Astronomija

Zakaj je Lunin terminator na tej sliki videti "narobe"?

Zakaj je Lunin terminator na tej sliki videti


We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

Slika Lune je v spletnem članku nacionalnega javnega radia Pripravite se na noč čarovnic, tako da nocoj gledate Lunino "okultacijo". Zdi se mi napačno - natančneje, stopnjevanje svetlosti v bližini zaključevalnika - ali pomanjkanje le-tega.

Slika je pripisana "Okulitacija padajoče lune bo vidna v torek zvečer v nekaterih delih ZDA. JPL / NASA", vendar se sprašujem, ali je to res. Tu je nekaj preprosto videti "narobe".

V prvotnem članku JPL / NASA vsebuje povezavo do te strani, ki trenutno vsebuje tudi to sliko, prikazano spodaj. Izgleda bolj kot dejanska fotografija.

In tu je slika NASA / JPL s https://svs.gsfc.nasa.gov/4404 za 19. 10. 2016 04:00 UT, ki, če pravilno razumem, pravzaprav ni fotografija, ampak simulirana iz podatkov LRO. To tudi ponazarja, da naj bi terminator stopnjeval od svetlobe do teme in vseboval kontrast zaradi senčenja.


nad: terminator iz vseh treh slik. Realistični terminator na desni kaže stopnjevano intenzivnost in močno senčenje iz močno poševne vpadne svetlobe.


Razlog, da je lunina slika videti napačno, je napačna. To ni resnična podoba lune $ - $ vsaj terminator ni resničen.

Izvirni članek, ki ga navedete, ima povezavo tik pod njihovo sliko, ki označuje vir njihove podobe lune. Ta vir je načrtovalec nočnega neba, ki ga gosti JPL. Na tej spletni strani boste našli isto sliko, čeprav nekoliko temnejšo (zdi se, da so si ljudje NPR sliko nekoliko posvetlili).

Če boste še malo kopali, boste videli, da je načrtovalec nočnega neba podobo te lune dobil od nekoga drugega. Znotraj html kode imajo sliko definirano kot:

the moonAmeriški nacionalni observatorij.

Po kopanju sem ugotovil, kaj točno se tu dogaja. Namen te strani je prikazati trenutno lunino fazo. Da bi to naredili, posnamejo eno samo sliko polne lune in umetno zasenčijo regijo, da je videti kot trenutna lunina faza. Njihov postopek si lahko ogledate tukaj in kako je to naredil neki tip po imenu R. Schmidt. Lunine faze so razdelili na 181 slik, ki jih lahko prenesete tukaj, če vas zanima.

Kot lahko vidite, je zaključevalec na tej sliki napačen, ker ne gre za resnično sliko trenutne faze lune, temveč za računalniško ustvarjeno "senčenje" polne lune, ki označuje trenutno lunino fazo.


Hibridni laboratorij astronomije / laboratorij v kampusu (108)

Veliko se lahko naučite tako, da preprosto opazujete Luno brez teleskopa, noč za nočjo, mesec za mesecem in celo leto za letom. 8. septembra 2013 se je zunaj stavbe za fiziko in astronomijo v kampusu tako pojavil tik po sončnem zahodu.


Svetla "večerna zvezda" ob njej je Venera. Takrat je bilo še na skrajni strani Sonca in se je začelo približevati Zemlji po svoji hitrejši orbiti. Mesece zatem, ko se je Luna zvečer spet pojavila, bi bila tam tudi Venera do aprila 2014, ko je šla mimo Zemlje in se nato preselila na jutranje nebo. Če bi imeli teleskop in bi videli Venero od blizu v noči, ko je bila ta fotografija posneta, bi bila napol osvetljena, kot Luna prve četrtine. Tik preden je šel mimo Zemlje, aprila naslednjega leta, je bil tudi tanek polmesec rezine sončne svetlobe.

Videz Lune (in Venere in Merkurja) je odvisen od tega, kje je glede na Sonce in Zemljo. Za razumevanje te slike si predstavljajte, da je Sonce pod obzorjem na vaši desni. Osvetljuje sferično Luno z zelo velike razdalje in osvetljuje polovico Lunine površine, ki je na strani, ki je najbližja Soncu. Z Zemlje vidimo le del te osvetljene krogle in se nam zdi ta polmesec. Vsak dan Luna napreduje dlje v svoji orbiti okoli Zemlje in bi se ponoči bolj pomikala proti vzhodu, prikazujoč vedno več osvetljene površine za tiste, ki smo na Zemlji.

Podrobnosti

Gibanje Zemlje in Lune določa, kako se nam zdi. Če bi se lahko odpravili v vesolje, ko bi gledali naš sončni sistem, bi videli Zemljo in Luno, ki krožita okoli Sonca, vendar v različnih ravninah in različnih hitrostih.

  • Vrtenje Zemlje na svoji osi vsakih 23 ur 56 minut
  • Zemeljska revolucija okoli Sonca 365.256 dni
  • Vrtenje lune na svoji osi vsakih 27,3 dni
  • Lunina revolucija okoli Zemlje 27,3 dni
  • Lunina revolucija glede na linijo Zemlja-Sonce 29,5 dni
  • Konica Zemljine osi do ravnine njene orbite 23,5 stopinje
  • Konica Lunine orbite do Zemljine orbite 5 stopinj
  • Konica Lunove osi do Lunine orbite 6,7 stopinje
  • Lunina orbita je eliptična, gledano glede na Zemljo ali glede na težišče Zemlje in Lune
  • Njegov najbližji pristop do Zemlje je približno 360.000 km, najbolj oddaljen od Zemlje pa približno 406.000 km. "Geocentrična" orbita ima pol-glavno os 384.400 km.


Tukaj je veliko za obdelavo, zato se osredotočimo na nekaj bistvenih idej, o katerih ste morda že slišali na tečaju astronomije

  • Luna se v povprečju vsakih 29,5 dni po večerni nebi spet pojavi po novi Luni
  • Delitev na 4, prvo četrtletje, polno, zadnjo četrtino in novo spet ločuje nekaj več kot 7 dni
  • Če pogledamo iz vesolja, Luna kroži okoli Zemlje v krajšem času, približno 27 dneh, vendar trajata še 2 dni, da dohiteva črto Zemlja-Sonce in spet pride do novega
  • Luna se vrti, ko kroži, in v povprečju drži enak obraz proti Zemlji ("blizu" stran) in stran od Zemlje ("daleč" stran)
  • Vrtenje je enakomerno, vendar se gibanje orbite pospeši in upočasni, med mesecem vidimo malo več vzhodno in zahodno od bližnje strani
  • Rotacijska os je nagnjena na orbitalno ravnino, vidimo nekaj več severa in juga kot le 50% Lune v mesecu
  • Orbitalna ravnina je nagnjena k Zemljinemu ekvatorju, naraščajoče in zahajajoče točke Lune na obzorju se med letom spreminjajo
  • Smer orbitalne ravnine se počasi "preklisira", pri čemer je potreben 18,6 leta, da se dokonča celoten obrat, saj ohranja skoraj konstantno konico do ravnine Zemljine orbite. Smer, ki jo gre, je videti v smeri urinega kazalca, ko gledamo navzdol po orbiti.
  • Smer pol glavne osi elipse, ki definira Lunovo orbito, traja približno 8,9 leta, da zaključi cikel. smer, v katero gre, je v nasprotni smeri urnega kazalca, kar se vidi tudi ob pogledu navzdol na orbito.

Če želite videti datume in položaje Lune, jo lahko zahvaljujoč Newtonu in natančnim meritvam, kje je bila, zelo natančno predvidimo iz zakonov gibanja in gravitacije ter nekaj zapletene geometrije. Na srečo obstaja program, ki bo to naredil za nas on-line.

Vizualizacija gibov

V zadnjem času je NASA vsako leto pripravila animacijo, ki prikazuje videz Lune skozi leto in poglejmo, kako se zapletenost orbit Zemlje in Lune ter njunih rotacij spreminja, kako se nam zdi Luna. Ta je za leto 2020. Če to ni tekoče leto ali leto, ki vas zanima, poskusite v YouTubu poiskati "NASA moon 2020" ali drugo leto, ki vas zanima.

Za boljši pogled kliknite ikono »celozaslonski« v spodnjem desnem kotu ali uporabite povezavo na strani z viri, da dobite animacijo v oknu brskalnika v polni velikosti. Če zaženete celozaslonski prikaz, se imena kraterjev prikažejo, ko so označena. Animacija zajema celo leto.

