Sterrekunde

Hoe ver kan ons weerlig in radioastronomie opspoor?

Hoe ver kan ons weerlig in radioastronomie opspoor?


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Die Wikipedia-artikel oor fluiters bevat die volgende inligting:

Voyager 1 en 2-ruimtetuie het fluiteragtige aktiwiteite in die omgewing van Jupiter, bekend as 'Jovian Whistlers', opgespoor, wat daarop dui dat daar weerlig daar is.

Dit het my verbaas, want dit impliseer 'n kort afstand vir die opsporing van weerlig, en deur atmosferiese ontladings word baie radiogeraas geproduseer, en radioteleskope op aarde moes dus voor die reisigers tekens van joviese weerlig gehad het. Dit lyk asof dit nie die geval is nie, wat maak dit moeilik om op 'n afstand lig op te spoor?


Aardfluiters se frekwensies is 1 kHz tot 30 kHz, terwyl radioteleskope 30 tot 300 gigahertz werk.

Radioteleskope moet 1000 keer groter wees om die rigting van buitenaardse fluiters op te los.


Wat is radiosterrekunde?

Radioteleskope bespeur en versterk radiogolwe vanuit die ruimte en verander dit in seine wat sterrekundiges gebruik om ons begrip van die heelal te verbeter.

Alle sterrekunde gaan oor die waarneming van liggolwe. Sterre, sterrestelsels en gaswolke in die ruimte straal sigbare lig sowel as lig uit ander dele van die elektromagnetiese spektrum uit in die vorm van radiogolwe, gammastrale, X-strale en infrarooi straling.

Optiese teleskope & ndash teleskope wat sigbare lig versamel & ndash wys vir ons skynende sterre, gloeiende gas en donker stof, maar dit gee ons nie die geheelbeeld van wat in die ruimte gebeur nie. Teleskope wat op verskillende dele van die elektromagnetiese spektrum ingestel is, kan verborge voorwerpe in die ruimte openbaar. Die resultate kan dan gekombineer word om 'n meer volledige prentjie te gee.

Radiogolwe uit die ruimte is die eerste keer in die dertigerjare opgespoor, maar daar is min gedoen om dit op te volg tot na die Tweede Wêreldoorlog. In die na-oorlogse periode was wetenskaplikes en ingenieurs van CSIRO onder die baanbrekers van radiosterrekunde.


Deur Al Aburto [email protected]>,
David Woolley [email protected]>

Verteenwoordigende resultate word in tabelle 1 en 2. aangebied. Die kort
antwoord is
(1) Opsporing van breëbandseine vanaf die aarde soos AM-radio, FM
radio- en televisiebeeld en -klank sou uiters belangrik wees
moeilik selfs teen 'n fraksie van 'n ligjaar ver van die
Son. Byvoorbeeld, 'n TV-prent met 5 MHz bandwydte en 5
MWatt krag kon nie buite die sonnestelsel opgespoor word nie
selfs met 'n radioteleskoop met 100 keer die sensitiwiteit van die
305 meter deursnee Arecibo-teleskoop.

(2) Opsporing van smalbandseine is meer geredelik
duisende ligjare afstand van die son afhangende van die
sender se sendkrag en die grootte van die ontvangsantenne.

(3) Instrumente soos die Arecibo-radioteleskoop kan opspoor
smalbandseine wat duisende ligjare van die
Son.

(4) 'n Goed ontwerpte amateurradio-teleskoop van 12 voet deursnee kan
smalbandseine van 1 tot 100 ligjaarafstand op te spoor
die veronderstelling dat die senderkrag van die sender in die
terawatt-reeks.

Hierna volg 'n basiese voorbeeld vir die beraming van radio en
mikrogolfdeteksie-reekse van belang vir SETI. Minimum sein
verwerking word aanvaar. 'N FFT kan byvoorbeeld in die
smalbandkas en 'n banddeurlaatfilter in die breëbandkas (met
sentrumfrekwensie natuurlik op die regte plek). Daarbenewens is dit
aanvaar dat die bandwydte van die ontvanger (Br) sodanig beperk is
dat dit groter as of gelyk is aan die bandwydte van die versende
sein (Bt) (dit wil sê, Br & gt = Bt).

Neem aan dat 'n krag Pt (watt) in bandbreedte Bt (Hz) isotrop uitgestraal word.
Op 'n afstand van R (meter) sal hierdie krag eenvormig versprei word
(gereduseer) oor 'n gebiedsfeer: 4 * pi * R ^ 2. Die bedrag hiervan
krag ontvang deur 'n antenne met effektiewe area Aer met bandwydte Br
(Hz), waar Br & gt = Bt, is dus:

As die antenna 'n riglyn is (dit wil sê die meeste van die
beskikbare krag word gekonsentreer in 'n smal straal) met kragwins Gt
in die gewenste rigting dan:

Pr = Aer * ((Pt * Gt) / (4 * pi * R ^ 2))

Die antennaversterking G (Gt vir die uitsending van antenna) word gegee deur die
volgende uitdrukking. (Die ontvangantenne het 'n soortgelyke uitdrukking
vir die wins daarvan, maar die wins van die ontvangsantenne word nie eksplisiet gebruik nie
in die reeksvergelyking. Slegs die effektiewe area, Aer, wat die onderskep
uitgestraalde energie op reikafstand R is nodig.)


Vir 'n antenne (hetsy stuur of ontvang) met sirkelvormige openings:


Die Nyquist-geraas, Pn, word gegee deur:


Die sein-ruis-verhouding, snr, word gegee deur:

As ons die uitset vir 'n tyd t gemiddeld, om die variansie te verminder
van die geraas, dan kan 'n mens die snr met 'n faktor van verbeter
sqrt (Br * t). Dus:

Die faktor Br * t word die "tydbandbreedteproduk" van die ontvang genoem
verwerking in hierdie geval, wat ons sal aanwys as:

Ons sal die integrasie- of gemiddelde wins aanwys as:

Integrasie van die data (wat beteken: twp = Br * t & gt 1, of
t & gt (1 / Br)) is sinvol vir ongemoduleerde "CW" seine
relatief stabiel oor tyd in 'n relatiewe stilstaande (bestendige) geluid
veld. Aan die ander kant maak integrasie van die data nie
sin vir tydvariërende seine, aangesien dit die
inligtinginhoud van die sein. Dus vir 'n gemoduleerde sein
twp = Br * t = 1 is gepas.

In elk geval kan die snr herskryf word as:

snr = (Pt * Gt) * Aer * twc / (4 * pi * R ^ 2 * Br * k * Tsys)

Pt * Gt word die Effektiewe Isotropiese Uitgestraalde Krag (EIRP) in genoem
die versende sein van bandwydte Bt. Dus:

snr = EIRP * Aer * twc / (4 * pi * R ^ 2 * Br * k * Tsys)

Dit is 'n basiese vergelyking wat gebruik kan word om SETI-opsporing te skat
reekse.


Let daarop dat vir die maksimum opsporingsbereik (R) 'n mens die uitsending wil hê
krag (EIRP), die area van die ontvangantenne (Aer), en die tyd
bandwydteproduk (twp) so groot as moontlik te wees. Daarbenewens een
wil die snr, die ontvangerbandwydte (Br) hê, en sodoende stuur
seinbandwydte (Bt), en die ontvangstelsel temperatuur (Tsys) te wees
so klein as moontlik.

