Sterrekunde

Gaan vanaf die tweede oomblikke van 'n voorwerp na sy elliptisiteit en halflig-radius

Gaan vanaf die tweede oomblikke van 'n voorwerp na sy elliptisiteit en halflig-radius


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Ek bestudeer elliptisiteitsverdelings van sterrestelsels en sukkel om van die tweede sentrale momentmatriks (kovariansiematriks) na eienskappe van 'n voorwerp soos die halfligstraal te beweeg.

Ek weet al hoe om $ e1 $ en $ e2 $ te bekom

Dit word deur die volgende gegee:

$ e = frac {Q_ {xx} - Q_ {yy} + 2iQ_ {12}} {N} $

Waar $ N = N (Q) $ en net die normalisering is. Die werklike komponent is $ e1 $ en die denkbeeldige komponent is $ e2 $

Ek wonder ook hoe om die halfligstraal te verkry.

Ek het gesien:

$ 2r ^ 2 = Q_ {xx} + Q_ {yy} $ vir 'n sirkelvormige profiel, dan kan 'n mens die HLR van $ r ^ 2 $ verkry, maar hoe gaan dit met nie-sirkelvormige profiele? Is bogenoemde vergelyking selfs geldig?


U kan eenvoudig nie verkry nie enige inligting oor die halfligstraal vanaf die kwadrupoolmoment slegs van 'n sterrestelsel, sonder om die sterrestelselprofiel te ken. Beskou byvoorbeeld twee (ekstreme) ligprofiele:

  1. 'N Sterrestelsel wat bestaan ​​uit 'n eenvormige skyf met 'n radius van $ R $ - dit wil sê die helderheid van die oppervlak is iets soos $ I (r) propto H (R_1 - r) $, waar $ H $ die Heaviside-funksie is.

  2. 'N Sterrestelsel wat bestaan ​​uit 'n puntbron + 'n eenvormige skyf - dit is $ I (r) propto delta (r) + H (R_2 - r) $.

U kan maklik 'n kombinasie van radius $ R_1 $ en $ R_2 $ vind sodat die vierhoekmomente van die twee sterrestelsels identies is. Dit kan egter duidelik wees dat hul halfligstrale nie kan wees nie (veral vir die tweede sterrestelsel verdwyn die halfligstraal).

Volgens wat ek kan sien, geld die verhouding wat u geskryf het vir 'n Gaussiese profiel, en selfs dan is dit nie korrek nie: u $ r $ is nie die halfligstraal nie, maar die standaardafwyking van die Gaussiese profiel. Vir verskillende profiele is daar geen waarborg dat u verhouding sal werk nie (oor die algemeen sal dit nie werk nie): oor die algemeen gee dit u net iets proporsioneel tot die vierkant van die halfligstraal, maar die proporsionaliteitskonstante hang af van die spesifieke ligprofiel.


KiDS-450 data vir swak lense

Die datastel met swak lense gebaseer op die KiDS DR3-datastel, word ook die KiDS-450-datastel genoem en is vrygestel as KiDS DR3.1. Die KiDS-450 datastel, gebaseer op dieselfde toevoerdatastel as die DR3-vrystelling, bevat 454 teëls. Maskering van helder sterre, satellietpaaie en ander beelddefekte word reeds in die vrystellingskatalogus toegepas, wat 'n effektiewe oppervlakte van 360,3 vk. Deeg tot gevolg het. Slegs sterrestelsels met betroubare vormmetings word in hierdie katalogus opgeneem. Onbetroubare bronne is verwerp op grond van verskeie kriteria wat in Hildebrandt & Viola et al. (2017, MNRAS, 465, 1454). Die dowwe limiet van die katalogus is r = 25.0, wat ooreenstem met 'n tipiese sein-tot-ruis van 5 & sigma. Die katalogus bevat altesaam 14 650 348 bronne, bestaan ​​uit 455 lêers (454 datalêers en 1 metadatalêer) en het 'n totale datavolume van 4,14 GB

Vir die metings van die melkwegvorm is die r-banddata verwerk met behulp van 'n lens-geoptimaliseerde pypleiding gebaseer op die THELI-datareduksiestelsel en die lensfit sagteware vir vormmeting. Bronopsporing is gedoen op gestapelde r-bandbeelde, waarna sterrestelsels op individuele subblootstellings gemeet word. Die ingeslote fotometrie en fotometriese rooi verskuiwings is gebaseer op die vier-band ugri-beeldstapels van die hoof DR3-weergawe.

Nota: Hildebrandt & Viola et al. (2017, MNRAS, 465, 1454) het in hul kosmiese skuifanalise bevind dat klein residuele c-terme (nie-nul gemiddelde skuif) in die katalogus voorkom. Dit is per pleister en per tomografiese vakkie afgetrek voordat die korrelasie-funksies van die skuif- en skuifrekenaar bereken is. Enige wetenskaplike analise waarvoor c-terme belangrik is, moet dit uit die data bepaal met behulp van die lensfit gewigte om die gemiddeldes te bereken.

Vrystellings notas

Raadpleeg die vrystellingsnotas vir meer inligting rakende die katalogus en die skep daarvan.

Toegang tot data

Die datastel met swak lense gebaseer op die KiDS DR3-datastel word ook die KiDS-450-datastel genoem. Die skuifkatalogus is vrygestel as KiDS DR3.1 en is publiek beskikbaar via ESO, CADC en direkte aflaai. Daar is ook 'n binêre masker van die voetspoor beskikbaar, asook die THELI-verminderde beelde. Skakels en inligting vir alle toegangsroetes word in die volgende tabel gegee.

Erkennings

Gebruikers van hierdie data moet die volgende erkenning aan die bron van die data insluit:

Gebaseer op data-produkte uit waarnemings wat met ESO-teleskope gedoen is by die La Silla Paranal-sterrewag onder program-ID's 177.A-3016, 177.A-3017 en 177.A-3018.

en moet Hildebrandt & AMP Viola et al. (2017), Fenech Conti et al. (2016) en meegaande referate soos volg:

Ons gebruik kosmiese skuifmetings uit die Kilo-Degree Survey (Kuijken et al. 2015, Hildebrandt & AMP Viola et al. 2017, Fenech Conti et al. 2016), hierna KiDS genoem. Die KiDS-data word verwerk deur THELI (Erben et al. 2013) en Astro-WISE (Begeman et al. 2013, de Jong et al. 2015). Skêr word met lensfit gemeet (Miller et al. 2013), en fotometriese rooi verskuiwings word verkry uit PSF-ooreenstemmende fotometrie en gekalibreer met behulp van eksterne oorvleuelende spektroskopiese opnames (sien Hildebrandt et al. 2016).

Katalogusformaat

Die onderstaande tabel bevat 'n lys van die kolomme in die KiDS-450 of KiDS-DR3.1 lensskaarskatalogus. Vir 'n aantal kolomme word addisionele inligting verskaf:


Verwante

Smul aan die eerste beeld van 'n swart gat

Rasbevooroordeelde mediese algoritme gee wit pasiënte prioriteit bo swart pasiënte

NOVA se groot idees van 2017

Beelde het uiteindelik die MU69 van 2014 (aanvanklik die bynaam "Ultima Thule") onthul, as 'n verrassend plat "kontakbinaar", 'n liggaam wat bestaan ​​uit twee eens geskeide gesteentes wat stadig na mekaar toe getrek het totdat hulle liggies aanraak en saamsmelt. Wetenskaplikes glo dat die vliegdata insig kan bied in hoe miljarde jare gelede planete in ons sonnestelsel gevorm het.

In November verander NASA die bynaam van die rots van Ultima Thule, 'n term met skakels na die Nazi-party, na "Arrokoth", wat in die Powhatan / Algonquian-taal "lug" beteken.

2014 MU69 word geopenbaar as 'n tweevlak sneeuman. Volgens die New Horizons-span ondersteun hierdie beeld die idee dat planete in ons stelsel gevorm word as stukkies rou planeetmateriaal wat mettertyd saamgeval het. Beeldkrediet: NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute

2. 'n Tweede MIV-pasiënt tree op by langtermyn remissie

Twaalf jaar nadat 'n eerste pasiënt van MIV ontslae geraak het, het 'n ander persoon vanjaar 'n soortgelyke mylpaal behaal. In Maart het die anonieme persoon met behulp van 'n stamseloorplanting van 'n virusbestande skenker 'n langtermyn remissie van MIV gekry.

