Sterrekunde

Die afleiding van die uur gebaseer op RA

Die afleiding van die uur gebaseer op RA


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Ek maak 'n tegnologiese projek. Die doel is om 'n program te skryf wat 'n beeld van die nightky kry en die uur voorspel waarop die foto geneem is.

Ek het 'n bekende metode geïmplementeer met behulp van die grootboom, maar dit is nie genoeg nie. Ek wil nie my program beperk om net te werk as die grootboom in die prentjie is nie.

Toe ek van die regte hemelvaart lees, het my ingewande my vertel dat ek 'n ster in die lug sou sien en die regte hemelvaart daarvan (RA) sou kon aflei hoeveel ure gelede die sonsondergang plaasgevind het, alhoewel ek nie kon verduidelik nie.

Ek is nie gemaklik genoeg met hierdie koördinaatstelsel nie, daarom het ek hulp nodig om hierdie vraag te beantwoord: Sê dat ek die plek waar 'n foto geneem is, ken en dat ek die hemelvoorwerpe in die lug kan identifiseer en RA kan kry, kan ek 'n paar berekeninge doen konw / benader u uur? Indien wel, hoe?

Dankie by voorbaat!


Weet u die datum en ligging vanwaar die foto geneem is? As u die groot romp suksesvol gebruik, gebruik u waarskynlik hierdie inligting. Daar is 'n 'ontaarding' tussen datum en tyd. Die lug draai een keer per dag (23 uur 56 minute) en een keer per jaar (wat 20 minute langer is as tropiese jaar: son in dieselfde posisie). Dus is die lug vanaand om 20:00 te sê dieselfde as die lug om 20:04 die vorige dag. Oor twee weke is dit 1 uur. U het dus die datum nodig.

Terselfdertyd (sê Universele Tyd == Londense tyd) kyk die waarnemer op elke lengte in 'n ander rigting. Dus 15 grade lank is gelykstaande aan 1 uur tyd. U het dus lengtegraad nodig. Ander het verwys na breedtegraad. U sien sterre op verskillende breedtegrade. Byvoorbeeld, aan die ewenaar is die poolster aan die noordelike horison en onsigbaar in die sothaarse halfrond.

Die kernverwantskappe is tussen regshoging (soos "lengtegraad" vir sterre), syagtyd en uurhoek. Die uurhoek is die hoek tussen die meridiale en die posisie van die ster. Of die sidetyd is die regte hemelvaart van sterre wat die meridiaan kruis. U kan dit uit 'n wye veldbeeld bewerk deur gebruik te maak van 'n diens soos https://nova.astrometry.net/ en dan 'sidetyd in plaaslike tyd' om te skakel. Daar is 'n stapeloorvloei-antwoord plus ander.


Alt Az na Ra Dec omskakeling

Ek het die wiskundige roetines nodig om Alt & amp Az na Ra & amp te omskakel. Ek kan nie die formules op die internet of in enige van die boeke wat ek het, vind nie.

Die omskakeling van Ra & amp Des na Alt & amp Az het ek al gedoen en dit werk goed, maar nou wil ek die ander kant toe gaan.

Kan iemand my wys waarheen ek kan kyk.

Die formules Ra & amp; Des tot Alt & amp Az is gevind by: http: //www.stargazin. pler / altaz.html

# 2 S.Boerner

# 3 jdupton

Hoofstuk 12 (getiteld Transformasie van koördinate) van "Astronomiese algoritmes" deur Jean Meeus bevat wat u nodig het. 'N Vinnige soektog op die internet toon verskeie webwerwe met kopieë van baie van die wiskunde wat in die boek behandel word.

Geredigeer deur jdupton, 06 Julie 2017 - 15:26.

# 4 Wm Rison

Dankie, ek het die boek en gaan kyk.

Weet nie hoe ek dit gemis het nie. Het verskeie formules in die boek gebruik.

# 5 Wm Rison

Dankie vir die ander Cloudy Nights-forumskakel.

# 6 jdupton

'N Lang papier kan ook gevind word by:

Ek dink dit het wat u nodig het plus nog baie meer.

# 7 katalogusman

Wees versigtig om soveel bronne aan te beveel. Die verskillende alt-az stelsels

sal verwarring skep vir die OP:

- In Meeus (1991 uitg., Bl. 89) word azimut weswaarts van die Suide gereken.

- In Duffett-Smith (1979 uitg., Bl. 24) en die Verklarende aanvulling tot die
Ephemeris (1977 uitg., P. 26), word azimut vanuit die noorde ooswaarts gereken.

- In Sferiese Sterrekunde deur Green (1985 uitg., p. 28), word azimut gereken
weswaarts vanaf die Noorde.

# 8 Wm Rison

Ek het die inligting wat ek benodig, gekry.

# 9 Wm Rison

Ek het die metode in "Praktiese sterrekunde met u sakrekenaar of sigblad" gebruik en die voorbeeld gekry om te werk, maar as ek my werklike wêreldtoets gebruik, werk die RA nie korrek nie. Opgemerk op bladsy 49 laaste sin praat oor GST is 0u 24m 05s, maar ek kan nie vind waar dit in die voorbeeld of sigblad gebruik word nie. Ek neem aan dat ek LST moet gebruik om die uurhoek aan te pas, want op bladsy 43 kry ek die forum H = LST - a. Dus as ek H en LST het, moet ek 'n (RA) kry.

# 10 DAVIDG

Sky en Tel het ook 'n BASIC-programlys gehad wat die omskakeling sou doen. Hier is 'n skakel na die Sky- en Tel-bladsy met al hul BASIC-programme, insluitend die Alt / Az-een.

# 11 Wm Rison

Het dit nie goedgekeur op die skakel wat u gegee het nie. Die program altaz.bas skakel Ra en Dec om na Alt en Az. Ek gaan die ander pad.

# 12 ChrisMoses

Ek het die metode in "Praktiese sterrekunde met u sakrekenaar of sigblad" gebruik en die voorbeeld gekry om te werk, maar as ek my werklike wêreldtoets gebruik, werk die RA nie korrek nie. Opgemerk op bladsy 49 praat die laaste sin van GST oor 0h 24m 05s, maar ek kan nie vind waar dit in die voorbeeld of sigblad gebruik word nie. Ek neem aan dat ek LST moet gebruik om die uurhoek aan te pas, want op bladsy 43 kry ek die forum H = LST - a. Dus as ek H en LST het, moet ek 'n (RA) kry.

William

Ek het al die sigblaaie in die boek in c # omgeskakel. Laat weet my net as iemand die kode wil hê


Die vermindering van die middelvlugspoed van MH370

Kontak is op 7 Maart 2014 omstreeks 17:20 UTC met die bemanning van Malaysia Airlines-vlug MH370 verloor. Ondanks uitgebreide soektogte is daar nog geen spoor gevind nie. Later in Maart 2014 het die Inmarsat maatskappy het beperkte inligting bekend gemaak rakende kommunikasie tussen MH370 en die Inmarsat-3F1 satelliet, wat twee hipotetiese spore suidwaarts tot in die Indiese Oseaan illustreer, een met 'n konstante snelheid van 400 knope en een met 450 knope. 'N Redakteerde weergawe van die Inmarsat die kommunikasielogboek is einde Mei 2014 vrygestel. Die Burst Timing Offset (BTO) -gegewens wat in die loglêer vrygestel is, het spesifiek 'n akkurater bepaling van die ligging van die sogenaamde 'ping rings' en die afstande van hierdie ringe moontlik gemaak. die sub-satellietposisie.

Omstreeks hierdie tyd het baie ander mense, Inmarsat en die ATSB onder hulle, het pogings aangewend om moontlike vliegroetes te illustreer, deur die aangenome snelhede te kies om die pingringe op die regte tye te onderskep. Dit was baie duidelik dat die spoedaannames nie veel meer was as raaiskote nie, en dat die meeste vliegroetes van vliegtuie na elke pingring moes verander, om in te pas by die bekende reistye tussen die ringe. Figure 1 en 2 illustreer sommige van hierdie raaiskote, maar baie ander voorbeelde kan gegee word.