Ta animacija vam ne prikazuje, kako se luna vzhaja in zahaja na obzorju med mesecem, mesecem ali celo letom v letu. To je sicer zelo zapleteno, toda arhitekti iz Stonehengea so to vedeli, ki so postavili vidne črte v strukturo, ki je na obzorju označevala skrajnost luninega napredovanja. Ugibajo se, da so te črte omogočale napovedovanje pojava Luninih in Sončevih mrkov. O tem obstaja kratko video predavanje, če vas zanima arheologija Stonehengeja in kako to deluje.

Prva vprašanja o opazovanju Lune

1. Kakšna je faza Lune zdaj? V odgovor na ta odgovor nam boste morali sporočiti tudi datum, da ga bomo lahko preverili. Identificirajte fazo kot novo, voskovni (naraščajoči) polmesec, prva četrtina, voskasti gibast, poln, padajoč (padajoč) gibast, zadnja četrtina padajoči polmesec. Izraza "voskanje" in "upadanje" se običajno uporabljata za opis videza Lune, vendar sta za vas morda nova. Potrebovali boste jasno noč in nekaj minut, da greste ven in se poiščete.

2. Kdaj bo Luna v zadnjem četrtletju in kdaj ponoči po lokalnem času bo naraščala? (Če je zdaj zadnje četrtletje, dajte naslednjega v naslednjem mesecu.) Za to uporabite spletne vire, povezane s strani z viri Moon.

3. Izmerite navidezno kotno velikost Lune na nočnem nebu. Kaj najdete Tukaj je opisano, kako to storiti.

Kako izmeriti kotno velikost Lune

Potrebovali boste nekaj za merjenje z majhnim ravnilom, merilom ali trakom. Prav tako boste potrebovali noč, ko boste lahko videli Luno. Samo počakajte na priložnost, da končate to. V celoti iztegnite roko in izmerite, kako daleč so konci prstov od očesa. Za večino ljudi bo to približno 1 dvorišče, malo manj kot 1 meter. Če uporabljate metrične enote, izmerite na najbližji centimeter. V enotah Imperial (ni priporočljivo za znanost) izmerite na najbližji centimeter.

Ko je Luna vidna, primite nekaj primerno majhnega na dolžini rok. Lahko poskusite z radirko na koncu svinčnika, vendar boste morda potrebovali nekaj manjšega od tega. Izberite predmet, ki je dovolj velik, da prepreči premer Lune. Če je premer predmeta, ki ste ga izbrali, (d ) in dolžina roke ( ell ), je kot, ki ga pokriva Luna, približno

( theta = 180 / pi krat d / ell = 57,3 krat d / ell )

v stopinjah. To deluje, dokler je kot majhen in je pogost približek astronomije. Za primer recimo, da ste ugotovili, da je predmet s premerom 6 mm pokrival Luno, ko je bila od vašega očesa oddaljena 750 mm. Kot bi bil

( theta = 57,3 krat 6/750 = 0,46 ^ krog )

V odgovoru na to vprašanje boste pozvani, da opišete podrobnosti, kako ste izvedli meritev. Pomaga si delati zapiske, nato pa naenkrat naenkrat izpolniti vse odgovore na tej spletni strani.

Polna luna

Na strani z viri kliknite "Polna luna" ali pojdite neposredno na to povezavo

za ogled teleskopske slike polne Lune. Ta je trajala nekaj dni, preden je bila popolnoma napolnjena, vendar prikazuje večino površine z neposredno osvetlitvijo sončne svetlobe, ki je značilna za to, ko je Luna v nasprotni smeri na nebu od Sonca. Luno vidimo s Soncem za seboj, v središču Lune pa ni senc. Nekaj ​​jih boste opazili ob levi strani (vzhod, saj je Luna na nebu).

Opazite svetle lastnosti z "žarki", ki segajo daleč po disku. Ti kraterji so bili ustvarjeni z nedavnimi (na luninem časovnem merilu) udarci, ki so razmetali ruševine po temnejši površini, material žarkov pa prečka starejše lastnosti, kot je temni bazalt, ki poudarja velike udarne bazene, imenovane lunina kobila (ali morja) . Na ta vprašanja odgovorite tako, da si ogledate to sliko in s pomočjo luninih zemljevidov ter povezav na strani virov poiščete imena.

Samo kratka beseda o navodilih. Običajno je označevanje planetarnih objektov po smereh, analognih smerim kompasa na Zemlji. Tako kot pri pogledu na zemeljski svet s severom navzgor, bi bila zahodna stran na vaši levi, vzhodna pa na desni, ko pogledate Luno na nebu, je njen "zahod" na vaši levi in njen "vzhod" je na vaši desni. To so navodila, ki bi jih uporabljal človek, ki hodi po Luni. Vendar je za nas tukaj na Zemlji vzhod levo od nas, zahod pa desno. Na nebu so smeri obrnjene levo-desno za nas, kot bi bile za osebo, ki prikazuje Luno na Luni. Tu se bomo sklicevali na smer kompasa z našega zornega kota, tako da bo s severa navzgor vzhod na našem nebu na naši levi. Če pa pogledate lunin zemljevid, se lahko obrnejo. Slike na naši strani z viri prikazujejo Luno, kot bi jo videli na lastne oči na našem nočnem nebu na severni polobli.

4. Na dnu ali južnem polarnem koncu je glavni žarkani krater. Za koga je poimenovana in po čem je bil znan?

5. Približno na sredini od zgoraj navzdol, proti levi pa je še en svetel velik krater z žarki. Zraven bolj proti vzhodu (levo) je manjši. Kako jim je ime?

6. Mare Imbrium, morje "deževja", je vidno na podobi polne Lune. Gre za veliko okroglo kotlino, napolnjeno z lavo, omejeno z gorsko verigo na 3/4 njegovega obrisa, ki je preostali rob kraterja, ki je zdaj napolnjen z bazaltom. Nekaj ​​žarkov ga prečka od spodaj. Na sliki prepoznajte Mare Imbrium. Določite tudi "Appenine". Če potrebujete pomoč, poskusite povezave v Wikipediji, ki vas bodo vodile do teh regij. Pri odgovoru jim boste prepoznali sliko, za zdaj pa si le zapišite, da boste to lahko kasneje izpolnili.

Apollo 15 je pristal v Mare Imbrium.

7. S pomočjo zaslona polne Lune in ravnila izmerite premer celotnega diska in približno izmerite premer krožnega Mare Imbrium. Kako daleč čez Mare Imbrium v ​​kilometrih? (V 1,0 km je 0,62 milje.)

Tukaj je, kako to ugotoviti. Poln premer Lune je 3474 km. Izmerite premer slike in jo pokličite (D_). Izmerite premer kobile z isto skalo (priporočeno v mm) in pokličite (d_). Nato preprosto razmerje daje velikost kobile v kilometrih

Pri podajanju odgovora pomislite na učinek ukrivljene lunine površine na način merjenja. Kaj bi bilo potrebno, če bi želeli izvesti natančno meritev? Za primerjavo, celinski del ZDA je približno 4300 km v širini, torej je večji od celotne Lune!

Luna iz prve četrtine

Zdaj izberite prvo četrtinsko sliko Lune na strani z viri ali pojdite neposredno sem

V tem primeru je kot od Lune proti Zemlji skoraj 90 stopinj od kota proti Soncu in Luna je videti napol osvetljena. Imenujemo jo "četrtina" in ne "polovica" Lune, kar razume, da vidimo le 25% njene površine.

8. Ploščata ovalna kobila, ki je na skrajni desni sredini (zahodna stran našega neba) strani slike, je vidna tudi na drugih slikah, ki so na strani z viri. Kako mu je ime in zakaj je videti bolj ovalno kot okroglo? Za namig si oglejte videz kraterjev tudi proti Luninemu južnemu polu.

Sliko povečajte s klikom na gumb "+", da boste videli čim več podrobnosti. Poglejte vzdolž terminatorja, črta, ki ločuje svetlo in temno stran navzdol po sredini. Če bi bili na terminatorju, bi bilo Sonce na obzorju in sence bi bile zelo dolge. Blizu vrha (severno), ki meji na Mare Imbrium, je okrogel krater z gorami, ki določajo njegov rob, ki se le drži sončne svetlobe. To je krater Platon, ki si ga bomo še naprej pozorno ogledali. Preden pa pridemo do tega, je takoj na desni luknji po robu Mare Imbrium, ki se pogosto imenuje Alpska dolina ali Vallis Alpes. Čeprav se zdi, da je to območje ob trku nekaj odneslo (Mare Imbrium je star več kot 3,8 milijarde let), je tudi to dno doline napolnjeno z lavo.