In albei gevalle volg remissie 'n oorplanting van beenmurg van 'n persoon met 'n mutasie in die geen wat die proteïen CCR5 kodeer, wat baie MIV-stamme gebruik om selle te infiltreer. Geen behandeling was oorspronklik bedoel om die infeksie self uit te skakel nie, maar om bloedkanker wat by albei individue versprei het, te behandel.

Alhoewel die ingryping waarskynlik slegs in 'n klein fraksie van MIV-positiewe individue effektief sal wees, toon die geval uit 2019 dat die doeltreffendheid daarvan meer as 'n eenmalige gebeurtenis was.

3. Wetenskaplikes openbaar die alledaagste swartgatbeeld

In April kon ons ons oog vestig op die allereerste beeld van 'n swart gat. Die swart gat, waarvan die beeld gegenereer is uit data wat vasgelê is deur 'n netwerk van agt radio-observatoriums waaruit die Event Horizon Telescope bestaan, woon in die middel van 'n sterrestelsel, ongeveer 55 miljoen ligjare van die aarde af.

Net so gewild soos die swartgatbeeld was, 'n ander aspek van die verhaal wat vinnig aanlyn ontvou het: die bydrae van die 29-jarige MIT-wetenskaplike Katie Bouman, wat 'n algoritme ontwerp het om die teleskoopdata in die swartgatbeeld te vertaal. Bouman, vasgevang op 'n foto met 'n skootrekenaar, stralend agter haar gevoude hande, het vinnig 'n simbool geword vir die prestasies van vroue in sterrekunde en rekenaarwetenskap. Maar, Marina Koren skryf vir Die Atlantiese Oseaan, "Hierdie een beeld het 'n menigte vrae aangespreek oor die rol van vroue in die wetenskap, die mite van die eensame genie en die druk wat wetenskaplikes het om hulself en hul werk op sosiale media te bevorder."

"Niemand het 'n algoritme of persoon hierdie beeld gemaak nie," het Bouman later in 'n Facebook-boodskap met verwysing na die swartgatfoto geskryf. "Dit vereis die ongelooflike talent van 'n groep wetenskaplikes van regoor die wêreld en jare se harde werk om die instrument, dataverwerking, beeldmetodes en ontledingstegnieke te ontwikkel wat nodig was om hierdie skynbaar onmoontlike prestasie te haal."

4. Die eerste CRISPR-kliniese proewe in die VSA vind plaas

CRISPR-Cas9 is 'n instrument waarmee wetenskaplikes klein stukkies DNA kan sny en invoeg op presiese gebiede langs 'n DNA-string. | Beeldkrediet: Ernesto del Aguila III, Nasionale Instituut vir Menslike Genoom, NIH

In April het navorsers begin met die eerste CRISPR-Cas9 geenbewerking kliniese proewe by mense in die Verenigde State. In die proewe het wetenskaplikes CRISPR, 'n kragtige geenbewerkingstegniek wat afkomstig is van 'n antieke bakteriële immuunstelsel, gebruik om kanker en bloedafwykings te bekamp. Daardie maand is twee kankerpasiënte — een met myeloom en een met sarkoom — met CRISPR behandel.

In die kanker- en bloedversteuringsproewe verwyder navorsers sommige selle uit die liggaam van 'n pasiënt, wysig die selle se DNA met behulp van CRISPR en spuit die selle weer in, "nou hopelik gewapen om siektes te beveg," skryf Tina Hesman Saey vir Wetenskapnuus. Maar in 'n ander proef wat deur Editas Medicine in Cambridge, Massachusetts, uitgevoer is, gebruik navorsers CRISPR om DNA direk in die menslike liggaam te wysig deur ''n klein stukkie DNA uit die selle te snip in die oë van mense met 'n oorerflike vorm van blindheid, ”Skryf Saey.

Die proewe kom op die hakke van die Chinese wetenskaplike He Jiankui se gene-redigering op tweelingmeisies wat in November 2018 gebore is, wat wyd gekritiseer is as voortydig en hoogs oneties. .

5. Nuwe fossiele vang die dag waarop die dinosourusse dood is - en die miljoen jaar daarna

Soogdierfossiele soos hierdie, ontdek deur 'n span paleontoloë en paleobotaniste onder leiding van Tyler Lyson in Corral Bluffs, Colorado, vul 'n ontbrekende stuk tydlyn in. Beeldkrediet: HHMI Tangled Bank Studios

Hierdie jaar het wetenskaplikes nuwe insig gekry in die dag toe die asteroïde wat die dinosourus doodmaak 66 miljoen jaar gelede op die aarde neergestort het, en die eerste miljoen jaar na die impak.

In April het die paleontoloog en afgestudeerde student Robert DePalma beweer dat hy 'n ongekende tydkapsule van die asteroïde-geïnduseerde ramp onthul het. Hy het berig dat hulle verskroeide boomstamme en honderde goed bewaarde fossielvisse onder sediment op 'n terrein in Noord-Dakota gevind het, wat 'n kiekie vorm van die eerste minute en ure na die impak. (Sommige kenners bly versigtig oor die bevinding, deels as gevolg van die feit dat DePalma se ontdekking die eerste keer in a Inwoner van New York artikel voor publikasie van die portuurbeoordeelde referaat.)

Toe, in Oktober, word nuwe fossiele onthul wat die tydlyn van die miljoen jaar van die lewe vang nadat die dinosourusse gesterf het. Die fossiele, wat in die Corral Bluffs in Colorado ontdek is deur die paleontoloog Tyler Lyson en sy span, toon die buitengewone veerkragtigheid van die lewe in die nasleep van 'n ramp en help om die evolusionêre reis van die soogdiere wat die asteroïde oorleef het, te onthul.

6. Rassisme duur voort in medisyne en wetenskap

Met die gebruik van kunsmatige intelligensie het een ernstige fout in 2019 steeds opslae gemaak: rasse-vooroordeel. In Oktober het navorsers aangekondig dat 'n spesifieke algoritme, wat voorspel wie kan baat vind by opvolgsorg en wat 100 miljoen Amerikaners beïnvloed, die behoefte aan swart pasiënte vir addisionele behandeling onderskat. Die algoritme onderskat die gesondheidsbehoeftes van swart pasiënte, selfs al is hulle sieker as hul wit eweknieë.

Daarbenewens bly die VSA een van die gevaarlikste ontwikkelde lande om swanger te wees en geboorte te gee, veral vir minderhede. "Swangerskapverwante sterftes neem toe in die Verenigde State en die grootste risikofaktor is swart," skryf Mike Stobbe en Marilynn Marchione vir AP Nuus. In 'n CDC-verslag word bevind dat swart vroue, sowel as inheemse Amerikaners en inboorlinge in Alaska, drie keer meer geneig is om voor, tydens of na die baba te sterf, en meer as die helfte van hierdie sterftes is voorkombaar, "skryf Stobbe en Marchione.

Ook hierdie jaar het navorsers verder ondersoek ingestel waarom swart wetenskaplikes minder geneig is om finansiering van die National Institutes of Health (NIH) te kry as hul wit eweknieë. 'N Studie wat in Oktober gepubliseer is, illustreer dat die keuse van onderwerpe bydra tot die laer pryse van NIH-toekennings wat aan swart wetenskaplikes toegeken word. "Spesifiek," skryf Jeffrey Mervis vir Wetenskapstydskrif, "Swart aansoekers is meer geneig om benaderings voor te stel, soos gemeenskapsintervensies, en onderwerpe, soos gesondheidsverskille, adolessente gesondheid en vrugbaarheid, wat minder mededingende tellings van beoordelaars ontvang."

7. 'n Nuwe skakel word getrek tussen mense en Denisovans

'N Replika van 'n fragment van 'n Denisovan-vinger in die Denisova-grot, Siberië, in 2008. Beeldkrediet: Thilo Parg, Wikimedia Commons

Nuwe bevindings in 2019 het bygevoeg tot die begrip van antropoloë van Denisovans, 'n soort vroeë mens wat waarskynlik die planeet gedeel het Homo sapiens so onlangs as 50 000 jaar gelede.

Hierdie herfs het wetenskaplikes geleer dat, alhoewel Denisovans se DNA hulle nouer aan Neanderdalmense verbind, hul vingers dalk meer soos ons s'n gelyk het, wat daarop dui dat Neanderdalmense se breër syfers ontwikkel het nadat hul geslag ongeveer 410 000 jaar gelede van die Denisovane afgeskeur het. 'Nog 'n paar fossiele,' skryf Bruce Bower vir Wetenskapnuus, “Plus genetiese ontledings het aangedui dat Denisovans nabye familielede was en soms paringsmaats van Neanderdalmense en Homo sapiens tienduisende jare gelede. Maar daar was te min bewyse om te sê hoe Denisovans daar uitsien of hoe hulle optree. '

8. Google maak aanspraak op kwantumheerskappy

Natuurkundiges het vanjaar 'n mylpaal in kwantumrekenaarskap bereik, 'n rekenaarmetode wat kwantumfisika gebruik om ingewikkelde probleme vinnig op te los.