Figuur 1: 'n vroeë voorbeeld van vermeende paadjies na die Suidelike Indiese Oseaan met veronderstelde snelhede van 450 knope (geel) en 400 knope (rooi).

Figuur 2: 'N Voorbeeld van streke met vroeë prioriteit (aangesien dit verkeerd erken). Die bedoeling om hierdie voorbeeld aan te toon, is om te illustreer hoe verskillende padmodelle rigtingveranderings op die ping-ring-plekke gebruik, wat natuurlik nie-fisies is.

Die doel van hierdie referaat is om aan te toon dat dit moontlik is om die spoed van MH370 in die middelvlugfase (spesifiek tussen ongeveer 19:41 en 20:41 UTC) af te lei deur minimale data van die Inmarsat logs. Die resulterende waarde vir die snelheid stem goed ooreen met die bekende snelheid van die vliegtuig kort nadat dit die cruisehoogte bereik het ná die opstyg en voor sy terugkeer om 17:21 UTC naby die punt IGARI.

Hierdie hipotese oor hoe die vliegtuigspoed afgelei kan word, is die eerste keer in Mei 2014 voorgestel (sien hieronder). Die berekening is oor die volgende paar weke verfyn en met nuwe data geleidelik opgedateer. Hierdie referaat is 'n samevoeging van 'n aantal blogbydraes gedurende die tydperk om die hipotese bondig aan te bied.

Voordat enige BTO-gegewens beskikbaar was, is sekere inligting op ongeveer 28 April 2014 in 'n inligtingsessie van die Chinese families van MH370-passasiers in die Lido Hotel in Beijing aangebied. Een van die voorgestelde skyfies het bekend geword as die 'Fuzzy Chart of Elevation Angles'. '. Hierdie grafiek word hieronder getoon as Figuur 3. Dit is interessant dat die hoogtehoeke (dws die oënskynlike hoekhoogte van die satelliet gesien vanaf die vliegtuig of 90 grade minus die hoogtepunt van die satelliet soos gesien vanuit die vliegtuig) afgelei is van berekeninge gebaseer op die BTO-data, maar op hierdie stadium is geen BTO-data in die openbaar bekend gemaak nie.

Figuur 3: Die wazige grafiek van hoogtehoeke
afgelei van Inmarsat BTO-waardes.

Terwyl hierdie grafiek slegs 'n paar datapunte toon, het dit die basis geword vir verskillende pogings om die BTO-data en daarvandaan die ping-ringe, en spesifiek die radius vir hierdie ringe, te reverse-engineering. Op die oomblik is die Inmarsat definisie vir die BTO kan op verskillende maniere geïnterpreteer word, en daar is kragtige debat gevoer onder waarnemers van buite om die korrekte interpretasie te bepaal. Verskillende interpretasies het gelei tot radiusvariasies van tot 50 NM (seemyl).

By die waarneming van die hoogte-datapunte is dit duidelik dat die vliegtuig direk na die opstyg van die satelliet af gereis het, dan sy spoor omgedraai het en ten minste tot ongeveer 19:40 UTC nader aan die satelliet gekom het, en daarna van die satelliet begin beweeg het. weer.

Die ommekeer tussen 19:40 en 20:40 (benadering tot satelliet-oorskakeling na resessie) is interessant deurdat daar duidelik 'n oomblik tussen hierdie twee tye is wanneer die vliegtuig die naaste aan die satelliet was, en die hoogtehoek dus maksimum was . Uit hierdie eenvoudige waarneming kan afgelei word dat die vliegtuig dus op die punt van die naaste aanpak tangensiaal na die satelliet vlieg.

Vanuit die onduidelike grafiek alleen kan 'n mens die tyd van die naaste benadering op 12 minute na 19:40 skat. Werk wat deur lede van die Independent Group (IG) gedoen is, het die skatting van die ping-ringradius * om 19:40 en 20:40 geskat. 'N Beraming van die hoogtehoek ten tye van die naaste benadering het ook die berekening van die raaklyn moontlik gemaak. Dit is die eerste keer voorgestel in 'n opmerking wat op 16 Mei geplaas is.

Gewapen met net drie stukke afgeleide inligting & # 8211 die geskatte tyd van die naaste benadering, en die radiusse van die 19:40 en 20:40 pingringe & # 8211 is dit moontlik om 'n skatting te maak vir die snelheid van die vliegtuig tussen hierdie keer (gepos 17 Mei sien ook verdere kommentaar gepos op 18 Mei en 20 Mei). Een substantiewe aanname is nodig: dat die vliegtuig tussen hierdie tyd, of byna so, in 'n reguit lyn gereis het. 'N Ietwat geboë baan sou daartoe lei dat 'n groter afstand afgelê word, en dus is 'n effens groter spoed geskik (as die laer spoed wat verkry word met die metode wat hier beskryf word). Natuurlik is dit ook nodig om 'n min of meer konstante snelheid tussen hierdie tye / tussen hierdie pingringe aan te neem.

Aangesien die meetkunde voorgestel kan word deur twee reghoekige driehoeke met 'n gemeenskaplike / gedeelde sy (sien Figuur 4), kan die vlakke meetkunde 'n oplossing bepaal vir die lengte van die basisse vir hierdie driehoeke, en dus die snelheid van die driehoeke. vliegtuie.

Figuur 4: Meetkunde wat die gemiddelde vliegtuigspoed tussen die
ongeveer. 19:40 en ongeveer. 20:20 ping te beraam.

r1 = radius vir die 19:40-pingring

r2 = radius vir die 20:40 pingring

r0 = radius op die raakpunt

t1 = tydsinterval van 19:40 tot die raakpunt (12 minute)

t2 = tydsinterval vanaf die raakpunt tot 20:40 (48 minute)

d1 = afstand afgelê van 19:40 tot die raakpunt

d2 = afstand afgelê vanaf die raakpunt tot 20:40

v = die gemiddelde snelheid van die vliegtuig tussen 19:40 en 20:40

(Die deel deur 60 skakel die tydsinterval om van minute na breuke van 'n uur.)

Let op dat die radius tot by die raakpunt (r0) hoef nie bekend te wees nie, aangesien dit uit die twee vergelykings hierbo verwyder kan word.

Die aanvanklike waardes vir r1 en r2 afgelei van die Fuzzy Chart was onderskeidelik 1815 en 1852 NM. Die gebruik van hierdie waardes en die oplossing van v gee die vliegtuigspoed 476 knope.

Hierdie spoed is aansienlik groter as die meeste gepubliseerde raaiskote wat destyds algemeen was.

'N Oplossing van 'n plat meetkunde vir 'n natuurlik 'n sferiese meetkundige situasie sal waarskynlik slegs 'n rowwe benadering tot gevolg hê, maar die resultate was beduidend en voldoende bemoedigend om met die metodologie voort te gaan terwyl ons op soek was na akkurate BTO-data, 'n akkurate satelliet-efemeris, en die oplossing van die driehoeke met behulp van sferiese meetkunde soos volg.

'N Redakteer Inmarsat teen die einde van Mei 2014 is die kommunikasie-log in die openbaar bekendgestel, wat 'n stel BTO-waardes (vertragingstye) verskaf. Teen daardie tyd, tien weke na die verlies van MH370, is die korrekte interpretasie van die Inmarsat BTO-berekening is vasgestel deur Mike Exner [1], 'n lid van die IG. Dit en die BTO-data het 'n akkurater bepaling van die siglyn (LOS) van die satelliet tot die vliegtuig moontlik gemaak, 'n meer presiese tydsberekening vir die onderskep van die pingring en 'n akkurate berekening van die hoogtehoeke wat die eerste keer in die Fuzzy aangebied is Grafiek (en dan agteruit ontwerp om die satellietvliegtuigreekse te verskaf wat vroeër gebruik is, soos in afdeling 3 hierbo).

Met nuwe en betroubare satelliet-efemeris-data was dit ook moontlik om akkurate berekeninge vir die ping-ringradiusse uit die korrek vasgestelde sub-satellietposisie uit te voer.

