Astronomija

Kaj bi povzročilo velike skoke svetlosti med sončnim mrkom?

Kaj bi povzročilo velike skoke svetlosti med sončnim mrkom?


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To vprašanje o Physics SE o navidezni svetlosti med Sončevim mrkom ima graf grafov intenzitete svetlobe glede na čas. Njegovi deli so v obliki, ki bi jo pričakoval: skoraj gladka krivulja, ki prehaja iz "izredno svetle" v "zelo zatemnjeno". Vendar pa je v grafu navidezen navidezen hrup s skoki skoraj celotne delitve grafa (kar ustreza približno dvakratni ali osemkratni spremembi svetlosti, odvisno od tega, ali gre za naravni dnevnik ali bazo-10 ). Kaj povzroča te skoke?


Eric Pauer, ki je izdelal tabelo, ima zanimivo spletno mesto, ki pokriva ta mrk. Očitno je, da vreme v času mrka z občasno oblačnostjo ni bilo čudovito in da bodo mimo oblaki povzročali nihanja v intenzivnosti.

Dokaze si lahko ogledate na tej strani http://www.pauerhome.com/eclipse/eclipse99/1contact/1contact.htm


Danjonova lestvica svetlosti luninega mrka

Videz Lune med popolnim Luninim mrkom se lahko zelo razlikuje od enega do drugega mrka. Očitno ima geometrija Lunine poti skozi umbra pomembno vlogo. Ni tako očiten učinek Zemljine atmosfere na mrke. Čeprav fizična masa Zemlje blokira vso sončno svetlobo iz umbra, planetova atmosfera lomi nekatere sončne žarke v senco. Zemeljska atmosfera vsebuje različne količine vode (oblaki, megla, padavine) in trdne delce (prah, organski ostanki, vulkanski pepel). Ta material filtrira in duši sončno svetlobo, preden se lomi v umbro. Na primer, velikim ali pogostim vulkanskim izbruhom, ki v ozračje odlagajo ogromne količine pepela, pogosto več let sledijo zelo temni, rdeči mrki. Obsežna oblačnost ob Zemljini okončini tudi mrk zatemni z blokiranjem sončne svetlobe.

Francoski astronom Andr & eacute-Louis Danjon je predlagal koristno petstopenjsko lestvico za oceno vizualnega videza in svetlosti Lune med popolnimi Luninimi mrki. Vrednosti „L“ za različne svetilnosti so opredeljene na naslednji način:

Dodelitev vrednosti 'L' luninim mrkom je najbolje opraviti s prostim očesom, daljnogledi ali majhnim teleskopom blizu časa srednjega obsega. Koristno je tudi preučiti videz Lune tik po začetku in pred koncem celote. Luna je nato blizu roba sence in daje priložnost, da zunanji umbri dodeli vrednost 'L'. Pri kakršnih koli ocenah morate zabeležiti tako instrumentacijo kot čas. Upoštevajte tudi morebitne razlike v barvi in ​​svetlosti na različnih delih trsnice ter navidezno ostrino roba sence. Bodite pozorni na vidnost luninih lastnosti znotraj umbre. Opombe in skice, narejene med mrkom, so neprecenljive za priklic podrobnosti, dogodkov in vtisov.


NE uporabljajte naslednjih metod za ogled sončnega mrka / mrka sonca Naslednje metode NISO VARNE!

Ne sme se ga uporabljati, če ni POSEBNO NAMENJEN OZORU SOLARNEGA ZAMRKANJA in NEŠKODBEN (tj. Ne vsebuje luknjic ali lukenj)!

Najpogostejši tip Sončevega mrka / mrka Sonca je delni sončni mrk / delni mrk sonca (ki vključuje sončne mrke / mrke sonca, opisane kot "okrogli" ali "hibridni"). Ta običajna vrsta Sončevega mrka je VEDNO NEVARNA. Nikoli si ne poskušajte neposredno ogledati te vrste Eclipse, če nimate ustreznega treninga in ustrezne opreme. Obstaja več načinov, kako posredno gledati takšen Mrk, kar lahko varno storite, če to storite previdno.

Obstaja samo eno kratko časovno obdobje ko je varno pogledati Sončev mrk / mrk Sonca neposredno, brez umetnih previdnostnih ukrepov. Takrat oseba išče, posebej, ob popolnem Sončevem mrku / popolnem mrku Sonca, posebej, ko je oseba znotraj Eklipsejeve poti celote, in posebej, v kratkem časovnem obdobju (nekaj minut, pogosto manj), ko je mrk v popolni fazi. Vendar pa so vse delne faze popolnega Sončevega mrka / popolnega Sončevega mrka (ki vključuje Sončne mrke / Sončeve mrke, opisane kot "hibridne"), ki vodijo do skupne faze in po skupni fazi, nevarne za ogled. neposredno, razen če imate ustrezen trening in ustrezno opremo za varno izvajanje. Sončno sevanje je nevarno, kadar koli je viden kateri koli del sonca ( edina izjema je pogled na Sončno korono med celotno fazo popolnega Sončevega mrka, ko Luna (vsi Sončni mrki nastanejo v fazi Mlade Lune) blokira vso neposredno sončno svetlobo). Ponovno obstaja več načinov, kako posredno gledati takšen Mrk, kar lahko varno storite, če to storite previdno.

Varno sončno gledanje, ko končate previdno!

Internet ali televizija & ndash Seveda je najvarnejši način za ogled katerega koli posebnega sončnega dogodka v spletnem oddajanju v spletu ali televizijski oddaji ali posebnem programu. Pogosto med posebnimi sončnimi dogodki, kot so Sončev mrk / Sončev mrk ali Sončni tranzit planeta, poklicne organizacije, kot so NASA, observatorij Griffith v Los Angelesu in Observatorij Skupnosti Slooh, zagotavljajo spletne oddaje takih posebnih dogodkov. določeno spletno mesto za razpored takšnih oddaj. Za poseben dogodek bodo včasih televizijske postaje in / ali omrežja, zlasti kabelske televizijske postaje, specializirane za novice ali znanost, predvajale tudi lokalne sezname dogodkov za čas in kanal.

Javni opazovalni dogodki & ndash Pogosto bodo znanstvene in izobraževalne ustanove sponzorirale javne opazovalne prireditve, kjer profesionalna astronomska oprema, ki jo upravljajo usposobljeni astronomi, zagotavlja varen javni ogled Sončevega mrka / mrka Sonca ali sončnega tranzita planeta. Takšne institucije lahko vključujejo tudi prenos video posnetkov dogodka v živo z NASA-e ali drugih znanstvenih organizacij, zlasti za Sončev mrk / mrk Sonca, kjer opazovanje teleskopa v instituciji ne more prikazati popolnega mrka ali kadar vreme izključuje lokalno opazovanje teleskopa v teleskopu. dogodek. Preverite pri lokalnem planetariju, astronomskem observatoriju, znanstvenem centru ali muzeju znanosti, oddelku za znanost (še posebej, če obstaja oddelek za astronomijo ali fiziko) lokalnega kolidža ali univerze (ali, morda, srednje šole), amaterskega astronomskega krožka ali lokalnega knjižnico, da bi ugotovili, ali sponzorirajo tak dogodek.

Ogledno okno sončne luknje & ndash Naslednja slika prikazuje posreden način varnega ogleda delnih faz Sončevega mrka / mrka Sonca (ki vključuje Sončeve mrke / mrke Sonca, opisane kot "obročasto" ali "hibridno") z gradnjo Solar Pinhole Viewing Box (znan kot Pinhole Camera). Ko zgradite to škatlo, se obrnite s hrbtom proti soncu in pustite, da sončna svetloba sije skozi luknjo (postavljena v list aluminijaste folije, pritrjena na sredino enega konca škatle) in sije na belo kos papirja za tipkanje, tiskalnik ali fotokopijo na drugem koncu škatle majhna slika delnega sončnega mrka / delnega mrka sonca (ki vključuje sončne mrke / mrke sonca, opisane kot "okrogle" ali "hibridne") je nato mogoče videti projicirano na belem papirju. Ne pričakujte velike ali svetle slike Sonca, saj luknja ne more povečati ali posvetliti slike. NIKOLI NE POGLEDAJTE KROZ ŠKOLJKO DO SONCA! Seveda obstaja več različic ideje o Solar Pinhole Viewing Box, vključno s preprosto uporabo dveh kosov papirja, enega belega, drugi pa ima luknjo v gozdovih, naravne luknjaste kamere so včasih oblikovane skozi gosto listje, z majhnimi podobe zatemnjenega Sonca, ki se pojavljajo na tleh.