9. Kaj je povzročilo to funkcijo? (Namig: Preberite več tukaj ali drugje, če želite najti odgovor.) Kako je ime druge kobile nepravilne oblike, ki je "severno" od Mare Imbrium in do katere se razprostira ta dolina? Razumevanje teh mejnikov olajša iskanje poti okoli Lune v kateri koli fazi in njene robustne značilnosti umestite v kontekst njihovega nastanka.

Platon

Krater Platon, ki ste ga našli na podobi Lune prve četrtine, je najbolje videti dan ali dva kasneje, ko sončna svetloba seže v krater. O tem imamo podrobnejšo sliko

in čeprav je bilo z zemeljskimi teleskopi posnetih nekaj boljših slik, ta prikazuje skoraj vse podrobnosti, ki jih je mogoče ujeti, razen če je nebo izjemno stabilno. Opazite, kako se neravne sence gora, ki tvorijo njen rob, dobro razširijo v krater čez tok lave, ki je zapolnil njegovo notranjost. Obstaja nekaj majhnih "kraterjev", ki so posledica udarcev na Luno po dogodku, ki je povzročil Platona. Vprašanje za vas je: "Kako visoke so gore nad tlemi kraterja?"

Če želite odgovoriti na to, si oglejte slike celotne četrtine in prve četrtine. Vsi prikazujejo Platona, vendar le na tej podrobni sliki dobro vidite sence. Vedeti moramo kot Sonca, kot ga vidimo nad obzorjem na Platonu. Če poznate ta kot, potem lahko izračunate višino gora.

Tukaj je opisano, kako to storiti, korak za korakom.

Premer Platona bomo uporabili kot "tehtnico" za merjenje gora, zato poiščite njegov premer tako, da si ogledate Lunino podobo, kjer lahko vidite celoten premer Lune in lepo definiran krater. Za iskanje premera Platona uporabite isto metodo, kot ste jo uporabili za iskanje premera Mare Imbrium. Seveda je Platon precej manjši od velikega udarnega bazena pod njim, vendar je ideja merjenja enaka.

Z istim ravnilom izmerite premer Lune na zaslonu, premer Platona in nato iz razmerja poiščite premer Platona v km.

10. Kakšen je premer Platona v km?

Na podrobni Platonovi sliki, ki je povezana zgoraj, kako daleč so gore, ki mečejo senco na dno kraterja od "terminatorja", ki določa črto sončnega zahoda na Luni. Za to uporabite platonov premer kot ravnilo in čim bolje pripravite oceno. Ne bo natančno, ker se zaključna črta spreminja glede na višino luninega terena, vendar lahko dobite oceno, ki je dobra do morda 20%, če ste previdni. To razdaljo boste uporabili za iskanje kota Sonca nad obzorjem. Denimo, da je ta razdalja (X ) podana v km. Obseg Lune je ( pi D ), kjer je (D ) Lunin premer. Ker gre celoten obseg za 360 stopinj, če so te gore (X ) od zaključka, so kot, gledan iz središča Lune, oddaljen od ekvatorja do gora v stopinjah

( theta = 360 krat (X / C) = 360 krat (X / ( pi krat 3474)) )

( theta = 0,033 krat X ) stopinj

če izmerite razdaljo (X ) gora od terminatorja v km. Upoštevajte, da Platon ni zelo velik krater in bo ta kot precej majhen. Zdaj vemo tudi, kako visoko je v tem trenutku Sonce na Platonovem nebu. Premisli.

Sonce je na obzorju za gledalca na terminatorju. Ko se razgledna točka premakne proti Soncu, se Sonce dvigne višje na nebu. To pomeni, da se Sonce za vsako stopinjo, ki se premika v tej smeri, dvigne za stopinjo. Če bi se razgledna točka premaknila za celih 90 stopinj, bi bilo Sonce nad glavo. Zares enostavno je slikati.

11. Kako visoko je Sonce nad luninim obzorjem, gledano iz središča Platona? Odgovor podajte v stopinjah. Če je vaš odgovor na Luni, lahko ugotovite, ali je vaš odgovor razumen, če upoštevate, da bo Sonce v enem luninem mesecu obšlo Luno. To pomeni, da gre v enem mesecu 360 stopinj ali približno 12 stopinj na dan. Če bi bil Platon danes točno na terminatorju, bi bilo Sonce na obzorju, gledano s Platona. Naslednji dan bi bilo Sonce na nebu 12 stopinj nad obzorjem.

Kako spet uporabljamo premer Platona kot merilno palico, kako dolga je senca gora na dnu kraterja v km? Če ima senca dolžino (S ) za Sonce pod kotom ( theta ) v stopinjah, če je kot majhen, je višina gora

Tu je "H" v km, če izmerite S v km. Uporabite ( theta ) v stopinjah. 57,3 pretvori iz stopinj v radiane.

12. Kako visoko je to gorsko platišče nad dnom kraterja Platona?

S to metodo lahko previdno izmerite globino kraterjev kjer koli na Luni, tako da ugotovite, koliko časa traja, da se črta sončnega vzhoda (terminatorja) premakne iz kraterja, nato pa čez nekaj časa poiščete dolžino sence od platišče Seveda natančneje zdaj smo Luno pregledali iz orbite okoli nje z radarjem in natančnimi meritvami nadmorske višine, tako da je teren zelo dobro preučen.

Libracija

Zaključili bomo s ponovnim obiskom ideje o »libraciji«, ki je navidezno prikimavanje Lune, ki nam omogoča, da vidimo več kot polovico njene površine. Utripanje na zemljepisni širini je sever-jug in je s konice rotacijske osi Lune, gledano z Zemlje. Dolžina nihanja je vzhod-zahod in je posledica sprememb v krožnici Lune, ker je njena orbita eliptična in ne popolnoma krožna.

13. Med slikami na spletni strani vira z našega teleskopa poiščite libracijo s primerjavo slik različnih faz in datumov. Kaj si našel Če imate težave z videnjem učinka, je to v videu NASA bolj dramatično. Po ponovnem ogledu videoposnetka se vrnite k slikam in preverite, ali ga lahko najdete.


Zakaj smo torej sliko poklicali & # 8220 Shakesperean? & # 8221

Shakespeare, Luna in človeške preizkušnje in stiske so zajeti skupaj. Kot pravi Andrew McCarthy o eni od svojih slik, & # 8220 V negotovih časih gledam v nebo in me tolažijo luna in zvezde. & # 8221 Če & # 8217 še niste čutili kakšnega podobnega čustva, preizkusite svojo DNK. Morda niste človek.

Tudi Shakespeare je bil naklonjen Luni. To se je pogosto pojavljalo v njegovem delu. Na primer, & # 8220 Vstani, lepo sonce in ubij zavidljivo luno, ki je že bolna in bleda od žalosti, da si ti, njena služkinja, veliko bolj poštena kot ona. . . & # 8221 To & # 8217 iz Romea in Julije.

Bard je tudi potegnil astrologijo v kralju Learu in opozoril na neumnost, ko je Luno in druga telesa obtoževal za svojo lastno nesrečo:

& # 8220To je izvrstna pepelnatost sveta, ki, ko smo srečni, & # 8211 pogosto izpušča svoje lastno vedenje, & # 8211 za svoje katastrofe krivimo sonce, luno in zvezde: kot da bili smo zlobneži po nujnosti, bedaki, knaji, tatovi in ​​izdajniki, sferični prevladujoči pijanci, lažnivci in prešuštniki, vsiljeno poslušnost planetarnih vplivov in vse, v čemer smo hudobni, z božanskim narivanjem na: čudovito utajo človeka, ki se ukvarja s kurbami, da bi se nagnil k kozji naklonjenosti zvezdi. & # 8221

William Shakespeare, 1564-1616. Zasluga za sliko: John Taylor & # 8211 Uradna povezava do galerije, Public Domain, https://commons.wikimedia.org/w/index.php?curid=5442977

Velikani, kot je Shakespeare, nas prisilijo, da dvakrat premislimo o stvareh: življenju, ljubezni, naravi, Luni, svoji usodi. Zaradi njih to vidimo z novimi očmi.