In Oktober het Google gesê dat hulle 'kwantumoorheersing' bereik het. Sy AI-kwantumspan het bewys gelewer dat hy 'n kwantumrekenaar gebou het wat slegs 200 sekondes benodig om 'n probleem op te los wat IBM se Summit, die wêreld se kragtigste superrekenaar, 10 000 jaar sou neem om te kraak. Hoewel IBM die bewering betwis het, is ander in die rekenaargemeenskap voorlopig optimisties oor die belofte van die deurbraak. As dit gevalideer word, kan dit ons nader bring aan 'n toekoms van ultra-doeltreffende rekenaars.

9. Saturnus het nou die meeste mane in die sonnestelsel

Saturnus, gesien vanaf die Cassini-ruimtetuig van die NASA tydens die equinox van 2009.

Net toe jy gedink het Saturnus kan nie meer wonderlik word nie, verseker dit nog 'n aanspraak op roem: die bekendste mane van enige planeet in ons sonnestelsel (jammer, Jupiter).

Op 7 Oktober het die International Astronomical Union se Minor Planet Center aangekondig dat navorsers 'n bykomende 20 mane ontdek wat Saturnus wentel, wat sy totale totaal op 'n yslike 82 te staan ​​bring. Jupiter, die grootste en oudste planeet in ons sonnestelsel, het 79.

Die nuutste ontdekkings is moontlik gemaak deur die Subaru-teleskoop in Hawaii. 'N Span onder leiding van Scott S. Sheppard van Carnegie Science het hulle die eerste keer in die lente van 2017 dopgehou, maar omdat verre mane dof en moeilik is om raak te sien, het navorsers Subaru gebruik om die lug die volgende jaar gereeld te skandeer om hul bevinding te bevestig. Daarna het hulle 'n rekenaaralgoritme gebruik om die data deur die tyd te koppel en te bevestig dat die mane inderdaad betroubaar om Saturnus wentel.

10. Klimaatsverandering neem toe, en die jeug veg terug

Terugtrekkende gletsers verhoog die Aarde en die seevlak stadig.

Minder as 'n week nadat die VN-klimaatsgesprekke vandeesmaand in Madrid tot 'n einde gekom het, het Australië sy warmste dag ooit aangeteken, een dag na sy vorige rekord. Slegs enkele maande gelede het veldbrande nie net in die Amerikaanse Weste en Australiese buitewyke gewoed nie, maar ook in Europa en die Amasone, wat volgens baie klimatoloë moontlik vererger is deur droogte en hoë temperature deur klimaatsverandering. En in Mei beweer 'n verslag van die Verenigde Nasies dat een miljoen plante- en diersoorte op die punt van uitwissing is - meer as in enige ander tydperk in die mensegeskiedenis - met kommerwekkende gevolge vir menslike voortbestaan. Die verwarmingsklimaat, wat die gevolge van oorbevissing, plaagdodergebruik, besoedeling en stedelike uitbreiding verhoog, is 'n belangrike faktor in die verslag.

Drie weke gelede het 'n 'somber' klimaatverslag, ook van die VN, voorspel dat die wêreldwye koolstofvrystelling gaan klim “ondanks beloftes van byna 200 lande om klimaatsverandering aan te spreek, die temperatuur opwaarts te dryf en dreig om die drempel van 2 ° C wat wetenskaplikes verbreek, te verpletter sê sou dramatiese veranderinge in die ekologie en die ekonomie uitlok, ”skryf Nathaniel Gronewald vir Wetenskapstydskrif. En baie het die COP25-klimaatsgesprekke van hierdie maand as 'n massiewe mislukking verklaar.

Maar klimaatsaktiviste, veral tieners, het vanjaar die kollig aangegryp. Greta Thunberg, 'n 16-jarige Sweedse klimaataktivis, is pas genoem TYD's Persoon van die Jaar. En op COP25 het amptelike verteenwoordigers van die kiesafdeling vir jeug hul teleurstelling uitgespreek teenoor leiers en amptenare, skryf Kartik Chandramouli vir Mongabay. 'Wil u onthou word as diegene wat die kans gehad het om op te tree, maar besluit het om nie as verraaiers van ons generasie, van inheemse mense en gemeenskappe wat desperaat op die grond veg nie?' Jeugverteenwoordigers gesê. 'Ons styg, ons veg en ons sal wen.'

Ontvang e-posse oor komende NOVA-programme en verwante inhoud, asook beriggewing oor huidige gebeure deur middel van 'n wetenskaplike lens.


Die vader van mikroskopie, Anton van Leeuwenhoek van Holland, begin as vakleerling in 'n droëwinkel waar vergrootglase gebruik word om die drade in lap te tel. Hy het homself nuwe metodes geleer om klein lense met groot kromming te slyp en poleer, wat vergrotings tot 270 diameters gegee het, die beste wat destyds bekend was. Dit het gelei tot die bou van sy mikroskope en die biologiese ontdekkings waarvoor hy bekend is. Hy was die eerste wat bakterieë, gisplante, die wemelende lewe in 'n druppel water en die sirkulasie van bloedliggaampies in haarvate gesien en beskryf het. Gedurende 'n lang lewe het hy sy lense gebruik om pionierstudies te maak oor 'n buitengewone verskeidenheid dinge, sowel lewend as nie-lewend, en het sy bevindings in meer as honderd briewe aan die Royal Society of England en die Franse Akademie gerapporteer.

Robert Hooke, die Engelse vader van mikroskopie, het Anton van Leeuwenhoek se ontdekkings van die bestaan ​​van klein lewende organismes in 'n druppel water weer bevestig. Hooke het 'n eksemplaar van die ligmikroskoop van Leeuwenhoek gemaak en daarna sy ontwerp verbeter.


Gaan vanaf die tweede oomblikke van 'n voorwerp na sy elliptisiteit en halflig-straal - Sterrekunde

Net soos daar elke 28 dae is, was daar die volle maan in die nag van 7 Augustus.

Maar vir al die volksbelangrikhede wat verband hou met hierdie maandelikse maangebeurtenisse, kondig hierdie een 'n monumentale hemelse gebeurtenis aan.

Dink net daaraan, ons is nou in die laaste siklus van die maan voor 'n sonsverduistering, het Jack Gabel, BS 94, PhD, 'n medeprofessor in die fisika aan die Creighton Universiteit, gesê. Hy het op 7 Augustus 'n toespraak gelewer oor die komende algehele sonsverduistering op 21 Augustus wat die hele kontinentale Verenigde State sal afknyp - die eerste in 99 jaar. Al die voorwaardes word gestel. Dit is nou 'n kwessie van twee weke wag vir die geleentheid self en om soos 'n klein deel van 'n groot stuk natuur te voel.

'N Skare van meer as 350 mense het die grootste lesinglokaal vir Rabel-wetenskapgebou gevul, wat die sterrekunde van die verduistering beklemtoon, prettige en nuttige feite oor ander sonsverduisterings, die seldsaamheid van sulke gebeurtenisse en veiligheidsmaatreëls om neem as u na die geleentheid kyk.

Die groot Amerikaanse verduistering, die 21 Augustus-gebeurtenis, het 'n sensasie in die VSA geskep, nie net onder wetenskaplikes soos Gabel nie, maar ook vir mense wat op die pad van die verduistering se totaliteit woon - ongeveer 70 kilometer breed band waaroor die maan se skaduwee sal streep, van Oregon tot Suid-Carolina, binne 'n kwessie van 90 minute en ander in die hoop om op die pad te kom vir 'n eenmalige ervaring.

'As u 'n weg in die pad van die totaliteit kan vind, sou ek sê dat dit 'n goeie idee sou wees om dit te probeer,' het Gabel gesê, wat saam met die Creighton Departement Fisika 'n uitreikgeleentheid sal lei met ongeveer 600 omgewingskoliere om die verduistering naby Tecumseh te besigtig. Selfs in Omaha gaan dit 'n baie opwindende, opwindende ding wees. Die son sal hier net 'n klein bietjie wees. Maar as u in die 70-myl-band van die maan se skaduwee kan kom, sal dit opvallend wees om te sien hoe die son heeltemal geblokkeer word en die spookagtige strome koronale lig wat voortspruit uit die donker gat waar die son moet wees.