(Hier is 'n klein tegniese komplikasie. Interstellêre ruimte
bevat 'n plasma. Die uitwerking daarvan op 'n voortplantende radiogolf, insluitend
verbreed die bandwydte van die sein. Hierdie effek was eerste
bereken deur Drake & Helou en later deur Cordes & Lazio. Die
die omvang van die effek is rigting, afstand en frekwensie
afhanklik, maar vir die meeste siglyne deur die Melkweg 'n tipiese
waarde kan 0,1 Hz wees teen 'n frekwensie van 1000 MHz. Dus, bandwydtes
baie onder hierdie waarde is onnodig, want daar sal min wees as
enige, seine met nouer bandwydte.)

Nou is ons in staat om eenvoudige beramings van
opsporing reeks. Dit word in Tabel 1 getoon vir 'n verskeidenheid radio's
senders. Ons aanvaar dat die ontvanger soortgelyk is aan Arecibo, met
deursnee dr = 305 m en 'n doeltreffendheid van 50% (& lteta & gtr = 0.5). Ons sal
neem aan snr = 25 is nodig vir opsporing (Die META-projek gebruik 'n snr
van 27--33 en SETI @ home gebruik 22 meer verfynde seinverwerking
lewer verhoogde opsporingsreekse met 'n faktor van 2 bo die in
die tabel 1.) Ons aanvaar ook dat twp = Br * Tr = 1. An
'opgeleide' raaiskoot vir sommige van die parameterwaardes, veral Tsys,
is geneem soos aangedui deur die vraagtekens in die tabel. As 'n
verwysingsnota dat Jupiter 5,2 AE van die son af is en Pluto 39,4 AE,
terwyl die naaste ster aan die Son 4,3 LY weg is. Ook enige sein
verswakking as gevolg van die aarde se atmosfeer en ionosfeer was
geïgnoreerde AM-radio, byvoorbeeld, vanaf die aarde, is vasgevang in die
ionosfeer.

Die ontvangantenne-area, Aer, is

Aer = & lteta & gtr * pi * dr ^ 2/4 = 36.5E3 m ^ 2.

(Wetenskaplike notasie word hier gebruik 1E1 = 10, 1E2 = 100, 1E3 =
1000, dus 36.5E3 is 36,5 keer 1000.) Vandaar die opsporingsbereik (lig
jaar) word

R = 3,07E-04 * sqrt [EIRP / (Br * Tsys)].

Tabel 1 Opsporingsreekse van verskillende EM-emissies vanaf die aarde en die
Pioneer-ruimtetuig met die aanvaarding van 'n sirkelvormige deursnee van 305 meter
diafragma ontvang antenne, soortgelyk aan die Arecibo radio
teleskoop. Gestel snr = 25, twp = Br * Tr = 1, & lteta & gtr =
0,5, en dr = 305 meter.


Dit moet dan uit hierdie resultate duidelik wees dat die opsporing van AM
radio-, FM-radio- of TV-foto's, veel verder as die baan van Pluto
uiters moeilik, selfs vir 'n Arecibo-agtige radio van 305 meter
teleskoop! Selfs 'n radioteleskoop met 'n deursnee van 3000 meter kon nie
kan die TV-program "I Love Lucy" opspoor (herlaai) op ​​'n afstand van 0,01
Ligjare!

Dit is slegs die smalband-emissie van hoë intensiteit vanaf die aarde
(smalband-radar oor die algemeen) wat op beduidend waarneembaar sal wees
reekse (groter as 1 LY). Miskien sal hulle baie opdaag soos
die smalband, seine en nie-herhalende, seine waargeneem deur
ons SETI-teleskope. Miskien moet ons al hierdie dinge dokumenteer
"nie-herhalende" opsporings baie noukeurig om te sien of daar enige langtermyn is
ruimtelike opsporingpatrone verskyn.

'N Ander vraag wat u moet oorweeg, is 'n amateur SETI radioteleskoop
kan bereik in terme van opsporingsreekse met behulp van smalband FFT
verwerking. Opsporingsreekse (LY) word in Tabel 2 gegee, met die aanname van 'n 12
3,7 m-skottelantenne (1,42 GHz) vir verskillende FFT
binwidths (Br), Tsys, snr, time bandwidth products (twp = Br * t), en
EIRP waardes. Dit blyk uit die tabel dat effektiewe amateur SETI
verkennings kan verder as ongeveer 30 ligjaar uitgevoer word
mits die verwerkingsbandwydte byna die minimum is (ongeveer
0,1 Hz), is die stelsel temperatuur minimaal (20 tot 50 grade Kelvin),
en die EIRP van die bron (sender) is groter as ongeveer
25 terawatt.

Tabel 2 Opsporingsreekse (LY) vir 'n amateur van 12 voet deursnee
radioteleskoop SETI-stelsel, werk op 1,420 GHz.


VERWYSINGS:
Radio Astronomy, John D. Kraus, 2de uitgawe, Cygnus-Quasar
Boeke, 1986, P.O. Box 85, Powell, Ohio, 43065.

Radio Astronomy, J. L. Steinberg, J. Lequeux, McGraw-Hill
Elektroniese Wetenskapreeks, McGraw-Hill Book Company, Inc,
1963.

Project Cyclops, ISBN 0-9650707-0-0, herdruk 1996, deur die
SETI League en SETI Instituut.

Buiteaardse beskawings, probleme van interstellêr
Kommunikasie, S. A. Kaplan, redakteur, 1971, NASA TT F-631
(TT 70-50081), bladsy 88.


13 kommentaar

HAMSCI is besig met 'n projek vir 'n ruimteweerstasie. Weerligopsporing sal opgeneem word. Die presiese SDR wat gebruik word, is tot dusver ongedefinieerd. ELF / VLH en HF sal aanvanklik gebruik word om die toepaslike golfvorms te identifiseer, en dan sal een of ander vorm van DSP-patroonaanpassing onderneem word om die identifikasie te bespoedig. Met GPS-tydsberekening en geografiese ligging is trilaterasie tyd van aankoms (vertraging) die mees waarskynlike stelsel. Uiteindelik sal die integrasie van die VHF / UHF / SHF-komponente van wolkwolk en intraklou flitse opgeneem word.

Ek het hierdie artikel toevallig gesien 'n paar uur voordat storms my omgewing binnegedring het. Gebruik Airspy met 'n Spyverter in GQRX: http://imgur.com/a/5ePGx

Geniet altyd hierdie interessante toepassings vir die SDR-dongle, wat vanweë die gebruik van spektrale vertonings en watervalle dit 'n kragtige instrument maak vir die tinker sowel as die luisteraar. Mooi so Kenn.

Afgesien daarvan, is DB Gain 'n uitstekende pennaam hi hi.

Dankie! Ons het vroeg vanoggend 'n storm gehad met baie weerlig tot wolk. Ek het CubicSDR gebruik en die waterval laat sak na maksimum 1024 lyne per sekonde, sodat ek die tyddomein van naderby kon bekyk.

In die beeld is die waterval

Ek het 'n wetenskapsbeursprojek gedoen oor weerligopsporing as 'n instrument vir weervoorspelling op hoërskool.

My metode was toe om 'n paar minute van die AM-uitsaaiband op te neem en dan die aantal pops te tel wat ek gehoor het. Ek sal dit dan vergelyk met huidige en toekomstige weerstoestande.

Met 'n SDR en moderne sagteware kan dit waarskynlik geoutomatiseer word, met groter presisie.

Kan iemand my asseblief rig na 'n webwerf wat verduidelik hoe om die HTML-tags van hierdie webwerf te gebruik?

Het u hoekhakies (& # 8220 & # 8221) om die etikette gesit?

Kom ons kyk of ek 'n blokaanhaling kan kry om te werk:

Raai nie. Iets vreet die hoekhakies.

