Light seconds, light years, light centuries: How to measure extreme distances - Yuan-Sen Ting

Prevodilac: Miloš Milosavljević Lektor: Mile Živković

Light is the fastest thing we know.

Svetlost je najbrža stvar koju poznajemo.

It's so fast that we measure enormous distances

Toliko je brza, da ogromne razdaljine merimo

by how long it takes for light to travel them.

time koliko je svetlosti potrebno da ih pređe.

In one year, light travels about 6,000,000,000,000 miles,

Za godinu dana, svetlost pređe oko 9,6 biliona kilometara,

a distance we call one light year.

razdaljinu koju nazivamo jednom svetlosnom godinom.

To give you an idea of just how far this is,

Da bi ste imali ideju koliko je to otprilike,

the Moon, which took the Apollo astronauts four days to reach,

Mesec, do koga je astronautima Apola trebalo 4 dana da stignu,

is only one light-second from Earth.

je udaljen samo jednu svetlosnu sekundu od Zemlje.

Meanwhile, the nearest star beyond our own Sun is Proxima Centauri,

Sledeća najbliža zvezda posle Sunca, Proksima Kentaura,

4.24 light years away.

je udaljena 4,24 svetlosne godine.

Our Milky Way is on the order of 100,000 light years across.

Naš Mlečni put je reda veličine 100.000 svetlosnih godina u prečniku.

The nearest galaxy to our own, Andromeda,

Najbliža galaksija našoj, Andromeda,

is about 2.5 million light years away

je udaljena oko 2,5 miliona svetlosnih godina.

Space is mind-blowingly vast.

Svemir je zapanjujuće ogroman.

But wait, how do we know how far away stars and galaxies are?

Ali čekajte, kako znamo koliko su udaljene zvezde i galaksije?

After all, when we look at the sky, we have a flat, two-dimensional view.

Kad pogledamo u nebo, imamo ravan, dvodimenzionalni pogled.

If you point you finger to one star, you can't tell how far the star is,

Ako izaberete jednu zvezdu, ne možete odrediti koliko je udaljena,

so how do astrophysicists figure that out?

pa kako to onda astrofizičari utvrde?

For objects that are very close by,

Za objekte koji su veoma blizu

we can use a concept called trigonometric parallax.

možemo koristiti koncept zvani trigonometrijska paralaksa.

The idea is pretty simple.

Ideja je prilično jednostavna.

Let's do an experiment.

Hajde da napravimo eksperiment.

Stick out your thumb and close your left eye.

Ispružite palac i zatvorite levo oko.

Now, open your left eye and close your right eye.

Sada otvorite levo oko i zatvorite desno.

It will look like your thumb has moved,

Izgledaće vam kao da se palac pomerio,

while more distant background objects have remained in place.

dok su udaljeniji objekti ostali na mestu.

The same concept applies when we look at the stars,

Isto važi i kad gledamo u zvezde,

but distant stars are much, much farther away than the length of your arm,

ali udaljene zvezde su mnogo dalje od dužine vaše ruke,

and the Earth isn't very large,

a Zemlja nije mnogo velika,

so even if you had different telescopes across the equator,

tako da čak i kad biste imali različite teleskope duž ekvatora,

you'd not see much of a shift in position.

ne biste videli veliko pomeranje u poziciji.

Instead, we look at the change in the star's apparent location over six months,

Umesto toga, posmatramo promenu vidljivog položaja zvezde tokom 6 meseci,

the halfway point of the Earth's yearlong orbit around the Sun.

polovinu Zemljine godišnje orbite oko Sunca.

When we measure the relative positions of the stars in summer,

Kada izmerimo relativne položaje zvezda u leto

and then again in winter, it's like looking with your other eye.

i onda ponovo u zimu, je kao da gledamo drugim okom.

Nearby stars seem to have moved against the background

Susedne zvezde kao da su se pomerile u odnosu na pozadinu

of the more distant stars and galaxies.

udaljenijih zvezda i galaksija.

But this method only works for objects no more than a few thousand light years away.

Ali ovaj metod funkcioniše samo za objekte

ne dalje od nekoliko stotina svetlosnih godina.

Beyond our own galaxy, the distances are so great

Izvan naše galaksije, razdaljine su toliko velike

that the parallax is too small to detect with even our most sensitive instruments.

da je paralaksa premala da bi se detektovala

čak i našim najosetljivijim instrumentima.

So at this point we have to rely on a different method

Tako da na ovoj tački moramo da se oslonimo na drugi metod:

using indicators we call standard candles.

koristeći indikatore koje zovemo standardne "sveće".

Standard candles are objects whose intrinsic brightness, or luminosity,

Standardne "sveće" su objekti čiju inherentnu sjajnost, ili luminoznost,

we know really well.

znamo vrlo dobro.