Wat die sien van 'n totale sonsverduistering so skaars maak, het Gabel gesê, is die groot ongelukke van fisika en sterrekunde. Aangesien ons maandeliks volmaan en nuwemaan ervaar, kan ons dink dat ons net so gereeld sonsverduisterings sal ervaar.

Sonverduisterings van 'n nie-totale aard vind wel twee keer per jaar plaas, maar hulle hou gewoonlik nie lank nie en die maan se plasing tussen die son en die aarde laat nie die totale donkerte toe wat 'n totale sonsverduistering meebring nie. Totale sonsverduisterings vind ook elke jaar of twee plaas, maar is vir 'n paar kort oomblikke sigbaar in 'n baie klein gebied van die aarde, dikwels in afgeleë gebiede of in 'n oop oseaan waar dit bykans ongemerk gaan.

Gabel het gesê tussen die hemelse omstandighede, die uitgestrektheid van die aarde en die tydsberekening van die gebeurtenis, kan die skaarsheid van 'n totale sonsverduistering nie oorskat word nie. Die een wat oor 'n groot hoeveelheid bewoonde lande gaan sny, maak die verduistering van 21 Augustus soveel meer spesiaal, het hy gesê.

Vir historiese konteks was dit 1954 die laaste keer dat 'n totale sonsverduistering vanaf enige plek in Nebraska sigbaar was. Die volgende keer dat 'n totale sonsverduistering vanaf enige plek in die staat sigbaar is, sal 2106 wees en die volgende keer dat 'n totale sonsverduistering vanaf Omaha sigbaar sal wees, sal die jaar 2245 wees - 228 jaar van nou af.

Voeg daarby die immer-ligte 5-grade kanteling van die maan se wentelbaan om die aarde, die relatiewe groottes van die betrokke hemelliggame en hul relatiewe posisie onder mekaar, 'n algehele verduistering is een van die ongelykste gebeure.

As die maan nader aan ons was, sou verduisterings baie meer sigbaar wees, het hy gesê. As dit net 'n bietjie verder weg was, sou ons dit nooit kry nie. Die relatiewe afstande en groottes van die maan en die son is op daardie lieflike plek waar die son vir 'n paar vlugtige oomblikke oor 'n klein area van die aarde heeltemal geblokkeer word. Met die een wat aanbreek, sal daardie spesiale plek deur Nebraska spoel. Die meeste van ons sal waarskynlik nooit weer die kans hê om 'n gebeurtenis soos hierdie te sien nie .

Die laaste totale sonsverduistering wat oor die VSA gesny het, het op 8 Junie 1918 plaasgevind, gevolg deur 'n pad van Washington na Florida. 'N Jaar later het Britse wetenskaplikes wat aan die kus van Wes-Afrika gewerk het, 'n totale sonsverduistering daar gebruik om die teorie van algemene relatiwiteit van Albert Einstein te bewys en die buiging in die lig van sigbare sterre rondom 'n massiewe voorwerp te meet - in hierdie geval, die son.

So verduisterings het die wetenskap bevorder, het Gabel gesê. Die waarneembare buiging van sterlig was 'n dramatiese bevestiging van Einsteins revolusionêre teorie

Die uitsig oor die verduistering van 21 Augustus oor Nebraska sal begin om 11:30, Central Daylight Time, wanneer die maan tussen die son en die aarde sal begin kruis, wat 'n bietjie hap uit ons naaste ster sal neem. Die maan sal geleidelik meer van die son okkulteer tot ongeveer 13:03, CDT, wanneer die verduistering in die pad van totaliteit tot twee en 'n half minute sal duur. In die pad van totaliteit moet die duisternis diep genoeg wees om sterre, veral die helder ster Regulus, naby die son in die sterrebeeld Leo te sien.

Spesiale verduisteringsbril is nodig om die gebeurtenis te besigtig, anders moet verduisteringswagte permanente, ernstige skade aanrig. Slegs in sy kort oomblikke van totaliteit kan die verduistering veilig gesien word sonder die spesiale bril. Die gesin van Gabel het tydens die gesprek op 7 Augustus 'n paar spesiale bril uitgedeel aan almal wat daar was.

Op verskeie punte gedurende sy toespraak het Gabel die belangrikheid van veiligheid in die sien van die verduistering beklemtoon. Fotografie en teleskopiese besigtiging moet ook deur middel van spesiale, donker verdonkerde lense plaasvind, het hy bygevoeg. Die enigste ding wat deur sulke lense sigbaar moet wees, het Gabel gesê, is die son.

'Daar is 'n baie groot potensiaal om u sig permanent te beskadig as u nie die regte voorsorgmaatreëls tref nie,' het Gabel gesê. Dit is baie eenvoudig. Behalwe vir die kort twee-en-'n-half minute gedurende die totale tyd, moet u die skakerings aanhou

In Omaha, het Gabel gesê, aangesien die verduistering nie die totale bereik sal bereik nie, maar tot ongeveer 98 persent okklusie sal kom, moet elkeen wat na die hemel kyk, die spesiale lense aanhou gedurende die hele verduistering.

Ander veilige besigtigingsopsies sluit in die skep van indirekte verduisteringsapparatuur vir verduistering, wat so eenvoudig kan wees as om na die lig te kyk wat die verduistering op die grond gooi deur 'n gaatjie in 'n stuk karton of deur vlegsels wat met mekaar verbind is. Gabel het meer inligting oor die verduistering en veilige besigtigingstegnieke op die webwerf van die Departement Fisika geplaas.

Gabel het gesê dit sal die eerste totale sonsverduistering wees wat hy ooit ervaar het en hy sien daarna uit om dit saam met die middelbare skoolleerlinge in Tecumseh te sien, op die pad van totaliteit.

Daar is regtig twee maniere om daarna te kyk, het Gabel gesê. Die eerste is die aarde-tot-die-hemel-gebeurtenis waarop ons almal 'n uitkykpunt het. Maar die tweede is om aan die geheelbeeld te dink. Dat ons gemiddelde ster, die son, in ons gemiddelde sterrestelsel uitgewis gaan word deur die kleinste, naaste ding aan ons planeet, die maan. Dit is gebeure waarna mense dekades lank uitsien, maar in die geheelbeeld is dit net 'n blip. Op aarde gaan dit egter iets wees om te aanskou


Beginner vas

My Meade Polaris 130-reflektor is op 'n Nexstar + SLT-berg.

Ek het 'n lyn van 2 sterre en Mars het my eerste toets gekies. Andromeda om net te flou te begin, ek dink ek het eers 'n helder voorwerp nodig om verder te leer.

Ek het die Mount Track Mars en fokus en fokus dan in my 6mm EP. (Ek het pas my bahtinov-masker gekry, maar het dit nog nie gebruik nie)

Nou het ek skerpkap gebruik om hierdie kamera in hierdie OTA vroeër in die PM op 'n boom te fokus. Ek dink ek is gereed om te gebruik.

Ek verander die blootstelling sekondes en versterk. Ek kyk na die histogram. Daar is geen helder ding in die beeld wat dalk mars kan wees nie.

Ek kry 'n fout: 'Laaste 200 beelde is nie gestapel nie, want hulle kon nie belyn word nie'

Ek verander van die histo-oortjie na die belyningstabel. Ek sien dit hoop op 15 sterre. Ek kan net daal tot 10. Dan vink ek die uitknoppie uit en kry ek uiteindelik 'n beeld op die skerm van my spieël en sekondêr.

Geredigeer deur erleichda, 27 September 2020 - 00:22.

# 2 barbarosa

U moet fokus met die kamera in plek. Gebruik die masker of gebruik die fokusgereedskap in SharpCap. As u 'n EP gebruik om die teiken te sentreer (iets wat baie van ons vroeër of later doen). Dan moet jy weer fokus as jy die kamera insit.

Mars is baie helder, baie keer helderder as die helderste ster. Om Mars as 'n skyf met funksies te sien, gebruik u gewoonlik 'n lae of geen wins en 'n baie kort blootstelling. As u die versterking en blootstelling hoog genoeg stel om sterre in die beeld te sien, sal Mars 'n kenmerkende opgeblase skyf wees.

As gevolg van daardie lewendige stapeling sal geen sterre gesien word nie, dus as alle rame gemerk is, sal alle rame geïgnoreer word. Selfs met ongekontroleerde rame, sal stapelwerk steeds nie nuttig werk nie. Die klein sensor in 'n 224 is effektief soos die gebruik van 'n kort brandpuntsafstand EP (iets & lt10m) vir groot vergroting. Dit beteken dat u byna altyd 'n bietjie spring as gevolg van onstuimigheid in die lug, sal sien. Stapel sal net 'n helder vlek skep.

