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

Translator: roina ochieng Reviewer: Joachim Mangilima

Light is the fastest thing we know.

Mwanga ndio kitu kilicho na kasi zaidi tunalojua.

It's so fast that we measure enormous distances

Lina kasi sana tunapima umbali mkubwa sana

by how long it takes for light to travel them.

kutumia muda ambao mwanga hutumia kuisafiri.

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

Kwa mwaka mmoja, mwanga husafiri takriban maili bilioni sita,

a distance we call one light year.

umbali tunaoita mwaka mmoja wa mwanga.

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

Kukupa wazo la umbali huu,

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

mwezi, lililowachukua wanaanga wa Apollo siku nne kuifikia,

is only one light-second from Earth.

ni sekundi moja tu la mwanga kutoka dunia.

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

Wakati huo huo, nyota lililo karibu kupita jua letu ni Proxima Centauri,

4.24 light years away.

umbali wa miaka ya mwanga 4.24.

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

Milky Way yetu iko kwenye mpango wa miaka ya mwanga 100,000 toka upande mmoja.

The nearest galaxy to our own, Andromeda,

Galaksi iliyo karibu sana na yetu, Andromeda,

is about 2.5 million light years away

ni umbali wa takriban miaka ya mwanga millioni 2.5

Space is mind-blowingly vast.

Anga una upana mkubwa kushangaza.

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

Lakini ngoja, tuanjuaje ubali wa nyota na magalaksi?

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

Ata hivyo, tunapotazama anga, tuna mtazamo wa mielekeo miwili.

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

Ukielekeza kidole chako kwa nyota moja, huwezi kujua umbali wa nyota hio,

so how do astrophysicists figure that out?

kwa hivyo wanaastrofysik wanajuaje?

For objects that are very close by,

Kwa vitu vilivyo karibu sana,

we can use a concept called trigonometric parallax.

tunaweza kutumia dhana inayoitwa "trigonometric parallax".

The idea is pretty simple.

Wazo hili ni rahisi sana.

Let's do an experiment.

Tufanye jaribio.

Stick out your thumb and close your left eye.

Elekeza gumba lako na ufumbe jicho lako la kushoto.

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

Sasa, fumbua jicho lako la kushoto na ufumbe jicho lako la kulia.

It will look like your thumb has moved,

Itaonekana ni kama gumba lako limesonga,

while more distant background objects have remained in place.

wakati ambapo vitu vingine vilivyo mbali kwenye usuli vimebaki pale pale.

The same concept applies when we look at the stars,

Wazo hilo linatumika tunapotazama nyota,

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

lakini nyota za mbali ziko na umbali mkubwa sana kuliko mkono wako,

and the Earth isn't very large,

na dunia sio kubwa sana,

so even if you had different telescopes across the equator,

kwa hivyo hata kama ungekuwa na darubini tofauti kwenye ikweta,

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

huautaona mbadiliko mkubwa wa nafasi.

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

Badala ya hivyo, tunatazama mabadiliko ya msimamo wa nyota baada ya miezi sita,

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

msimamo nusu wa mzunguko mmoja wa dunia kwa jua.

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

Tunapohesabu misimamo wa nyota kwenye msimu wa kiangazi,

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

na tena kwenye msimu wa majira ya baridi, ni kama kutazama na jicho lako jingine.

Nearby stars seem to have moved against the background

Nyota za karibu zinaonekana zimesongea kwenye usuli

of the more distant stars and galaxies.

wa nyota na galaksi na nyota zilizo mbali.

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

Lakini mbinu hii inatumika kwa vitu vilivyo chini ya miaka ya mwanga elfu.

Beyond our own galaxy, the distances are so great

Kupita galaksi yetu, umbali ni mkubwa sana

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

kiasi cha parallax ni ndogo sana kuchunguza na vyombo vyetu vyovyote.

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

Kwa hivyo kwa wakati huu inabidi tutumie mbinu nyingine

using indicators we call standard candles.

kutumia viashiria tunavyoita mishumaa ya kiwangogezi.

Standard candles are objects whose intrinsic brightness, or luminosity,

mishumaa ya kiwangogezi ni vile vitu ambavyo mwangaza wao

we know really well.

tunaujua vizuri sana.