Die spoedaftrekking is verbeter deur die gebruik van hierdie data en ook 'n meer akkurate skatting van die tyd van voorkoms van die raakpunt, met behulp van die minimum LOS L-band-oordragvertraging [1].

Figuur 5 toon die berekende vertragings van die L-band-oordrag vir BTO-data na 18:28 UTC.

Figuur 5: Die vertraging van die L-band vir die vliegtuig-satellietverbinding as 'n funksie van tyd tydens die vlug van MH370.

'N Derde-orde polinoomkurwe word op die datapunte in Figuur 5 aangebring, wat lei tot 'n oplossing:

Y = -0.0038x 3 + 0.4433x 2 - 13.116x + 237.91

Om hierdie vergelyking te onderskei om die tyd van die minimum LOS-reeks tussen die satelliet en die vliegtuig te bepaal:

dy / dx = -0,0114x 2 + 0,8866x - 13,116

As u dit omskakel na 'n tyd, lewer dit 'n interval van 11,20 minute na 19:41 UTC.

Let daarop dat dit geensins seker is dat die BTO vir 18:28 UTC gemaklik moet pas op die gladde kurwe wat by die LOS-reeksvertraging pas nie. Dit kan impliseer dat die vliegtuigbaan van destyds min of meer 'n reguit lyn was, maar daar is geen inligting wat daarop dui dat dit so is nie.

Om die betekenis van die datapunt te verminder (om 18:28), is 'n nuwe nominale punt om 19:01 uur bekendgestel. 'N LOS-reeks is vir hierdie punt bepaal deur aan te pas by die LOS-reekskurwe. Daar is veronderstel dat draaie wat die vliegtuig omstreeks 18:28 gemaak het om 'n spoor suid te vestig, teen 19:01 goed voltooi sou wees, en daarom behoort hierdie punt op die min of meer reguit baan te sit wat deur 19 strek: 41 en 20:41. 'N Nominale BTO-syfer is vir hierdie nominale punt omgekeer.

Met die nuwe data is dit ook moontlik om meer akkurate pingringradiusse vir die nuwe presies bepaalde tye, 19:41:03 en 20:41:05, te bereken (in teenstelling met die geskatte 19:40 en 20:40 lees die Fuzzy Chart), tesame met die akkurate satelliet-efemeris. Radius van 1757.25 en 1796.56 NM is gebruik om die twee reghoekige driehoeke weer op te los, maar hierdie keer met sferiese meetkunde.

Gebruik dieselfde benaming:

r1 = radius vir die 19:41 pingring, uitgedruk in radiale

r2 = radius vir die 20:41 pingring, uitgedruk in radiale

r0 = radius op die raakpunt, uitgedruk in radiale

t1 = tyd na 19:41 dat die raaklyn plaasvind (11,2 minute)

t2 = tyd na die raakpunt tot 20:41 (48,8 minute)

D = Groot sirkel afstand afgelê tussen 19:41 en 20:41

v = gemiddelde snelheid van die vliegtuig tussen 19:41 en 20:41

Die grondspoed wat volgens hierdie metode bereken word, is nou 494 knope.

Die windspoed en -rigting vir 'n potensiële suidelike baan oor hierdie segment is ongeveer 21 knope van 65 grade waar [2]. Met behulp van hierdie windinligting en die bogrondsnelheid van 494 knope op 'n baanasimut van 186 grade, kan 'n mens die KTAS (ware lugsnelheid, knope) vir die vliegtuig bereken as ongeveer 484 knope.

Die feit dat die KTAS ooreenstem met die vliegtuigspoed tydens die vaart in die rigting van IGARI in die vroeë gedeelte van die vlug, gee 'n mate van vertroue in hierdie resultaat en bied 'n waardevolle basis vir skatte op die baan en later vir die vlug.

Die skerpsinnige kan daarop let dat daar steeds 'n benadering (of implisiete aanname) gemaak word in die uitvoering van hierdie berekening. Dit is te wyte aan die feit dat die satelliet nie stilstaan ​​nie (alhoewel dit byna so is om ongeveer 19:41, nadat hy die apogee bereik het in sy amper-sirkelvormige, 1,7 grade skuins baan). Dit beteken dat die toppe van die reghoekige driehoeke wat deur die twee pingradius en die raaklyn gevorm word nie presies toevallig is nie. Die fout wat deur hierdie aanname geïntroduceer word, is klein en binne die waarskynlike foutmarge van die geraamde windvektore vir daardie plek, en moontlike variasies in pingringradiusse van bekende BTO-afkapping en jitter. Die reeks sub-satellietposisies word in Figuur 6 geïllustreer.

Figuur 6: Die beweging van die sub-satellietposisie tydens die vlug van MH370. In werklikheid veronderstel die metode wat in hierdie artikel gebruik word dat die satelliet tussen 19:41 en 20:41 in dieselfde posisie bly, die fout wat deur hierdie noodsaaklike aanname veroorsaak word, is klein.
Bron: bogenoemde is Figuur 8 in die referaat gepubliseer in die Journal of Navigation deur Ashton et al. (2014).

Aangesien die snelheid wat uit hierdie berekening verkry word, afhang van die presiese skatting van die tyd van die naaste benadering tot die satelliet (dit wil sê die raaklyn), is dit verstandig om die moontlike snelheidsperke te ondersoek wat kan voortspruit uit variasies in hierdie skatting.

Dit is voldoende om 'n maksimum spoed uit gepubliseerde Boeing 777-prestasiedata vas te stel. 'N Machgetal M = 0,85 kan as 'n boonste limiet beskou word, en dit lei tot 'n KTAS van ongeveer 510 knope, afhangend van die aannames van die hoogte en omgewingstemperatuur.

'N Spesiale geval bestaan ​​wanneer die raaklyn presies om 19:41 plaasvind (d.w.s. op die pingring). In hierdie geval is daar net een reghoekige driehoek wat opgelos moet word. Die grondspoed vir hierdie geval is 392 knope. Om hierdie gebeurtenis te waar te maak, moet die LOS-reeks vanaf die satelliet sy minimum presies om 19:41 vertoon. Ondersoek van die getalle vir LOS-reeks, die BTO en die hoogtehoeke dui daarop dat dit nie die geval is nie, en dat die raakpunt na 19:41 (en ver voor 20:41) plaasvind.

'N Mens kan dus aflei dat snelhede van minder as 400 knope, of groter as 510 knope, nie aanneemlik is nie. Dit kan ook redelik wees om tot die gevolgtrekking te kom dat die vliegtuig in werklikheid naby die normaal verwagte vaarspoed was, en ook naby die normaal verwagte vaarthoogte van 35.000 voet.

In terme van die algehele begrip van die vlug en dus die snelheid van die vliegtuig, is dit nuttig om te weet watter outopiloot-koste-indeks (GI) in die Flight Management Computer (FMC) vir hierdie vlug geprogrammeer is. Die IG het verskeie kere 'n beroep gedoen op die CI wat gebruik / geprogrammeer is, maar tot dusver weier Malaysia Airlines om dit te doen. Met sulke inligting in die hand, sou die IG sy begrip van die beperkings wat op die vlug geplaas kan word, verfyn: om byvoorbeeld te weet dat die CI moontlik is om die waarskynlike snelheid (s) te verminder, en om die brandstoflading te ken haalbare vliegafstand beter gedefinieer sou word en sodoende die kennis van die waarskynlikste eindpunt verfyn.

Erkennings:

Ek bedank almal wat gehelp het met die bespreking van hierdie idee. Dit sluit lede van die IG in, maar ook die verskillende mense wat gehelp het met hul eie kommentaar en voorstelle toe ek die konsep vir die eerste keer voorgestel het.