[Grafični vir: Eric G. Canali, nekdanji vodja talnih operacij prvotnega planetarja Buhl in Inštitut za popularno znanost (znan tudi kot Buhl Science Center), muzej znanosti in tehnologije v Pittsburghu od 1939 do 1991 in ustanovitelj astronomije astronomov South Hills Backyard klub. Grafika prvotno izdelana za pokrovitelje planeta Buhl, za Sončev mrk iz leta 1991, 11. julija.]

"Sončna očala Eclipse & rdquo & ndash V zadnjih 30 letih je tehnologija zagotovila še en varen način za ogled Sončevega mrka / mrka sonca. & LdquoSolar Eclipse očala & rdquo ali pogosto imenovana & ldquoEclipse očala & rdquo imajo leče iz aluminiziranega in optičnega stekla Mylar (POSEBNA OPOMBA: Mylar, ki se uporablja na Mylar balonih ali zavitkih za hrano, je NE optičnega razreda), tako gosto, da je s takšnimi očali Eclipse mogoče videti le svetlobo sonca (več kot 1000-krat temnejša od običajnih sončnih očal!). Poceni ponarejena očala Eclipse so bila razpisana za prodajo, vendar bi morala NIKOLI NE UPORABLJAJTE! Da bi se izognili nakupu ponarejenih očal Eclipse, kupite ali uporabite očala Eclipse, ki jih je odobrilo Ameriško astronomsko društvo, pojdite na to spletno stran na spletnem mestu Ameriškega astronomskega društva in preberite seznam odobrenih prodajalcev varnih očal Eclipse:

Sledijo navodila za pravilno ravnanje z očali Eclipse in njihovo uporabo:

a) Očala Eclipse so krhka in jih je treba ves čas nežno ravnati. Najbolje bi bilo, da očala Eclipse shranite v

b) PRED VSAKO UPORABO usmerite očala Eclipse proti umetnemu viru svetlobe (tj. prižgani žarnici). Če je skozi očala Eclipse vidna svetloba ali če so na lečah vidne poškodbe (praske, raztrganine ali majhne luknje ali luknjice) (preverite sprednjo in zadnjo stran leč) ali če se leče Mylar zaženejo da se ločijo od kartonskih okvirjev očal Eclipse, je treba ta par očal Eclipse zavreči (očala Eclipse raztrgati ali narezati na majhne koščke, tako da jih nihče nenamerno ne uporablja). UPORABA OŠKODLJENIH OČAL EKLIPSE BI DOVOLILA NEVARNO SONČNO, DA VSTOPE V OČI, KI LAHKO VODIJO DO ŠKODE OČI.

c) Za ljudi, ki nosijo očala, je treba očala Eclipse postaviti nad očala - to pomeni, da sončna svetloba vstopi v očala Eclipse, preden vstopi v očala.

d) NIKOLI ne uporabljajte očal Eclipse s katero koli kamero (vključno s kamerami za mobilne telefone ali pametne telefone), teleskopom, daljnogledi ali kakršnim koli optičnim pripomočkom ali napravo (razen očal), ki poveča sliko (ali odsev povečane slike) Eclipse Očala so zasnovana samo za uporabo s prostimi očmi ali z očali.

e) NE poskusite očistiti ali razkužiti leče Eclipse Glasses z vodo ali katerim koli drugim čistilnim sredstvom. Če skrbno skrbite za očala Eclipse, vključno s shranjevanjem v ovojnici, čiščenje leč ne bo potrebno. Če je prah zaskrbljujoč, naredite le prah, ki ga ne odpihnete.

f) NIKOLI uporabite kakršna koli "domača" ali "ročno izdelana" očala Soc Eclipse ali katera koli očala Soc Eclipse, ki jih proizvaja prodajalec in ki jih Ameriško astronomsko društvo ni odobrilo. Takšna očala Eclipse nimajo nadzora kakovosti v proizvodnji, zato ni mogoče vedeti, ali so ta očala Eclipse varna za vid.

g) Očala Eclipse NISO igrače. OČALA ECLIPSE MORAJO UPORABLJATI SAMO OTROKI, Z NADZOROM ODRASLIH!

5. OTENČENO ŠTEVILO ŠTEVILKA 14 VARILO STEKLO & ndash OTENKOVO ŠTEVILO ŠTEVILO 14 VARILO STEKLO (IN SAMO STEKLO ZA VARILEC, OCENJENO V ODTENKU ŠTEVILKA 14, NAJTEMNEJŠA ODTENKA JE DOVOLJ MOČNO, VARNO ZA OČI) je dovolj varno za običajna varilna dela in je lahko varno (vendar ni nobenih jamstev) za ogled Sončevega mrka / mrka kozarec za varjenje sonca je zasnovan posebej za varilna dela, ne za opazovanje sonca. VSEBE pa uporabljajte samo Welder's Glass, ki je ocenjen na senco številka 14, tako kot pri sončnih očalih NI VARNO da skupaj zložimo več svetlejših odtenkov varilnega stekla. Čeprav je senčilo s številko 14 Welder's Glass morda varno, saj je sonce tako svetlo, je uporaba Welder's Glass št. 14 lahko neprijetno.

NE MENITE Sončevega mrka / mrka Sonca z Luninim mrkom / mrkom Lune, kjer Luna delno ali v celoti zakriva Zemljina senca. Vsak Lunin mrk / Lunin mrk je varno gledati s prostimi očmi (z eno močjo), daljnogledi ali teleskopom.

Za nadaljnja vprašanja o varnem ogledu Sončevega mrka / mrka Sonca pošljite elektronsko sporočilo na

Če ste na območju Pittsburgha, lahko tudi telefonirate: 412-561-7876 veljajo običajne medkrajevne pristojbine za telefonske klice zunaj območja Pittsburgha. Vprašanje pustite na telefonskem odzivniku.

Pred sončnim mrkom se bomo potrudili, da vrnemo vaše elektronsko sporočilo ali telefonski klic.


Vsebina

Obstajajo štiri vrste sončnih mrkov:

  • A popolni mrk se zgodi, ko temna silhueta Lune popolnoma zakrije močno svetlobo Sonca, kar omogoča, da je vidna precej šibkejša sončna korona. Med katerim koli mrkom se celota v najboljšem primeru pojavi le v ozkem tiru na površju Zemlje. [6] Ta ozka pot se imenuje pot celotnosti. [7]
  • An obročast mrk se pojavi, ko sta Sonce in Luna natančno v skladu z Zemljo, vendar je navidezna velikost Lune manjša od velikosti Sonca. Sonce je torej videti kot zelo svetel obroč ali obroč, ki obkroža temni disk Lune. [8]
  • A hibridni mrk (imenovano tudi obročast / popoln mrk) se premika med popolnim in obročastim mrkom. Na določenih točkah na površju Zemlje je videti kot popolni mrk, na drugih točkah pa kot obročast. Hibridni mrki so razmeroma redki. [8]
  • A delni mrk se pojavi, ko Sonce in Luna nista ravno v skladu z Zemljo in Luna le delno zakrije Sonce. Ta pojav je običajno mogoče videti z velikega dela Zemlje zunaj tira obročastoga ali popolnega mrka. Nekatere mrke pa lahko vidimo le kot delni mrk, ker umbra prehaja nad polarna območja Zemlje in nikoli ne seka zemeljske površine. [8] Delni mrki so glede na Sončevo svetlost tako rekoč neopazni, saj je potrebno več kot 90-odstotno pokritost, da se sploh zatemni. Tudi pri 99% ne bi bil nič temnejši od civilnega mraka. [9] Seveda lahko delne mrke (in delne stopnje drugih mrkov) opazimo, če gledamo Sonce skozi zatemnitveni filter (ki ga je treba vedno uporabiti zaradi varnosti).

