section of this article—I may be a little curmudgeonly, but my heart’s in the right place.

The phase of the moon is shown the wrong way.

As the Doodle cycles, you see the moon rising on the left and setting on the right (which is correct for someone in the Northern Hemisphere facing south east is to the left and west to the right). The first time we see the moon, it’s a crescent rising in the east at sunset, oriented with the wide part to the left, and the horns of the crescent pointing to the right.

But that’s not possible. When the moon is opposite the sun in the sky, it het to be full. Hier is hoekom.

The reason we see phases of the moon is due to the geometry among the Earth, moon, and sun, which changes as the moon orbits the Earth. When the sun and moon are in the same part of the sky, the moon is new. A few days later, as the moon circles the Earth, it pulls away from the sun in the sky, and we see a crescent, with only part of it lit. A few days more (a week after new moon), and the moon is half-lit (what we call, weirdly, first quarter, because it’s a quarter of the way through its monthly cycle). A few more days, and the moon gets fatter, and has what’s called a gibbous shape. Then, two weeks after new moon, it’s opposite the sun in the sky and we see it as full, a completely lit disk.

After that, the cycle reverse. The moon becomes gibbous, then half-lit, then a crescent again. Since it’s at the end of its cycle, we call that the old moon.

You can see all this in an animation put together by the folks at NASA’s Goddard Space Flight Center:

For some reason, the Google Doodle starts with the old moon. That’s fine, but the way it’s depicted is incorrect: The crescent moon has to be near the Sun in the sky. That’s why it’s a crescent. It’s shown as opposite the Sun, rising in the east as the Sun sets in the west, which only happens when the moon is full.

The phases are out of order.

So the moon’s phases go through a cycle once per month, which is how long it takes the moon to orbit the Earth (and is where the word month comes from think moonth).

So it starts new, is then a thin crescent, a fatter crescent, half-full, gibbous, then full. After that the lit portion shrinks, going through gibbous, half-lit, then a crescent again (the old moon). Lather, rinse, repeat.

As I pointed out, the Doodle starts with the old moon (the horns point to the right). * But the next phase we see is the gibbous moon. That’s not correct the next phase should be the new moon.

The old moon is nearly aligned with the sun (on the right of the sun from the Northern Hemisphere). As the moon orbits the Earth a bit more, it gets nearer the sun, then starts to pull away to the left. So the next phase after the old moon is actually the new moon, a thin crescent with the horns pointing to the left.

I’ll note that this gets a bit more complicated, because the Earth is a ball, too. Travel south, to the Southern Hemisphere, and things get reversed because you’re upside-down compared with the Northern Hemisphere. The new moon will have the horns pointing to the right, not left, as you face the setting sun. So in that sense, some of the Doodle might be saved, because now the animation starts with the new moon, not the old one, and the next phase would be half-lit, then gibbous. But even then, the crescent moon is still in the wrong part of the sky. Worse, the motion of the sun, moon, and stars would be right to left, not left to right. So in either hemisphere the Doodle won’t work.

Did I mention you have to be anal-retentive to spot all this? Ja.

The stars don’t move.

We see the moon move in the Doodle as it rises and sets, but the stars are stationary. In reality they almal rise and set, which is really just a reflection of the Earth spinning on its axis.

As it happens, because the moon is orbiting the Earth, it doesn’t move at the same speed as the stars in the sky. On top of the motion due to the Earth’s spin (called diurnal motion), which makes the moon, sun, and stars move east to west, the moon is moving slowly to the east. That means it moves a little bit slower than the stars. Over the course of the night, it’s barely noticeable, but it’s enough to cause the moon to rise about an hour later every day.

So in the Doodle, the stars and moon should be moving almost exactly together.

The dark part of the moon is transparent.

This one always cracks me up. We see a crescent moon because it’s a sphere, and only part of it to the side is lit by the sun. You can see this for yourself pretty easily: Go outside on a sunny day with a ping-pong ball (or some other sphere). Hold it up near the sun (don’t look directly at the sun, please!), and you’ll see the ball is lit just like a crescent moon. Rotate yourself so the sphere moves farther away from the sun, and more of it will be lit, mimicking the moon’s phases.

But the dark part of the moon is just unlit landscape it’s still part of the solid moon. So when the moon passes in front of stars, it blocks those stars, and it doesn’t matter if the part blocking it is lit or not. You can’t see the stars through the solid (and very, very opaque) moon.

In the Doodle, you can see stars right through the unlit part of the moon, which is pretty common in cartoons and drawings. This could only happen if the moon were transparent, like made of glass or crystal.

Which, to be fair, would be totally cool.

The rising and setting sun (and moon) speed up.