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

Kwa mfano, kama unaujua mwangaza wa taa lako,

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

na umuulize rafiki yako alichukue hilo taa na atembee mbali na wewe,

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

unajua kiasi cha mwangaza utakayopata kutoka rafiki yako

will decrease by the distance squared.

itapungua na umbali.

So by comparing the amount of light you receive

Kwa hivyo kufananisha kiasi cha mwanga utakayopata

to the intrinsic brightness of the light bulb,

na mwangaza wa taa ile,

you can then tell how far away your friend is.

unaweza kujua umbali wa rafiki yako.

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

Kwa somo la falaki, taa lako linakua aina spesheli ya nyota

called a cepheid variable.

inayoitwa "cepheid variable".

These stars are internally unstable,

Nyota hizi hazina msimamo wa kindani,

like a constantly inflating and deflating balloon.

kama baluni inayofutuka na kutoa hewa.

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

Na kwa ajili kufutuka na kupoteza hewa inarekebisha mwangaza wao,

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

tunaweza kuhesabu mwanga wao kwa kuhesabu muda wa mzunguko huo,

with more luminous stars changing more slowly.

na nyota zilizo na mwanga nyingi na zinazobadilika polepole.

By comparing the light we observe from these stars

Kwa kufananisha mwangaza wa nyota hizi

to the intrinsic brightness we've calculated this way,

kwa mwangaza tuliohesabu kwa mbinu hii,

we can tell how far away they are.

tunagundua umbali wao.

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

Kwa bahati mbaya, huu sio mwisho wa hadithi.

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

Tunaweza kutazama nyota zilizo takriban miaka milioni arubaini ya nyota pekee,

after which they become too blurry to resolve.

Baada ya hapo, hazionekani vizuri.

But luckily we have another type of standard candle:

Kwa bahati nzuri tunayo aina nyingine ya mshumaa:

the famous type 1a supernova.

ya umaarufu aina ya "1a supernova".

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

"Supernovae", milipuko mikubwa ndio moja wa njia ambazo nyota hufa.

These explosions are so bright,

Milipuko hii ina mwangaza sana,

that they outshine the galaxies where they occur.

inashinda mwangaza wa galaksi zilipo.

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

Kwa hivyo tunaposhindwa kuona nyota moja-moja ya galaksi,

we can still see supernovae when they happen.

bado tunaweza kuona "supernovae" zinapotokea.

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

Na aina ya "type 1a supernovae" inaweza kutumika kama mishumaa

because intrinsically bright ones fade slower than fainter ones.

kwa ajili zilizo na mwanga mkubwa sana hufifia polepole kushinda zile dhaifu.

Through our understanding of this relationship

Kwa kuelewa uhusiano huu

between brightness and decline rate,

kati ya mwanga na kiwango cha kufifia,

we can use these supernovae to probe distances

tunaweza kutumia "supernovae"kupata umbali

up to several billions of light years away.

wa bilioni kadhaa ya miaka ya mwanga.

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

Lakini ni nini umuhumu wa kutazama vitu vilivyo mbali nasi?

Well, remember how fast light travels.

Basi kumbuka kasi ambao mwangaza husafiri.

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

Kwa mfano, mwangaza wa jua unachukua dakika nane kutufikia,

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

kumaanisha kuwa mwangaza tunaouona sasa hivi ni picha ya jua dakika 8 zilizopita

When you look at the Big Dipper,

Unapoiangalia "Big Dipper",

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

unaangalia jinsi ilivyokuwa miaka 80 iliyopita.

And those smudgy galaxies?

Na galaksi zisizoonekana vyema?

They're millions of light years away.

Zina umbali wa mamilioni ya miaka ya mwangaza .

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

Imezichukua mamilioni ya miaka kutufikia.

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

Kwa hivyo ulimwengu wenyewe kwa njia, ina mashine ya wakati.

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

Tunapotazama mbali zaidi, tunagundua ulimwengu mchanga zaidi.

Astrophysicists try to read the history of the universe,

Wanaastrofysiks hujaribu kusoma historia ya ulimwengu,

and understand how and where we come from.

na kugundua lini na wapi tunapotoka.

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

Ulimwengu unaendelea kututumia habari kwa njia ya mwangaza.

All that remains if for us to decode it.

Kilichobaki ni sisi kuisimbua.