Sončeva oddaljenost od Zemlje je približno 400-krat večja od Lunine, premer Sonca pa približno 400-krat večji od Luninega. Ker sta ta razmerja približno enaka, se zdi, da sta Sonce in Luna, gledano z Zemlje, približno enake velikosti: približno 0,5 stopinje loka v kotni meri. [8]

Ločena kategorija Sončevih mrkov je kategorija Sonca, ki jo zapre telo, ki ni Zemljina Luna, kar lahko opazimo na točkah v vesolju stran od Zemljine površine. Dva primera sta, ko je posadka Apolla 12 leta 1969 opazovala Zemljin mrk Sonce in ko je Cassini sonda je opazila, da je Saturn leta 2006 zasenčil Sonce.

Lunina orbita okoli Zemlje je rahlo eliptična, prav tako zemeljska okoli Sonca. Navidezne velikosti Sonca in Lune se zato razlikujejo. [10] Velikost mrka je razmerje med navidezno velikostjo Lune in navidezno velikostjo Sonca med mrkom. Mrk, ki se zgodi, ko je Luna blizu najbližje razdalje do Zemlje (tj. blizu njegovega perigeja) je lahko popoln mrk, ker se bo zdelo, da je Luna dovolj velika, da v celoti pokrije Sončev svetel disk ali fotosfero. Celotni mrk ima velikost večjo ali enako 1.000. Nasprotno pa mrk, ki se zgodi, ko je Luna blizu najbolj oddaljene od Zemlje (tj. blizu apogeja) je lahko le obročast mrk, ker se zdi, da je Luna nekoliko manjša od Sonca, je velikost obročastoga mrka manjša od 1. [11]

Hibridni mrk se zgodi, ko se velikost mrka med dogodkom spremeni iz manjšega kot večjega od enega, zato se zdi, da je mrk popoln na lokacijah bližje srednji točki, obročasti pa na drugih mestih bližje začetku in koncu, saj se stranice Zemlja je nekoliko bolj oddaljena od Lune. Ti mrki so izjemno ozki v svoji širini poti in so na kateri koli točki razmeroma kratki v primerjavi s popolnoma popolnimi mrki. Skupnost hibridnih mrkov 20. aprila 2023 traja več kot minuto na različnih točkah na poti celotnosti. Tako kot žariščna točka sta širina in trajanje celote in obročastosti blizu točk, kjer se pojavita spremembi med njima. [12]

Ker je tudi Zemljina orbita okoli Sonca eliptična, se oddaljenost Zemlje od Sonca skozi leto spreminja podobno. To vpliva na navidezno velikost Sonca na enak način, vendar ne toliko kot na različno oddaljenost Lune od Zemlje. [8] Ko se Zemlja v začetku julija približa svoji najbolj oddaljeni oddaljenosti od Sonca, je popoln mrk nekoliko bolj verjeten, medtem ko razmere favorizirajo obročast mrk, ko se Zemlja v začetku januarja približa najbližji razdalji od Sonca. [13]

Terminologija za osrednji mrk

Centralni mrk se pogosto uporablja kot splošni izraz za popolni, obročast ali hibriden mrk. [14] To pa ni povsem pravilno: opredelitev osrednjega mrka je mrk, med katerim se osrednja črta umbre dotakne Zemljine površine. Možno je, čeprav izjemno redko, da se del umbre seka z Zemljo (s čimer se ustvari obročast ali popoln mrk), ne pa tudi njene osrednje črte. Takrat se imenuje necentralni popolni ali obročast mrk. [14] Gama je merilo, kako osrednje udari senca. Zadnji (umbralni še) necentralni Sončev mrk je bil 29. aprila 2014. To je bil obročast mrk. Naslednji necentralni popolni Sončev mrk bo 9. aprila 2043. [15]

Faze, opažene med popolnim mrkom, se imenujejo: [16]

  • Prvi stik - ko je Lunin krak (rob) natančno tangenten na Sončev ud.
  • Drugi stik - začenši z Bailyjevimi kroglicami (ki jih povzroča svetloba, ki sije skozi doline na Lunini površini) in učinkom diamantnega obroča. Pokrit je skoraj celoten disk.
  • Totalnost - Luna zakrije celoten disk Sonca in vidna je samo sončna korona.
  • Tretji stik - ko postane prva močna svetloba vidna in se Lunina senca oddalji od opazovalca. Spet lahko opazimo diamantni prstan.
  • Četrti stik - ko se zadnji del Lune preneha prekrivati ​​s sončnim diskom in se mrk konča.

Geometrija

Diagrami na desni kažejo poravnavo Sonca, Lune in Zemlje med sončnim mrkom. Temno sivo območje med Luno in Zemljo je umbra, kjer je Luna popolnoma zaprta od Sonca. Na majhnem območju, kjer se umbra dotakne Zemljine površine, lahko opazimo popoln mrk. Večje svetlo sivo območje je penumbra, v kateri je viden delni mrk. Opazovalec v antumbri, območju sence onkraj umbre, bo videl obročast mrk. [17]

Lunina orbita okoli Zemlje je nagnjena pod kotom nekaj več kot 5 stopinj glede na ravnino Zemljine orbite okoli Sonca (ekliptike). Zaradi tega bo v času nove lune Luna običajno prehajala na sever ali jug Sonca. Sončev mrk se lahko zgodi šele, ko se mlada luna zgodi blizu ene od točk (znanih kot vozlišča), kjer Lunina orbita prečka ekliptiko. [18]

Kot smo že omenili, je tudi Lunina orbita eliptična. Lunina oddaljenost od Zemlje se lahko razlikuje za približno 6% od svoje povprečne vrednosti. Zato se navidezna velikost Lune spreminja glede na njeno oddaljenost od Zemlje in prav ta učinek vodi do razlike med popolnimi in obročastimi mrki. Tudi razdalja Zemlje od Sonca se med letom spreminja, vendar je to manjši učinek. Zdi se, da je Luna v povprečju nekoliko manjša od Sonca, gledano z Zemlje, zato je večina (približno 60%) osrednjih mrkov obročastih. Šele ko je Luna bližje Zemlji od povprečja (blizu njenega perigeja), se zgodi popoln mrk. [19] [20]

Luna Sonce
V perigeju
(najbližje)
Ob apogeju
(najbolj oddaljeno)
V periheliju
(najbližje)
Pri afeliju
(najbolj oddaljeno)
Povprečni polmer 1.737,10 km
(1.079,38 mi)
696.000 km
(432.000 mi)
Razdalja 363.104 km
(225.622 milj)
405.696 km
(252.088 mi)
147.098.070 km
(91.402.500 mi)
152.097.700 km
(94.509.100 mi)
Kotna
premer [21]
33' 30"
(0.5583°)
29' 26"
(0.4905°)
32' 42"
(0.5450°)
31' 36"
(0.5267°)
Navidezna velikost
za merjenje
Naroči po
zmanjšuje
navidezna velikost
1. 4. 2. 3.