Die manier om dit te omseil is gelukkige beelding. U maak 'n video met 'n klein ROI en kort blootstelling en hoër wins as wat u normaalweg sou gebruik. Gebruik 'n gratis program soos Registax om die rame te onttrek en te stapel. Baie gereedskap, histogramme, golwe - almal probeer dit ten minste een of twee keer.

Alhoewel dit die sentrering van Mars in die kamerasig sal bemoeilik, kan u 'n Barlow, 2x of selfs 3x oorweeg. Hier is hoe Mars net met die kamera en met 'n 3x Barlow in fokus sal lyk. Die nadeel is natuurlik dat enige beweging nog meer sigbaar sal wees. Maar dit is wat dit is, die beeld spring en kom in en uit die fokus. Jy geniet die oomblikke tussenin.

Geredigeer deur barbarosa, 27 September 2020 - 01:21.

# 3 sg6

'N Oogstuk moet in effek verder na buite sit as 'n kamer moet.

Wat gebeur, is dat u die okularis insit en die fokuser "skuif" om 'n goeie beeld te gee.

As u die oogstuk uittrek en die kamera in die kamera sit, is dit te ver buite sig, en so buite fokus. Geen sterre in fokus beteken dat die sagteware geen sterre het om by te pas nie.

Met die kamera binne moet u die fokuser na binne draai totdat dit 'n skerp beeld kry - vertoon die uitvoer op 'n skootrekenaar.

Die werklike probleem is waarskynlik dat die fokuser onvoldoende beweeg vir die kamera om 'n skerp beeld te kry. Kom algemeen voor op 'n weerkaatser, aangesien hulle beperkte reisfokusse het. Skywatcher maak om hierdie rede 'n 130/150/200 vir visuele en 'n effens ander variant vir beeldvorming.

Die oplossing is om by die spieëlsel te kom en die spieëlbewegings te skuif of die hele spieëlsel na bo te skuif. Geen idee wat die beste of selfs die moontlike is nie. Die spieël sal waarskynlik 25-50 mm moet beweeg volgens die metode.

As ons aanneem dat dit werk, die fokusvlak na buite beweeg, die ligkegel by die sekondêre groter is, kan u vignettering kry, maar u sal nou vind dat die fokusvlak te ver na buite is om 'n okular te gebruik. U het dus 'n verlengbuis van 25-50 mm nodig om in die fokuser te pas om 'n okular te gebruik.

Nadat u die spieël geskuif het, moet u die omvang volledig opneem, want alles sal uitkom.

Die algemene denkproses is dat u 'n reikwydte het en 'n kamera het, wat alles nodig is vir beeldvorming. U moet regtig die regte omvang en regte kamera hê.

Lees maar die kamera ASI224, aangesien die flens / sensorafstand klein is, 6,5 mm, kan u genoeg fokusverstelling hê sonder om die spieël te beweeg. As mense spieëls skuif, is dit dikwels vir gebruik met 'n DSLR, en soos gewoonlik het Canon 'n flens / sensor-skeiding van ongeveer 45 mm gehad. U het baie minder, dus dit is goed met u. Moet dit probeer en sien.

# 4 GazingOli

Ek gebruik 'n ASI224 op 'n CPC800. Ek doen gewoonlik die belyning met die okular en as dit klaar is, het ek na 'n ster geslag - nie te helder nie.

Sodra die ster goed gesentreer is, verander ek die oogstuk vir die kamera en fokus die kamera op die ster. No need for histogram at this point. Just watch the monitor and focus. In order to do this you have to know or find out about what exposure time and gain you need for the camera to be able to show the star.

You need to be near the focus or know which way your camera is out of the focus, to be able to get to the focus. The problem is: if you are too far out of the focus you will see absolutely nothing on the monitor! So: if you see nothing, be patient and try as long as it takes to get at least a big faint dot on the monitor. then turn at the focus wheel so that this dot gets smaller and smaller.

That is basically it. I usually start with longer exposure and higher gain and as soon as I can focus on the star I reduce exposure and gain so that the image of the star gets smaller and smaler. By the time usually fainter stars in the area appear. And soon as you get a really sharp image of the fainter stars you are perfectly in focus.

Mars is only good for rough focussing, because it is too bright and therefore it is also hard to focus on fainter stars in its sourrounding.

Edited by GazingOli, 27 September 2020 - 04:10 AM.

#5 erleichda

Got it, thanks all. I did not realize how bright Mars could be. I do attain focus with the camera in, but understand the issue with my DSLR and XT8 trial and errors. Barbarosa, thanks for the reminder about planetary doing best with video/registax.

I'll try again on a star and see if I can get the focus with that same workflow. MO

#6 erleichda

#7 GazingOli

Did you do darkframe substraction? This is absolutely neccessary!

edit: next time you are on please make a screenshot and post it

Edited by GazingOli, 28 September 2020 - 01:30 AM.

#8 erleichda

I followed this from Howie, so no I'm not at the point of adding flats and blacks. https://www.youtube. eature=youtu.be

Would you like screenshot of static, high-noise black images or my primary and secondary mirrors? LOL.

I'll go through getting focus with something during the day again, which worked fine on a leaf on a tree down the street. Then start with high gain, 2 seconds and work from that histogram.

Is it possible that the FOV is just too narrow to see many stars in Bortle 6?? I am only 2 star aligning as well, and the drift off Altair was significant. Thus, though my 11mm EP had the star in view when I checked later, it was out of view at 6mm. So I assume the FOV of the 224 is more like 6mm from using astronomy tools.

#9 GazingOli

if you can reach the focus with an eyepiece after my experience it should work also with a camera. the focus of an ASI camera is not too far away given the same image train. however I am working with a C8 and a refractor. might be different with a newtonian.

Do you see anything on the monitor? That is why I wanted a screenshot. I do not know why you refer to the histogram, I never did for focussing. Stars are bright enough anyway.

I recommend to try by night rather than day, just make sure your scope is properly aligned with a star. If it does not work you might need to get closer to the scope with the camera.

Flats and darks are only required for live stacking. I am even not sure about flats, darks are definitely required because SharpCap needs to detect stars properly and without dark substraction you get too many hot pixels. But you will not need to live stack unless you are in focus.

Edited by GazingOli, 28 September 2020 - 12:09 PM.

#10 GazingOli

This is what you get when you point at M57 with your scope and the ASI224:

enough brigth stars to detect for SharpCap live stacking

Even with my f/10 scope CPC800 it works perfectly on a really narrow FOV, as you can see here:

Edited by GazingOli, 28 September 2020 - 12:21 PM.

#11 dmanuel

I am imaging using the ASI120MC-S that I bought for planetary imaging a few years ago. Indeed it does give a narrow field of view and makes it a little more challenging to get your targets on the sensor. My first few tries were at 560mm FL, not much less than the 650mm FL of your scope. From my experience, if you have the target centered in your eyepiece at say, 6 mm, you should be hitting the sensor somewhere. Focusing is not a trivial task. Can you attempt to focus on the moon through the camera? It is bright enough that even when extremely out of focus you should be able to tell that your aimed at it. Its size also helps.

My guess is that you might not have enough in-focus with a Newtonian configured for visual. I know that you were able to focus on some leaves during the day - how far away were they? Can you try focusing on something more than 1/4 mile away? If so, mark that location on your focuser drawtube and use that as the starting point for the camera after you center the star or moon in your FOV with an eyepiece. That should be close enough to infinity that you'd see the star to center and do fine focusing.

#12 erleichda

Leaves were about 300 yards away. I'll try the new cannabis grow that lights up on top of bald peak 10 mi away tonight.

I can see the moon as superbly bright but not able to focus it with the camera in.

I note that after 2 star align, when I slew to those stars, the are no longer centered but up too high. I just read about the last up - right move when aligning to resolve this. Can someone explain? Up -right in the goto direction? I also cannot use the slew buttons once it is aligned and tracking, pushing them does nothing. Is this normal? I have realigned a few times to fix, but still end up with the star out of center when i slew to it. Perhaps I'm then trying to focus on a bunch of faint stars. I do see a "Hot Pixel" warning in all red letters, as Oli notes above. I can add some blacks tonight to also try that.

Last, when trying to focus and eventually just see the mirrors. I'm guessing my focus is way out, and that the general area of focus would be opposite direction? I can check and mark my focuser with tape tonight.