Die afleiding van die uur gebaseer op RA - Astronomie

Kursusbeskrywing en doelwitte:
In hierdie klas sal ons leer oor die basiese komponente van radioteleskope en hoe dit prakties werk om ons heelal te verken. Ons bestudeer die emissiemeganismes wat radiogolwe produseer, en wat ons deur radiostudies oor astrofisiese voorwerpe geleer het. Ons gaan ook die konsepte van sintese-beelding ondersoek wat baie klein teleskope gebruik om 'n enkele, groter opening te sintetiseer. As 'n integrale deel van die klas sal ons waarnemings doen van kosmiese radiobronne met behulp van die Very Large Array (VLA), bedryf vanuit Socorro, NM, en die Long Wavelength Array (LWA) wat deur UNM bedryf word. Elke student, wat as deel van 'n span werk, sal leer om LWA- en VLA-data te kalibreer, te beeld en te analiseer. Indien moontlik, neem ons 'n ekskursie van 1 dag na die VLA / LWA.

Kursus tekste:
RW: Rohlfs & Wilson (hoofstukafdelings sal bladsye aangedui word indien nodig).
SI: Synthesis Imaging in Radio Astronomy II deur Taylor, Carilli & Perley (elektroniese weergawe beskikbaar vir afsonderlike hoofstukke hieronder, of u kan die boek lees (45 MB).)

Klastyd en plek: Begin aanvanklik, later miskien PAIS 1140, M / W, 14:00 - 15:15

Instrukteur: Greg Taylor, [email protected], PAIS 3236, tuisblad, kantoorure: Maandae 09-11 of op afspraak.

TA: Megan Lewis, [email protected], kantoorure: Dinsdae 14:00 of op afspraak.

Huiswerk: Daar is verskeie huiswerkopdragte, wat elk aan die begin van die klas een week moet wees vanaf die tydstip waarop dit toegeken word, tensy anders vermeld.

Grade: Grade sal gebaseer word op twee middeleksamens (40%), die tuiswerkstelle (25%), die skriftelike aanbiedings van die projekte (25%) en die mondelinge aanbiedings van die projekte (10%). Daar is geen finale eksamen nie.

Nuttige skakels: Greg Taylor se tuisblad NASA Extragalactic Database: nuttige inligting oor interessante bronne. NVSS-posseëlbediener Beelduitsnydings uit die hele lug word met die VLA op 1,4 GHz in D-konfigurasie (45 boogsek-resolusie, mJy-sensitiwiteit) afgebeeld. VLSSr Posseëlbediener Beelduitknipsels uit die hele lug word met die VLA op 74 MHz in B-konfigurasie (90 boogsek resolusie, 100 mJy sensitiwiteit) afgebeeld. LWA-tuisblad VLA-sterrekundeblad VLBA-sterrekundeblad ADS (literatuursoektog) astro-ph preprint-bediener


Die keuse van voorbehoeding kan die risiko van outo-immuniteit met rumatoïede artritis beïnvloed

Vroue wat intrauteriene toestelle (IUD's) gebruik, kan 'n verhoogde risiko hê vir die vervaardiging van motorweëliggame wat verband hou met die risiko om rumatoïede artritis (RA) te ontwikkel, volgens nuwe navorsingsbevindinge wat hierdie week op die American College of Rheumatology Annual Meeting in Boston aangebied is.

Rumatoïede artritis is 'n chroniese siekte wat pyn, styfheid, swelling en beperking in die beweging en funksie van veelvuldige gewrigte veroorsaak. Alhoewel gewrigte die vernaamste liggaamsdele is wat deur RA beïnvloed word, kan inflammasie ook in ander organe ontwikkel. Na raming het 1,3 miljoen Amerikaners RA, en die siekte tref vroue gewoonlik drie keer so gereeld as mans.

In 'n studie van die Studies of the Etiology of RA (SERA) -projek het navorsers in Colorado, Nebraska, Kalifornië, New York en Washington gekyk na die potensiële gevolge van verskillende voorbehoedmiddels op bloedvlakke van RA-verwante motorweëliggame op sitrullineerde proteïenantigenen ( ACPA). In hierdie studie het ACPA-toetsing die antisikliese sitrullineerde peptied (anti-CCP) toets ingesluit. Verhoogde vlakke van anti-CCP kan jare in die bloed gevind word voordat gewrigsimptome in RA ontwikkel. Hierdie periode van RA-ontwikkeling word dikwels die prekliniese periode van RA genoem.

Met verhoogde anti-CCP-vlakke word die toekomstige ontwikkeling van gewrigsiektes en 'n diagnose van RA sterk voorspel, en onlangse data dui daarop dat ACPA direk patogeen kan wees. Daarom is dit belangrik om faktore te verstaan ​​wat die ontwikkeling van hierdie RA-verwante motorweëliggame beïnvloed, selfs in die afwesigheid van inflammatoriese artritis.

Vorige navorsing dui daarop dat hormonale faktore vroue meer vatbaar kan maak vir RA-ontwikkeling as mans. Aangesien RA meer algemeen by vroue voorkom, wou die navorsers kyk na faktore spesifiek vir vroue, soos voorbehoeding en swangerskap, om te bepaal of hierdie faktore die ontwikkeling van RA-verwante motorweëliggame by vroue beïnvloed. Die navorsers het gehoop dat indien hulle sekere vroulike faktore wat verband hou met die ontwikkeling van RA-verwante motorweëliggame identifiseer, dit die algemene begrip van die rede waarom vroue RA meer as mans kry, kan verbeter. As daar gevind word dat sekere faktore die ontwikkeling van outo-immuniteit by RA beïnvloed, kan dit belangrike faktore wees om te voorkom in die voorkoming van siektes by vroue met 'n hoë risiko vir RA in die toekoms, soos 'n familielid van die eerste graad van iemand met RA wat gediagnoseer is. .

Vanuit die SERA-projek het die navorsers 976 vroue bestudeer wat 'n eerstegraadse familielid met RA gehad het en dus op grond van familiegeskiedenis van RA 'n verhoogde risiko het vir toekomstige RA. Hierdie vroue het 'n basiese studiebesoek ondergaan waar hulle bloedtoetse gedoen het vir ACPA met behulp van 'n klinies beskikbare ACPA-toets genaamd anti-CCP. Hierdie vroue het ook 'n vraelys ingevul om inligting te kry oor hul vorige en huidige gebruik van voorbehoeding en swangerskapverwante geskiedenis. Al die vroue wat bestudeer is, het geen kliniese bewyse van inflammatoriese artritis tydens die toets van die teenliggaampie nie, en het dus geen diagnose van RA gehad nie.

Die navorsers het bevind dat vroue wat tans 'n IUD gebruik, 'n statisties beduidende verhoogde risiko vir anti-CCP-positiwiteit het. Daar was ook 'n neiging tot 'n verlaagde risiko vir anti-CCP-positiwiteit by vroue wat mondelinge voorbehoedmiddels (OCP's) gebruik het, tans of in die verlede. Die navorsers het geen beduidende verband gevind tussen anti-CCP-positiwiteit en swangerskap of borsvoeding nie.

"Ons dink hierdie bevindings is baie opwindend en sal lei tot toekomstige studies wat ons begrip van RA-ontwikkeling by vroue verbeter," het Kristen Demourelle, besturende direkteur van die Universiteit van Colorado Denver, en 'n hoofskrywer van die studie gesê. "Dit is egter belangrik om te onthou dat hierdie studie uitgevoer is in 'n groep vroue wat alreeds 'n verhoogde risiko vir RA het. Hierdie bevindings is moontlik nie van toepassing op die algemene bevolking nie, en addisionele studies oor vroue oor 'n langer tydperk is Dit is nodig om hierdie bevindinge te bevestig en uit te brei. Verder het nie alle vroue wat anti-CCP-positief was, IUD's gebruik nie, dus is daar waarskynlik ander faktore wat verband hou met die opwekking van hierdie motorweëliggame, en dit sal ook ondersoek moet word. "

Die skrywers van die studie het tot die gevolgtrekking gekom dat daar 'n verband is tussen die huidige IUD-gebruik en 'n hoër voorkoms van anti-CCP-positiwiteit in die bloed. Alhoewel hierdie studie nie in staat is om aan te spreek of spiraaltjies die risiko verhoog om RA regtig te ontwikkel nie, dui dit daarop dat spiraaltjies moontlik verband hou met die ontwikkeling van RA-verwante motorweëliggame by sommige vroue wat 'n verhoogde risiko vir RA het. Alhoewel die meganismes wat voorbehoedmiddelfaktore aan ACPA-generasie kan koppel, onbekend is, kan spiraaltjies inflammatoriese reaksies in die baarmoeder veroorsaak. Daarom kan die assosiasie van IUD-gebruik en ACPA verband hou met inflammasie wat deur IUD veroorsaak word by vroue met 'n risiko vir RA. Verdere studie is nodig om vas te stel watter meganismes 'n rol kan speel in die gebruik van OCP wat beskerm word teen RA-verwante outo-immuniteit.