In če to ni preveč velika izjava, mislim, da McCarthyjeva podoba Lune počne enako. Tudi v dobi, ko nam superteleskopi dajejo čudovite podobe kozmosa in vseh predmetov, ki ga naseljujejo, je preprosta, a nedosegljiva podoba Lune nekako bolj humanistična.


Teh številk nisem preveril, toda ne glede na to ne bi mogli upoštevati iluzije - te majhne razlike nikoli nihče ne bi mogel zanesljivo zaznati.

Diagrami večinoma obravnavajo sonce pod obzorjem ali na obzorju, kar bi to vajo nekoliko otežilo.

Če bi bila Zemlja prosojna in bi si predstavljali ravno črto od sonca (celo pod obzorjem) do lune, bi bila ta črta pravokotna na zaključek do stopnje, potrebne za razpravo o tej težavi. To ugovarjam diagramu - črta med soncem in luno v diagramu ni pravokotna, vemo pa, da je.

Strinjam se, da bi bilo težko mentalno potegniti to mejo med skoraj polno luno in soncem - ker bi bili opazovalci med njimi - vendar ni tako, da bi gledali polno luno in sklepali, da sonce sije zadaj nas ne glede na to, v katero smer se obrnemo.

Tukaj je sprehod skozi model igrač, ki bi lahko pomagal pri vizualizaciji. Predpostavljamo, da zemeljska orbita, lunina in Zemljin ekvator ležijo v isti ravnini. To poenostavi vizualizacijo brez kakršnega koli nasilja nad dejanskim stanjem.
Zdaj pa se pogovorimo z naraščajočo gibljivo luno, na polovici prve četrtine do polne.
Gremo na severni pol in pogledamo na luno in sonce. Zaradi naših poenostavitvenih predpostavk oba ležita na obzorju, luna pa je od Sonca oddaljena 135 stopinj. Njegova popolnoma osvetljena stran je obrnjena proti soncu, zaključevalnik pravokoten na obzorje. Na nebu lahko narišemo vodoravno črto, vzporedno z obzorjem, ki povezuje sonce in luno, prav tako pa je pravokotna na lunin terminator. To je pot svetlobnih žarkov, ki potujejo od sonca do lune in vse se zdi dosledno in normalno.
Zdaj pojdite na ekvator. Na ekvatorju poiščite točko, kjer sonce sedi na zahodnem obzorju. Gibljiva luna je 45 stopinj nad vzhodnim obzorjem (tj. Še vedno 135 stopinj od sonca). Njegova osvetljena stran je usmerjena proti zenitu: torej je obrnjena navzgor, kljub temu da je sonce na obzorju. Črta, ki smo jo narisali na nebu, ki povezuje sonce in luno, se zdaj vzpenja navpično od zahodnega obzorja, prečka zenit in se spusti proti vzhodu, dokler ne zadene lune, ki je še vedno pravokotna na lunin (zdaj vodoraven) terminator. Po nekoliko premisleku lahko ugotovimo, da je to pravilno: sončni žarki sijejo daleč nad našimi glavami, da osvetlijo luno, tako da lahko vidimo malo poti & quotunder & osvetljenega obraza na senčno stran.
Zdaj pa si predstavljajte linijo opazovalcev, razpeta vzdolž dolžinske črte, ki povezuje našo ekvatorialno opazovalno točko s severnim tečajem. Za vsakega od njih bo sonce na obzorju. Za vsakega od njih bo lunin osvetljen obraz usmerjen v neko smer, vmesno med naravnost navzgor (ekvatorialna situacija) in vodoravno (polarna situacija). Torej vsak opazovalec v teh srednjih zemljepisnih širinah bo osvetljena stran Lune do neke mere nagnjena navzgor, kljub temu da vsi vidijo sonce na zahodnem obzorju. Počakajte nekaj trenutkov, da sonce zaide, in vsi bodo imeli pogled, podoben tistemu, opisanemu v OP.
Za te opazovalce se zdi, da se črta, ki smo jo potegnili na nebu, zdaj zavija navzgor od sončnega položaja, doseže visoko točko proti jugu in se nato zavije navzdol, da se sreča z luno, pravokotno na njen zaključek.
Ampak to je ista črta. Mislili smo, da je ravno, ko je vzporedno z obzorjem, in prepričali smo se, da je ravno, če teče navpično. Toda naši možgani niso zadovoljni s konvergenco, ki je neizogiben del gledanja dolgih vzporednih črt v perspektivi, ki pokriva velik kotni lok. Dolga črta, ki se konvergira na obeh obzorjih (kot sončni žarki ob sončnem zahodu), se zdi, da mora nekje imeti krivuljo. Torej v teh vmesnih zemljepisnih širinah se zdi kot bi morali biti sposobni narisati a naravnost črta med luno in soncem, podrezovanje črte na nebu, za katero smo se prej dogovorili, da bo ravna!
Toda predstavljajte si (za trenutek) vas lahko naredi to. Zato narišite novo črto, ki spodreže našo prvotno črto in izgleda bolj naravnost. Zdaj se vrnite na pol, tako da naša prvotna črta poteka vzdolž obzorja in povezuje sonce in luno. Kje je naša nova linija? Verjetno zapušča sonce, se zavija pod obzorje in nato spet navzgor, da zadene luno! Torej ne more biti bolj naravnost.

Torej je vse samo trik perspektive. Če bi na neki vmesni zemljepisni širini lahko izvedli poskus, pri katerem bi držali glavo mrtvo mirno in raztegnili kos vrvice od desnega palca (ki pokriva sonce na obzorju) do levega palca (ki pokriva gibasto luno visoko v nebo), boste ugotovili, da je vrvica šla višje od vaše glave in potem spustite se proti vašemu pogledu na Luno, ki jo srečujemo pravokotno na njen zaključek.

Hvala, Grant, spoštujem vaše znanje in razlago, vendar sem še vedno zmeden. Prepričan sem, da je ta navidezna neumnost z moje strani preprosto pomanjkanje inteligence ali razumevanja, pa naj bo tako.

Iz vaše razlage sem zaključil naslednje

1) da se s severnega pola Zemlje lunin terminator zdi navpičen in pravokoten na sonce
2) da se z zemeljskega ekvatorja lunin terminator pojavi vodoravno in pravokotno na sonce

imam pa težave z delom, ki pravi

3) da mora biti med zemeljskim ekvatorjem in severnim tečajem Zemljinega pola lunin terminator namesto pravokoten na sonce, pravokoten na točko, višjo od sonca.

Predstavljajte si, da sem na severnem polu Zemlje in je lunin terminator navpičen, vzhodna (leva) stran lune je temna in zahodna (desna) stran lune sveti. Če zamrznemo čas in grem proti Luni proti jugu, bo sonce ostalo na obzorju in luna se bo dvignila na nebu. Ko pridem do ekvatorja, bo luna visoko nad vzhodnim nebom, vzhodna stran bo temna, zahodna stran pa bo osvetljena, terminator pa bo videti vodoravno. Če pa analizirate prehod zaključevalnika iz navpičnega na polu (temna stran vzhod ali levo) v vodoravni položaj na ekvatorju (temna stran vzhod), se je terminator preprosto zasukal v smeri urinega kazalca za 90 stopinj. V nobenem trenutku se ne vrti v levo. In kar vidim skozi okno, pomeni vrtenje zaključka v nasprotni smeri urnega kazalca.


Pojemajoča Luna s panoramskim razgledom vzdolž terminata sončnega zahoda

Te slike predstavljajo podatke, ki so ostali nedokončani od lanskega 24. avgusta 2019. Pred tem sem že objavil posnetke Kopernika in Mare Orientale, vendar nabora podatkov za celotno Luno do zdaj še nisem dopolnil. Poleg običajnih časovnih omejitev pri obdelavi večjih količin podatkov se je iz različnih razlogov izkazalo tudi nekoliko težavno deloma, deloma zaradi spreminjanja svetlosti neba vsake plošče, ki je bila zajeta zaporedoma blizu zore, vendar tudi uporaba 1,4-kratnega balona nikakor ni pomagala. Dejansko je bila končna slika (na voljo prek povezave) zmanjšana na 50%, deloma tudi zato, ker je bila prvotna lestvica slike prevelika, vendar sem tudi spoznal, da večina spletnih brskalnikov prikazuje slike veliko večje, kot bi si želel ( nad 100% slikovnih pik), kar je v večini primerov neprijetno.