Luna kroži okoli Zemlje v približno 27,3 dneh glede na določen referenčni okvir. To je znano kot zvezdniški mesec. Vendar pa se je Zemlja v enem zvezdenem mesecu obrnila delno okoli Sonca, tako da je bil povprečni čas med novo luno in naslednjim daljši od zvezdnega meseca: približno 29,5 dni. To je znano kot sinodični mesec in ustreza tistemu, kar se običajno imenuje lunin mesec. [18]

Luna prehaja od juga proti severu ekliptike v njenem naraščajočem vozlišču in obratno pri padajočem vozlišču. [18] Vendar se vozlišča Lunine orbite postopno premikajo v retrogradnem gibanju zaradi delovanja sončne gravitacije na gibanje Lune in vsakih 18,6 leta naredijo celotno vezje. Ta regresija pomeni, da je čas med vsakim prehodom Lune skozi naraščajoče vozlišče nekoliko krajši od zvezdenega meseca. To obdobje se imenuje nodični ali drakonski mesec. [22]

Nazadnje se Lunin perigej premika naprej ali predeluje po svoji orbiti in v 8,85 letih naredi celotno vezje. Čas med enim perigejem in naslednjim je nekoliko daljši od zvezdnega meseca in je znan kot anomalistični mesec. [23]

Lunina orbita se seka z ekliptiko na obeh vozliščih, ki sta oddaljeni 180 stopinj. Zato se mlada luna pojavlja blizu vozlišč v dveh obdobjih leta v razmiku približno šestih mesecev (173,3 dni), znanih kot sezone mrkov, in v teh obdobjih bo vedno vsaj en Sončev mrk. Včasih se mlada luna v dveh zaporednih mesecih zgodi dovolj blizu vozlišča, da obakrat v dveh delnih mrkih zasenči Sonce. To pomeni, da bosta v katerem koli letu vedno obstajala vsaj dva mrka Sonca, lahko pa jih bo tudi pet. [24]

Mrki se lahko pojavijo le, kadar je Sonce znotraj približno 15 do 18 stopinj vozlišča (10 do 12 stopinj za osrednje mrke). To se imenuje meja mrka in je podana v obsegu, ker se navidezne velikosti in hitrosti Sonca in Lune skozi leto spreminjajo. V času, ko se Luna vrne v vozlišče (drakonski mesec), se je navidezni položaj Sonca premaknil za približno 29 stopinj glede na vozlišča. [2] Ker meja mrka ustvari okno priložnosti do 36 stopinj (24 stopinj za centralne mrke), je možno, da se delni mrki (ali redko delni in centralni mrk) pojavijo v zaporednih mesecih. [25] [26]

Med osrednjim mrkom se Lunina umbra (ali antumbra v primeru obročastoga mrka) hitro premika od zahoda proti vzhodu po Zemlji. Tudi Zemlja se vrti od zahoda proti vzhodu, približno 28 km / min na Ekvatorju, toda ker se Luna giblje v isti smeri kot vrtenje Zemlje s približno 61 km / min, se zdi, da se umbra skoraj vedno premika v približno smer zahod – vzhod preko zemljevida Zemlje s hitrostjo Lunine krožne hitrosti minus hitrost vrtenja Zemlje. [28] Redke izjeme se lahko pojavijo v polarnih regijah, kjer lahko pot gre čez ali blizu pola, kot je bilo leta 2021 10. junija in 4. decembra.

Širina sledi osrednjega mrka se spreminja glede na navidezne premere Sonca in Lune. V najugodnejših okoliščinah, ko se popolni mrk zgodi zelo blizu perigeja, je proga lahko široka do 267 km (166 mi) in traja celo več kot 7 minut. [29] Zunaj osrednjega tira je delni mrk viden na veliko večjem območju Zemlje. Običajno je umbra široka 100–160 km, premer penumbra pa presega 6400 km. [30]

Beselijski elementi se uporabljajo za napovedovanje, ali bo mrk delni, obročast ali popoln (ali obročast / popoln) in kakšne bodo okoliščine mrka na kateri koli lokaciji. [31]: Poglavje 11 Izračuni z besselijskimi elementi lahko določijo natančno obliko sence umbre na zemeljski površini. Toda pri čem dolžine na zemeljsko površino bo padla senca, je odvisna od vrtenja Zemlje in od tega, koliko se je to vrtenje sčasoma upočasnilo. Število, imenovano ΔT, se uporablja pri napovedovanju mrka, da se to upočasnitev upošteva. Ko se Zemlja upočasni, se ΔT poveča. ΔT za datume v prihodnosti je mogoče le okvirno oceniti, ker se vrtenje Zemlje nepravilno upočasnjuje. To pomeni, da čeprav je mogoče napovedati popolni mrk na določen datum v daljni prihodnosti, v daljni prihodnosti ni mogoče natančno napovedati, v katerih dolžinah bo ta mrk popoln. Zgodovinski zapisi o mrkih omogočajo ocene preteklih vrednosti ΔT in vrtenja Zemlje.

Trajanje

Naslednji dejavniki določajo trajanje popolnega Sončevega mrka (po padajočem pomenu): [32] [33]

  1. Luna je skoraj natančno v perigeju (zaradi česar je njen kotni premer čim večji).
  2. Zemlja je zelo blizu afelija (najbolj oddaljena od Sonca v svoji eliptični orbiti, zaradi česar je njen kotni premer skoraj čim manjši).
  3. Sredina mrka je zelo blizu Zemljinega ekvatorja, kjer je vrtilna hitrost največja.
  4. Vektor mrkove poti na sredini mrka se poravna z vektorjem rotacije Zemlje (tj. Ne diagonalno, ampak proti vzhodu).
  5. Sredina mrka je blizu podsončne točke (najbližji Soncu del Zemlje).

Najdaljši do zdaj izračunani mrk je mrk 16. julija 2186 (nad Severno Gvajano je trajal največ 7 minut 29 sekund). [32]

Popolni sončni mrki so redki dogodki. Čeprav se v povprečju pojavljajo nekje na Zemlji vsakih 18 mesecev [35], se ocenjuje, da se v katerem koli kraju v povprečju ponovijo le enkrat na vsakih 360 do 410 let. [36] Popolni mrk na katerem koli mestu traja le nekaj minut, ker se Lunina umbra premika proti vzhodu s hitrostjo več kot 1700 km / h. [37] Celotnost trenutno ne more trajati več kot 7 min 32 s. Ta vrednost se skozi tisočletja spreminja in se trenutno zmanjšuje. Do 8. tisočletja bo najdaljši teoretično možen popolni mrk manj kot 7 min 2 s. [32] Zadnjič je bil mrk, daljši od 7 minut, 30. junija 1973 (7 min 3 sek). Opazovalci na nadzvočnem letalu Concorde so lahko celoten mrk raztegnili na približno 74 minut, ko so leteli po poti Lunine umbre. [38] Naslednji popolni mrk, ki traja več kot sedem minut, se bo zgodil šele 25. junija 2150. Najdaljši popolni Sončev mrk v obdobju 11.000 let od leta 3000 pred našim štetjem do vsaj 8000 našega štetja se bo zgodil 16. julija 2186, ko bo zadnjih 7 min 29 s. [32] [39] Za primerjavo, najdaljši popolni mrk 20. stoletja s 7 minutami 8 s se je zgodil 20. junija 1955, v 21. stoletju pa ni popolnih sončnih mrkov, daljših od 7 minut. [40]

Z uporabo ciklov mrkov je mogoče predvideti druge mrke. Saros je verjetno najbolj znan in eden najbolj natančnih. Saros traja 6.585,3 dni (nekaj več kot 18 let), kar pomeni, da se bo po tem obdobju zgodil praktično enak mrk. Najbolj opazna razlika bo premik proti zahodu za približno 120 ° po dolžini (zaradi 0,3 dni) in malo po zemljepisni širini (sever-jug za lihoštevilčne cikle, obratno za sodoštevilčne). Serija saros se vedno začne z delnim mrkom v bližini enega od polarnih območij Zemlje, nato se premakne po svetu skozi vrsto obročastih ali popolnih mrkov in konča z delnim mrkom v nasprotni polarni regiji. Serija saros traja od 1226 do 1550 let in od 69 do 87 mrkov, pri čemer jih je približno 40 do 60 osrednjih. [41]

Pogostost na leto

Vsako leto se zgodi med dvema in petimi mrki sonca, pri čemer je vsaj eden na sezono mrka. Odkar je bil leta 1582 uveden gregorijanski koledar, so bila leta pet pet mrkov 1693, 1758, 1805, 1823, 1870 in 1935. Naslednji dogodek bo 2206. [42] V povprečju je približno 240 sončnih mrkov. stoletja. [43]

Pet sončnih mrkov leta 1935
5. januarja 3. februarja 30. junija 30. julij 25. decembra
Delno
(južno)
Delno
(sever)
Delno
(sever)
Delno
(južno)
Obročast
(južno)