Waarvoor word die blokaanhaling gebruik?

blockquote cite = & # 8221 Ek gebruik 'n RTL-SDR-weergawe 3-dongle en GQRX in Linux, maar enige SDR- en spektrum-analiseerdersagteware wat VLF kan afstem, moet dit doen & # 8221

& # 8211 Sommige vrae, hopelik het iemand die antwoorde in 'n ander boodskap van hi gelees, sodat ek die seinsterkte wat hy ontvang, kan verstaan
? Gebruik hy HF-modus vir direkte steekproefneming? Indien ja, hoe sensitief is die Dongle onder 600 kHz?

blockquote cite = & # 8221so ek het gekies om 0 tot 600 kHz te monitor. Die antenne is 'n dipool van 1/2 golf vir HF, maar enige draad van minstens 'n paar meter lank sal werk. & # 8221

? Het iemand in 'n ander berig van hom gelees watter antenna-afmetings hy gebruik?
By 600 kHz is die golflengte al 500m, hoe laer die frekwensie van die golflengte tot onafhandelbare afmetings, tensy u militêr is.
SW is ongeveer 160 m vir HAM & # 8217

29 MHz), dus is dit 'n groot verskil as sy 1/2 golf dipool 80 m of net 5 m is.

Alhoewel dit lekker is om die spektra te sien, wonder ek of die opsporing nie makliker sou wees met behulp van 'n aktiewe lus nie, gevolg deur 'n IF-versterker / limiter van 'n NBFM-demodulator (bv. NE-604 of soortgelyk) en 'n diodeverklikker.

Dan is daar href = & # 8221 weerligbeskerming & # 8221 title = & # 8221https: //www.rtl-sdr.com/forum/viewtopic.php? F = 6 & ampt = 1871 # p4945 & # 8243 om te oorweeg, aangesien ek net 'n 'n kort tydjie gelede in antwoord op 'n vraag.

Ek het 'n draad van 70 voet gehad wat 'n rukkie 'n transmissie via 'n balun en tweeledig gevoer het. Op 'n dag het ek opgemerk nadat ek 'n zap gehoor het wat lyk asof dit van die transmatch af kom, dat die dwarsnaalde van die swr-meter in die transmatch stadig tot stilstand kom en dan hoor ek 'n knal en hulle sal net weer nul val om weer stadig te bou. Helder lug, droë, mooi dag. Die naaste storm was 100 km ver. Die storm laai die draad en dus die swr-stroombaan totdat die afstemkap boog buig. Dit was 'n redelike betroubare metode om storms op te spoor, maar stowwerige wind en sneeu het dieselfde gedoen.

Lang drade met isolasie en wind wat daaroor waai, kan lei tot aansienlike statiese ladings. Ek stel voor dat 'n RF-verstikking of 'n hoë waarde-weerstand (sê 100 k ohm) na u stasiegrond geskuif word. Dit sal die statiese op u antenna ontlaai.

Plaas 'n opmerking Kanseleer antwoord

Hierdie webwerf gebruik Akismet om strooipos te verminder. Lees hoe u kommentaardata verwerk word.


E.T., Phone Earth! Reuse radioteleskoop kan luister na uitheemse seine

Dit was 'n visie van die soeke na buitenaardse intelligensie wat nooit bedoel was nie. In 1971 het die NASA se Ames-navorsingsentrum onder leiding van twee van SETI se groot swaargewigte - Hewlett – Packard se Barney Oliver en NASA se hoof van lewenswetenskappe, John Billingham - 'n werksessie van drie maande geborg wat daarop gemik was om SETI op groot skaal te koördineer.

Terwyl hy die grondslag gelê het vir baie van die volgende dekades vir SETI, soos die bestaan ​​van die 'watergat' tussen 1420 en 1666 MHz, het dit ook ondersoek ingestel na wat SETI, formeel die soeke na buitenaardse intelligensie, sou kon doen as geld en hulpbronne was geen opsie nie. Aan die einde van die drie maande het hulle met Project Cyclops vorendag gekom, wat die planne uiteensit vir 'n groot verskeidenheid radiogeregte, tot duisend in totaal, elke gereg 100 meter breed, met 'n totale versameloppervlak van tot 20 vierkante kilometer. . Cyclops sou die vaagste fluistering, die stilste murmureringe van ET, kon hoor, wat skelm lekkasies uit hul beskawings kon opneem of deur die skreiende sein van 'n doelbewuste baken kon doof.

Cyclops is nooit gebou nie, natuurlik was dit nooit bedoel nie. Dit was eerder 'n gedagte-eksperiment, 'n blik op wat moontlik was as SETI-wetenskaplikes 'n carte blanche gehad het om te bou wat hulle wou. Inderdaad, skottelgoed van 100 meter is omtrent die grootste wat ons kan bou voordat dit struktureel onstabiel word. Dit is ook duur, maar slim radiowetenskaplikes het besef dat die koppeling van baie kleiner en goedkoper radiogeregte in 'n proses wat bekend staan ​​as interferometrie, 'n gekombineerde versamelarea kan skep wat gelyk is aan of groter is as die enkelgeregte, en baie meer doeltreffend.

As sodanig staan ​​ons vandag op die spits van 'n nuwe era in radiosterrekunde, een wat SETI die hupstoot kan gee om te ontdek dat ons nie alleen is nie. [10 wildste pogings om vreemdelinge te kontak]

Ontmoet die Square Kilometer Array

In Mei is aangekondig dat die Square Kilometer Array (SKA) - 'n ambisieuse netwerk van duisende radio-antennas - in Suid-Afrika (benewens buurlande) en Australië gebaseer sou wees. As ons aanneem dat befondsing beskikbaar is, sal die bouwerk aan fase een in 2016 begin, fase twee in 2019, en die hele onderneming sal teen 2024 voltooi wees.

Suid-Afrika kry die meeste radioskottels, elk 15 meter breed, wat ontwerp is vir geteikende waarnemings, terwyl Australië die lae frekwensie-antennas en skottelgerigte middellange frekwensie-skottelgoed het vir breë veldopmetings. Dit is nie heeltemal op die skaal van Project Cyclops nie, maar oor die algemeen is die grootte van die SKA nog steeds enorm, met aanvanklike basislyne (die breedste afstand tussen teleskope in die interferometer hoe langer die basislyn, hoe groter die hoekoplossing) van honderde kilometers. Fase twee sal dit tot 3000 kilometer uitbrei. 'N Ware radioantenne op twee verskillende vastelande wat na die sterre luister.

Terwyl Cyclops ontwerp is om 'n SETI-toegewyde skikking te wees waarop ander astronomiese projekte kan vlieg, is die SKA die spieëlbeeld, 'n instrument wat hoofsaaklik gebruik word om neutrale waterstof in die vroeë heelal te soek, om die emissie van pulse en swart gate te ondersoek en kosmiese magnetisme te ondersoek. . Tog was die soeke na lewe en die oorsprong daarvan nog nooit ver van die SKA se prioriteite nie, met planne om die binnekant van planeetvormende stofskywe rondom jong sterre te ondersoek om na die boustene van die lewe in daardie planetêre konstruksiewerwe te soek.

Daar is ook SETI en die moontlikheid dat die SKA 'n kunsmatige radiosein van 'n ander wêreld kan toeval. Sou SETI-eksperimente welkom wees op die SKA, miskien met geen ekstra koste op ander astronomie-eksperimente soos SETI op Arecibo nie?

Dit is bevestigend, het Michiel van Haarlam, die tussentydse direkteur-generaal van die SKA, gesê. & ldquoDit is nog nie op die proef gestel nie, maar dit word beslis oorweeg, & rdquo het hy verduidelik. & ldquo Dit is op ons lys van wetenskaplike gevalle, so ek dink dit sal daar wees, in kompetisie met al die ander voorstelle wat daar is. & rdquo

E.T., telefoon Aarde!