Slika je bila posneta s fotoaparatom C9.25 Edge HD z uporabo kamere ASI183mm z zelenim filtrom (Baader, pasovni pas 500-575nm). Uporabil sem tudi 1,4-krat barlow podjetja Siebert Optics (prodaja se kot 1,3-krat, deluje pa kot 1,4-krat). Kot je bilo omenjeno zgoraj, barlow ni dodal nič koristnega, v resnici pa je obdelavo naredil bolj bolečo in končno sliko zmanjšal. Končna slika je le 38 milijonov slikovnih pik, vendar mislim, da ji je uspelo v to velikost vnesti veliko podrobnosti. Do slike lahko dostopate tako, da sledite ustreznim povezavam za prenos na naslednji povezavi:

Spodaj nudim tudi nekaj obrezanih slik, ki ustrezajo regijam ob zaključku sončnega zahoda, ki se premikajo od severa proti jugu. These needed to be compressed, so they may or may not be equivalent to the same regions of the original image, but they should be pretty similar. The main feature along the terminator is Copernicus, acting as a bullseye near the apparent center of the Moon, but there are many other interesting features as well. I particularly like the crater Bullialdus, which is located along the terminator slightly to the south of Copernicus, and also the craters Wilhelm and Longomontanus, which are prominent along the southern terminator. Owing to a favorable libration, Mare Orientale is visible along the western limb, which I have posted about previously.

In all cases, please click to view the larger images.

Edited by Tom Glenn, 27 December 2019 - 05:00 AM.

#2 Tom Glenn

#3 Tom Glenn

#4 Tom Glenn

#5 Tom Glenn

#6 Tom Glenn

#7 gfstallin

These images represent data that has remained unfinished since last August 24, 2019. I have previously posted images of Copernicus and Mare Orientale, but have not completed the set of data for the entire Moon until now. Aside from the usual time constraints when dealing with large amounts of data, this data also proved to be somewhat difficult to deal with for a variety of reasons, owing in part to the changing sky brightness of each panel as captured in sequence near dawn, but also the use of a 1.4x barlow did not help in any way. In fact, the final image (available by link) was downsized to 50%, in part because the original image scale was too large, but also, I've come to realize that most web browsers display images much larger than I would prefer (above 100% pixel scale), and in most cases this is unflattering.

The image was captured with a C9.25 Edge HD using the ASI183mm camera with a green filter (Baader, bandpass 500-575nm). I also used a 1.4x barlow from Siebert Optics (sold as 1.3x but functions as 1.4x). As mentioned above, the barlow added nothing useful, and in fact made processing more painful, and the final image was downsized. The final image is only 38 megapixels, but I think it manages to pack a lot of detail into that size. You can access the image by following the appropriate links for download at the following link:

August_24_2019_TG.jpg

Excellent work - per usual. Your craters are so. dark. I've been been playing around with various settings attempting to improve performance around dark edges and the limb of the moon, but I cannot avoid rebounds. Any minimal amount of processing of the final image appears to create them, so I'm at a loss on that front.

I've got a couple questions for you. I received the Baader Q-barlow for Christmas, which is advertised as 1.3x when screwed into the eyepiece. I'll see what how that works when screwed into the nosepiece of the camera. I'm also using a 183mm these days. You noted that it made processing more painful. Can you elaborate on how/why?

#8 BillHarris

#9 james7ca

These are all very nice, but I think my favorite may be Sinus Iridum.

#10 Tom Glenn

George, Bill, and James, thanks for the comments.

George, your questions all touch on interesting topics. Sorry if this strays off topic, but in an attempt to address to your questions, I will briefly discuss the issue with the barlow, and then a separate issue about artifacts. The problem with the barlow is twofold. Keep in mind this is all very specific to this particular imaging system (C9.25 Edge and ASI183mm) as it relates to capturing the entire Moon with as much detail as possible in one session.

First, and most importantly, is the loss of field of view (FOV). A 1.4x barlow decreases the area of the FOV by 2x, so it takes about twice as many panels to cover the Moon. This would be trivial if the camera were using a fast frame rate, but it isn’t, and so each image panel takes about 4-5 minutes to capture. Total capture time for these mosaics is generally 20-30 minutes, depending on the lunar phase. But an increase in time to cover the Moon when using the barlow greatly increases the probability that seeing and/or transparency do not remain consistent throughout all recordings. Also, more image panels increase the workload required to compose the mosaic, and also increases the total number of capture files, which can easily fill a hard drive very quickly with this camera.

Second, the use of the 1.4x barlow reduces the amount of light by a full stop, so the exposure has to be adjusted accordingly, usually by increasing the gain. This is not necessarily a deal breaker, but it isn’t ideal, mostly because once again, the number of frames you can capture is limited by slow frame rates and file size.

Both of these issues would be completely inconsequential if the final image outcome was improved in some way. But it isn’t. I have noticed zero improvement in resolution imaging with the barlow versus imaging at f/10 and then drizzling and resizing the output so they are the same scale. The increased scale can sometimes trick you into thinking there is improvement, but comparing the barlow to the drizzle output, they are identical. So, the actual benefit to the barlow is zero, but there are negatives, so there is really no reason to use it. Results can be different on planets, in which you can take many recordings with far more frames, and higher gain is largely irrelevant. But for the Moon, I don’t see much reason to try this again. In fact, for this very reason, in the lunar imaging I have done after these images were captured, I have reverted back to imaging at f/10. Examples below.

Concerning your other question about dark crater floors and “rebound”, I can only assume that by rebound you are referring to some type of ringing artifact. Nearly two years ago I started a thread about some artifacts in lunar images (link here). It started as a simple question, because at the time I was not very experienced at image processing. There were some interesting discussions, although it largely ended inconclusive, with the consensus being that the artifacts are multifactorial in origin. I should probably update the thread with some additional observations, but suffice it to say that artifacts in lunar images are not all created equal.

It is a common assumption that artifacts are a result of over-processing an image, usually by deconvolution or sharpening. This is not always the case, however. Many ringing artifacts are indeed caused by deconvolution , but some are caused by diffraction. I now believe that the ubiquitous white rings that hover inside many craters and along other sharp edges on the Moon are primarily caused by diffraction. Evidence for this is based on several observations. First, when I go back and look at my raw data, I can easily find examples of the white rings inside craters in the raw stack that has not been sharpened or deconvolved at all. Although deconvolution exaggerates the artifact, the artifact is actually present in the raw data. Second, the white ring artifacts are always hovering at a uniform distance away from crater rims throughout the image, and this distance is exactly the angular separation predicted by calculating the distance between alternating energy maxima and minima of an Airy pattern produced by the aperture of the telescope. And this distance scales perfectly with aperture, such that my 6” scope and 9.25” scope have different measurements to the artifacts, that are predicted by their aperture. Third, it is not possible to recreate the white ring artifact inside the craters by simple deconvolution of a “perfect” image, such as an LRO image. You can introduce other ringing artifacts, but not the diffraction ringing that produces the hovering white ring. (More on LRO images at the end). The other prediction here is that the angular size of the artifact depends upon wavelength, but all of my images are fairly close in that respect (green and red filters, really too close to measure a difference with this setup).

This is not to say that all artifacts are caused by diffraction. Deconvolution itself causes ringing and other distortions along sharp edges. Strong deconvolution can cause a crater to look like it has a double rim, etc. I’m NOT referring to those types of artifacts here, which can be mitigated by simply sharpening less aggressively. But the faint white rings that float inside (and outside) crater rims (and the lunar limb) do appear to have their origins in diffraction, that is then exaggerated by deconvolution. This puts the artifact in the same category as artifacts along the bright limb of Mars and Venus, which are similarly caused by diffraction, and are then strengthened by sharpening. In hindsight, I think this all makes good sense. We are frequently sampling at the diffraction level (on purpose), and so diffraction is exactly what we are recording.