Thanks everyone, I'll be SUPER excited once I figure this out. so close.

#13 barbarosa

I do not have a Newtonian but I do have an ASI224 and a 2X Barlow on an f/7 85mm refractor. My sky, near a large urban area, is a bit darker than yours, but I am confident that you will see stars. By all means try the moon. There won't be much shadow relief but areas close to the terminator should be crisp enough to test focus.

I am not clear that focus is your problem. I think the problem is partly how you are using SharpCap. Be sure that you have the latest ZWO native drivers and the latest version of SharpCap

But let's get focusing first. Using SharpCap, without Live stacking, the display histogram at the default, and with no "auto" for exposure and gain. Brightness set to zero or <10. In the Exposure settings un-check the LX mode and use the slider to set the exposure. The exposure time will be very fast (ms) and the gain at very low or zero. Can you get focus?

If you can get focus, aim at any bright star away from the moon and above say 50 degrees. Is the image sharp? If you can't see the star or any star, set a longer exposure by checking the LX mode, selecting 4s exposure from the drop down list and setting the gain at 300. If no stars rack the focuser in and out a little. If still no stars set the exposure to 8s. That should get you stars. If you get no stars or only the one bright star, move to a different area of the sky, well away from the moon and closer to the zenith and try again.

If you get an image with one or more stars post it and the .txt camera settings file.

If none of this works, take a snap of your best moon focus, and of a star field at 4 and 8 seconds. Also attach the camera settings .txt file that is created for each image.

Also download and install ASI Studio v1.2.1 so that we have an alternative to SharpCap. But lets get the first diagnostics out of the way.

#14 donstim

I am not clear that focus is your problem. I think the problem is partly how you are using SharpCap. Be sure that you have the latest ZWO native drivers and the latest version of SharpCap

.

SharpCap uses the ZWO SDK rather than the ZWO drivers. Unless you need the drivers for another application, I recommend not installing the drivers in order to avoid any conflicts between the two. The log for the Sept 26th SharpCap update says it includes an updated ZWO SDK, which I assume includes any changes they may have made to the latest drivers.

#15 erleichda

Thanks so much! I'll get to moon and some retry at stars along Barbarosa tutorial tonight. I just fired it up during daytime, and aimed about 1/4 mile away at a tree. I can get focus (of course, low exposure and gain because daylight) at just under 1/2 half turn of the focusing knob away from fully in. When I compare, this is closest to my 11mmEP. The 6mm EP focus point was way further out.

I will hold off on changing drivers for now. I have been trying ASI Studio as well.

#16 erleichda

OK, too early for stars so I jumped on Jupiter. Bam! Got it. Focus knowledge really helped me get it right. Using the EP that was about the same focus is a great tip for idiots like me.

I need to get my tracking better (see above. up and right last?) and polar align (though, polaris is the name of my scope. actual polaris is behind my house until late) My mount is also (an old Nexstar GT) waaaay too bouncy. Current laptop is Windows 7, only USB2. I'm going to try to add some darks tonight too, and have a few questions how to use once capture>capture dark.

Is this hobby going to lead to me asking endless questions? If so, hello there new friends. Appreciate you all.

#17 GazingOli

learning curves in EAA are steep . you are on the right track

#18 barbarosa

Glad to see the breakthrough. Darks are easy in SharpCap and they do help with hot pixels but don't get side tracked. You are still getting to know your mount and scope, and jumping right into imaging is a big jump. How many learning curves at one time?

I would suggest the first thing is to get the mount operation down pat, alignment of course, then learning to replace or rest alignment stars, as the session progresses, also the menu items for setting anti-backlash, and calibrate go to accuracy (might not be the right name but menu item to correct slightly inaccurate go tos

Then when you are comfortable, not perfect in using the mount for video, start the climb on SharpCap (or ASI Studio which you may find is easier to use, if not a fully featured).

Looking forward to some images.

Another thing you might do, depending a bit on your location, is take a look at NightSkiesNetwork.com. If sign up as broadcaster you may find other SharpCap users will join you broadcast and many of them will gladly answer questions. If you join but do not broadcast you can watch others and ask questions via your microphone or the chat box. It is 8:57 PST and there are two broadcasts, both guys are very knowledgeable and one of them is using SharpCap.

#19 erleichda

Great advice. My alignment is a part of the issue it seems. So I'm taking a step back and working on aligning but hitting snags that are not in Michael Swanson's materials.

I'm on a 5.32 HC of the GT Nexstar+. I'm using Auto 2 star, and starting with Altair. Of the choices given after that is aligned, Mirach is pretty easy off to the East and at a good height. After selecting, the mount goes way off where it thinks Mirach should be (it goes too low and to the left). I start over with Mirach first, and it is off trying to get back to Altair, where it goes much too high and to the right. I'm relatively level, I do the Up and Right move last. I checked my coordinates, time/date. (no gps) I even checked my star knowledge with Sky Safari (I was correct, whew!)

Power is via a Celestron AC adapter.

I then cycled power and did a solar align on Jupiter and it held for about 30 min.

Weirdly, I'm getting issues where the slew buttons don't move the mount after alignment and now once this happened when aligning. The slew speed does appear in the HC screen when pushed. And last time I tried to align, I gave up and yet no amount of pushing the Back button would return to main menu. Grrr.

Will keep troubleshooting. (secretly, this old $50 mount may not be long for the world. and advice on next option appreciated from those who have moved on)

#20 barbarosa

With 2 star auto align, the mount slews to where an internal table in the hand control says the second star should be assuming that everything is perfect. When the second star is not centered or not in the field of view all you do is slew the mount to put the star in the center of the field of view and press Enter or whatever key it is. If the alignment is accepted the internal sky map now corresponds to the actual sky and adjusts for any out of level condition.

The reason for advising you to level the mount is to minimize the error in the slew to the second star.

The fact that you were able to get a reasonable alignment on Jupiter says the mount is working as it should.

My Nexstar 8 mount went to a new home and I don't have anyway to try and duplicate what's happening with the slew buttons. I don't want to speculate either. Hopefully Mr. Swanson or some other expert will chime in.

But I think that you are just about to master all that a $50 mount can do.

#21 alphatripleplus

You may get detailed advice on alignment issues with a GT Nexstar by asking questions about the mount in the Celestron Computerized Telescopes Forum. In this Forum we can help with EAA specific issues.

#22 erleichda

#23 erleichda

Hello friendly experts! I'm further along, and wanted to loop back. I am now getting 2 star auto align down to the point I can pick objects and bring them into focus in Sharp Cap! Thank you for your patience and help.

I'll work on my biggest issue: my cheap nexstar GT mount is very tough to keep targets centered in the field of view with my setup. I can get them centered, but they drift off and I have to chase with difficult slew movements from my hand controller. I'll keep an eye out on the classifieds but would you think the cheapest upgrade is an AVX? Orion Atlas? Etc? Appreciate your advice. Think it is lack of polar alignment? Just the GT mount?

But I can focus with a bahtinov mask, slew to a new target, sync that target to better the tracking and then tweak the histogram.

To follow are captures of M32, only because it was quick and easy to target from my site. My histogram was seemed pretty good around 2 seconds and 250 gain. Recall I'm using a cheap 130 reflector with 650mm focal length, F/5.

I just looked at the October challenges and if I get a good night will try for M57.

Thanks for any feedback/advice you may have. I truly appreciate that there is a forum with such great advocates.

Attached Thumbnails

Edited by erleichda, 05 October 2020 - 10:43 PM.

#24 erleichda

You have to focus with the camera in place. Use the mask or use the focus tools in SharpCap. If you use an EP to center the target (something many of us do sooner or later). Then you have refocus when you put in the camera.

Mars is very bright, many times brighter than the brightest star. To see Mars as a disk with features normally you use low or zero gain and a very short exposure. If you set the gain and exposure high enough to see stars in the image, Mars will be a featureless bloated disk.

Because of that live stacking won't see any stars, so if align frames is checked, all frames will be ignored. However even with align frames unchecked, stacking still won't work usefully. The small sensor in a 224 is effectively like using a short focal length EP (something <10m) for high magnification. That means that you will almost always see some jumpiness from air turbulence. Stack will just create a bright blob.

The way to work around this is lucky imaging. You make a video, setting a small ROI and short exposure and higher gain than you would use normally. Use a free program such as Registax to extract and stack the frames. Lots of tools, histograms, wavelets-everyone tries it at least once or twice.