"Dit kan wees dat ander faktore nodig mag wees vir iemand met motorweëliggame om te vorder tot die punt waar hulle gewrigsiektes ontwikkel," het dr. Demourelle gesê. "Om die ontwikkeling van outo-teenliggaampies gedurende die prekliniese periode van RA te verstaan, is baie belangrik om die algehele proses van RA te kan verstaan. As ons kan verstaan ​​hoe auto-teenliggaampies in RA ontwikkel, kan ons moontlik maniere identifiseer om die ontwikkeling van gewrigte te voorkom. siekte in RA. "


Die skaal van tsoenami's af te lei van die 'rondheid' van afgesette gruis

Wetenskaplikes van die Metropolitaanse Universiteit van Tokio en die Universiteit van Ritsumeikan het 'n verband gevind tussen die "afgeronde" verspreiding van tsoenami-afsettings en hoe ver tsoenami's die binneland bereik. Hulle het die "rondheid" van gruis uit verskillende tsoenami's in Koyadori, Japan, beproef en 'n algemene, skielike verandering in die samestelling gevind, ongeveer 40% van die "inundasie-afstand" vanaf die oewer, ongeag die omvang van die tsoenami. Skattings van antieke tsoenami-grootte deur geologiese afsettings kan help om effektiewe rampversagting te help.

Tsoenami's is een van die mees verwoestende gevare van die natuur om hul omvang te verstaan, en meganisme is van die grootste wetenskaplike en sosio-ekonomiese belang. Nieteenstaande ons beste pogings om dit te bestudeer en te verstaan, kan die ongereelde voorkoms daarvan kwantitatiewe studies moeilik maak om seismiese gebeure rondom die subduksie-sones (waar een tektoniese plaat onder 'n ander plaat daal), tsunami-veroorsaak, een keer elke 100 tot 1000 jaar, wat die aantal aansienlik verminder van akkuraat gedokumenteerde gebeure. Dit is baie wenslik dat ons 'n bietjie begrip kry deur eerder na geologiese afsettings te kyk. Ondanks 'n mate van sukses om die aantal en die ouderdom van gebeure in die verlede te bepaal, is dit nog nie moontlik om die omvang van die antieke tsoenami's te skat nie, veral nie in smal kusvlakte soos die Sanriku-kus in Japan, getref deur die Tohoku-aardbewing in 2011 en tsoenami nie.

Daarom het assistent-professor Daisuke Ishimura van die Tokio Metropolitaanse Universiteit en die postdoktor Keitaro Yamada van die Universiteit van Ritsumeikan studies uitgevoer oor gruismonsters wat versamel is uit boorgate en die loopgraaf in Koyadori, geleë in die middel van die Sanriku-kuslyn. Geologiese monsters is geneem wat ooreenstem met drie tsoenami-gebeurtenisse (AD 1611, 1896 en 2011) waarvan die grootte bekend is, spesifiek hul 'inundasie-afstand', of hoe ver hulle die binneland bereik. Hulle gebruik outomatiese beeldanalise om te bestudeer hoe elke gruisdeeltjie in hul steekproewe 'rond' is, en gee 10 tot 100 keer meer data as bestaande, handmatige metodes. As hulle verspreidings vergelyk met metings van moderne strand- en fluviale (rivier) gruis, het hulle gevind dat hulle die getalverhouding tussen strand en fluvial gruis kon karteer. Hulle het ontdek dat hierdie verhouding skielik op 'n sekere afstand van die see af verander. Hierdie punt is die "Tsunami Gravel Inflection Point" (TGIP) genoem. Dit word vermoedelik voortspruit uit 'aanloop' (inkomende) golwe wat strandmateriaal na die binneland bring en 'retourgolwe' wat binnelandse materiaal na die see trek. Alhoewel die TGIP op verskillende plekke vir elke gebeurtenis plaasgevind het, het hulle gevind dat dit altyd ongeveer 40% van die oorstroomafstand was. Hulle het hierdie bevinding toegepas op monsters wat ooreenstem met selfs ouer tsoenami's, wat ramings gee vir die grootte van gebeure langs die Sanriku-kus wat vir die eerste keer ongeveer 4000 jaar teruggaan.

Alhoewel die navorsers van mening is dat hierdie verhouding spesifiek vir die plaaslike topografie is, kan dieselfde analise toegepas word om ander tsoenami-liggings te karakteriseer. 'N Akkurate skatting van die omvang van antieke tsoenami's sal die aantal geleenthede wat beskikbaar is vir toekomstige navorsing uitbrei om die meganismes agter tsoenami's te bestudeer, wat help om effektiewe rampversagting en die beplanning van kusgemeenskappe in te lig.


Die afleiding van die uur gebaseer op RA - Astronomie

Die Utils-voorwerp gee toegang tot algemeen gebruikte astronomie-verwante roetines en omskakelings. Die roetines sluit in die vermoë om die posisiehoek en hoekskeiding tussen voorwerpe te bereken, die uurhoek, lugmassa, breking en stygende transito-tye van 'n voorwerp, die plaaslike seestyd, universele tyd, Juliaanse datum van TheSky sowel as die vermoë om koördinate van en na die tydperk 2000 te benodig.

The conversions include the ability to convert a string to a double and vise versa for both equatorial coordinates (right ascension/declination) and horizon coordinates (azimuth/altitude), the ability to convert between equatorial and horizon coordinates and vise versa, convert a calendar day (year, month, day, hour, minute, second) to a Julian date and vise-versa as well as the ability to format most any "sexagesimal" to a string with a wide variety of formats.


The J2000 Epoch and RA

At the moment I'm trying to put together a little spreadsheet calculator. The idea is to roughly indicate the position of an object based on a viewing time and date.

To do this I need to work out how RA coordinates are is calculated from the J2000 epoch.

From what I understand RA is calculated from an equinox at a given point in time. Throughout the months of the year the object gains time behind the Sun and ends up in the same position behind Sun 12 months later.

What I need to know is from which equinox (if it is an equinox) is the RA from J2000 epoch calculated.

Is it the northern hemisphere vernal equinox (roughly March 21 2000)?

Or is it not an equinox and January 1st 2000 12:00 Terrestrial Time?

Slightly confused, if anyone could shed some light on this it would be appreciated.

#2 Paul Skee

#3 ButterFly

When you say "position of an object based on a viewing time and date", do you mean the object's current RA and Dec, or something else?

Based on your description, you may be confusing precessing J2000.0 to the present epoch with the much simpler calculation of "hour angle" (and then presumably onto Alt/Az).

If it really is precession you are looking for, consult the math at: Precessing positions from B1950 to J2000, and view the javascript source code of the following calculator: Astronomical Coordinate Calculator version 0.31.

BTW: you can run the above source code on pretty much any browser, even on a phone.

Edited by ButterFly, 06 June 2020 - 07:05 PM.

#4 catalogman

All of the usual libraries do the calculation but the OP specifically asked for a spreadsheet.

To compute the change of mean place at equinox and epoch over 20 years, one method is to compute
the annual rates and then multiply by 20.

As an example, take the mean place B1980.0 for Arcturus and bring it up to J2000.0.