Saros 111

Saros 149

Saros 116

Saros 154

Saros 121

Končna celota

Popolni sončni mrki so na Zemlji vidni zaradi naključnega spleta okoliščin. Tudi na Zemlji je danes raznolikost mrkov, ki so znani ljudem, začasen (v geološkem časovnem merilu) pojav. Stotine milijonov let v preteklosti je bila Luna bližje Zemlji in zato na videz večja, zato je bil vsak Sončev mrk popoln ali delni, obročastih mrkov pa ni bilo. Zaradi plimnega pospeška se orbita Lune okoli Zemlje vsako leto oddalji za približno 3,8 cm. Milijoni let v prihodnosti bo Luna predaleč, da bi popolnoma zaprla Sonce in do popolnih mrkov ne bo prišlo. V istem časovnem obdobju lahko Sonce postane svetlejše in postane večje. [44] Ocene časa, ko Luna ne bo mogla zapreti celotnega Sonca, če gledamo z Zemlje, se v prihodnosti gibljejo med 650 milijoni [45] in 1,4 milijardami let. [44]

Zgodovinski mrki so za zgodovinarje zelo dragocen vir, saj omogočajo natančno datiranje nekaj zgodovinskih dogodkov, iz katerih je mogoče razbrati druge datume in starodavne koledarje. [46] Sončev mrk 15. junija 763 pr. N. Št., Omenjen v asirskem besedilu, je pomemben za kronologijo starodavnega Bližnjega vzhoda. [47] Do danes so obstajali tudi drugi zahtevki za mrke. Knjiga Jozue 10:13 opisuje sonce, ki je ves dan mirovalo na nebu. Skupina učenjakov Univerze v Cambridgeu je ugotovila, da gre za obročast Sončev mrk, ki se je zgodil 30. oktobra 1207 pr. [48] ​​Kitajski kralj Zhong Kang naj bi odsekal glavo dvema astronoma, Hsi in Ho, ki pred 4000 leti ni napovedal mrka. [49] Morda je najzgodnejša še vedno nedokazana trditev arheologa Brucea Masseja, ki domnevno povezuje mrk, ki se je zgodil 10. maja 2807 pr. N. Št., Z možnim vplivom meteorja v Indijskem oceanu na podlagi več starodavnih mitov o poplavah, ki omenjajo popolni Sončev mrk. [50]

Mrki so bili interpretirani kot znamenja ali znaki. [51] Starogrški zgodovinar Herodot je zapisal, da je Tales iz Mileta napovedal mrk, ki se je zgodil med bitko med Medi in Lidijci. Obe strani sta odložili orožje in zaradi mrka razglasili mir. [52] Natančen mrk ostaja negotov, čeprav je to vprašanje preučevalo na stotine starodavnih in sodobnih avtoritet. Eden od verjetnih kandidatov je potekal 28. maja 585 pred našim štetjem, verjetno blizu reke Halys v Mali Aziji. [53] An eclipse recorded by Herodotus before Xerxes departed for his expedition against Greece, [54] which is traditionally dated to 480 BC, was matched by John Russell Hind to an annular eclipse of the Sun at Sardis on February 17, 478 BC. [55] Alternatively, a partial eclipse was visible from Persia on October 2, 480 BC. [56] Herodotus also reports a solar eclipse at Sparta during the Second Persian invasion of Greece. [57] The date of the eclipse (August 1, 477 BC) does not match exactly the conventional dates for the invasion accepted by historians. [58]

Chinese records of eclipses begin at around 720 BC. [59] The 4th century BC astronomer Shi Shen described the prediction of eclipses by using the relative positions of the Moon and Sun. [60]

Attempts have been made to establish the exact date of Good Friday by assuming that the darkness described at Jesus's crucifixion was a solar eclipse. This research has not yielded conclusive results, [61] [62] and Good Friday is recorded as being at Passover, which is held at the time of a full moon. Further, the darkness lasted from the sixth hour to the ninth, or three hours, which is much, much longer than the eight-minute upper limit for any solar eclipse's totality. Contemporary chronicles wrote about an eclipse at the beginning of May 664 that coincided with the beginning of the plague of 664 in the British isles. [63] In the Western hemisphere, there are few reliable records of eclipses before AD 800, until the advent of Arab and monastic observations in the early medieval period. [59] The Cairo astronomer Ibn Yunus wrote that the calculation of eclipses was one of the many things that connect astronomy with the Islamic law, because it allowed knowing when a special prayer can be made. [64] The first recorded observation of the corona was made in Constantinople in AD 968. [56] [59]

The first known telescopic observation of a total solar eclipse was made in France in 1706. [59] Nine years later, English astronomer Edmund Halley accurately predicted and observed the solar eclipse of May 3, 1715. [56] [59] By the mid-19th century, scientific understanding of the Sun was improving through observations of the Sun's corona during solar eclipses. The corona was identified as part of the Sun's atmosphere in 1842, and the first photograph (or daguerreotype) of a total eclipse was taken of the solar eclipse of July 28, 1851. [56] Spectroscope observations were made of the solar eclipse of August 18, 1868, which helped to determine the chemical composition of the Sun. [56]

John Fiske summed up myths about the solar eclipse like this in his 1872 book Myth and Myth-Makers,

the myth of Hercules and Cacus, the fundamental idea is the victory of the solar god over the robber who steals the light. Now whether the robber carries off the light in the evening when Indra has gone to sleep, or boldly rears his black form against the sky during the daytime, causing darkness to spread over the earth, would make little difference to the framers of the myth. To a chicken a solar eclipse is the same thing as nightfall, and he goes to roost accordingly. Why, then, should the primitive thinker have made a distinction between the darkening of the sky caused by black clouds and that caused by the rotation of the earth? He had no more conception of the scientific explanation of these phenomena than the chicken has of the scientific explanation of an eclipse. For him it was enough to know that the solar radiance was stolen, in the one case as in the other, and to suspect that the same demon was to blame for both robberies. [65]

Looking directly at the photosphere of the Sun (the bright disk of the Sun itself), even for just a few seconds, can cause permanent damage to the retina of the eye, because of the intense visible and invisible radiation that the photosphere emits. This damage can result in impairment of vision, up to and including blindness. The retina has no sensitivity to pain, and the effects of retinal damage may not appear for hours, so there is no warning that injury is occurring. [66] [67]

Under normal conditions, the Sun is so bright that it is difficult to stare at it directly. However, during an eclipse, with so much of the Sun covered, it is easier and more tempting to stare at it. Looking at the Sun during an eclipse is as dangerous as looking at it outside an eclipse, except during the brief period of totality, when the Sun's disk is completely covered (totality occurs only during a total eclipse and only very briefly it does not occur during a partial or annular eclipse). Viewing the Sun's disk through any kind of optical aid (binoculars, a telescope, or even an optical camera viewfinder) is extremely hazardous and can cause irreversible eye damage within a fraction of a second. [68] [69]


NASA science during the 9 March total solar eclipse

As the Moon slowly covers the face of the Sun on the morning of 9 March 2016, in Indonesia, a team of NASA scientists will be anxiously awaiting the start of totality &mdash because at that moment, their countdown clock begins. They plan to take 59 several-second exposures of the Sun in just over three minutes, capturing data on the innermost parts of the Sun’s volatile, superhot atmosphere &mdash a region we can only observe during total solar eclipses when the Sun’s overwhelmingly bright face is completely blocked by the Moon.

“The Sun’s atmosphere is where the interesting physics is,” said Nelson Reginald, one of several space scientists from NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who will conduct an experiment in Indonesia during March 2016’s total solar eclipse. “A total solar eclipse gives us the opportunity to see very close to the solar limb.”

The lower part of the Sun’s atmosphere, the corona, is one of the most scientifically interesting areas of the Sun. It’s thought to hold the keys to several solar mysteries, from the acceleration of the solar wind, to the birth of explosive clouds of solar material called coronal mass ejections, to the mysterious heating of the corona as a whole. Using a new instrument, the NASA science team will observe aspects of polarised light that carry information about the temperature and velocity of electrons in the lower corona.

Though it’s about as bright as the full Moon, the corona is ordinarily drowned out by the Sun’s much brighter face, except during total solar eclipses. To study the corona outside of total solar eclipses, scientists use instruments called coronagraphs, which create artificial eclipses by using solid discs to block Sun’s bright face and reveal the comparatively faint corona. But because light bends around sharp edges &mdash a phenomenon known as diffraction &mdash coronagraph discs obscure the inner corona, as well as the solar surface, to combat this effect.