For example, if you know how bright your light bulb is,

Na primer, ako znate koliko je vaša sijalica sjajna,

and you ask your friend to hold the light bulb and walk away from you,

i zamolite prijatelja da je drži i odmiče se od vas,

you know that the amount of light you receive from your friend

znate da će se količina svetlosti koju primate od prijatelja

will decrease by the distance squared.

smanjivati sa udaljenošću na kvadrat.

So by comparing the amount of light you receive

Tako da, upoređujući količinu svetlosti koju primate

to the intrinsic brightness of the light bulb,

sa inherentnom svetlošću sijalice,

you can then tell how far away your friend is.

možete odrediti koliko je udaljen vaš prijatelj.

In astronomy, our light bulb turns out to be a special type of star

U astronomiji, našu sijalicu predstavlja posebna vrsta zvezde

called a cepheid variable.

zvana cefeida.

These stars are internally unstable,

Te zvezde su nestabilne,

like a constantly inflating and deflating balloon.

kao balon koji se neprestano naduvava i izduvava.

And because the expansion and contraction causes their brightness to vary,

A pošto zbog širenja i skupljanja njihova sjajnost varira,

we can calculate their luminosity by measuring the period of this cycle,

možemo izračunati njihov sjaj merenjem perioda ovog ciklusa,

with more luminous stars changing more slowly.

sa sjajnijim zvezdama koje variraju sporije.

By comparing the light we observe from these stars

Poređenjem svetlosti koju vidimo od ovih zvezda

to the intrinsic brightness we've calculated this way,

sa inherentnom sjajnošću koju smo izračunali na ovaj način,

we can tell how far away they are.

možemo odrediti koliko su udaljene.

Unfortunately, this is still not the end of the story.

Nažalost, ovo još uvek nije kraj priče.

We can only observe individual stars up to about 40,000,000 light years away,

Možemo samo posmatrati pojedinačne zvezde

do udaljenosti od oko 40 miliona svetlosnih godina,

after which they become too blurry to resolve.

posle čega postaju suviše mutne da bi se razlučile.

But luckily we have another type of standard candle:

Ali, srećom, imamo drugu vrstu standardne "sveće":

the famous type 1a supernova.

čuvenu vrstu 1a supernova.

Supernovae, giant stellar explosions are one of the ways that stars die.

Supernove, džinovske zvezdane eksplozije, su jedan od načina umiranja zvezda.

These explosions are so bright,

Te eksplozije su tako sjajne

that they outshine the galaxies where they occur.

da nadmašuju sjaj galaksija u kojima se javljaju.

So even when we can't see individual stars in a galaxy,

Tako da, čak i kad ne možemo da vidimo pojedinačne zvezde u galaksiji,

we can still see supernovae when they happen.

možemo da vidimo supernove kada se dogode.

And type 1a supernovae turn out to be usable as standard candles

I 1a supernove mogu da se koriste kao standardne "sveće",

because intrinsically bright ones fade slower than fainter ones.

jer inherentno sjajnije blede sporije nego one bleđe.

Through our understanding of this relationship

Razumevanjem ove veze

between brightness and decline rate,

između sjajnosti i stope smanjenja

we can use these supernovae to probe distances

možemo koristiti te supernove da ispitamo udaljenosti

up to several billions of light years away.

i do nekoliko milijardi svetlosnih godina.

But why is it important to see such distant objects anyway?

Ali zašto je uopšte važno videti tako udaljene objekte?

Well, remember how fast light travels.

Setite se koliko brzo svetlost putuje.

For example, the light emitted by the Sun will take eight minutes to reach us,

Na primer, svetlosti koju emituje Sunce treba 8 minuta da stigne do nas,

which means that the light we see now is a picture of the Sun eight minutes ago.

što znači da je svetlost koju vidimo slika Sunca od pre 8 minuta.

When you look at the Big Dipper,

Kada pogledate Velika kola,

you're seeing what it looked like 80 years ago.

vidite kako su izgledala pre 80 godina.

And those smudgy galaxies?

A one zamrljane galaksije?

They're millions of light years away.

One su milionima svetlosnih godina daleko.

It has taken millions of years for that light to reach us.

Toj svetlosti je trebalo na milione svetlosnih godina da dođe do nas.

So the universe itself is in some sense an inbuilt time machine.

Tako da je svemir, u neku ruku, prirodni vremeplov.

The further we can look back, the younger the universe we are probing.

Što dalje gledamo unazad, to mlađi svemir ispitujemo.

Astrophysicists try to read the history of the universe,

Astrofizičari pokušavaju da pročitaju istoriju svemira

and understand how and where we come from.

i da shvate kako, i odakle smo postali.

The universe is constantly sending us information in the form of light.

Svemir nam konstantno šalje informacije u vidu svetlosti.

All that remains if for us to decode it.

Nama samo ostaje da ih dešifrujemo.