This is just a nitpick—well, all of this is, but it’s fun—but in the Doodle, as the sun rises it’s moving faster than when it’s high in the sky, and then speeds up as it sets, too. Same with the moon. In reality, the motion of the sun, moon, and stars is constant throughout the night. Remember, the motion of the objects in the sky is actually just due to the Earth spinning, which it does at a constant rate. So the motion of those objects is constant, too.

Though, to get really super-anal (a superpower to use very, very sparingly), the Earth’s atmosphere screws that up a bit. It acts like a lens, bending light. This bending (called refraction) is greatest when an object is near the horizon. But it goes the opposite way than shown in the Doodle: It actually slows down the apparent motion of the rising and setting sun (and moon).

I’ll note this is the same effect that causes the sun and moon to sometimes look flattened, squished, when they’re on the horizon, and plays a part in why they look red on the horizon, too. It’s a very cool and lovely effect, and one of my favorite things to see!

And one more that I know I’ll get mail about …

In the Doodle, the Earth is shown as being flat. It isn’t. But then, it’s not a perfect sphere, either …

I know, I know. I only mention this out of completeness. If you think I’m being anal, you can’t even imagine the comments I’d get if I left that part out. So daar gaan jy.

Dandy Doodle

Just to be clear, let me say again I really like this Doodle. It’s adorable, and quirky, and fun. And, like I also said, all my points are nitpicky. Still, it’s fun to point them out, and maybe show you the way things really work.

And it’s more than just me seeing something wrong on the Internet. You have to remember: All of the things shown in the Doodle are actually happening above your head in the sky right now. The moon is ceaselessly circling the Earth, and the Earth is moving around the sun once per year as it has for eons. The motion of the celestial orbs is an amazing, graceful, and predictable dance. The laws of gravity and of motion are so well understood that we can launch probes from Earth to other worlds, and have them travel for many years and hundreds of millions of kilometers, and still thread an incredibly narrow needle to reach their targets. We can land a one-ton nuclear-powered laser-eyed rover on another freaking planet, and it’s because of science.

And all that knowledge gained, all that wonderful math and physics and engineering and exploration, it all starts because someone had the curiosity to look up, and the audacity to suppose that all that intricate motion must be due to some underlying rules.

That’s what looking up does. It shows you the whole universe. And honestly, if today’s Google Doodle (and even my silly analysis) sparks someone to go outside and just look up, then mission accomplished.

So stop reading the Internet, go outside, and look up. Go.

Correction, April 22, 2013: This post originally misstated that the horns of the crescent moon as drawn in a Google Doodle were pointing left. They were pointing right.


If you’re looking at a galaxy from the edge, it appears flat, more or less. If you’re looking down on it…well, you see the whole thing spread out in front of you.

You notice that when you see the Milky Way from earth, it’s just a relatively narrow band of stars across the sky, and that’s because you’re looking at it edge-on. If you were looking down on it, you’d see the middle of it and the spiral arms flinging around it.

I BETTER not have just answered a homework question.

Val123 ( 12709 />) “Great Answer” ( 2 />) Flag as… />¶

@Val123: @Haroot asked for the case of a binary system, not a galaxy. However, the same basic idea applies.

An edge-on binary system is where our observing angle corresponds with the orbital orientation of the stars. In such a system, we see the stars eclipsing one-another at regular intervals. You can record a “light curve” that might look something like this. The valleys are where one star is in front of the other, and then again when they “reverse” position. The high plateaus are where both stars are visible. You would also observe a periodic doppler-shift of the light as the stars move towards and away from us while they circle eachother.

A face-on binary system is where we are looking directly “down” on the plane of the orbit. If our resolution is good enough, we can physically see the stars circling one another.

In reality, most systems are neither perfectly face-on or edge-on, but are inclined at some angle (usually called i). Additionally, you can’t easily tell from direct observation what the inclination angle is, unless the system is perfectly edge-on. This wikipedia article might help. An edge-on system has an inclination angle of 90 degrees, while a face-on system has an inclination of zero degrees.

hannahsugs ( 3238 />) “Great Answer” ( 3 />) Flag as… />¶

Regso. I think I got it. Dankie.

@Val123 And no, it wasn’t. Just something I was confused about.

Haroot ( 2118 />) “Great Answer” ( 0 />) Flag as… />¶

Put a lemon and a lime on a table top.

Look down on them: face-on. You’ll see the tops of the two fruits. ˚ ˚

Put your face on the edge of table and look at the fruit edge-on. You’ll see the silhouette of the outline of the two fruits. 0 0

gailcalled ( 54584 />) “Great Answer” ( 0 />) Flag as… />¶

Goed. I’m posting something I’ve been holding off on, waiting for @hannahsugs to report to me on. Here goes….