This does, however, mean that these crater artifacts are largely impossible to prevent, although there are several methods to try and reduce their influence. Because deconvoluton exaggerates the strength of the artifact, you can choose to use less deconvolution. However, this can have the consequence of less real detail in the image, and because the artifact is present in the raw data, it will appear with any amount of deconvolution. Another method is to hide the artifacts in shadow. Unfortunately, the very regions of the lunar surface in which the artifact is most noticeable (near the terminator) tend to be the exact regions that often benefit from raising shadows, if the goal is to achieve a realistic looking image that matches natural illumination of the Moon. On rugged, mountainous terrain, you can easily reduce the black level to zero without consequence, but if you do this along regions of the terminator that pass through maria, you will destroy fine detail on the lunar surface and the image won’t actually look like the Moon did at the time. To me, that amounts to sacrificing one artifact for another, namely, an unnatural looking illumination. It’s up to each individual to decide what compromises to make in their images.

The other takeaway here, which is somewhat relevant to the ever-present discussions on this forum about the advantage of large aperture telescopes, is that large scopes have much lower diffraction limits, which means you are less likely to be sampling diffraction. Especially if an image is downsized, the diffraction ringing might actually become so small that it’s inconsequential. In this respect, an image from a large aperture scope that is downsized should be cleaner and higher quality than an equivalently scaled image that was captured with a smaller scope and not rescaled. For an extreme example of this, you can look at NASA’s LRO composite that has been downscaled to a scale of 474m/px, which is approximately the image scale that can be produced with a C8.

What you will notice, however, is that the downsampled LRO image has far more detail than you will ever find in a C8 image, because the image is totally noise free. In fact, despite the image scale being approximately what you can obtain with a C8, the NASA image generally has more fine detail than what you find in the very best examples of C14 images that are presented at higher image scales! Just zoom in and look at the floor of Plato and see how many craters you see. The image is all signal and no noise. And that shows the limitations of imaging through an atmosphere, as well as the benefit to capturing and processing a much higher resolution raw image, and then downsizing. I think many amateur images of the Moon could benefit from some downsampling after processing. For the images in this thread, I downsampled precisely because I did not like how the image was looking at the original scale. There are still obvious artifacts if you look closely, but my goal with these images is almost always the overall composition, rather than how it looks at 200% pixel peeping levels. If the original image was made into a 30 inch print, for example, it would look completely free from artifact.

I guess my advice would be to never stop experimenting with different processing schemes, deconvolution methods, and ways to modify the shadow and black levels in final editing. It is, however, basically impossible to create a perfect image, so you have to pick and choose which compromises to make.


Moon Phase and Libration, 2021

Click on the image to download a high-resolution version with feature labels and additional graphics. Hover over the image to reveal the animation frame number, which can be used to locate and download the corresponding frame from any of the animations on this page, including unlabeled high-resolution Moon images. The data in the table for the entire year can be downloaded as a JSON file ali as a text file.

The animation archived on this page shows the geocentric phase, libration, position angle of the axis, and apparent diameter of the Moon throughout the year 2021, at hourly intervals. Until the end of 2021, the initial Dial-A-Moon image will be the frame from this animation for the current hour.

Lunar Reconnaissance Orbiter (LRO) has been in orbit around the Moon since the summer of 2009. Its laser altimeter (LOLA) and camera (LROC) are recording the rugged, airless lunar terrain in exceptional detail, making it possible to visualize the Moon with unprecedented fidelity. This is especially evident in the long shadows cast near the terminator, or day-night line. The pummeled, craggy landscape thrown into high relief at the terminator would be impossible to recreate in the computer without global terrain maps like those from LRO.

The Moon always keeps the same face to us, but not natančno the same face. Because of the tilt and shape of its orbit, we see the Moon from slightly different angles over the course of a month. When a month is compressed into 24 seconds, as it is in this animation, our changing view of the Moon makes it look like it's wobbling. This wobble is called libration.

The word comes from the Latin for "balance scale" (as does the name of the zodiac constellation Libra) and refers to the way such a scale tips up and down on alternating sides. The sub-Earth point gives the amount of libration in longitude and latitude. The sub-Earth point is also the apparent center of the Moon's disk and the location on the Moon where the Earth is directly overhead.

The Moon is subject to other motions as well. It appears to roll back and forth around the sub-Earth point. The roll angle is given by the position angle of the axis, which is the angle of the Moon's north pole relative to celestial north. The Moon also approaches and recedes from us, appearing to grow and shrink. The two extremes, called perigee (near) and apogee (far), differ by as much as 14%.

The most noticed monthly variation in the Moon's appearance is the cycle of phases, caused by the changing angle of the Sun as the Moon orbits the Earth. The cycle begins with the waxing (growing) crescent Moon visible in the west just after sunset. By first quarter, the Moon is high in the sky at sunset and sets around midnight. The full Moon rises at sunset and is high in the sky at midnight. The third quarter Moon is often surprisingly conspicuous in the daylit western sky long after sunrise.

Celestial north is up in these images, corresponding to the view from the northern hemisphere. The descriptions of the print resolution stills also assume a northern hemisphere orientation. (There is also a south-up version of this page.)


Thread: Why does the moon's terminator not appear orthogonal to the direction of the sun?

The moon on the horizon can be zoomed in, so that the photo actually shows it larger on the horizon than higher in the sky. That's a distortion that is similar to the photo that appears in this thread--because if care is taken to not distort the image, the line can appear straight even in the photo.

I can take a series of pictures of a bus starting with the right front wheel, proceed over the bus to the left rear wheel, and stitch them together. The result would show both wheels visible, but that is only because of the distortion of the photo, and is not something that we can actually see.

I need photography lessons from lek, but here's my equatorial-mount panorama. It's not a true ecliptic mount.
I just shortened 1 leg on my camera tripod until it was pointing at what was my best guess as to where Polaris is.

In the panaroma the Moon is noticable, but too small to tell phase. I've labeled the Moon and the approximate position of the Sun.
I can't tell exactly where the Sun is because a large cloud moved in front of it about a minute earlier.

Panaroma:

And this is the portion of the panorama that contains the Moon, zoomed in so you can see phase.

We've already mentioned refraction effects. It's not a matter of "thinking" in this case--the line between the sun and moon is not curved. It's not a matter of refraction or reflection or optical distortion of any sort. It just looks curved to some people. I'm not denying that there are refraction effects in the atmosphere, there are--but not at the level that we are discussing.

I understand how perspective works--parallel lines appear to converge at infinity. But this is not the same thing. The line can even appear in a photograph to not be curved--if the pan is along the line, which is as it should be if we didn't want to distort the line.

I have said that. I've also shown how it is not actually curved.We've already mentioned refraction effects. It's not a matter of "thinking" in this case--the line between the sun and moon is not curved. It's not a matter of refraction or reflection or optical distortion of any sort. It just looks curved to some people. I'm not denying that there are refraction effects in the atmosphere, there are--but not at the level that we are discussing.

I understand how perspective works--parallel lines appear to converge at infinity. But this is not the same thing. The line can even appear in a photograph to not be curved--if the pan is along the line, which is as it should be if we didn't want to distort the line.

This bab about moving the camera along a curved line and stitching the shots together to produce a final photograph showing a straight line is total crap. Jesus, I could take lots of photographs of the circumference of a circle, turning the camera slightly between each shot, and then stitch them together to make the circle look like a straight line. It's a trivial and worthless claim. Wow I could even make a zig-zag line look straight as long as I turn the camera properly and stitch the shots together just right.

I maintain that if the sun and moon are close enough together in the sky for you to take a single photograph with both of them in the frame, the straight line between them (the ecliptic) would have to be drawn as an arc on the photograph, it would not be a straight line on the photograph, unless you're under the ecliptic.

The sun follows the ecliptic, the moon does not.

But what we are discussing here is the straight line between the sun and moon (which would be a straight line in such a picture, ignoring distortion) and whether it would be perpendicular to the terminator. It would.

But that's my point. Stitching the photos together can distort the view--I mentioned doing it to both sides of a bus.The sun follows the ecliptic, the moon does not.

But what we are discussing here is the straight line between the sun and moon (which would be a straight line in such a picture, ignoring distortion) and whether it would be perpendicular to the terminator. It would.

The moon follows the ecliptic closely enough for us to use the approximation.

If the sun and moon had been closer in the sky (or if he'd had a slightly wider angle lens) he could have taken a single photograph with them both in the frame. No stitching. No distortion. And a straight line drawn between the sun and moon on the photograph would ne have been perpendicular to the moon's terminator. Would you like me to draw a line on Lek's photograph for you?

Five degrees then is our allowed error

But what you say below cuts to the heart of the matter and makes the ecliptic issue irrelevant.

lek is wrong there, though, it is not a necessity. For instance, a pinhole camera would do it without the need for the line going through the center of view.