So, wat sou SETI op die SKA kon doen? Dit is voldoende om te sê dat uitheemse soektogte selde op baie lang basislyne probeer is. SETI is al dikwels op enkelgeregte uitgevoer, en wanneer interferometrie gebruik is, soos op die Allen Telescope Array (ATA), is dit eerder gelokaliseer met kort basislyne, maar 'n baie lang basisinterferometrie (VLBI) kom al hoe meer in die mode . Hoe presteer SETI op teleskope van so 'n grootte?

Die baan van SETI is aardse inmenging van televisies en radio's, selfone, satelliete en 'n lughawe-radar. Is dit haalbaar om alle steurings uit te roei, met 'n lang basislyn met soveel teleskope oor so 'n wye stuk grond?

Dit blyk dat u dit nie nodig het nie, het Hayden Rampadarath van die International Centre for Radio Astronomy in Perth, Australië, gesê. Hy het 'n SETI VLBI-eksperiment gelei om na die Gliese 581-stelsel te luister - 'n rooi dwerg met ten minste vier aardplanete om die baan - met behulp van die drie teleskope van die Australiese Long Baseline Array. Die verslag oor die eksperiment, wat in The Astronomical Journal gepubliseer moet word, beskryf hoe die stelsel ondanks geen ontvangs van buitenaardse seine 222 smal- en breëbandseine van aardse oorsprong opgespoor en suksesvol geïdentifiseer het nie.

& ldquo Vanweë die groot skeidings tussen die individuele teleskope, honderde tot duisende kilometers, sou dieselfde radiofrekwensie-interferensie gewoonlik slegs deur een of twee teleskope gesien word en sou dit nie gekorreleer word nie, & rdquo Rampadarath gesê. & ldquo Soms is dit egter nie waar nie en interferensie wat korreleer, sal eerder 'n geometriese vertraging ervaar - en dus 'n fase-vertraging - wat ontstaan ​​as gevolg van die radio-emissie wat vroeër by sommige van die teleskope aankom as by ander. & rdquo

Hierdie fase-vertraging kan dan gebruik word om enige skelm uitstoot uit te skakel - die punt is dat lang basisinterferometrie op die SKA nie hoef te bekommer oor inmenging deur aardse seine nie, wat die skikking dus 'n uitstekende hulpmiddel vir doelgerigte SETI-operasies maak.

Buitelandse aardse inmenging

Terwyl ons inmenging 'n hindernis vir SETI is, kan radiointerferensie buite die buiteland 'n geleentheid bied.

Die SKA se promosieliteratuur het gereeld gepraat oor die feit dat hulle die aardse radioseine van 'n E.T. kan afluister, en die vraag of buitenaardse mense die hulpbronne sal bestee om doelbewus 'n sein na ons te stuur, netjies te omseil.

Ons eie skelm radioseine dring beslis al byna 'n eeu in die ruimte deur, maar hulle is swak en val afstand na aanleiding van die omgekeerde vierkantige wet. Seth Shostak, SETI-instituut, het vroeër daarop gewys dat ons nie eens ons radioseine kon opspoor met ons huidige toerusting by die naaste ster, Proxima Centauri, 4,2 ligjare weg. Watter hoop het ons dan om E.T. se weergawe van taai reality-televisie en sepies op te spoor?

Dit hang af van wie ons vra. & ldquo Vir die eerste fase van die SKA kan ons 'n lughawaradar op 50 tot 60 ligjare opspoor, & rdquo van Haarlam.

Professor Abraham Loeb, voorsitter van die Departement Sterrekunde aan die Harvard Universiteit, gaan nog verder. In 2006 skryf hy 'n referaat met sy Harvard-kollega Matias Zaldarriaga wat in die Journal of Cosmology and Astroparticle Physics gepubliseer word, waarin hy beskryf hoe opkomende radiowaarnemings soos die SKA radio-uitsendings kan afluister.

& ldquo Militêre radars in die vorm van vroeë waarskuwingstelsels met ballistiese rakette gedurende die Koue Oorlog was die helderste, het Lod aan Astrobiology Magazine gesê. & ldquo Ons het getoon dat dit met 'n SKA-teleskoop op 'n afstand van honderde ligjare waarneembaar is, hoewel TV- en radio-uitsendings baie flouer is en op korter afstande gesien kan word. & rdquo

Aarde se radio-teenwoordigheid

Dit is onbetwis dat ons radar oor die horison kragtig in die ruimte uitgelek het. Hierdie radars vir vroeë waarskuwing word egter in die meeste gevalle, soos die Berlynse muur, 'n oorblyfsel van 'n vorige tyd, gebruik vir 'n paar dekades voordat dit verouderd geraak het.

Vandag is hulle meestal vervang deur breëbandradars wat oor frekwensies spring, wat dit onopspoorbaar maak vir buitenaardse weermag, 'n tema wat in 'n artikel gepubliseer is in The International Journal of Astrobiology deur Duncan Forgan van die Universiteit van Edinburgh en Bob Nichol van die Instituut. kosmologie en swaartekrag aan die Universiteit van Portsmouth. Hulle is bekommerd dat, as buitelandse beskawings ons tegnologiekurwe volg, met die oorskakeling na digitale breëbandseine, hulle radiolekkasie sou verminder het en hul planete 'radiostil' sou maak, en 'n venster van slegs 'n eeu sou agterlaat waar ons kan afluister hulle.

& ldquoAs ons in staat is om ons tegnologie te verbeter sodat ons sein nie in die sterrestelsel uitlek nie en as ons dit op 'n sekere tydskaal verbeter, dan dui ons beramings daarop dat selfs al is ons sterrestelsel goed bevolk, maar met menslike intelligensie wat besluit om om die seinlekkasie drasties te beperk, word dit baie moeilik om dit op te spoor, & rdquo Forgan gesê. As dit die geval is, sal die kans dat die SKA bestaan, saamval met een van daardie relatief kort tydvensters van buiteaardse lekkasie klein wees.

Alhoewel Forgan aanvaar dat radar steeds die ruimte ingestuur sal word om potensieel gevaarlike naby-aarde asteroïdes te ondersoek, is hierdie gebruik van radar lukraak en nie-herhalend, wys James Benford van Microwave Sciences, Inc., wat saam met John Billingham ons die sigbaarheid van die eie beskawing in 'n referaat wat tydens die besprekingsvergadering van die Royal Society in 'Towards a Scientific and Social Agenda on Extraterrestrial Life' in Oktober 2010 aangebied is. Hulle het bereken dat 'n uitsending doelbewus in die ruimte deur die 70 meter Evpatoria-radioantenne op die Krim, ver kragtiger as ons TV- en radiolekkasie, sou dit slegs waargeneem kon word as 'n samehangende boodskap deur 'n SKA-ontvanger tot 19 ligjare, en as 'n rou uitbarsting van energie wat geen inligting bevat tot 648 ligjare nie.

Erger nog, hulle voer aan dat Loeb se berekeninge vir ons TV- en radiolekkasie tot 75 ligjaar waarneembaar is - berekeninge wat gebaseer is op baie lang integrasietye in die orde van maande - is nie haalbaar nie omdat radiostasies oor die ledemaat sal draai. 'n planeet wat voorkom dat die sein vir 'n lang tyd aan die sein vasgesluit word om opsporing te vergemaklik (Benford lewer dieselfde kritiek op die skatting van Van Haarlam om die lughawe-radar tot 50 ligjaar op te spoor).