Val123 ( 12709 />) “Great Answer” ( 0 />) Flag as… />¶

OK. My next thought was, take a plate, hold it edge on to your face. What you see then, just the edge of the plate, is very different than if you flipped it up and looked at the plate face on….but then @hannahsugs came in with how it applied to a binary star system (noted in your question…)
I read his/her post (thought about it…) and I came up with this simplistic explanation (and this is what I sent to hannahsugs, and waited to see if it was accurate…no answer so I don’t know….) So, here’s how I perceive it. Take two balls that are trailing tracers of light behind them, revolving around each other, more or less evenly. If you look down on them from above, or directly above their equal trajectories, the tracers form a circle. If you look at them from other angles, (since their trajectories aren’t presies the same) they form other, varying patterns, such as @hannahsugs‘s graph showed, because they probably aren’t going exact circle around circle around each other. One is going faster, one is going slower, one is going up and down, the other isn’t….it’ll create different “light” patterns, depending on the angle you’re viewing them from.

Val123 ( 12709 />) “Great Answer” ( 0 />) Flag as… />¶

D & # 8217oh! I wrote that post right before signing off my computer for a few hours. oops!

@Val123 has sorta the right idea, as far as if the stars were emitting “tracers” and seeing different patterns over time. However, I’m afraid I might have confused things with the link to the graph. In a binary star system, if the stars were emitting “tracers” of light as they moved, if you looked at them “face-on”, their paths would form too overlapping circles or ellipses. Try this website, changing the mass of the purple planet to

150, and you have an idea of what that would look like.

If you looked at the system edge-on, you’d just see a line, with two bright “dots” moving back and forth along the line as they looked at eachother. As @Val123 and @gailcalled suggested, this is similar to taking a dinner plate or a CD and holding it flat, even with the plane of your eyes.

For a system that is somewhere between edge-on and face-on, we would simply see similar overlapping ellipses as in the face-on case, they would just be “squished” or flattened. Play with the simulation i linked to above, and try these initial inputs:
Body 1: 200 -90 0 -90 0
Body 2: 150 150 0 -80 40
Try to imagine, those could be more circular orbits, but because of an inclination angle, the appear to us to be elliptical.

The graph i showed is something different. That is a “light curve” for an edge-on binary system. It shows the totaal brightness of the whole system, as perceived by us, as the stars orbit eachother. It assumes that the stars are not of equal brightness. On the plateaus, from our perspective the stars are “next to” one another, so we see the full brightness from both of them. When the brighter star passes behind the dimmer star, we get the first dip in the graph, because we ONLY see the light from the dimmer star. The bright star emerges again, and we see the same brightness level as before, until the dim star passes behind the brighter star. Now we ONLY see the light from the brighter star, so there’s a dip again. Does that make more sense? The graph does NOT show position, it shows overall brightness over time.

Edge-on binary stars are very useful to astronomers. They are the only system where the inclination angle can be truly and surely known, because we can SEE the stars passing in front of one another. With systems that are inclined, we can only make an educated guess as to what the inclination angle is, or if the system is 100% face-on. When a system is edge-on, we can get true orbital velocities of the stars, which means we can get their masses, the radius of the orbit, etc. Unfortunately, as you can probably guess, edge-on or perfectly face-on binaries are rare. Random-inclination binaries are much more common. Luckily, more than ½ the stars in our galaxy seem to be in binary systems. Our sun is one of the odd-ball lonely stars. With 300 billion stars in the galaxy, at least half of them binaries, there’s some edge-on systems for us to study!

hannahsugs ( 3238 />) “Great Answer” ( 0 />) Flag as… />¶

@hannahsugs THAT is VERY cool! I could spend hours playing! (Be right back)

Ag skat. I set the mass of the purple star to 1000….oops! I hope they didn’t have populated solar systems.

Neat! I made a hydrogen atom!

Oh! I created a four star system and created a traffic jam!

Oh crap! Don’t give purple a mass of 150 and a position of 142, and the yellow a mass of 50 and DON’T make both of their velocities a 10. DON’T DO IT!

@Haroot give it 4 stars. You can see a better example of the wave thing he had going on above.

Shoot…I can’t get them to stop getting into head on collisions. I wanted to check something, but I am God and I’ve screwed up my binary star system. I have the power to keep recreating them, but I can’t figure out how to reset them so they orbit, instead of crash….what would a good default be?

Also, IS there such a thing as a 4 star system.

Val123 ( 12709 />) “Great Answer” ( 0 />) Flag as… />¶

@hannahsugs I found the original settings, so I could check what I wanted to see.

@Haroot take the link with it’s original settings of:

Yellow: Mass=200 / All three positions at 0/ velocity at -1.

Purple: Mass=10 / Position X=142, next two positions at zero / Velocity=140

Now set the velocity of Purple at 80…you can see how it makes the yellow star wobble, which creates the waves whch the instruments will read as going up and down, or side to side, or towards us and away from us (all which create the dopple shifts)

(Or, set it at 50, tell your girlfriend this is for her, go away for 4 minutes, look again and viola!) It gets better

Val123 ( 12709 />) “Great Answer” ( 0 />) Flag as… />¶

What Does an Orange Moon Mean?