PS: If we are talking about getting both bodies in the same frame. Looking at those posts again, lek is talking about a situation where we cannot get both bodies in the same frame, unless he uses a fisheye lens--which distorts the images. So, lek was not wrong, but he is talking about a situation that doesn't pertain to our basic disagreement there.

I was trying too hard to untangle the thread. I like the single statement, agree or disagree better:

If the sun and moon had been closer in the sky (or if he'd had a slightly wider angle lens) he could have taken a single photograph with them both in the frame. No stitching. No distortion. And a straight line drawn between the sun and moon on the photograph would not have been perpendicular to the moon's terminator. 1

The notion has been suggested that a photograph taken with a
fisheye lens is distorted, while one taken with a normal lens
is not distorted. I've thought about this question and related
questions for many years. (Which is a good reason for me to
feel embarrassed at having given an incorrect explanation of
the illusion early in the thread.)

All representations of three-dimensional objects in 3-D space
on two-dimensional surfaces are distorted. The question is
whether you notice the distortion.

Any image projected on the eye's retina is curved. Some shapes
and figures can seem less curved than others, depending on the
detail they contain, how they are positioned on the retina, and
whether the person is trying to see the curvature. I notice it
if the detail makes it possible and I want to see it. I do not
notice it if I'm not looking for it.

All that is also true of photographs. In addition, changing
focal length or film size or cropping alter the size of the
field. Generally, the larger the field, the greater the
curvature, and the more noticeable the curvature is. Fisheye
lenses have particularly large fields and large curvature from
edge-to edge. Panoramic cameras capture wide fields without
such obvious curvature, but introduce other distortions, which
is evidenced by, for example, the ability of a single person
to show up in more than one place in a single photo!

Pinhole cameras distort as much as any other. If the image is
projected onto a flat surface, it is distorted progressively
more away from the center, like a camera with a lens. If it
is projected onto the inside of a sphere, the resulting image
is essentially distortion-free when viewed from the pinhole
location, but that is the same as an imge made by a camera
with a lens when viewed from the position of the lens. Viewed
from any other position, of course, the image will be highly
distorted.

A straight line which passes through the center of the field
is not distorted from side-to-side, but it is distorted from
end-to end. Imagine a straight line with tick marks on it at
equal intervals. The tick marks appear widely-separated near
the center of the field, and closely-packed near the edges.

That's more or less my point.

Perspective cannot be blamed for this illusion. Lines get mapped to lines.

So how does that work, if you're standing between two parallel railway lines, that stretch from the horizon on your left to the horizon on your right? They meet at the horizon on both sides of you, but if you look down they pass each side of your feet, maybe twenty degrees apart.
Zero degrees apart twenty degrees apart zero degrees apart.
I think you'd be hard pressed to process the converging lines to your left and the converging lines to your right as forming parts of the same pair of straight lines inside your head. It certainly doesn't work for me.

That's my point. It is inside your head.

That's what makes it an illusion, rather than something physical. In the case of either line, if you draw a straight line along it, it stays along it. Some people can look at rail lines and not be convinced that they actually converge.

That's my point. It is inside your head.

That's what makes it an illusion, rather than something physical.

Which is my point, referring to your remark "Perspective cannot be blamed for this illusion."
Surely perspective is inside your head, rather than something physical? And the apparent curvature is part of the process of perceiving perspective, just as the apparent convergence is.

Then you're in something of a minority, I think, since the illusion as described by the OP is well reported. It's certainly very striking to me.
Do you do a lot of sky-watching? (I'm wondering if the habit of orientating yourself along great circles might make you better at seeing straight lines as running straight over arcs wider than your central visual field.)

All of us here do a lot of skywatching, no?

But I'd say from my experience, it's engineers that have a developed three dimensional sense. Astronomers too maybe. And mathematicians. Taxi drivers. And artists. Hunters. Climbers. I suppose I could fit in any of those groups. Also pilots I'd imagine. But I'm not convinced it's necessary.

Yes, okay, but do you do a lot?

Originally Posted by [url=http://www.bautforum.com/showthread.php?p=698829#post698829]hhEb09'1[/url]

Can somebody please take a photograph of the moon and sun in the same frame and show hhEb09'1 that he's sadly wrong. The moon is more or less full now but should be a nice quarter crescent and only 45 degrees from the sun in about 10 days time. That should allow them both to appear in the frame using a 50mm lens, which closely represents the magnification of the eye, so there shouldn't be any distortion due to wide-angle or telephoto lensing.

The clock is ticking hhEb09'1. Maybe you'd like to place a wager?

A 50 mm lens on a 35 mm camera doesn't have a wide enough field
to capture Sun and Moon in one frame when 45 degrees apart.

A 50 mm lens on a 35 mm camera doesn't guarantee elimination
of distortion. It does minimize distortion to a large extent,
but it is only an approximation. The human mind accomodates
a considerable amount of distortion without noticing it. Torej
the distortion in a photograph has to be quite large before
you think, "That doesn't look quite right."

As I said previously, a straight line through the center of any
lens should be undistorted from side-to-side. A straight line
drawn in the sky from Sun to Moon, and photographed so that the
image of the line passes through the center of the lens, should
be perpendicular to the Moon's terminator in the photo.

A 50 mm lens on a 35 mm camera doesn't have a wide enough field
to capture Sun and Moon in one frame when 45 degrees apart.

A 50 mm lens on a 35 mm camera doesn't guarantee elimination
of distortion. It does minimize distortion to a large extent,
but it is only an approximation. The human mind accomodates
a considerable amount of distortion without noticing it. Torej
the distortion in a photograph has to be quite large before
you think, "That doesn't look quite right."

As I said previously, a straight line through the center of any
lens should be undistorted from side-to-side. A straight line
drawn in the sky from Sun to Moon, and photographed so that the
image of the line passes through the center of the lens, should
be perpendicular to the Moon's terminator in the photo.

Well then we'll just have to wait and see won't we. No matter how hard I try I can't imagine a photograph of the ecliptic projected in a planetarium showing a straight line, even if the image of the line passes through the centre of the lens (which is a pretty pointless requirement in my opinion - good quality camera lenses around 50mm do not distort straight lines very much, even at the edge of the frame), unless you have the camera in the plane of the ecliptic.

Nice picture.. if I had a landscape monitor i'd make it my desktop background,
might be worth submitting it to APOD/EPOD

I quite by coincidence took an image on 8 March that illustrates the illusion.

That isn't relevant. A straight line between the Sun and Moon
is a straight line nomatter where you view it from.

I'm not sure why you talk about lines on a planetarium dome.
A planetarium dome is a poor simulation of the sky, because
the sky is not a dome! It resembles a dome in some ways,
but only some.

I agree with Grant's analysis, based in part on your excellent
diagrams. A straight line between the Sun and Moon can be made
by, for example, a yardstick or a piece of string stretched
between your hands. That straight line is the thick, gray line
in your diagrams. It is curved in your diagrams because of the
way it is projected onto the diagrams. And it actually looks
curved in exactly the same way as your diagrams. (If they were
drawn to accurate scale and so forth. You just drew them by
eye, which was accurate enough for the purpose.)

If you want to accurately draw a straight line across the sky,
you need to hold up a yardstick, or a piece of string, or hire
a skywriter to make a trail on a windless day, or get lucky
and see crepuscular rays which stretch all the way from the
Sun to a point on the far side of the sky. Such a line will
look straight or curved depending on how you look at it.

I think you posted the wrong link. I'd like to see your photo
when you get the link straightened out.

I think you posted the wrong link. I'd like to see your photo
when you get the link straightened out.


Photographer Creates 'Impossible' Image Of The Moon's Surface

A photographer has created an image of the moon that has never been seen before.

Using thousands of photographs taken over a couple of weeks, astrophotographer Andrew McCarthy built a composite picture, showing the incredible depth of the Moon's surface.

The California-based snapper posted the super-clear pic to his Instagram account. Titled 'All Terminator', Andrew described it as an 'impossible scene'.

He wrote: "This moon might look a little funny to you, and that's because it is an impossible scene.

"From two weeks of images of the waxing moon, I took the section of the picture that has the most contrast (right before the lunar terminator where shadows are the longest), aligned and blended them to show the rich texture across the entire surface.

Andrew spent two weeks creating this incredible image. Credit: SWNS

"This was exhausting to say the least, namely because the moon doesn't line up day over day, so each image had to be mapped to a 3D sphere and adjusted to make sure each image aligned."