Verder, in reaksie op Seth Shostak se bewering dat 'n ontvanger van die grootte van Chicago ons radiolekkasie na honderde ligjare kan opspoor, reageer Benford en Billingham deur daarop te wys dat so 'n antenne, met 'n totale versameloppervlak van 24 800 vierkante kilometer, sou kos $ 60 biljoen, van soortgelyke orde as die totale BNP van die planeet (ter vergelyking sal die SKA ongeveer $ 1,5 miljard kos). As E.T. gaan ons hoor, sal hulle hulpbronne ver voor ons eie hê, wat beteken dat ons eie pogings om die SKA af te luister, nutteloos gaan wees.

Sal ons van E.T. hoor?

Die prentjie wat deur Forgan en Nichol, Benford en Billingham geskilder is, is redelik donker vir die afluister van die SKA. Loeb tellers, & ldquo Die periodisiteit as gevolg van rotasie van 'n planeet is 'n groot pluspunt wat kan help om die kunsmatige aard van die sein te identifiseer. & Rdquo Hy het bygevoeg, & ldquo Benewens planetêre rotasie, kan 'n mens na periodisiteit soek as gevolg van die baan van die planeet om sy ster. & rdquo

Benford is nie oortuig deur Loeb se argumente nie. & ldquo Afwesigheid van sein [soos die planeet draai] beteken dat daar geen opsporingstyd is nie en die sein-ruis-verhouding word verminder, & rdquo het hy gesê.

Ons het egter aanvaar dat ons vreemdelinge planeetgebonde is. Gestel hulle het ruimtevaart. Dit kan dinge nogal verander. Radiokommunikasie tussen satelliete, ruimtestasies en ruimtetuie is nie onderhewig aan planetêre rotasie nie. [7 Enorme wanopvattings oor vreemdelinge]

Duncan Forgan gee toe dat hy nie ruimtevaart of interplanetêre kolonisasie in sy visie van 'n radio-stil heelal verreken het nie, maar waarsku: & ldquo Dit is onduidelik presies hoeveel radioverkeer sou voortspruit uit 'n beskawing met veelvuldige planete rondom verskeie sterre. & Rdquo Daar is ander metodes van kommunikasie, het hy bygevoeg, soos lasers of selfs kortstondige neutrino-strale. Aan die ander kant, het Jim Benford opgemerk, kan 'n beskawing op 'n planeet mikrogolfstraal gebruik om hul ruimtetuie aan te dryf, wat hul lekkasie-handtekening dramaties verhoog.

Debatteer oor seine van die sterre

Uiteindelik, ongeag watter kant van die debat u ook al val, is daar baie onbekendes en aannames wat in elke argument ingebou is wat nie een van hulle heeltemal oortuigend maak nie. Miskien sal die SKA ET nie kan afluister nie, maar daar is beslis geen skade daaraan om te probeer nie. As dit misluk, is daar altyd meer tradisionele SETI om op terug te val, naamlik die soeke na doelbewuste bakens.

Benford verbeel hom die bestaan ​​van kortstondige bakens, wat ontwerp is om kostedoeltreffend te wees, en net een keer binne 'n gegewe tydsraamwerk na ons kant toe flikker. Hierdie, het hy gesê, lyk baie soos pulsars, iets wat die SKA voorberei om te soek, miskien sal 'n verbygaande baken sigbaar word in een van die SKA se pulserende vee? Dit is die potensiaal vir hierdie soort ernstige ontdekking wat die SKA so 'n kragtige instrument vir SETI kan maak, solank die mannekrag en hulpbronne daar is om deur al die onbewerkte data te soek wat die SKA sal produseer.

Daar sal beslis baie wees: om al die data wat miljoene een hertz breë smalbandkanale dek, te verwerk, is exaflop-rekenaars nodig wat in die orde van 'n miljoen triljoen bewerkings per sekonde kan verrig. Daar is net een probleem: sulke kragtige rekenaars is nog nie uitgevind nie, maar die wet van Moore en die onlangse vooruitgang in rekenaars vertel ons dat hulle op pad is en gereed sal wees teen die tyd dat die SKA aanlyn is.

Jim Benford stel voor om dinge nog eenvoudiger te maak. Om na kortstondige bakens te soek, sal baie kyk en wag nodig wees, en onbelemmerd staar in die hoop om die kort sarsie van 'n kortstondige sein op te tree - iets soos die geheimsinnige 'Wow!' - sein.

Volgens Benford sou 'n klein verskeidenheid radiogeregte, wat elkeen die taak gehad het om 'n spesifieke stuk lug onophoudelik dop te hou, die truuk doen. Dit is nie nodig om die hele SKA te gebruik nie. Hy sê die klein verskeidenheid geregte wat ASKAP, die SKA-prototipe van Australië, vorm, sal voldoende en baie doeltreffender wees teen 'n fraksie van die koste om die hele SKA te gebruik.

Ongeag die SKA se werklike vermoë om lekkasies buite die buiteland op te spoor, is dit steeds baie beter as enigiets wat ons tans deur SETI doen, insluitend die Allen Telescope Array wat gesukkel het om finansiering. Wat die SKA wel bewys, is dat, selfs al sluit die ATA, dit nie die einde van SETI self is nie.

& ldquoRadio SETI gaan 'n ware hupstoot kry, want ons het fantastiese teleskope wat soos die SKA kom en die spelveranderers vir radiosterrekunde is, & rdquo Forgan. & ldquo Dit is 'n baie opwindende tyd. & rdquo

En daar is beslis geen skade aan soek nie, net vir ingeval. & ldquo Die aard van SETI-navorsing is verkenning, & rdquo sê Loeb. & ldquo Ons moet optree as ontdekkingsreisigers en minimale opgeleide raaiskote maak, bloot omdat buitenaardse mense dalk baie anders as ons is en ons ervaring miskien nie 'n nuttige gids is nie. & rdquo

Aan die ander kant, as hulle soos ons is en lekkasies het wat hoofsaaklik van militêre radar afkomstig is, wil ons miskien wegbly, het Loeb gewaarsku. Die gevolgtrekking wat ek wil maak, is dat militante beskawings waarskynlik op groter afstande sigbaar sal wees as vreedsame, en ons moet baie versigtig wees voordat ons antwoord op enige bespeurde sein. & rdquo

Maar dis 'n debat vir 'n ander keer.

Hierdie verhaal is verskaf deur Astrobiology Magazine, 'n web-publikasie wat geborg word deur die NASA-astrobiologie-program.


Welkom by die tuisblad van Jürgen Kerp

HI Sterrekunde HI is die eenvoudigste, maar die meeste voorkomende atoom is ruimte. Met behulp van vandag se radio-astronomiese tegnologie is dit 'n maklike taak om die HI-lynemissie te meet. Die sensitiwiteit van die wêreld se grootste radioteleskope laat die neutrale spesies opspoor tot volumedigtheid waar die dominante gasfraksie reeds geïoniseer is. HI is of scientific key-importance for our understanding of galaxy formation, evolution and merging history, because even at large radial distances from the stellar body we can study in great detail the density, temperature and velocity structure of the neutral gas.

Single Dish Astronomy HI covers the whole sky! The Lockman area and the Chandra deep-field south area denote minimum column density regions where warm neutral medium reaches local minimum column densities, these are the windows to high-energy astrophysics sky. Despite the fact that neutral hydrogen itself has not the largest photo-electric cross section it is the tracer for the spacial distribution of heavier species, in particular for helium. HI full-sky single dish surveys are accordingly of high importance to quantify the amount of matter distributed along the line of sight. Towards high galactic latitudes the HI column density value itself is a measure for this quantity, within the Galactic plane, the radial velocity information allows to disentangle the HI line emission of different portions of the Galactic disk. Sophisticated modelling is necessary to disclose the complex structure of cold and warm gas but also offers the unique possibility to disclose the distribution of gravitational matter far beyond the stellar disk.

