The Explanation of light years?

Question

How can scientists predict that the most distant star object, the unaided eye can see, is 2 million light years away?

Answer 1

The most distant object visible to the naked eye is M31, also known as the Andromeda Galaxy. It is a bit over 2 million light years away.

Its distace was determined by timing of Cepheid variables. These are very bright stars that brighten and fade at regular intervals. We can observe Cepheids in nearby star clusters, and when we do, we see that the brightest Cepheids have longer time periods between fading than less bright Cepheids. Further, the brightness of a Cepheid can be predicted simply by timing the period between intervals. Since we know the distance to these nearby clusters, we can determine the distance to any Cepheid simply by timing it, determining its absolute magnitude from the interval, and doing a simple computation.

Since Cepheids are intrinsically bright, some individual Cepheids within M31 can be seen by large telescopes and their periods can be timed. This gives us the absolute magnitude of the star, and therefore its distance -- and of course the distance to the M31 galaxy itself.

Answer 2

A lot of people confuse light-years with the distance light travels in a year as if it were a straight line. In fact, because of the way space in our universe is distorted on a macro-scale, the distance light travels in a year may vary. In reality, the wavelength of light gets stretched as it travels through the universe--known as cosmological red shift. Astronomers can look at a distant light source and measure the spectral and cosmological shift of the light waves and determine the amount of time the light has been traveling. That is the origin of a light year. Thus, a light year, technically, is not how far light has traveled but how long. However, the term has been adopted as a type of shorthand for cosmological distances which are so vast that they lack other analogies.

Answer 3

It's not a prediction, it's an observation. The most distant object readily visible to the naked eye is M31, the Andromeda galaxy, which is estimated to be about 2.3 million light years away.

Light years are used to describe distances like this because it's simpler than saying M31 is 13.5 million trillion miles away.

How do they know the distance? They use certain stars in the galaxy whose true brightness is known, and calculate how far away they have to be to look as dim as they do.

Answer 4

It is how far light will travel in one year..Which is a huge amount as it goes something like 180,000 miles per second.. Or something like that..The number would be too long so they use light years

Answer 5

the distance light travels in a year