'Lunar terminator' is the term used to describe the line between the light and dark side of the moon.

The sun creates larger and longer shadows in the terminator, which help give the image a three-dimensional appearance.

They also make the moon's surface much clearer, giving the craters much more focus and making them more prominent in the photo.

The California-based snapper used thousands of photos to create one detailed image. Credit: SWNS

Sadly, Andrew's photo couldn't shed on any more light on claims made last week that there were cities on the moon.

Self-styled UFO and alien hunter Scott C Waring claims he's seen proof that aliens not only exist but also that they're on the moon.

On his website, The ET Database, he shared what he calls ' 100% Indisputable Proof ' of 'alien cities'.

Waring says he was looking at some detailed images that 'partially reveal the dark side of the moon, or almost dark side because Earth cannot view this part of the moon, but a little sun light does hit part of it'.

He continued: "The white dots, which so many inexperienced people have called photo flaws, are real. My proof is the shadow. Look at the shadow covering them."

He then added: " You will notice like I did that there is some unusual formations of white dots. These are evenly spaced apart and stay close to one another. That is because you are looking at cities on the moon."


Why Is It Called a Quarter Moon (Not a Half Moon)?

When you’re looking at a Moon that’s half-illuminated—like half a pie—why is it called a “Quarter Moon” instead of a “Half Moon”? Seems confusing, right? Bob Berman defines the Quarter Moon—and explains why it’s the most interesting Moon phase in his eyes. Let’s take a closer look at the beautiful Quarter Moon.

Why Do We Call It the Quarter Moon?

We’ve all looked up at the night sky and seen half of the Moon’s disk illuminated. If you had two half Moons and fit them together, you’d get a full Moon. But when you’re looking at a Half Moon, the official name is “Quarter Moon.” There’s no half-moon phase, at least not in any official way. But it appears as half-illuminated. This may seem odd, but let me explain.

Think of the Moon going around the Earth as a runner going around baseball plates (first base, etc.).

  • Earth is the pitcher. When the runner hits the ball, it goes to first base (one quarter of the way around). Similarly, at the Quarter Moon, the Moon is one quarter of the way through its orbit.
  • Then, the runner goes to second base (half way around), then to third base (three quarters around). The Moon is three-quarters of the way through it’s orbital cycle and, therefore, is called the Third Quarter Moon.

At first base or third base, you get the quarter Moons.

First Quarter vs. Third Quarter

With the Quarter Moon—which looks like half the Moon—we can see exactly 50% of the Moon’s face illuminated from Earth.

Sometimes it also gets confusing to remember which “Quarter” we are seeing:

  • The Moon appears lit on the right half of the Moon during the First Quarter.
  • The Moon appears lit on the left side during the Third Quarter because the Moon is on the other side of Earth.

Again, if you think of the baseball analogy, and you’re standing at home plate, the first base or First Quarter is on your right side. The third base or Third Quarter is on your side.

The First Quarter happens around day 7 of a Moon’s cycle (one week after the New Moon) and the Third Quarter usually happens around day 22 (three weeks after the New Moon).

Why the Quarter Moons Are Special

To me, the Quarter Moon is much more interesting than the Full Moon. This is the Moon that’s at its highest at sunset just around dinner time.

While the Full Moon provides a lot of light on Earth, if you’re observing the Moon’s surface, most beginning astronomers can’t see much beyond the blinding orb. The Sun then shines straight down like a flash camera to erase all shadows and highlights.

Luna iz prve četrtine

But take a look at the Quarter Moon. The First Quarter Moon is the “Half Moon” that we see most.

The shadowing is perfect. You see all the mountains and craters. It’s fascinating to look at. The First Quarter Moon explodes with breathtaking detail for anyone with binoculars, spotting scope, or even the smallest telescope.

Last Quarter Moon

With the Last Quarter Moon, the left half appears to be lit up by sunshine and the rest immersed in shadow.

It doesn’t even rise until midnight and it’s not at its highest until around dawn. Who’s up then? Nobody! Most of us don’t want to haul our telescopes out at 5 A.M. or 6 A.M. to look at the Half Moon when you could look at the “other Half Moon” (the First Quarter Moon) at six in the evening when it’s convenient. Everyone’s used to the First Quarter Moon.

More Cool Quarter Moon Facts

The Quarter Moon aims its terminator, the day-night line that is home to all the juicy detail, straight at us. It’s lies directly ahead of us as Earth is zooming through the universe. This means highlighted craters then face you like actors hamming it up, instead of pointing, foreshortened, in other directions the way the rest of the lunar phases do.

You’d think a Half Moon would be half as bright as a Full Moon, right? Oddly enough, a Half Moon is only one tenth as bright as a Full Moon. Yet why does it seem so bright? This is because the Full Moon throws sunlight straight back at us like a movie screen, while the First Quarter’s sideways illumination creates innumerable unseen shadows in the Moon’s powdery surface.

How to Best View the Quarter Moon

Point the cheapest telescope towards the Quarter Moon. Stay below 60 power and the entire Moon will fill the field like a scene from 2001.

Even ordinary binoculars reveal the lunar Apennines, that mountain range just above dead center, whose jagged Himalaya-sized peaks tower straight up at you like skyscrapers.

Then there’s the badlands, the southern region, crazily pockmarked with a generous sampling of the 30,000 craters visible from Earth.

The scene changes dramatically each night as the terminator slithers over the Moon’s surface at 10 miles per hour. (A lunar jogger with enough stamina could keep nightfall at bay!)

Yes, this is a Moon phase packed with misconception. Even its name is misleading: how many realize that the Quarter Moon is the same thing as a Half Moon?


Moon's Phases Are a Lunar Delight for Stargazers

If you have recently received a telescope as a holiday gift, it is likely that your very first target will be our nearest neighbor in space: the moon.

When is the best time to observe the moon with a telescope? Most astronomy neophytes might say it is when it's at full phase, but that's probably the worst time to look at it! When the moon is full it tends to be dazzlingly bright as well as flat and one-dimensional in appearance.

In contrast, the interval when the moon is at or just past first quarter phase, or at or just before last quarter phase, is when we get the best views of the lunar landscape right along the sunrise-sunset line or terminator. The terminator can also be defined as that variable line between the illuminated portion and the part of the moon in shadow.

Along with the fact that a half moon offers more viewing comfort to the eye as opposed to a full moon, using a telescope with just small optical power (magnifications of 20- to 40-power), or even with good binoculars, we can then see a wealth of detail on its surface. Around those times when the moon is half-lit or gibbous phase, those features lying close to the terminator stand out in sharp, clear relief. [The Moon: 10 Surprising Lunar Facts]

In contrast to a half moon, a full moonis almost completely illuminated, especially right around its center the sun shines straight down even into all the microscopic crevices and except for perhaps around its immediate edges, you will find no visible shadows at all.

The moon will arrive at last quarter phase on Thursday, Feb 11, at 10:50 p.m. EST (0350 Feb. 12 GMT). That will be the moment when the moon's disk is exactly 50-percent illuminated. Lunar mountains will be visible as the sun lights them from the right.

How does a last quarter moon's brightness compare with a full moon? You might think it would be half as bright as a full moon, but in reality astronomers tell us that the last quarter (or first quarter) moon is only 1/11th as bright as full. This is due to the fact that, a half moon is heavily shadowed, even on its illuminated half. And believe or not, it isn't until just 2.4 days before full that the moon actually becomes half as bright as full!

Finally, have you ever noticed that when artists portray the moon, they invariably seem to show it as either a slender crescent or full?

Half-moons are shown far less frequently, while gibbous moons are rarely depicted at all. The word gibbous is derived from the Latin word "gibbus" meaning, "hump." An unusual word to be sure, but in describing the moon between half and full, it's the correct term.

Yet interestingly, the gibbous moon, the phase of the moon that we are now seeing in our current evening sky is the most-seen phase. It occurs for the half month between first and last quarter (although for many it looks "full" for two or even three nights around the time of full moon).

Because it is in the sky for more than half the night we're more apt to see the gibbous moon. In fact, it is even visible during the daytime hours, as will be the case during this upcoming week in mid or late afternoon. In contrast, the oft-pictured crescent moon is visible only during the early evening or early morning hours, and sometimes only briefly.


Poglej si posnetek: Терминатор Т-800 CSM-101 имя, происхождение, миссия ОБЪЕКТ terminator 1984 (December 2022).