Radio Interferometry within the coming decade radio interferometers will survey at an unequaled angular resolution the whole sky. The prime scientific aim is to study the HI distribution at high red-shifts. Because of their construction radio interferometers blind for the radiation of very extended structures. Combining both, single dish and radio interferometer data, allow to disclose the whole structure of external galaxies even far away from the stellar body. APERTIF (The Netherlands) and ASKAP (Australia) will use focal plane arrays (FPAs) to observe the whole sky within a period of a few years. The combination of single dish and FPA interferometric data is a new task, which we like to establish as a member of an international consortium.

Effelsberg Bonn HI Survey (EBHIS) EBHIS is the first all-sky survey which aims to perform a blind survey of the Milky Way HI distribution and the local volume in parallel. Present day spectrometer allow to resolve the cold neutral medium lines and to measure the HI radiation of a Milky Way galaxy at a red-shift of 0.07 within a single dump. Making use of this ability we optimized EBHIS to cover the full northern sky at an unique signal-to-noise ratio for the Milky Way Galaxy and towards the Sloan-Digital-Sky Survey (SDSS) area with a signal-to-noise ratio that we can detect the HI emission of a $10^7,< m M_odot>$ galaxy at the distance of the Virgo cluster. While on cosmological scales the Universe appears isotropic and homogeneous, we know that the local volume towards the northern hemisphere offers a unique view towards the closest larger galaxy clusters, our large and massive local group spiral galaxies and a large variety of high-velocity cloud complexes which show-up with unique signatures of an on-going interaction with the Milky Way Galaxy.


How far can we detect lightning in radioastronomy? - Sterrekunde

Amateur radio operators combined with amateur astronomers are using RTLSDR dongles (small usb radio receivers with software) to set up home satelite communications as well as radio telescope applications. I my self have a satellite dish and have been studying the means to use it with my RTLSDR receiver and thus want to discuss this here in this forum.

Here are some starter references:

Some of the issues that you might want to consider in doing this is such issues as using a German Equatorial telescope mount for you satellite dish or Yagui antenna array. Also low noise amplifiers as additions to the equipment. And which software are best suited for radio astronomy. SDRuno would be a software I would recommend because of its features.

Please remember that you will be able to listen to a signal and hence if there is a signal worth investigating by SETI being able to hear and record it is advantageous. Furthermore SDR software allows you to record the signal two ways, as and audio file or as a spectrum file that can be replayed by the SDR software showing the spectrum of signals of which one can click on the desired signal or any adjacent signal and listen to it.

If interested I can set up a web site to house information and articles by site users that would be of interest and we can advance this as a technology through breakthroughs in such things as low noise amps. We could also use liquid nitrogen in some applications of which amateur radio operators have been known to do just as well as radio astronomers.

Interesting Stuff ! Thanks Dannie.

This is indeed good stuff. or not.
I have posted my past ability to ping a US satellite in orbit and accidentally got into it's navigational systems.
I damn near brought it down to near earth orbit. I was able to recognize what I had done, and reversed the command.
It could have been a fatal crash.
It was by accident. I was just innocently hacking for fun. But I got in.
Just to see if I could./ And I could.

If it had been a military satellite, I suppose I might have been contacted by now.
Just to see if I had downloaded anything. Which I did not. I was not trying to get anything.
Just trying to see if I could contact a satellite.
A ping. which the damned thing answered.
And it should not have. ever with an unencrypted ping from an unknown source.
It sent me freaking data. Long since deleted all related files, because I was very scared.
Even that hard drive was destroyed years ago. Nothing remains except my memories of it.
And I suspect I could not duplicate the attempt to this day.
I could not.
And shall not try.

What is troubling is that if I could, others could as well, with less than honorable intentions.
Mine were. Others, maybe not so. I'm just a stray kitty cat. Soon may the kittyman come.

kittyman I am sure I would not want to do that. In the idea I have here however this is strictly for receiving and you can use this to receive satellite programming such as single channel per carrier audio for radio networks if you are into that, or radio astronomy and hence for both. And since you can tune around in the spectrum you are not confined to looking for intelligent signals at 1.4 GHz but can do some general radio astronomy by studying various frequencies. Of course having software to compile the data and make pictures would be the thing but I am sure that can be found given a search. But looking at 1.4 GHz would be the idea for SETI research. An array of multielement beam antennas would probalby be the thing over a dish antenna and some low noise amplifiers.

I have a low noise amplifier that cost under $10 I got from Banggood rated at 32dB from 1 MHz to 2 GHz. If needed it can be immersed in liquid nitrogen. Below is the preamp I bought for my SDR receiver.

A sideline application for using the SDR radio receiver and software is for shortwave radio listening so with this one radio and its software you can do just about anything in radio you can imagine in terms of receiver technologies and applications. It does not transmit but they do have SDR transceivers so you can do that too. But I would not be pinging satellites.

I no longer, sad to say, have the equipment to do star searches.
If things play out and I can retire from my work building fire trucks soon enough, I might try again.
I already have the knowledge/. I could perhaps again tap into what I know and try again to tap into what my tax dollars have paid for.
Lord know that what the government does with it is shit.
There is more information coming from the satellites already up there than the gov knows what to do with.
Believe me, I know.
We do not need any more satellites right now.
Like Seti, we need to start working in ernest, on the data we already have./
We need to look at what we already have in hand.

Once that is truly done,, worry about getting more data and where from. I'm just a stray kitty cat. Soon may the kittyman come.


How far can we detect lightning in radioastronomy? - Sterrekunde

Welcome to CASPER, the Collaboration for Astronomy Signal Processing and Electronics Research. We are a group of scientists and engineers producing resources to aid in astronomy research.

The primary goal of CASPER is to streamline and simplify the design flow of radio astronomy instrumentation by promoting design reuse through the development of platform-independent, open-source hardware and software.

Our aim is to produce tools which allow astronomers to rapidly design and deploy new instruments using FPGA, GPU, and CPU processors.

CASPER has members all around the world, and our hardware and software is used by dozens of experiments — check out the variety of CASPER instruments and their results in the scientific literature, or the 2016 CASPER overview paper.

Members of the CASPER collaboration typically meet once per year in a community workshop, where academics and engineers present their work and teach newcomers how to use CASPER tools.

If you are a CASPER collaborator, or you’re just interested in what we’re up to, join our mailing list by sending a mail to [email protected]

If you are a developer, or are interested in becoming one, we also have a dedicated mailist for announcements about developer meetings. Join by sending a mail to [email protected]

CASPER collaborators around the world!


How far can we detect lightning in radioastronomy? - Sterrekunde

Beginner's Guide to Radio Astronomy and SETI

I am continually amazed by the number of people I run into who have total misconceptions about the work done at the Big Ear Radio Observatory. I have talked to people who (not knowing that I'm a staff member) have made comments relating both radio astronomy and SETI (the Search for ExtraTerrestrial Intelligence) to some kind of fringe or cult activity involving UFOs and talking to Martians. Therefore, I have decided to put this page together to explain what it is that we do. Just in case there is someone who is a total novice at this stuff, I'll start at the very beginning. (Those of you who already know this, just bear with me.)

The science of astronomy is the study of the universe beyond the Earth, which includes objects such as the planets, asteroids, comets, stars and galaxies. This study is done by analyzing the energy (photons) in the electromagnetic spectrum that is emitted from these objects.

The Electromagnetic Spectrum

To help visualize the electromagnetic spectrum, think of a rainbow of colors. When you see a rainbow, you are seeing light (photons) spread out into varying wavelengths or frequencies. It starts with deep violet, which is light at 0.4 microns, and extends through red, which is light at 0.8 microns. (A mikron is one millionth of a meter, and is used to measure things that are very, very tiny.)