“You can’t see the corona that close to the surface with a coronagraph. You cut off a large portion of the innermost corona,” said Nat Gopalswamy, principal investigator of the eclipse experiment at Goddard. “The main advantage of the total solar eclipse is seeing much closer to the Sun’s surface.”

The team will use their three minutes of totality to examine the polarised light coming from the Sun’s inner corona, light that contains information about the temperature and velocity of the electrons there. Light is polarised when its electric field oscillates along one axis, for instance, up-and-down or side-to-side. Unlike dust, electrons mainly scatter polarised light, meaning that isolating the polarised light can give information about the temperature and flow speed of coronal electrons. Polarised light scattered by these electrons dominates in the regions of the corona closest to the solar surface &mdash so total solar eclipses are our best chance to gather this information.

“We first used this instrument during the 1999 total solar eclipse in Turkey,” said Reginald.

The minutes-long timeframe of total solar eclipses limits the amount of data we can collect during our occasional glimpses at the inner corona, so the team rebuilt their instrument over the last year to make it even faster.

“Before, we would have had use a polariser that would turn through three angles for each wavelength filter,” said Reginald. “The new polarisation camera eliminates the need for a polarisation wheel.”

Rather than using a hand-turned polarisation wheel to take three separate images in each polarised direction, the new camera uses thousands of tiny polarisation filters to read light polarised in different directions simultaneously. Each pixel in the new camera is made of four subpixels with differently-oriented polarisation filters, which provides the team with four separate but simultaneous images of the corona and cuts out the need to change polarisation filters between exposures.

“We’ve cut down the length of time required for our experiment by more than 50 percent,” said Gopalswamy. “The polarisation camera is faster and less risky, because it’s one less moving part.”

Though the team will be performing the experiment for the first time in the province of North Maluku, Indonesia &mdash chosen for its accessibility and high chances of clear skies during the eclipse &mdash they’ve already given their updated instrument a test run.

“The brightness of the full Moon is about equal to the brightness of the total solar eclipse,” said Reginald. “So we set up our telescope in the parking lot for practice.”


Author information

Pripadnosti

University of Hawaii, Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, Hawaii, USA

National Optical Astronomy Observatories, National Solar Observatory, 950 North Cherry Avenue, Tucson, Arizona, 85726, USA

Department of Physics and Astronomy, University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canada

Astrophysics Division, Rutherford Appleton Laboratory, Chilton, Didcot, 0X11OQX, UK

James Clerk Maxwell Telescope, Joint Astronomy Center, 665 Komohana Street, Hilo, Hawaii, 96720, USA

Department of Astronomy, University of California at Los Angeles, Los Angeles, California, 90024, USA

Astrophysics Branch, NASA/Ames Research Center, MS 245-6, Moffet Field, California, 94035-1000, USA

Department of Physics, University of Lethbridge, Lethbridge, Alberta, T1K 3M4, Canada

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Past observations

In the 20th century, two "vintage" years stand out so far as shadow-band visibility is concerned. The first case is the eclipse of Jan. 24, 1925. Since this event came a few days after a heavy snowfall for the Northeast United States, shadow bands were readily seen upon the fresh snow by most eclipse watchers. Meteorologist Edward Brooks who observed this eclipse from Groton, Connecticut, noted in 1978: "The snow offered the ground offered the best backdrop for viewing the eerie fleeting shadow bands at any of the nine total eclipses I have gone to."

At the eclipse of March 7, 1970, which nearly paralleled the U.S. East Coast, many shadow-band sightings were recorded. To astronomer Glenn Schneider, watching from Greenville, North Carolina, the shadow bands resembled "jail bars."

Even outside the totality path, shadow bands can sometimes be observed. For instance, from Hyderabad, India, in 1980, where a partial eclipse covered more than 99 percent of the sun, a person who was among a group of eclipse watchers was heard to suddenly yell, "There’s fire on the ground!" But what he was witnessing was a sensational display of shadow bands. Not knowing at first what they were, they were described as "flames leaping 6 to 10 feet off the ground."

Interestingly, I have been to 11 total eclipses, yet my only view of shadow bands came during an annular eclipse (when a ring of the sun's disk remains visible around the moon). On May 30, 1984, from Greenville, South Carolina, for about 90 seconds before and after the annular phase I caught sight of very weak smoky bands that displayed little movement but appeared to shimmer, resembling sunlight passing over a radiator or ripples of sunshine at the bottom of a breeze-stirred pool.


Solar Eclipse Information and Viewing Guide

On Monday, August 21, the continental United States will experience the "Great American Eclipse". Viewers located in the narrow path of totality will see a total eclipse, during which the Moon will completely block the Sun's light for up to two minutes and forty seconds. Here in Southern California, we will be able to see a partial eclipse, in which the Moon partly blocks the Sun over a period of about two and a half hours starting at 9:06 am. This page provides information and links for everyone interested in viewing the eclipse, including important eye safety information.

What is an eclipse?

Solar eclipses happen when the Sun, the Moon, and the Earth are all aligned along a line, with the Moon in between the Sun and the Earth. The Moon casts a shadow on the Earth, and the shadow quickly sweeps across the Earth's surface as the Earth rotates and the Moon and Earth move in their orbits. In a total solar eclipse, viewers in a narrow band of locations on Earth can see the Moon briefly cover the entire surface of the Sun. See the NASA web site for an explanation of How Eclipses Work with pictures and videos, or this article that contains clear explanations and animations. The last time a total solar eclipse happened in the continental United States was in 1979, and the next one after this year will be in 2024. NASA's eclipse web site lists the dates and shows maps for the locations of past and future eclipses.

Where can I find general information about the eclipse?

Two of the best and most informative web sites are the NASA Eclipse site, and the American Astronomical Society (AAS) Eclipse site. Both of these web sites contain maps, educational information, viewing instructions, and eye safety information.

For smartphones, the Smithsonian Eclipse App has an interactive map and eclipse timing, eye safety information, and more.

Where is the eclipse happening? Where is the path of totality?

Check the NASA Eclipse web site for an interactive map. The path of totality is a narrow band running diagonally across the country from Oregon to South Carolina. Only observers within that narrow band will get to experience the glory of the total eclipse, when the moon completely covers the Sun's surface, the sky goes dark, and the Sun's corona becomes visible. Outside the path of totality, other locations in the United States will see a partial eclipse, in which the moon doesn't fully cover the Sun. At the peak of the eclipse as seen from Irvine, 60% of the Sun's disk will be covered by the Moon, so the event as seen from here will not be nearly as exciting or dramatic as a total eclipse, but a partial eclipse seen from here is still a rare and interesting event.

When does the eclipse happen in Southern California?

In Irvine, the partial eclipse begins at 9:06 am on August 21, when the Moon will just begin to cover the Sun. Maximum eclipse will be at 10:22 am, when 60.75% of the Sun will be covered by the Moon. The partial eclipse will end at 11:45 am. From other locations in Southern California, the timing will be very similar to this, with variations of just a few minutes in the start and end times across Southern California.

You can use the NASA Eclipse map to find out the exact timing of the eclipse from your location. This map lists times in Universal Time (equivalent to Greenwich Mean Time) and the page gives information on how to convert UT to your local time zone. Or, try the Smithsonian Eclipse smartphone app which will give you the eclipse timing details at your precise location, in your local time zone.

How can I view the partial eclipse safely?

Eye safety is extremely important when viewing the partial eclipse. DO NOT look directly at the Sun without using special protective equipment! Looking at the Sun, even momentarily, can cause permanent eye damage. Before the eclipse, take a few minutes to read the AAS Eclipse Eye Safety page for detailed information and instructions on how to view the eclipse safely. The AAS also provides a handy 1-page pdf on eye safety. Ordinary sunglasses will NOT protect you from eye damage if you look at the Sun.

Fortunately, you can use safe and inexpensive "eclipse glasses" with special plastic filters that block out nearly all of the Sun's light. Using eclipse glasses, you can enjoy the partial eclipse safely. Look for eclipse glasses that are certified to be compliant with the ISO 12312-2 safety standard. The AAS maintains a list of reputable vendors of eclipse glasses and other safe viewing equipment, and a lot of detailed information on what to look for. And, beware of counterfeit eclipse glasses that aren't certified for the ISO standard.