From the Astronomical Almanac, the B1980.0 positions are

RA0 = 14 14 44.9, DEC0 = +19 17 09

RA0 = 15*(14 + 14/60 + 44.9/3600) = 213.6870 deg
DEC0 = 19 + 17/60 + 9/3600 = +19.2858 deg

t1 = 1980.0
t2 = 2000.0
dt = t2 - t1 = 20
t = (t1 + t2)/2 = 1990.0
T = (t - 1900.0)/100 = 0.90

e0 = 23.452294 - 0.0130125*T = 23.464005 deg

psi' = (50.3708 + 0.0050*T)/3600 = 50.3753/3600 deg

l' = (0.1247 - 0.0188*T)/3600 = 0.10778/3600 deg

and the annual precession rates

m = psi' * cos e0 - l' = 0.012806 deg

n = psi' * sin e0 = 0.0055717 deg

Apply precession over dt = 20 years to get

RA' = RA0 +(m + n*sin RA0 * tan DEC0)*dt = 213.9215 deg

DEC' = DEC0 + (n*cos RA0)*dt = +19.19308

This is the position at equinox 2000.0.

To apply proper motion, get the annual rates from SIMBAD

d(muRA) = -1093.39 mas/yr
d(muDEC) = -2000.06 mas/yr

d(RA) = d(muRA)/3.6E6 * dt = -0.006074 deg
d(DEC) = d(muDEC)/3.6E6 * dt = -0.011111 deg

so the position corrected for proper motion is

RA = RA' + d(RA) = 213.9154 deg = 14.26103 h = 14 15 39.7
DEC = DEC' + d(DEC) = +19.18197 deg = +19 10 55

The value in SIMBAD rounds to RA = 14 15 39.7, DEC = +19 10 57.

This is the mean place at equinox and epoch 2000.0.

Edited by catalogman, 06 June 2020 - 08:16 PM.

#5 Tony Flanders

What I need to know is from which equinox (if it is an equinox) is the RA from J2000 epoch calculated.

Is it the northern hemisphere vernal equinox (roughly March 21 2000)?

Or is it not an equinox and January 1st 2000 12:00 Terrestrial Time?

J2000.0 is 12:00:00h, January 1, 2000 TT. Julian days run from noon to noon rather than midnight to midnight, which is handy for people interested in viewing the night sky.

As is so often the case, the Wikipedia article on the subject is excellent.

#6 Waddensky

Don't confuse epoch and equinox, an epoch is a moment in time and the equinox defines the zero point of the coordinate system. The catalogues based on the Hipparcos data for example, list coordinates for epoch 1991.25 and equinox 2000.0. The zero point of J2000.0 is the vernal equinox (intersection between the equatorial plane and the ecliptic plane) on 1 January 2000, 12:00 TT (JD 2451545.0).

If you want to calculate the correct coordinates for another epoch in the same coordinate system, only apply corrections for proper motion of the star. If you want to express the coordinates in the epoch and equinox of the date, first correct for proper motion, then reduce the coordinates for precession (because the zero point has also changed as the Earth's axis has shifted). Be careful, most precession formulae (like the examples in Astronomical Algorithms by Jean Meeus) are valid only for a few centuries around J2000.0. More rigorous expressions, valid for long time intervals, can be found here.

#7 Andrekp

J2000.0 is 12:00:00h, January 1, 2000 TT. Julian days run from noon to noon rather than midnight to midnight, which is handy for people interested in viewing the night sky.

As is so often the case, the Wikipedia article on the subject is excellent.

could you explain exactly HOW This info is “handy for people interested in viewing the night sky?” I’m a bit curious how 12 hours of Earth time makes a practical difference in the precision of the pole, or the celestial coordinates of a star?

# 8 Tony Flanders

could you explain exactly HOW This info is “handy for people interested in viewing the night sky?” I’m a bit curious how 12 hours of Earth time makes a practical difference in the precision of the pole, or the celestial coordinates of a star?

Sorry, my grammar may have been twisted.

What I meant is that whereas conventional days, which run from midnight to midnight, are handy for most purposes, astronomers prefer Julian days, which run from noon to noon. That way, an entire night's observing happens on a single date.

#9 csrlice12

Sorry, my grammar may have been twisted.

What I meant is that whereas conventional days, which run from midnight to midnight, are handy for most purposes, astronomers prefer Julian days, which run from noon to noon. That way, an entire night's observing happens on a single date.

So that's why a work day lasts forever.

#10 Andrekp

Sorry, my grammar may have been twisted.

What I meant is that whereas conventional days, which run from midnight to midnight, are handy for most purposes, astronomers prefer Julian days, which run from noon to noon. That way, an entire night's observing happens on a single date.

ok, that makes more sense. Thanks for clarifying.

For the record, there are actually three different uses of “Julian” when it comes to dates:

1. The Astronomers who use noon to noon as you mentioned.

2. The ordinal dates of the year, which are midnight to midnight.

3. A standardly written date, noted as being Julian so as to specifically differentiate it from the same Gregorian date.

most people, if they use them at all, use the second type. The military uses the second type. Probably the third type is used by historians and academics. I’m not sure anyone outside of Astronomy uses the first type (to be honest, I’d never ever heard of that prior to you bringing it up. It seems pretty impractical, outside of the stated use-case.).

I would be curious, if you know, why using a single date is really that much simpler across the astronomical spectrum? Seems to be that a lot of “observing” of various types also is going on during the day, not to mention the fact that the connected world has made dates and times far less local than they once were. It seems like you would still run into cases of dates being straddled, despite noon being the switchover. And I’d imagine that this is a universal time? Meaning that you’d still have the Undiminished problem of date straddling in other parts of the world. Maybe there is another reason it is used thusly?


Islamic Folk Astronomy #2

Era means a definite space of time, reckoned from the beginning of some past year, in which either a prophet, with signs and wonders, and with a proof of his divine mission, was sent, or a great and powerful king rose, or in which a nation perished by a universal destructive deluge, or by a violent earthquake and the sinking of the earth, or a sweeping pestilence, or by intense drought, or in which a change of dynasty or religion took place, or any grand event of the celestial and the famous tellurian miraculous occurrences, which do not happen save at long intervals and at times far distant from each other. Al-Bîrûnî (1879:16)

Time is relative. Given the modern world’s reliance on formalized calendars and machines that define time for us, it is easy to forget that the expansion of Islam occurred at a time when telling time was not dependent on a formal science of astronomy. How time is measured is not only a practical issue but also reflective of the desired interval of duration and the precision in defining it. Simple observation of the sun rising and setting, as well as its location, can easily yield calendars to determining hours, days, months and years. Similarly, the moon’s phases made it a useful measure for the Islamic lunar calendar. Observations of movements by the stars, as well as the planets, also provided practical ways of measuring units of time both short and long.

The 13th century North African scholar Ibn al-Ajdâbî (1964:28) began his treatise on time reckoning (hisâb al-azmina) with the claim that all known peoples use four basic time divisions: hour, day, month, year. The hour (sâ‘a) is the division of day and night into 24 equal divisions. This in fact assumes knowledge of a formal calendrical system, since there was nothing in direct observation of the sun to mandate such a division. The day (yawm) comprises daytime (nahâr) and nighttime (layl), an obvious universal distinction. While other peoples started the day at dawn, Ibn al-Ajdâbî notes that the Arab Bedouins began the day at sunset. This use of “Arab†time is still found throughout the region (for example, rural Yemen) alongside the standard reckoning. According to al-Bîrûnî (1979:5), the Arabs did this because their months were based on the phases of the moon, which become visible towards sunset. The month (shahr) could be either sidereal or synoptic, the latter regulating the Islamic lunar calendar. The year was defined by the basic seasonal change over the course of twelve months.

Our understanding of how ordinary Arabs at the beginning of Islam measured time is complicated by references in the texts that refer both to formal astronomical reckonings, which were not necessarily widely known or used, with folk knowledge. Ibn Qutayba (1956:1-3) states that the traditional Bedouin Arabs of the peninsula did not divide up the year according to the formal four-season model of the astronomers, but rather from what they knew locally about the timing of hot and cold weather, and the presence and disappearance of plants and pasture. Thus, he notes, they began their year with the autumn rain called rabı‘, followed by a sequence of recognized rain periods. Other Arabs were said to separate the year into two parts: shitâ’, which is male because of the rain in it, and sayf, which is female because of the pasture. The clear message is that telling time seasonally was adapted to local contexts and reflected a symbolism of natural fertility. A major problem in reconstructing such local seasonal systems with any degree of specificity is that the terms used may refer to different times or seasons from one system to another. Added to this is the general lack of information as to which tribe or group used a particular seasonal reckoning system.