The retina of the human eye can only process photons in the range of 0.4 to 0.8 microns. Therefore, this portion of the electromagnetic spectrum is referred to as visible light. However, the electromagnetic spectrum extends in both directions (shorter than 0.4 microns and longer than 0.8 microns), and is composed of photons that are not visible as light.


The Electromagnetic Spectrum

The portion of the electromagnetic spectrum shorter than 0.4 microns is composed of extremely short-wavelength photons, such as ultraviolet light, x-rays, and gamma rays. The part of the electromagnetic spectrum longer than 0.8 microns contains longer-wavelength photons such as infra-red light (used by the military in night-vision goggles, for example), and radio waves. Radio waves can be anywhere from a fraction of one millimeter long to 300 meters long.

Many objects in the universe emit photons across the entire electromagnetic spectrum, although we can only see those that fall in the visible portion of the spectrum.

Optical Versus Radio Astronomy


Optical
Observatory

Optical
Teleskoop

Optical Astronomy
Foto

Astronomy is divided into several branches, each involving a different portion of the electromagnetic spectrum. Optical astronomy, which is the most widely-known and popular branch of astronomy, is the study of the universe in the visible light region of the electromagnetic spectrum. When we think of optical astronomy, we think of looking through a telescope. Optical telescopes have mirrors or lenses which collect or refract light.


Steerable Dish
Radio Telescope

Fixed Kraus-Type
Radio Telescope

Radio astronomy is the study of the universe in the radio portion of the electromagnetic spectrum, which is from a fraction of one millimeter to 300 meter wavelengths. Radio waves cannot be seen by the human eye however, a great many celestial objects do emit photons in the radio wave region of the spectrum. To study the universe at radio wavelengths, radio astronomers use radio telescopes, which are entirely different from optical telescopes. Radio telescopes use wires or solid surfaces to focus the radio waves, which are then collected by a receiver similar to the receiver that you use to listen to a radio station (although at a different frequency). Although radio waves can't be seen, they can be heard as a hiss not unlike the static between stations on the radio.

Radio astronomers have made some exciting discoveries. Pulsars (rotating neutron stars) and quasars (dense central cores of extremely distant galaxies) were both discovered by radio astronomers.

There are other branches of astronomy as well (gamma ray, x-ray, ultraviolet, and infra-red to name a handful), but I won't cover those here.

Sky Surveys Done by Big Ear


What the Sky Would Look Like
If Your Eyes Could See Radio Waves

The Big Ear radio telescope was used in the 1960s to form a giant picture of what the sky looks like in the radio region of the electromagnetic spectrum. This is what we call a Sky Survey. We are currently doing a follow-up survey to compare with the original. The telescope is systematically scanning the entire sky and storing the results in a computer. This data is then used to print images of what the sky might look like if our eyes could see photons in the radio region of the spectrum. These sources are naturally occurring that is, they are not artificial, but come from celestial objects in the universe.

In addition to surveying the sky for naturally-occurring radio sources, Big Ear is listening for possible signals from non-naturally-occurring sources in the universe. Those signals would be created by intelligent civilizations like ours. This is referred to as the Search for ExtraTerrestrial Intelligence (SETI).

Next, a word of explanation about our universe.

One light year is the distance that a light ray or radio wave would travel in one year going at approximately 186,000 miles per second. 186,000 miles would be the equivalent of circling the Earth about seven and a half times. Imagine that distance spread out in a straight line. That's how far light travels in one second. Now imagine how far the light could travel in 31,536,000 seconds (one year) - almost 5 trillion 866 billion miles! That's 5,866,000,000,000 miles!! It's a distance so vast that it's hard to fathom! And that's only one light year. The nearest star, Alpha Centauri, is 4.3 light years away! If you could travel at the speed of light, it would take you 4.3 years to get there! (In reality, Einstein's General Theory of Relativity predicts that it would be impossible to travel by the speed of light since it would require an infinite amount of energy to accelerate an object with significant mass to light speed.)

Our Home Galaxy, The Milky Way

You are here. The arrow points to the location of our sun within our home galaxy, the Milky Way.

Our star, the sun, is only one of about 100 billion stars - that's 100,000,000,000 - that make up our own galaxy, the Melkweg, which is approximately 100,000 light years in diameter. (If you could travel at the speed of light, it would take you 100,000 years to go from the outer edge on one side to the outer edge of the opposite side.) The Milky Way galaxy is a relatively flat disk which has a spiral shape with "arms" radiating outward from the center. We are located in the galactic boondocks more or less, toward the outside of one of these arms, about 30,000 light years from the center of the galaxy.

The Andromeda Galaxy is the nearest galaxy similar in size and shape to our own Milky Way. The Andromeda Galaxy is 2 million light years away.

Our galaxy is not the only galaxy in the universe. There are about 100 billion other galaxies. The nearest galaxy similar in size and shape to our own is the Andromeda galaxy, which is about 2,000,000 (two million) light years away. Other galaxies are billions of light years away.

Are We Alone in the Universe?

If there are 100 billion stars in 100 billion galaxies in the universe, that means that there are 10,000,000,000,000,000,000,000 (ten sextillion) stars in the universe (1 times 10 to the 22nd power when expressed in scientific notation). With this many stars, it would be hard to believe that there isn't life somewhere else in the universe.

Frank Drake, a famous radio astronomer, came up with a formula for estimating the number of communicating civilizations. This is called Drake's equation. It involves 7 factors:

The rate of star formation per year TIMES
The fraction of those stars that have planets TIMES
The number of those planets that have suitable environments for life to develop TIMES
The number of those planets where life actually does develop TIMES
The fraction of beings on those planets that actually develop intelligence TIMES
The fraction of intelligent civilizations that develop communications TIMES
The number of years that an intelligent civilization can survive

Dr. John Kraus, who built the Big Ear radio observatory, has estimated each of the seven factors as conservatively as possible for our home galaxy, the Milky Way, and has come up with the number 40. As many as forty intelligent, communicating civilizations in our galaxy alone! If the same equation were applied to the 100 billion other galaxies in the universe, we could estimate there to be 4,000,000,000,000 intelligent, communicating civilizations in the universe! That's 4 trillion!

We have little way of knowing whether this estimate is close to being correct, but even if it's off by a factor of 10,000, that would still leave 400 million intelligent, communicating civilizations in the universe!

How Would They Communicate?

Civilizations might communicate in one of two ways.

The first way is by sending signals unintentionally. We do this all the time ourselves. For over fifty years now, our first television and radio signals have been radiating out into space like a giant shock wave, or like waves radiating out from a pebble dropped into a pond. Another intelligent civilization could intercept them and wonder what they say. Imagine an alien race picking up one of our television signals, decoding it, and then sending what they believe to be an intelligent reply: "Lucy, I'm home!" or "So you want to be a wise guy, eh?"

The second way of communicating would be to purposefully send out a beacon with encoded information. The beacon could contain a simple instruction set that periodically repeats, along with a more complex message.

Perhaps there are civilizations that are very much more advanced than we are. If so, it's possible that they may have set up beacons to instruct fledgling civilizations such as ours. Maybe they would be broadcasting an "Encyclopedia Galactica" of some sort. Just imagine the wealth of knowledge that would be at our fingertips if we were to discover such a signal and decipher it. Perhaps it would teach us how to build a space ship that travels close to the speed of light. Or maybe it would tell us how to solve our planetary ecological crisis. How about if it told us how to solve our global political problems? The benefits of such a discovery could be beyond our wildest dreams!

Where Would They Broadcast It?

Sky noise diagram showing the radio quiet region and the water hole. An intelligent extraterrestrial civilization might choose this region to broadcast a message.