Although it will complicate centering Mars in the camera field of view, you might consider a Barlow, 2x or even 3x. Here is how Mars will look in focus with just the camera and with a 3x Barlow. The downside of course is that any motion will be even more visible. But that is what it is, the image jumps and comes in and out of focus. You enjoy the moments in between.

astronomy_tools_fov (7).png

Well, this was great advice. I took video in between clouds tonight. It's REALLY hard to tell when perfectly focused and there is not great seeing with quite a ring of haze around the planet even with visual. My mount is just a pain as every time I touch focus it moves it slightly out of alignment. Is there a thread on next steps to improve? What to upgrade next? (C6 or 8 that much better than my 130 reflector?) Mount? 2 stage focuser?

#25 alphatripleplus

My mount is just a pain as every time I touch focus it moves it slightly out of alignment. Is there a thread on next steps to improve? What to upgrade next? (C6 or 8 that much better than my 130 reflector?) Mount? 2 stage focuser?

I'm not sure what mount comes with your 130 reflector, but it sounds you may be undermounted (a common problem with beginner scope packages). Even though mount requirements are less stringent for EAA than for astrophotography, a mount upgrade to one that can adequately handle the weight of your reflector without shifting when you focus is probably something to consider. I would not spend money on a new focuser unless you are certain it is not the mount that is the problem.


5 Temperature Profile

Unlike the Geometric Test, to construct detailed models of the gravitating matter distribution we must have some knowledge of the temperature profile of the gas. We extracted the ACIS spectra in three circular annuli containing ≈ 3000 background-subtracted counts over 0.3-3 keV: 0 arcsec − 30 arcsec , 30 arcsec − 70 arcsec , and 70 arcsec − 140 arcsec . We fit these spectra with an apec thermal plasma 6 6 6 http://hea-www.harvard.edu/APEC/ modified by Galactic absorption ( < N G a l H >= 1.55 × 10 20 cm − 2 ). The spectral fitting was performed with xspec v11.1.0v (Arnaud, 1996) .

Attempts to fit this model to the 0.3-3 keV data were unsuccessful for two reasons. First, below ∼ 0.5 keV the data lie well below the model and can only be reproduced if absorption column densities of < N G a l H >≈ 10 × 10 20 cm − 2 are fitted. This effect is undoubtedly related to existing problems in the low-energy calibration mentioned on the Chandra web site. We suspect that because the diffuse gas of NGC 720 has a relatively low temperature ( ∼ 0.6 keV) this calibration problem is more serious for NGC 720 than hotter systems. And it is more serious for the diffuse gas than for the harder discrete sources (see Jeltema et al., 2002) .

If we exclude data below 0.7 keV then much better fits can be obtained for Galactic absorption. However, there is also excess emission above the model for energies ≳ 2 keV. Since this excess is most pronounced in the outer annulus it is very likely associated with the background normalization. (Recall that the background varied throughout the observation – § 2 .) To largely avoid this excess we then excluded data above 2 keV.

Fitting the models over 0.7-2 keV yields temperatures of ∼ 0.6 keV in each annulus. Since, however, we have restricted the bandwidth to such a narrow region (which also does not enclose the energy corresponding to the best-fitting temperature) the constraints on the spectral model are relatively weak. In particular, the best-fitting metallicity is ∼ 0.1 < Z ⊙ >but it is not well constrained and depends sensitively on the chosen upper limit of the bandpass. The temperatures have best-fitting values of 0.62, 0.58, and 0.62 keV respectively in the three annuli each has 1 σ errors of ≈ 0.1 keV. These values are fully consistent with the ROSAT and ASCA values obtained in these regions (Buote & Canizares, 1994, 1997 Buote & Fabian, 1998)

Hence, the Chandra data confirm that the hot gas in NGC 720 is consistent with being isothermal. Given the extenuating issues mentioned above, this is the only robust conclusion we believe can be drawn from the spectrum of the diffuse gas at this time.


NGC 4340

460 in blue luminosity. We use this large, homogenous dataset to examine the innermost structure of these galaxies and tocharacterize the properties of their compact central nuclei. We presenta sharp upward revision in the frequency of nucleation in early-typegalaxies brighter than MB

-15 (66% =4.2 pc, with the sizes of individual nucleiranging from 62 pc down to =-2.49+/-0.09 dex (σ=0.59+/-0.10), isindistinguishable from that of the SBH-to-bulge mass ratio, =-2.61+/-0.07dex (σ=0.45+/-0.09), calculated in 23 early-type galaxies withdetected supermassive black holes (SBHs). We argue that the compactstellar nuclei found in many of our program galaxies are the low-masscounterparts of the SBHs detected in the bright galaxies. If thisinterpretation is correct, then one should think in terms of ``centralmassive objects''-either SBHs or compact stellar nuclei-that accompanythe formation of almost all early-type galaxies and contain a meanfraction

0.3% of the total bulge mass. In this view, SBHs would be thedominant formation mode above MB

-20.5.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS5-26555.

1.4h). Late-type bars extend to only

0.05-0.35R25 and 0.2-1.5h their mean sizes are

0.6h. Sb galaxies resemble earlier-type galaxiesin terms of bar size relative to h their smallerR25-relative sizes may be a side effect of higher starformation, which increases R25 but not h. Sbc galaxies form atransition between the early- and late-type regimes. For S0-Sbcgalaxies, bar size correlates well with disc size (both R25and h) these correlations are stronger than the known correlation withMB. All correlations appear to be weaker or absent forlate-type galaxies in particular, there seems to be no correlationbetween bar size and either h or MB for Sc-Sd galaxies.Because bar size scales with disc size and galaxy magnitude for mostHubble types, studies of bar evolution with redshift should selectsamples with similar distributions of disc size or magnitude(extrapolated to present-day values) otherwise, bar frequencies andsizes could be mis-estimated. Because early-type galaxies tend to havelarger bars, resolution-limited studies will preferentially find bars inearly-type galaxies (assuming no significant differential evolution inbar sizes). I show that the bars detected in Hubble Space Telescope(HST) near-infrared(IR) images at z

1 by Sheth et al. have absolutesizes consistent with those in bright, nearby S0-Sb galaxies. I alsocompare the sizes of real bars with those produced in simulations anddiscuss some possible implications for scenarios of secular evolutionalong the Hubble sequence. Simulations often produce bars as large as(or larger than) those seen in S0-Sb galaxies, but rarely any as smallas those in Sc-Sd galaxies.

SDSS g and z) are being used to study thecentral regions of the program galaxies, their globular cluster systems,and the three-dimensional structure of Virgo itself. In this paper, wedescribe in detail the data reduction procedures used for the survey,including image registration, drizzling strategies, the computation ofweight images, object detection, the identification of globular clustercandidates, and the measurement of their photometric and structuralparameters.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.

Sloan g and z), 100 early-type galaxies inthe Virgo Cluster using the Advanced Camera for Surveys on the HubbleSpace Telescope. We describe the selection of the program galaxies andtheir ensemble properties, the choice of filters, the field placementand orientation, the limiting magnitudes of the survey, coordinatedparallel observations of 100 ``intergalactic'' fields with WFPC2, andsupporting ground-based spectroscopic observations of the programgalaxies. In terms of depth, spatial resolution, sample size, andhomogeneity, this represents the most comprehensive imaging survey todate of early-type galaxies in a cluster environment. We brieflydescribe the main scientific goals of the survey, which include themeasurement of luminosities, metallicities, ages, and structuralparameters for the many thousands of globular clusters associated withthese galaxies, a high-resolution isophotal analysis of galaxiesspanning a factor of

450 in luminosity and sharing a commonenvironment, the measurement of accurate distances for the full sampleof galaxies using the method of surface brightness fluctuations, and adetermination of the three-dimensional structure of Virgo itself.ID="FN1"> 1Based on observations with the NASA/ESA Hubble SpaceTelescope obtained at the Space Telescope Science Institute, which isoperated by the association of Universities for Research in Astronomy,Inc., under NASA contract NAS 5-26555.

3 using the Hubble Space Telescope GOODS ACS and Hubble Deep Fieldimages.

logM /L ).Our study is based on near-IR (H -band: λ =1.65μm)observations, for the first time comprising early- and late-typesystems. Our data confirm that the mean effective dynamicalmass-to-light ratio M /L of the E+S0+S0a galaxies increases withincreasing effective dynamical mass M , as expected from the existenceof the Fundamental Plane relation. Conversely, spiral and Im/BCDgalaxies show a broad distribution in M /L with no detected trend of M/L with M , the former galaxies having M /L values about twice largerthan the latter, on average. For all the late-type galaxies, the M /Lincreases with decreasing effective surface intensity I e ,consistent with the existence of the Tully-Fisher relation. Theseresults are discussed on the basis of the assumptions behind theconstruction of the κ -space and their limitations. Our study iscomplementary to a previous investigation in the optical (B -band:λ =0.44μm) and allows us to study wavelength dependences ofthe galaxy distribution in the κ -space. As a first result, wefind that the galaxy distribution in the κ 1 -κ2 plane reproduces the transition from bulgeless tobulge-dominated systems in galaxies of increasing dynamical mass.Conversely, it appears that the M /L of late-types is higher (lower)than that of early-types with the same M in the near-IR (optical). Theorigins of this behaviour are discussed in terms of dust attenuation andstar formation history.