Some online retailers from this list may be out of stock as the eclipse date approaches. The AAS eclipse glasses information page also has a list of brick-and-mortar retail stores that carry certified eclipse glasses. This includes some national chains with branches in and around Irvine, but local stores are selling their inventory of eclipse glasses rapidly and might not have any in stock in the days leading up to the eclipse.

If you'll be in the path of totality for the eclipse, then samo during the brief total eclipse is it safe to look at the Sun directly, when the Moon completely covers the Sun's surface. You'll still need eclipse glasses to view the partial phases of the eclipse.

Another fun way to view the eclipse is to make a pinhole projection screen. Using a pinhole projector is the safest way for young children to view the eclipse, because adult-sized eclipse glasses might not fit well on small faces. Just take a piece of cardboard or card stock (like cardboard from a cereal box) and punch or cut small round holes in it, with holes of around 1/4-inch diameter. Then, during the eclipse, hold your projection screen a few feet above the ground so that rays of sunlight go through the holes, and look at the shadow that it casts on the ground, or use it to cast a shadow on a wall. Each of the holes will project the shape of the eclipsed Sun. Here's a video that shows an example of a pinhole projection screen. You can also make another kind of pinhole viewer using a cereal box and aluminum foil: see this NASA video for easy instructions.

Where should I go to see the eclipse?

To experience the total eclipse, you have to be in the path of totality, which unfortunately is a long trip from Irvine.

If traveling to the path of totality isn't an option for you, you can view the partial eclipse from anywhere you happen to be in North America on August 21, as long as you're under clear skies and you've got your eclipse glasses or pinhole projector ready. You don't really need to be anywhere special to view the partial eclipse: just get your eclipse glasses, go outside, and enjoy the view!

For those on the UCI campus or close by on the 21st, UCI astronomy students will be setting up a viewing station on campus starting at 9 am, with a solar image projector for viewing and eclipse glasses to share with visitors. The event will be held on the Physical Sciences Plaza area, next to Frederick Reines Hall and Rowland Hall. Click here for more information and to RSVP for the viewing party.

The UCI Astronomy Outreach Program will also be hosting a partial eclipse viewing event at the UC Yosemite Field Station near Wawona inside Yosemite National Park. If you'll be at Yosemite on August 21, please join us there!

NASA TV will be broadasting a live stream of eclipse news and viewing events on August 21, and there wlll be extensive media coverage and news, so even if you can't make it to the path of totality, there will be lots of great pictures and video to look at as the eclipse occurs.


This Is the Gear You Need to View the Upcoming Solar Eclipse

On August 21, North America will experience the first total solar eclipse visible across the continent in nearly a century–and, while it may seem illogical, this period of semi-darkness is an important time to practice sun safety.

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That’s because while during an eclipse, you won’t want to tear your eyes away from the show, staring directly at the sun can lead to solar retinopathy, a condition where light floods the eye’s retina. In 1999, 45 patients visited an eye clinic in Leicester, England, after viewing a solar eclipse without proper eyewear. About half of the patients suffered from eye pain the others reported impaired vision. Although these eclipse watchers were not totally blinded, several incurred long-term damage.

The United States hasn’t experienced a total eclipse since 1979, and that one only passed over a small swath of the Northwest. This year, in contrast more than 500 million people in North America, plus parts of South America and northwestern Europe, will be able to see at least a partial eclipse. Those within a 70-mile wide path between Oregon and South Carolina will witness a total eclipse.

A partial eclipse occurs when the moon blocks part of the sun from view. A total eclipse, in contrast, is when the moon completely blocks the sun. "Totality," the part of the total eclipse when the sun is completely covered, lasts only around two minutes.

Most people in the continental United States live within a one- to two-day drive of the total eclipse’s path. Madhulika Guhathakurta, the lead program scientist for NASA’s “Living With a Star” initiative, says the breadth of the path makes the eclipse accessible to everyone. She says observing a total eclipse is transformative: “It’s akin to the way astronauts describe their first trip to space. You're just so in awe of nature.”

To view the solar eclipse, you’ll need proper equipment. It may seem odd to don protection in the semi-darkness of a partial eclipse, but staring at the sun can cause retinal injury. The only time it’s safe to look at the sun without protection is during totality. Keep your equipment on hand, and put it back on when the sun starts to reappear.

Opt for gear featuring ISO-approved solar filters, which are about𧅤,000 times darker than everyday sunglasses. The American Astronomical Society’s website includes a list of manufacturers that have certified their products meet the ISO 12312-2 standard. If you purchase equipment from other outlets, double check that their merchandise meets ISO standards.

Whether you’re a stargazing neophyte or dedicated astronomer, this gear will help you make the most of a spectacular event.

These solar viewers give 2x magnification and protection from the sun during the partial eclipse. (Celestron)

Eclipse glasses and handheld viewers

Eclipse glasses look like hybrids of 3-D movie glasses and sunglasses. As Guhathakurta explains, these glasses have the added protection of a solar filter. Whereas sunglasses only block UV rays, eclipse glasses also cut off visible light.

If you’re a casual observer or part of a large group, you’ll like these glasses’ low prices and bulk packaging. You can buy a pack of five paper glasses from Rainbow Symphony for around $12. If you want a sturdier option, try these plastic glasses from American Paper Optics. And feel free to go for style: TSE17 has a $5.05 stars-and-stripes five-pack, and American Paper Optics features everything from Bill Nye glasses to astronaut-themed frames.

Looking for something between basic glasses and high-tech binoculars? Check out this handheld viewer from Celestron. For $9.95, you’ll receive two viewers with 2x magnification capabilities and a pocket eclipse guide.

Binoculars and telescopes

Binoculars and telescopes are pricier than eclipse glasses and handheld viewers but can be worth the investment. They feature a higher magnification, but higher magnification results in a shakier image––as power increases, the equipment becomes more sensitive to its holder’s small hand movements.

Binoculars are rated with two numbers. The first number is the magnification, the second is the aperture—the diameter of the front lens, measured in millimeters. If you're buying a pair of binoculars and plan to use them for other astronomy viewing, the bigger the aperture, the better, but bigger lenses also mean heavier equipment.

The following options offer a range of viewing strengths. Celestron’s EclipSmart binoculars feature non-removable solar filters, so you’ll only be able to use them for solar viewing. A㺊x25 pair (10x magnification and 25mm aperture) costs around $35, while a㺊x42 pair costs just about twice as much. A cheaper option is Lunt's mini SUNocular. A 6x30 pair costs $29.95.

If you prefer binoculars with removable solar filters, Meade has a $69.99㺊x50 pair that works for both solar viewing and nighttime stargazing. Once you remove the solar filters, the binoculars will operate like a normal pair.

Telescopes offer some of the best eclipse views, but you’ll pay more for added detail if you want an advanced model. A basic lightweight option is the Explore Scientific Sun Catcher 70mm telescope. It costs $59.99 and can be used during both the day and night. A more advanced option is the $99.95 Celestron EclipSmart telescope. It offers 18x magnification, 50mm aperture and non-removable solar filters.

Another choice is the Meade EclipseView telescope. The cheapest model is a $79.99 82mm reflecting telescope designed for on-the-go use. A sturdier long-term bet is the 76mm reflecting telescope, which costs $129.99. Both models feature removable solar filters and are suitable for solar and nighttime use.

The Meade EclipseView 82mm telescope is designed to be portable, for eclipse watching anywhere. (Meade)

Add-on solar filters

Another category of eclipse viewing gear is add-on filters. These can be attached to binoculars, telescopes and cameras not originally designed for solar viewing and are mainly used by experienced observers. Similarly to eclipse-specific gear, add-on filters prevent retinal damage. They also protect your equipment’s optics from the heat of the sun, as the intensity of an eclipse can damage gear designed for nighttime observing.

Filters are typically made of metal on glass (sturdy but most expensive), aluminized polyester film (also known as Mylar) or black polymer (also used in eclipse glasses). Rainbow Symphony sells black polymer and silver Mylar filters starting at $19.95. Thousand Oaks Optical and Orion offer higher-end filters ranging in price from $22 to $150-plus.