Comparative ethnographic findings suggest that how people reckon time is contextual to their needs as well as other systems they may have been exposed to. Arab pastoralists and farmers would have been primarily interested in seasonal patterns of weather, as we see reflected in the anwâ’ genre discussed below. Sailors would have been more interested in weather patterns that influenced the ability to sail and the presence of favorable winds. Fishermen and pearl divers would have their own interests, merchants and rulers theirs. Thus, we should not expect to find a discrete set of folk astronomical systems as we have come to expect from the formal science of astronomy. As Islam spread, Muslims would follow their own local traditions, adapt those of others with whom they came in contact, and build on the evolving literature of the religion and science.

What makes the folk astronomy of Islamic peoples “Islamic†is not simply that people were now Muslim. Reckoning time in the practical sense now took on an added dimension of a historical time frame in which the God of Abraham, Moses, Jesus and Muhammad dealt with the world. This Islamic rendering of history built on Judaism and Christianity, starting with the creation of Adam, and also covered the evolving Islamic polity of the caliphate, dynasties, military and missionary expansion. Not surprisingly, the eras of relevance to Muslims were at times defined according to astronomical events. The God who created sun, moon and stars for time-keeping purposes was also perceived as sending signs for Muslims to interpret and metaphors for a better appreciation of what Islam should mean for the believer.

al-Bîrûnî, Abû al-Rayhân Muhammad. The Chronology of Ancient Nations (al-Athâr al-bâqiya). Translated by C. E. Sachau. London: W. H. Allen, 1879.

Ibn al-Ajdâbî. Kitâb al-Azmina wa-al-anwâ’. Damascus: Wizârat al-Thaqâfa wa-al-Irshâd al-Qawmî, 1964.

Ibn Qutayba, Abû Muhammad ‘Abd Allâh. Kitâb al-Anwâ’. Hyderabad: Matba‘at Majlis Dâ’irat al-Ma‘ârif al-‘Uthmânîya, 1956.

Excerpt from Daniel Martin Varisco. Islamic Folk Astronomy, In The History of Non-Western Astronomy. Astronomy Across Cultures, pp. 615-650. Edited by Helaine Selin. Dordrecht: Kluwer Academic Publishers, 2000.


Deducing the hour based on RA - Astronomy


One of the earliest advanced civilizations, Ancient Egypt, had a rich religious tradition which permeated every aspect of society. As in most early cultures, the patterns and behaviors of the sky led to the creation of a number of myths to explain the astronomical phenomena. For the Egyptians, the practice of astronomy went beyond legend. Huge temples and pyramids were built with specific astronomical orientations. Thus astronomy had both religious and practical purposes.

Creation and protection came from the gods. Today we associate these gods with Ancient Alien Theory and Reality as a Consciousness Hologram.

The Egyptian gods and goddesses were numerous, pictured in many paintings and murals with celestial alignments. Certain gods were seen in the constellations, and others were represented by actual astronomical bodies. The constellation Orion, for instance, represented Osiris, who was the god of death, rebirth, and the afterlife. The Belt Stars of Orion align with the three pyramids on the Giza Plateau.

The Milky Way represented the sky goddess Nut giving birth to the sun god Ra.

The stars in Egyptian mythology were represented by the goddess of writing, Seshat, while the Moon was either Thoth, the god of wisdom and writing, or Khons, a child moon god.

The horizon was extremely important to the Egyptians, since it was here that the Sun appeared and disappeared daily. A hymn to the Sun god Ra shows this reverance: 'O Ra! In thine egg, radiant in thy disk, shining forth from the horizon, swimming over the steel firmament.' The Sun itself was represented by several gods, depending on its position. A rising morning Sun was Horus, the divine child of Osiris and Isis. The noon Sun was Ra because of its incredible strength.

The evening Sun became Atum, the creator god who lifted Pharoahs from their tombs to the stars. The red color of the Sun at sunset was considered to be the blood from the Sun god as he died. After the Sun had set, it became Osiris, god of death and rebirth. In this way, night was associated with death and day with life or rebirth. This reflects the typical Egyptian idea of immortality.

The center of Egyptian civilization was the flooding of the Nile River every year at the same time and provided rich soil for agriculture. The Egyptian astronomers, who were actually priests, recognized that the flooding always occurred at the summer solstice, which was also when the bright star Sirius rose before the Sun. The priests were therefore able to predict the annual flooding, which made them quite powerful.

Many Egyptian buildings were built with an astronomical orientation. The temples and pyramids were constructed in relation to the stars, zodiac, and constellations. In different cities, the buildings had different orientations based on the specific religion of that place. For instance, some temples were constructed to align with a star that either rose or set at harvest or sowing time. Others were oriented toward the solstices or equinoxes. As early as 4000 B.C., temples were built so that sunlight entered a room at only one precise time of the year.

An alternative building method was to gradually narrow successive doors into a specific room, in order to concentrate the sunbeams onto a god's image on the wall. The designs sometimes became quite complex. At the temple of Medinet Habu, there are actually two buildings which are slightly off-kilter. It has been suggested that the second one was built when the altitude of the other temple's orientation stars changed over a long period of time.

The Egyptians were a practical people and this is reflected in their astronomy in contrast to Babylonia where the first astronomical texts were written in astrological terms. Even before Upper and Lower Egypt were unified in 3000 BCE, observations of the night sky had influenced the development of a religion in which many of its principal deities were heavenly bodies.

In Lower Egypt, priests built circular mud-brick walls with which to make a false horizon where they could mark the position of the sun as it rose at dawn, and then with a plumb-bob note the northern or southern turning points (solstices). This allowed them to discover that the sun disc, personified as Ra, took 365 days to travel from his birthplace at the winter solstice and back to it. Meanwhile in Upper Egypt a lunar calendar was being developed based on the behavior of the moon and the reappearance of Sirius in its heliacal rising after its annual absence of about 70 days.

After unification, problems with trying to work with two calendars (both depending upon constant observation) led to a merged, simplified civil calendar with twelve 30 day months, three seasons of four months each, plus an extra five days, giving a 365 year day but with no way of accounting for the extra quarter day each year. Day and night were split into 24 units, each personified by a deity.

A sundial found on Seti I's cenotaph with instructions for its use shows us that the daylight hours were at one time split into 10 units, with 12 hours for the night and an hour for the morning and evening twilights. However, by Seti I's time day and night were normally divided into 12 hours each, the length of which would vary according to the time of year.

Key to much of this was the motion of the sun god Ra and his annual movement along the horizon at sunrise. Out of Egyptian myths such as those around Ra and the sky goddess Nut came the development of the Egyptian calendar, time keeping, and even concepts of royalty.

An astronomical ceiling in the burial chamber of Ramesses VI shows the sun being born from Nut in the morning, traveling along her body during the day and being swallowed at night.

During the Fifth Dynasty six kings built sun temples in honor of Ra. The temple complexes built by Niuserre at Abu Gurab and Userkaf at Abusir have been excavated and have astronomical alignments, and the roofs of some of the buildings could have been used by observers to view the stars, calculate the hours at night and predict the sunrise for religious festivals.

Claims have been made thatprecession of the equinoxes was known in Ancient Egypt prior to the time of Hipparchus. This has been disputed however on the grounds that pre-Hipparchus texts do not mention precession and that "it is only by cunning interpretation of ancient myths and images, which are ostensibly about something else, that precession can be discerned in them, aided by some pretty esoteric numerological speculation involving the 72 years that mark one degree of shift in the zodiacal system and any number of permutations by multiplication, division, and addition."