There is a portion of the radio spectrum that is relatively quiet from naturally occurring noise from stars and the atmosphere. This is called the radio quiet region. Additionally, within this region there is a portion of the radio spectrum known as the "water hole", from 1420 Megahertz (the emission wavelength for neutral hydrogen) to 1638 Megahertz (the emission wavelength for the hydroxyl radical). This region is called the "water hole" because when hydrogen and hydroxyl are combined, they form a molecule of water.

Some people believe that an extraterrestrial civilization might choose this region to broadcast a message, especially if they are a life form based on water like us. They might choose to broadcast in this region, hoping that we would be thinking along similar lines.

An alien message would also most likely be what we call a narrowband signal. This means a signal at a very precise frequency. Radio stations are examples of narrowband signals. Between radio stations you hear a hissing sound. This is broadband noise. The stars (and other celestial objects) also put out broadband noise. An intelligent, communicating civilization would probably use a narrowband signal rather than a broadband one for a beacon, since they wouldn't want their message to be mistaken for regular, ordinary star noise.

Would They Come Here? SETI Versus UFOs

The chances that an extraterrestrial civilization would actually come to the Earth are slim. The amount of time and energy required for the travel would be enormous. The amount of energy required to accelerate a spacecraft weighing several thousand tons to a speed even a moderate fraction of the speed of light would be billions of times more than the energy needed to send out a radio beacon. Therefore, it's more likely that they would communicate instead. For that reason, the Big Ear staff is highly skeptical of reports of UFO sightings. (Translate: we think they're BS.)

[Webmaster's note: No professional astronomer in his right mind would be caught dead stating publicly that he'd seen a UFO or been abducted by aliens. He would be ostracized by his colleagues. Serious educational institutions and research facilities would treat him as though he had suddenly acquired the ebola virus. His career would be finished. Note. The same would be true for female astronomers.]

So far the SETI search, at Big Ear and at other radio observatories around the world, has not uncovered any ETI (ExtraTerrestrial Intelligence) signals. The search is being conducted at many different frequencies over many parts of the sky. However, if a signal comes and we're not looking, we would miss it. SETI systems up to this point have been fairly limited in their searching capabilities, however this is now improving with systems such as Big Ear's SERENDIP which can process 4 million channels at once. The problem with only being able to look at one portion of the sky at a time may be solved in the future with Big Ear's "Argus" system. This system would form a picture of the entire radio sky at once, thereby greatly diminishing the chances of a signal being missed.

One thing is for certain when it comes to SETI, if we never look, then we're guaranteed never to find anything!

Copyright © 1996-2005 Ohio State University Radio Observatory and North American AstroPhysical Observatory.

Originally designed by Point & Click Software, Inc.
Last modified: August 15, 2005.


70th Anniversary of the Discovery of Radio Emissions from Neutral Hydrogen

David K. Ewen ([email protected]) sent SARA the following. David is the son of Harold “Doc” Ewen and he supplied the transcript of a conversation between Doc Ewen and Ed Purcell and the images below. See original article about the discovery in the 1 September 1951 issue of Nature*.

True space exploration began in 1951 at Harvard University. We are approaching the celebration of the 70th anniversary on March 25, 2021. On March 25th, 1951, the very first detection of hydrogen using a radio telescope with a horn antenna sticking out of a window on the 4th floor of the Lyman Physics laboratory at Harvard University was accomplished. This capability is the foundation of further discoveries allowing us to see the universe in a way never possible before. In 1951, on the 4th floor of the Lyman Laboratory, Harold "Doc" Ewen, Ph.D. was the first to observe and detect neutral hydrogen. His Harvard University thesis advisor was Edward, M. Purcell, Ph.D. This day made history in scientific space exploration.

Harold "Doc" Ewen, Ph.D. and Horn Antenna mounted on 4th floor window of Lyman Physics Laboratory at Harvard University Used to Detect Neutral Hydrogen on March 25, 1951

Since that time, radio astronomy has detected many new types of objects including pulsars and quasars. We can see a universe that radiates at wavelengths and frequencies we can’t see with our eyes. Objects in the universe give off unique patterns of radio emissions. Different wavelengths are generated by different objects and radio astronomers use a variety of methods and instruments to detect them. The radio signals detected by radio telescopes are converted into data that can be used to make images. For example, they are used to measure clouds of gas, which are abundant in the spiral arms of the Milky Way Galaxy making it possible to map the galaxy’s overall layout. Today, new radio telescopes provide ever more detailed views of the Milky Way.

In radio astronomy, radio waves that are in the electromagnetic spectrum, and radio astronomers use radio waves to see through all the large clouds of dust and darkness, to show even how gases swirl around Neptune and Uranus. When the hydrogen atoms crash, they make a bigger atom called a star, and a radio telescope helps us learn about them more by showing us those stars near us. Also, if you want to see some weird objects in the universe and even solve some mysteries, use radio telescopes.

Left: Harold "Doc" Ewen, Ph.D. in 1951 (note waveguide from the horn antenna at head level behind Ewen) Right: Harold "Doc" Ewen, Ph.D. and the Horn Antenna at Green Bank Observatory.

In 1987 Harold "Doc" Ewen and Edward M. Purcell, Ph.D. looked back to reminisce and spoke about the events that occurred on Easter weekend on the morning of March 25, 1951 that would forever change how we looked at our universe.

Doc Ewen – Originally, we didn't know whether the radio waves would actually be detectable. And the only thought at the time was if they were, they probably would be concentrated somewhere along the Milky way. And as a result, the best place to be looking would be toward the South in the vicinity, just north of Sagittarius, which is the center of the Milky way or our galaxy and just take a chance on the fact that there's a good concentration of material there.

Ed Purcell – Well, actually a good deal had been deduced from rather indirect evidence by the astrophysicist concerning the gas in our galaxy. And people know it was mostly hydrogen and that it was very empty. There were very few gas atoms per cubic centimeter. And in this empty thing, they're emitting this very thing, very characteristic radiation. The amount of hydrogen out there, and his temperature was such that the radiation at this frequency that we're concerned with is very special frequency amounted to only one watt landing on the entire earth

Doc Ewen – To attempt to detect a signal of that intensity less than a million millionth part of a lot, as far as what I was dealing with would be extremely difficult, even building an excellent radar receiver. I was concerned that we might be dealing downstream somewhere with a negative thesis and a negative thesis is extremely difficult and could take an extra year or two to tidy up and calibrate and put some numbers on it. If you don't detect something, then you must carefully state at what level you're capable or incapable of detecting it. So that was my concern. Ed's comment [Edward M. Purcell, Ph.D.] to that was so it's a couple of years of your life and but it's certainly worth it. And if you do detect it, you'll be in LIFE magazine and he was right.

Ed Purcell – Well, as I remember, it was in the morning. So he'd been up all night and I'd been at home in bed.
And as I remember, he said, I think I have a thesis. And I came dashing over.

Doc Ewen – It was over the weekend of Easter. And the first time I turned on the scanning of such as I was tuning, looking for this hydrogen hyperfine station, broadcasting from space, I was tuning through the spectrum. As you might just turn a knob. And I noticed at the end of the first scan, the signal was on its way up

Ed Purcell – And here on the Esterline paper from Esterline Angus Recorder, you know, it looked as wiggly line and looked as though there might be some bumps in and we rolled out about 20 feet of it and got down inside it along it, you see? And then we can see this bump like that.

Doc Ewen – It's just the way you designed it. It's just the way you thought about it. There was just a chill goes up your back and you say, I got it. And you'll just never, ever forget the excitement of doing something like that.
And yet it's so common in the field of science to go through these steps and feel that excitement. It's just
beautiful.