The Moon can appear orange or red when it is near the horizon because of the longer path that its light must take through the air before reaching the observer. Oxygen in the Earth's atmosphere scatters optical light with short wavelengths, and the effect, known as Rayleigh scattering, is more pronounced as light travels through more air. Particles in the air from smoke or dust accentuate the scattering of light.

The Moon emits no light of its own, and it simply reflects the sunlight striking its highly reflective surface. This light must then pass through Earth's atmosphere before it can be seen on the ground. Earth's atmosphere tends to scatter light from the blue end of the visible spectrum. This scattering effectively strips moonlight of its bluer wavelengths and makes it appear artificially reddened. The effect is difficult to notice when the Moon is high overhead, because its light travels through comparatively little air before reaching the observer and therefore scatters less than it does on the horizon.

If the Moon appears unusually red or orange or the effect persists while the Moon is overhead, it is possible that fine-grained particles of dust or smoke have saturated the atmosphere and are scattering the light more than normal.


Happy Vernal Equinox 2016! But What Does That Mean?

Saturday is the vernal equinox! Well, Saturday night is, depending on where on Earth you are. The moment happens at 04:30 UTC on March 20 this year, which is, for example, March 19 at 10:30 p.m. Mountain (U.S.) time, where I live.

But what does that mean, exactly? Why, let my friend Joe Hanson explain it to you in an episode of “It’s Okay to Be Smart”

Die equilux point he makes is a good one. It’s even worse than he describes our atmosphere scatters sunlight, spreading it out. That’s why we have twilight the air is lit up even when the Sun is well below the horizon. There are different definitions for twilight depending on what you mean by it, but a fair one is when the center of the Sun is about 12° below the horizon. The Sun moves across the sky at about a degree every four minutes * , so twilight is bright for very roughly a half hour before sunrise and after sunset.

So equilux can be hard to define if you dive into the details about it.

One thing I always notice this time of year, too, is that the Sun seems to set noticeably farther north every day. At the December solstice it’s as far south as it can be on the horizon for Northern Hemisphere observers. At the June solstice it’s as far north as it gets. At the equinoxes it sets due west.

But the koers at which the sunset point moves north from winter to summer changes. It’s very slow at first, then speeds up to a maximum at the equinox, then slows again. So right now, not only is it setting farther north every day, the amount it moves north every day is largest. Starting after the equinox it begins to slow, and stops at the solstice (which literally means “the Sun stands still”).

If you’re mathematically inclined, the point on the horizon where the Sun sets is like a sine wave, moving south to north and back again with a period of one year. The speed at which that point moves along the horizon is the derivative of that, which is a cosine curve. Call due west on the horizon 0°, north +90°, and so on. When the Sun sets due west, on the equinox, the sine value is 0, but the cosine is maximized. That means the change in the position where the Sun sets is moving at its fastest speed. At the solstices the sine is maximized (the actual value depends on the Earth’s tilt and your latitude) but the absolute value of the cosine is minimized at 0, and then the cosine switches sign. In other words, the sunset point slows to a stop and then reverses direction the next day.

This gets worse because the Earth’s orbit is an ellipse, which messes with things, as Joe pointed out in his video. But it’s close enough. People make analemma photos all the time, showing the Sun’s position in the sky over the course of a year. I’d love to see the same thing, but instead showing the Sun just at sunset every day of the year. Then this speeding up and slowing of the Sun’s sunset point would be obvious. That’d be quite an effort, though, and I’ve never seen one made. Any takers?

* Correction, March 19, 2016, at 17:15 UTC: I originally wrote the Sun moves a degree every two minutes. I meant to write it moves through its own diameter, 1/2 a degree, every two minutes. Anyway, the correction should be more clear.


What About Cosmology and Astrophysics?

Cosmology and Astrophysics are two other fields that are often confused with astronomy and astrology. Here is what these two terms mean:

  • Cosmology entails the study of the origin and development of the universe. Right now, the Big Bang Theory is the prevailing model.
  • Astrophysics applies the principles and laws of physics to explain how the stars, planets, galaxies, and the universe in general works.

To Wrap Up

Even though the two areas started as one, they are now two distinct fields.

Astronomy is a scientific and academic field, while astrology is now considered a form of divination and superstition.

Still, both of them remain popular practices even in the modern world.

If you’re interested in celestial objects such as stars, planets, comets, asteroids, nebulas, and galaxies, all these fall under astronomy and so do space travel and alien life.

But if you’d like to know your personality traits and how you’re likely to behave as dictated by your star sign, you will be operating in the realm of astrology.


Kyk die video: Wat Wat Wat VIDEO Song. Tamasha. Ranbir Kapoor, Deepika Padukone. T-Series (November 2022).