If stars are billions of years away...?

Question

And we judge their distance by their light, then that would mean we are looking at what billions of years ago looked like. How could anyone figure out the vastness of the universe if the information we depend on is billions of years out of date?

Answer 1

Everyone seems to use billions too freely. Yes there are galaxies billions of light years away, but most of the stars you can see with the naked eye are within 1000 light years. Some, like bright stars Sirius and Alpha Centauri are less than 10 light years away.

But a light year is a huge figure - it is nearly 6 million million miles. At 4.3 light years away, Alpha Centauri is nearly 10,000 time as far away as Neptune on the edge of our planetary system, and just about a quarter million times as far from us as the sun.

So, in the scheme of things, when the universe is 15 billion years old, who cares that the light from the star Canopus is 1200 years old.

And, yes, if the light from distant galaxies and quasars are billions of years old, those objects will not be the same now, but that does not stop us from gaining knowledge of the universe, past and present.

Answer 2

We look back in the past when we look at anything because the light from the object always takes some time to travel to our eye. The farther away the object is, the farther back in time we look. For Earth based things, the time period is short enough that we consider what we see a few miles away as present time but when looking into soace, yes, some of the light has been traveling for millions, even billions of years.

We do not know the universe as it actually exists right now but for most things in the local universe, we can assume it looks much the same now as we are seeing it. Maybe some stars no longer exist or have changed phase but space is so vast and it takes things so long to travel a noticable distance from our perspective that it's almost as if the stars we see in the sky have barely moved....just a few inches in fact.

This becomes less true the farther away things get though.

Answer 3

Every single star you can see in the night sky (without a VERY powerful telescope) is right here in our own galaxy -- so none of them are billions of light-years away, the furthest is only a few hundred thousand light years away.

We see lots of other galaxies in big telescopes, ranging from a couple of million to many billion light years away -- but we're unable to resolve individual stars in any that are more than a few million light years away -- except for the occasional supernova.
Within our galaxy, and with some nearby galaxies, we can use stars (such as cephied and RR Lyrae variable stars) to help figure out distances. Where we can't resolve stars, we use Type IA supernovae and galaxy red-shifts to help determine distances, as well as gamma-ray bursts. Fortunately, we can infer a lot about even those very distant galaxies, since the laws of phyiscs are the same everywhere in the universe...so we can use orbital periods and velocities to determine masses of galaxies, and use masses of galaxies to determine absolute magnitudes (brightness), etc.
Things to get more uncertain (meaning the bounds of error on measurements gets bigger) as you go further out, but it doesn't mean we can't measure anything that far away.

Answer 4

ok this is kind of a wierd question but according to relativity no matter can travel faster than light, and since everything in the universe came from one point, we can look in any direction and see where all these stars were billions of years ago. there is also this thing called "red shift" or "blue shift" which is caused by how fast something is moving away from us. by measuring the shift in color, we can determine how fast the thing we are looking at is moving away from us and since we know how far it is away from us we just have to multiply its distance in light years by its speed and we can figure out where the object is today. theres alot of math involved, but its still possible to figure it out.

Answer 5

Many stars, including all the naked eye stars that make up the constellations, are much closer, a few hundred light years away. It is only distant galaxies that are billions of light years away. And a billion years is not that long in the life of a galaxy.

Answer 6

There is an error in your assumption that light traveling through space after time becomes "outdated".

Scientists have not pinpointed the age or the size of the universe, because we can only base that on what we observe. Therefore the universe as we know it is part of the "observable universe". The observable universe's size and age, however can be ascertained through multiple methods.

Observation of the cosmic background radiation, as well as measurements on the movement of galaxies and stars help us determine the size.

Answer 7

There are objects called Cephid Variables...they are star like objects whose intensity varies at a constant rate.

The rate of that intensity change is directly related to the true intensity of the star's brightness.

This means we can tell what a Cephid's TRUE brightness based on the rate of it's variation...and then using that you measure it's APPARENT brightness (how bright it appears in the sky)...then using the inverse square law you can calculate it's distance.

Answer 8

Even though the light is billions of years old, it still carries doppler shifted signatures of common elements. The amount of the red shift tells us how far away and how fast it is moving.

Answer 9

The nearest star is 4.2 light years away. We know how far away they were and how fast they were moving. This is the essence of understanding the vastness of the universe.

Answer 10

even the light that you see from the sun is 8 minutes old.
go to www.nasa.gov to look at some of the photos
that were taken by the Hubble telescope, they will make you feel very small.