Pinhole projectors

If you want to view the eclipse without spending money on special equipment, you’re in luck. Stand with your back to the sun, and use your hands, a hole-punched index card or even a patch of leaves to create a tiny opening. As sunlight flows through the empty space, an image of the sun will project onto a nearby surface. For more detailed instructions, visit the American Astronomical Society’s pinhole projection page.

Guhathakurta’s final words of advice are simple: During the partial eclipse, “do not look at the sun without glasses on, but absolutely look at the total solar eclipse without glasses on. These are two binary events. When you wear glasses and you cannot see anything anymore, that's totality.”


How to Photograph a Solar Eclipse

Whereas lunar eclipses are safe to view with the naked eye, solar eclipses are not. You must take the necessary precautions to keep from harming your eyesight. In fact, you also need to use a &ldquosolar filter&rdquo to keep from harming your camera&rsquos imaging sensor as well as for correct exposure.

A solar eclipse occurs whenever the moon&rsquos shadow falls on Earth. This can only occur during a new moon, when the moon passes between the sun and Earth. There are two or more solar eclipses a year which occur when the geometry lines up just right, so that part of the moon&rsquos shadow falls on Earth&rsquos surface and an eclipse of the sun is seen from that region.

Partial and Total Solar Eclipses

The moon&rsquos cone-shaped shadow has two parts, the penumbra in umbra. The penumbra is the moon&rsquos faint outer shadow and partial eclipses are visible from within the penumbral shadow. The umbra is the moon&rsquos dark inner shadow and total solar eclipses are visible from within the umbral shadow. The track of the moon&rsquos umbral shadow across Earth is called the Path of Totality, and it covers less than 1 percent of Earth&rsquos surface area (typically 10,000 miles long and about 100 miles wide.)

A solar eclipse begins as a small notch slowly appears along one edge of the sun. During the next hour, the moon will gradually cover more and more of the sun&rsquos bright disk. If the eclipse is a total solar eclipse, the last remaining minutes of the partial phases can be dramatic. The crescent of the sun grows thinner as the moon&rsquos shadow approaches. The abrupt darkness of totality is stunning to view, and the solar corona is an awe-inspiring sight. The sun&rsquos corona can only be seen during the few brief minutes of totality.

Annular Solar Eclipses

A total solar eclipse occurs when the moon is on the near side of its elliptical orbit. When the moon is on the far side of its orbit, it appears smaller and can&rsquot completely cover the sun. It is during these eclipses that the moon&rsquos antumbra shadow (the extension of the umbra) reaches Earth, causing an obročast eclipse for people who are within the track of the antumbra (also called the path of annularity). During this type of eclipse, you will see a ring or annulus of bright sunlight surrounding the moon at the maximum phase.

Just as with the partial eclipse of the sun, you must take precautions and use a solar filter to view the annular eclipse. Annularity can last up to 12 minutes.

Hybrid Eclipse

A third type of solar eclipse, that may rarely occur, is called a hybrid eclipse. A hybrid eclipse is the name given to a total eclipse that changes to an annular eclipse or an annular eclipse that changes to a total eclipse. They are sometimes called annular/total eclipses. Hybrid eclipses occur when the curvature of Earth brings different points of the path into the total and annular shadows respectively.

Solar Filters

When viewing or photographing the partial phases of a solar eclipse or the maximum phase of an annular eclipse, you must use a solar filter. Even if 99% of the sun is covered by the moon, the remaining 1% crescent is dangerous to view with the naked eye and can cause serious eye damage or blindness.

You can find information on solar filters and where to purchase them from astronomy websites and magazines. Safe solar filters for cameras and telescopes are available as either "Full-Aperture" and "Off-Axis" filters. Both of these filters fit over the objective (front end of the telescope) or camera lens. Do not place a solar filter in the filter slot of the larger telephoto lenses that feature those filter slots!

Full-aperture solar filters are the preferred filters of choice. This is because the filter completely covers the front of the telescope so the entire mirror or lens is used. No refocusing of the telescope or camera lens will be needed when you remove the filter at the beginning of totality or when it is replaced back on the telescope/camera lens at the end of the total phase.

Please note that Nikon does not manufacture solar filters. Consult with your camera dealer to find a proper solar filter to fit your lens.

Starting Exposure

Solar eclipses may be viewed and photographed, provided certain precautions are taken. You can photograph a solar eclipse with any type of camera: DSLR, COOLPIX or Nikon 1. The longer the focal length of the lens, the larger the images of the sun you&rsquoll be able to make. While you can also use film cameras to photograph eclipses, this article specifically discusses digital camera use.

With a DSLR, you can also combine a super telephoto lens with a teleconverter to increase the focal length. You can also increase the relative size of the eclipse image by selecting an FX camera&rsquos "DX Crop Mode". If you&rsquore photographing the solar eclipse using a COOLPIX compact digital camera, turn the built-in flash to OFF.

How large you want the sun to be in the frame will determine what focal length lens to use. For a DSLR camera with a full frame FX sensor, choose a focal length of 2000mm or less. For a DSLR camera that has a DX sensor, the maximum focal length is about 1300mm any longer and you won&rsquot be able to get the entire sun in the frame.

However, if you also want to capture the sun&rsquos corona during the phase of totality, then you should choose a focal length that&rsquos shorter still&mdashno more than 1400mm for an FX (full frame sensor) camera, or 900mm for a Nikon DX camera.

Place your camera on a sturdy tripod, and manually focus the camera, setting it to infinity.

If you are using a telescope on an equatorial mount, the electric drive will track the sun keeping it centered in your camera throughout the eclipse.

A solar filter must be used on the lens throughout the partial phases for both photography and safe viewing. These filters typically attenuate the sun&rsquos visible and infrared energy by a factor of 100,000. Almost any ISO can be used because the sun gives off abundant light. The actual filter factor and choice of ISO will play critical roles in determining the correct exposure.

The easiest way to determine exposure is to run a calibration test on the un-eclipsed sun on a clear day prior to the eclipse. Digital cameras are ideal as you can see your results almost instantaneously. Shoot the mid-day sun at a fixed aperture, (choose an aperture between f/8 and f/16) using every shutter speed from 1/4000 second to 1/30 second. Looking at the exposures, choose the best shutter speed/aperture combination and use them to photograph the partial phases of the solar eclipse. Your camera&rsquos histogram function is an excellent way to evaluate the best exposure. The histogram should not be clipped but should lie toward the upper end of brightness values. Because the sun&rsquos brightness stays the same throughout the partial phases, no exposure compensation will be needed. You may also decide to bracket your exposures to ensure that you photograph the solar eclipse with a perfect exposure. If you ran your test on a sunny day and the eclipse occurs on a hazy day, increase the bracket of exposures an additional f/stop.

Photographing the Totality Phase of a Solar Eclipse

Certainly the most spectacular phase of the solar eclipse is totality. For a few brief seconds or minutes, the sun&rsquos pearly white corona, red prominences, and chromosphere are visible.

The great challenge is to obtain a set of photographs that captures these fleeting phenomena. During the total phase, all solar filters must be removed. This is because the sun&rsquos corona has a surface brightness a million times fainter than the sun&rsquos visible disk or photosphere, so photographs of the corona must be made without a filter. Furthermore, it is completely safe to view the totally eclipsed sun directly with the naked eye. No filters are needed, and in fact, they would completely hide the view.

The average brightness of the korona varies inversely with the distance from the sun&rsquos limb. The inner corona is far brighter than the outer corona thus, no single exposure can capture its full dynamic range. The best strategy is to choose one aperture and bracket the exposures over a range of shutter speeds from 1/1000 second to 1 second. You should rehearse the actions of setting up the camera and adjusting exposures because it is common for photographers to become easily distracted when viewing this phase of the solar eclipse, so much so that you forget to make pictures.

Click here for Mr. Eclipse&rsquos Solar Eclipse Exposure Guide. This guide features various exposure suggestions for the different features of a solar eclipse. Whichever exposures you do choose, bracket by one or two f/stops to ensure you get the best possible image. Use RAW format if your camera has this option because it allows greater flexibility in adjusting the exposure when processing your images after the eclipse.


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