1.5. We use the tightcorrelation between V-I and zspec for this red subset toestimate redshifts of the remaining E/S0's to an accuracy of

10%, withthe exception of a small number (16%) of blue interlopers at lowredshift that are quantitatively classified as E/S0's but are notcontained within the red envelope. Constructing a luminosity function ofthe full sample of 145 E/S0's, we find that there is about 1.1-1.9 magbrightening in rest-frame B-band luminosity back to z

=0.8 from z=0,consistent with other studies. Together with the red colors, thisbrightening is consistent with models in which the bulk of stars in redfield E/S0's formed before zfor>

1.5 and have beenevolving rather quiescently, with few large starbursts since then.Evolution in the number density of field E/S0 galaxies is more difficultto measure, and uncertainties in the raw counts and their ratio to localsamples might amount to as much as a factor of 2. Within thatuncertainty, the number density of red E/S0's to z

=0.8 seems relativelystatic, being comparable to or perhaps moderately less than that oflocal E/S0's, depending on the assumed cosmology. A doubling of E/S0number density since z=1 can be ruled out with high confidence (97%) ifΩm=1. Taken together, our results are consistent withthe hypothesis that the majority of luminous field E/S0's were alreadyin place by z

1, that the bulk of their stars were already fairly old,and that their number density has not changed by large amounts sincethen.

2.2. We demonstrate the influence of group-dominant galaxies on the fitand present evidence that the relation is not well modelled by a singlepower-law fit. We also derive estimates of the contribution to galaxyX-ray luminosities from discrete-sources and conclude that they provideLdscr/LB

=29.5ergs-1LBsolar-1. Wecompare this result with luminosities from our catalogue. Lastly, weexamine the influence of environment on galaxy X-ray luminosity and onthe form of the LX:LB relation. We conclude thatalthough environment undoubtedly affects the X-ray properties ofindividual galaxies, particularly those in the centres of groups andclusters, it does not change the nature of whole populations.


NGC 2419

=-0.3, although interpretation of thehigh-metallicity end of the MDF is limited by photometric completenessthat affects the detection of the reddest, most metal-rich stars. NGC3377 appears to have an enrichment history intermediate between those ofnormal dwarf ellipticals and the much larger giants. As yet, we find noclear evidence that the halo of NGC 3377 contains a significantpopulation of ``young'' (

26.7 mag arcsec-2and a total apparent magnitude of Vtot

16.1, which at thederived distance modulus, (m-M)0

24.12-24.34, yields anabsolute magnitude of MV

-8.1+/-0.5 these values are quitecomparable to those of Andromeda IX, a previously discoveredlow-luminosity M31 satellite. The discoveries of Andromeda X and ofnumerous other extremely faint satellites around M31 and the Milky Wayin the past few years suggest that such objects may be plentiful in theLocal Group.

10 Gyr),metal-poor clusters. Five have [Fe/H]

-2.1, while an additional fourhave -1.9

50 days five of these are likely Population IICepheids of the W Virginis class, associated with the bulge or halo ofNGC 5128. Based on the period and V- and I-band luminosities of asubsample of 42 classical (Population I) Cepheids, and adopting an LMCdistance modulus and extinction of 18.50+/-0.10 mag and E(B-V)=0.10 mag,respectively, the true reddening-corrected distance modulus to NGC 5128is μ0=27.67+/-0.12 (random)+/-0.16 (systematic) mag,corresponding to a distance of 3.42+/-0.18 (random)+/-0.25 (systematic)Mpc. The random uncertainty in the distance is dominated by the error onthe assumed value for the ratio of total to selective absorption,RV, in NGC 5128, and by the possible metallicity dependenceof the Cepheid period-luminosity relation at V and I. This representsthe first determination of a Cepheid distance to an early-type galaxy.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.

0.1 mag in J-Ks, which we ascribe to photometric systemtransformation issues. Some of the models fail to reproduce the behaviorof the integrated-light colors of the Galactic globular clusters nearsolar metallicity.

2 mag fainter than the turnover magnitude,which occurs at MTOMV=-7.60+/-0.06 for an assumedm-M=29.77. Two GC metallicity subpopulations are easily distinguishable,with the metal-poor subpopulation exhibiting a smaller intrinsicdispersion in color compared to the metal-rich subpopulation. There arethree new discoveries. (1) A metal-poor GC color-magnitude trend hasbeen observed. (2) The fact that the metal-rich GCs are

17% smallerthan the metal-poor ones for small projected galactocentric radii (lessthan

2') has been confirmed. However, the median half-light radii ofthe two subpopulations become identical at

3' from the center. This ismost easily explained if the size difference is the result of projectioneffects. (3) The brightest (MV

106Msolar per orbital period.Hubble Space Telescope images of three of the PNe reveal well-developedbipolar morphologies, and provide clear detections of the central stars.All three stars with deep spectra show WR lines, suggesting that theprogenitor mass and metallicity determines whether a PN central stardevelops a WR spectrum. One Sgr PN belongs to the class of IR-[WC]stars. Expansion velocities are determined for three nebulae. Comparisonwith hydrodynamical models indicates an initial density profile of ρ

r-3. This is evidence for increasing mass-loss rates on theasymptotic giant branch. Peak mass-loss rates are indicated of

10-4Msolaryr-1.The IR-[WC] PN, He2-436, provides the sole direct detection of dust in adwarf spheroidal galaxy, to date.

220 kpc. Based on the SDSS data, we estimate an absolutemagnitude of MV

-7.9, a central surface brightness ofμ0,V

28 mag arcsec-2, and a half-light radiusof

550 pc at the measured distance). The outer regions ofCanes Venatici appear extended and distorted. The discovery of such afaint galaxy in proximity to the Milky Way strongly suggests that moresuch objects remain to be found.

-1.6) sample shows peak magnitudes systematicallybrighter by about 0.36mag than those of the metal-rich (MR) ([Fe/H]>-1.0, (

-0.6) one, in substantial agreement with thetheoretical metallicity effect suggested by synthetic Globular Clusterpopulations with constant age and mass function. Moving outside theMilky Way, we show that the peak magnitude of the MP clusters in M31appears to be consistent with that of Galactic clusters with similarmetallicity, once the same MV(RR)-[Fe/H] relation is used fordistance determination. As for the GCLFs in other external galaxies,using Surface Brightness Fluctuations (SBF) measurements we giveevidence that the luminosity functions of the blue (MP) GlobularClusters peak at the same luminosity within

0.2mag, whereas for the red(MR) samples the agreement is within

0.5mag even accounting for thetheoretical metallicity correction expected for clusters with similarages and mass distributions. Then, using the SBF absolute magnitudesprovided by a Cepheid distance scale calibrated on a fiducial distanceto Large Magellanic Cloud (LMC), we show that the MV(TO)value of the MP clusters in external galaxies is in excellent agreementwith the value of both Galactic and M31 ones, as inferred by an RR Lyraedistance scale referenced to the same LMC fiducial distance. Eventually,adopting μ0(LMC) = 18.50mag, we derive that the luminosityfunction of MP clusters in the Milky Way, M31, and external galaxiespeak at MV(TO) =-7.66 +/- 0.11, - 7.65 +/- 0.19 and -7.67 +/-0.23mag, respectively. This would suggest a value of -7.66 +/- 0.09mag(weighted mean), with any modification of the LMC distance modulusproducing a similar variation of the GCLF peak luminosity.

4°on the sky, corresponding to

1 kpc in projected length. The orientationof the tails is in good agreement with the cluster's Galactic orbit, asjudged from the proper-motion data.


7. CONCLUSION

I have now spent over a third of my working life, the past 24 years plus brief periods before that, working in astrophysics. It has been a true joy trying to understand and explain the rarely or never-seen phenomena of the universe. I thank friends and colleagues who shared insights, results, inspiration, and mental perspiration. I especially thank Gerry Brown for his unwavering support. Without him, I would never have begun, or continued, the scientific journeys I have taken in this quarter century.