Note however that the observation that a stellar alignment has grown wrong does not necessarily mean that the Egyptians understood or even cared what was going on. For instance, from the Middle Kingdom on they used a table with entries for each month to tell the time of night from the passing of constellations: these went in error after a few centuries because of their calendar and precession, but were copied (with scribal errors) for long after they lost their practical usefulness or possibly the understanding of them.

Nabta Playa

Egyptian astronomy begins in prehistoric times, in the Predynastic Period. In the 5th millennium BCE, the stone circles at Nabta Playa may have made use of astronomical alignments. By the time the historical Dynastic Period began in the 3rd millennium BCE, the 365 day period of the Egyptian calendar was already in use, and the observation of stars was important in determining the annual flooding of the Nile. The Egyptian pyramids were carefully aligned towards the pole star, and the temple of Amun-Re at Karnak was aligned on the rising of the midwinter sun. Astronomy played a considerable part in fixing the dates of religious festivals and determining the hours of the night, and temple astrologers were especially adept at watching the stars and observing the conjunctions, phases, and risings of the Sun, Moon and planets.

In Ptolemaic Egypt, the Egyptian tradition merged with Greek astronomy and Babylonian astronomy, with the city of Alexandria in Lower Egypt becoming the centre of scientific activity across the Hellenistic world. Roman Egypt produced the greatest astronomer of the era, Ptolemy (90-168 CE). His works on astronomy, including the Almagest, became the most influential books in the history of Western astronomy. Following the Muslim conquest of Egypt, the region came to be dominated by Arabic culture and Islamic astronomy.

The astronomer Ibn Yunus (c. 950-1009) observed the sun's position for many years using a large astrolabe, and his observations on eclipses were still used centuries later. In 1006, Ali ibn Ridwan observed the SN 1006, a supernova regarded as the brightest steller event in recorded history, and left the most detailed description of it. In the 14th century, Najm al-Din al-Misri wrote a treatise describing over 100 different types of scientific and astronomical instruments, many of which he invented himself.

In the 20th century, Farouk El-Baz from Egypt worked for NASA and was involved in the first Moon landings with the Apollo program, where he assisted in the planning of scientific explorations of the Moon.

Egyptian astronomy begins in prehistoric times. The presence of stone circles at Nabta Playa dating from the 5th millennium BCE show the importance of astronomy to the religious life of ancient Egypt even in the prehistoric period. The annual flooding of the Nile meant that the heliacal risings, or first visible appearances of stars at dawn, was of special interest in determining when this might occur, and it is no surprise that the 365 day period of the Egyptian calendar was already in use at the beginning of Egyptian history. The constellation system used among the Egyptians also appears to have been essentially of native origin.

The precise orientation of the Egyptian pyramids affords a lasting demonstration of the high degree of technical skill in watching the heavens attained in the 3rd millennium BCE. It has been shown the Pyramids were aligned towards the pole star, which, because of the precession of the equinoxes, was at that time Thuban, a faint star in the constellation of Draco. Evaluation of the site of the temple of Amun-Re at Karnak, taking into account the change over time of the obliquity of the ecliptic, has shown that the Great Temple was aligned on the rising of the midwinter sun. The length of the corridor down which sunlight would travel would have limited illumination at other times of the year.

Astronomy played a considerable part in religious matters for fixing the dates of festivals and determining the hours of the night. The titles of several temple books are preserved recording the movements and phases of the sun, moon and stars. The rising of Sirius (Egyptian: Sopdet, Greek: Sothis) at the beginning of the inundation was a particularly important point to fix in the yearly calendar.

From the tables of stars on the ceiling of the tombs of Rameses VI and Rameses IX it seems that for fixing the hours of the night a man seated on the ground faced the Astrologer in such a position that the line of observation of the pole star passed over the middle of his head. On the different days of the year each hour was determined by a fixed star culminating or nearly culminating in it, and the position of these stars at the time is given in the tables as in the centre, on the left eye, on the right shoulder, etc. According to the texts, in founding or rebuilding temples the north axis was determined by the same apparatus, and we may conclude that it was the usual one for astronomical observations. In careful hands it might give results of a high degree of accuracy.

Macrobius Ambrosius Theodosius (floruit AD 395-423) attributed the planetary theory where the Earth rotates on its axis and the interior planets Mercury and Venus revolve around the Sun which in turn revolves around the Earth, to the ancient Egyptians. He named it the "Egyptian System," and stated that "it did not escape the skill of the Egyptians," though there is no other evidence it was known in ancient Egypt.

Greco-Roman Egypt

The Astrologer's instruments (horologium and palm) are a plumb line and sighting instrument. They have been identified with two inscribed objects in the Berlin Museum a short handle from which a plumb line was hung, and a palm branch with a sight-slit in the broader end. The latter was held close to the eye, the former in the other hand, perhaps at arms length. The "Hermetic" books which Clement refers to are the Egyptian theological texts, which probably have nothing to do with Hellenistic Hermetism.

Following Alexander the Great's conquests and the foundation of Ptolemaic Egypt, the native Egyptian tradition of astronomy had merged with Greek astronomy as well as Babylonian astronomy. The city of Alexandria in Lower Egypt became the centre of scientific activity throughout the Hellenistic civilization.

The greatest Alexandrian astronomer of this era was the Greek, Eratosthenes (c. 276-195 BCE), who calculated the size of the Earth, providing an estimate for the circumference of the Earth.

Following the Roman conquest of Egypt, the region once again became the centre of scientific activity throughout the Roman Empire. The greatest astronomer of this era was the Hellenized Egyptian, Ptolemy (90-168 CE).

Originating from the Thebaid region of Upper Egypt, he worked at Alexandria and wrote works on astronomy including the Almagest, the Planetary Hypotheses, and the Tetrabiblos, as well as the Handy Tables, the Canobic Inscription, and other minor works. The Almagest is one of the most influential books in the history of Western astronomy. In this book, Ptolemy explained how to predict the behavior of the planets with the introduction of a new mathematical tool, the equant.

A few mathematicians of late Antiquity wrote commentaries on the Almagest, including Pappus of Alexandria as well as Theon of Alexandria and his daughter Hypatia. Ptolemaic astronomy became standard in medieval western European and Islamic astronomy until it was displaced by Maraghan, heliocentric and Tychonic systems by the 16th century.

Arabic-Islamic Egypt

Following the Muslim conquest of Egypt, the region came to be dominated by Arabic culture. It was ruled by the Rashidun, Umayyad and Abbasid Caliphates up until the 10th century, when the Fatimids founded their own Caliphate centered around the city of Cairo in Egypt. The region once again became a centre of scientific activity, competing with Baghdad for intellectual dominance in the medieval Islamic world. By the 13th century, the city of Cairo eventually overtook Baghdad as the intellectual center of the Islamic world.

Ibn Yunus (c. 950-1009) observed more than 10,000 entries for the sun's position for many years using a large astrolabe with a diameter of nearly 1.4 meters. His observations on eclipses were still used centuries later in Simon Newcomb's investigations on the motion of the moon, while his other observations inspired Laplace's Obliquity of the Ecliptic and Inequalities of Jupiter and Saturn.

In 1006, Ali ibn Ridwan observed the supernova of 1006, regarded as the brightest stellar event in recorded history, and left the most detailed description of the temporary star. He says that the object was two to three times as large as the disc of Venus and about one-quarter the brightness of the Moon, and that the star was low on the southern horizon.

The astrolabic quadrant was invented in Egypt in the 11th century or 12th century, and later known in Europe as the "Quadrans Vetus" (Old Quadrant).

In 14th century Egypt, Najm al-Din al-Misri (c. 1325) wrote a treatise describing over 100 different types of scientific and astronomical instruments, many of which he invented himself.


In the 20th century, Farouk El-Baz from Egypt worked for NASA and was involved in the first Moon landings with the Apollo program, where he was secretary of the Landing Site Selection Committee, Principal Investigator of Visual Observations and Photography, chairman of the Astronaut Training Group, and assisted in the planning of scientific explorations of the Moon, including the selection of landing sites for the Apollo missions and the training of astronauts in lunar observations and photography.