# How do we see light-years away?

We will know which stars to visit. Our descendants will then skim the light years, the children of Thales and Aristarchus, Leonardo and Einstein.

Staring at the stars was like staring backward in time, since some stars are so far away that their light takes millions of years just to reach us. That we see stars not as they look now, but as they were when dinosaurs roamed the earth. The whole concept just struck me as amazing somehow.

There is much that science doesn’t understand, many mysteries still to be resolved. In a Universe tens of billions of light-years across and some ten or fifteen billion years old, this may be the case forever. We are constantly stumbling on new surprises.

Now whenever we watch a Star Wars film, we find myself wondering how the Empire had the technology to make long-distance holographic phone calls between planets light-years apart, and yet no one had figured out how to make a remote-controlled TIE Fighter or X-Wing yet.

Paste might just be my favourite music magazine. They have shed light on many incredible, under-appreciated folks over the years, helping me find new tunes to accompany me through life. We were honoured to give a song in return.

## Light-year in general

For most space objects, we use light-years to describe their distance. A light-year is the distance light travels in one Earth year. One light-year is about 6 trillion miles (9 trillion km). That is a 6 with 12 zeros behind it!

If there’s one thing we’ve experimentally determined to be a constant in the Universe, it’s the speed of light in a vacuum, c. No matter where, when, or in which direction light travels, it moves at 299,792,458 meters-per-second, traveling a distance of 1 light-year (about 9 trillion km) every year. It’s been 13.8 billion years since the Big Bang, which might lead you to expect that the farthest objects we can possibly see are 13.8 billion light-years away. But not only isn’t that true, the farthest distance we can see is more than three times as remote: 46.1 billion light-years. How can we see it so far away?

### What is a Light-year?

A light- time is a dimension of distance and not time (as the name might indicate). A light- time is the distance a ray of light peregrination in a single Earth time, which equates to roughly 6 trillion country miles (9.7 trillion kilometres).

On the scale of the macrocosm, measuring distances in country miles or kilometres is clumsy given the exceedingly large figures being bandied. It’s important simpler for astronomers to measure the distances of stars from us in the time it takes for light to travel that breadth. For illustration, the nearest star to our sun, Proxima Centauri, is 4.2 light- times down, meaning the light we see from the star takes a little over four times to reach us.

### Can You see the past from Light years Away?

While sound peregrination is about a kilometre every three seconds, light peregrination kilometres every second. When we see a flash of lighting three kilometres down, we’re seeing commodities that happened a hundredth of a millisecond ago. That’s not exactly the distant history.

But as we look further amiss, we can blink further back. We can see seconds, twinkles, hours and times in history with our own eyes. Looking through a telescope, we can indeed look further into history.

The night sky is full of stars, and those stars are incredibly distant. The distances are measured in light times, which corresponds to the distance travelled by light at one time. That’s about 9 trillion km.

Nascence Centauri, the nearest star visible to the unaided eye, is at a distance times the distance between Earth and the Sun. That’s 4 light times, so we see Alpha Centauri as it was 4 times agone.

Some bright stars are much more distant still. Betelgeuse, in the constellation Orion, is about 640 light times away. However, we wouldn’t know about it for centuries, if Betelgeuse exploded hereafter (and it’ll explode one day).

Indeed, without a telescope we can see much further. The Andromeda world and the Magellanic Shadows are fairly near worlds that are bright enough to be seen with an unaided eye.

The Large Magellanic pall is a bare light times down, while Andromeda is 2.5 million light times down. For comparison, ultramodern humans have only walked the Earth for about a time.

With an unaided eye, you can look millions of times into history, but how about billions? Well, you can do that at the eyepiece of an amateur telescope.

Quasar 3C 273 is an incredibly luminous object, which is brighter than individual worlds, and powered by a huge black hole.

But it’s times fainter than what the unaided eye can see because it’s 2.5 billion light times down. That said, you can spot it with a 20 cm orifice telescope.

A bigger telescope allows you to blink indeed further into space, and I formerly had the pleasure of using an eyepiece on a 1.5-metre periphery telescope. Quasar APM 08279 5255 was just a faint fleck, which isn’t surprising as it’s 12 billion light times down.

Earth is just 4.5 billion times old, and indeed the macrocosm itself is 13.8 billion times old. Fairly many people have seen APM 08279 5255 with their own eyes, and in doing so they (and I) have looked back across nearly the entire history of our macrocosm.

So when you look up, remember you aren’t seeing the effects as they’re now; you ’re seeing the effects as they were.

Without really trying, you can see times in history. And with the aid of a telescope, you can see millions or indeed billions of times in history with your veritably own eyes.

## How many years is a light-year away?

A light- time or light-year (symbol ly) is a unit of dimension of length, specifically the distance light travels in a vacuum at one time.

While there’s no authoritative decision on which time is used, the International Astronomical Union (IAU) recommends the Julian time.

A light-time is equal to km (about9.461 Pm; enactment country miles; about astronomical units or about 0.3066 parsecs.

The exact length of the light- time depends on the length of the reference time used in the computation, and there’s no wide agreement on the reference to be used.

The numbers over are grounded on a reference time of exactly 365.25 days (each of exactly SI seconds).

Many exemplifications of distances for light to travel are Reflected sun from the Moon’s face takes 1.3 seconds to travel the 4.04 × 10-8 light times to Earth.

It takes 8.3 twinkles for light to travel from the Sun to the Earth (a distance of 1.58 × 10-5 light- times).

The most distant space inquiry, Voyager 1, was 13 light hours ( only 1.5 × 10-3 light times) down from Earth in September 2004.

It took Voyager 27 times to cover that distance.

The nearest known star ( other than the Sun), Proxima Centauri, is 4.22 light times down.

The centre of our world, the Milky Way, is about light times down.

### How can we see 46.1 billion light-times down in 13.8 billion year old Universe?

We can start by imagining a Universe where the most distant objects we could see really were 13.8 billion light-times down. For that to be the case, you’d have to have a Universe where

• objects remained at the same, fixed distance from one another over time,
• where the fabric of space remained stationary and neither expanded nor contracted over time,
• and where light propagated through the Universe in a straight line between any two points, no way being diverted or affected by the goods of matter, energy, spatial curve, or anything differently.

Still, y, and z axis — where space itself is fixed and unchanging, If you imagine your Universe to be a three-dimensional grid — with an. Objects would emit light in distant history, that light would travel through the Universe until it arrived at our eyes, and we’d admit it the same number of “times” latterly as the number of “light-times” the light travelled.

In the environment of Einstein’s General Relativity, this led to a sure-fire conclusion that the Universe was expanding.

This is indeed more profound than people generally realize. The fabric of space itself doesn’t remain constant over time, but rather expands, pushing objects that aren’t gravitationally bound together piecemeal from one another. It’s as if individual worlds and groups/ clusters of worlds were raisins bedded in an ocean of unnoticeable (space-suchlike) dough, and that as the dough leavened, the raisins were pushed piecemeal. The space between these objects expands, and that causes individual objects to appear to retire from one another.