A star '10 light years away' from the earth. how is this distance measured by the scientist?

Question

how light years are measured ( where even the light reaches after the several thousands years) accurately.

Answer 1

The light year is simply a unit of distance measurement, they do not use light somehow to determine how far away something is. The distance to a nearby star is measured using parallax:

http://en.wikipedia.org/wiki/Parallax

Parallax only works for very close stars. After that there are all sorts of tricks astronomers have come up with to measure the distance of objects from Earth:

http://hyperphysics.phy-astr.gsu.edu/Hba...

Answer 2

A light-year is equal to exactly 9,460,730,472,580.8 km.

Light takes about a year to travel this distance. as the distance between stars is collosal multiplied by gigantic [in other words incomprehensible by man]. Hence light is used  to measure such distances.It is very convenient way to calculate[ and sometimes estimate] the distance between astronomical objects.

Imagine this:

The distance between sun and the earth is 150 million kilometers on an average. but light takes merely 8 secs to reach our Mother earth.

henc ten light years means 9,460,730,472,580.8 km x 10.[Phew!]

Answer 3

actually, a lightyear is not typically used in astronomy. Most astronomers use parsecs and AU's. However, there are different types of ways astronomers measure distances. For relativley close objects, they use parallax. Here is a link:

http://imagine.gsfc.nasa.gov/docs/ask_as...

you can also look on wikipedia.

Answer 4

The are roughly 31536000 seconds in a year. Thus light travels at

299792.458km/second. Thus if it is 10 light years away then it would be

31536000*10*299792.458 = 94542549554880 km. Scientists cannot measure it precisely since a difference of a milisecond would mean thousands of kilometers.

Answer 5

I think you have a misconception of the order of understanding.  It's not that someone says, "Oh, that star is ten light years away, let's determine how long/far it is!"

The distances to the stars are determined from parallax (triangulation).  This is very approximate, especailly for the much distant stars (for other galaxies, we seek "Cephid Variable" stars, which all have an exact light output, so thier apparent magnitude from us is a direct result of the distance).  

The speed of light was determined a few different ways, the most conclusive was when predicting eclipses of the moons of Jupiter, they seemed to not happen "precisely" when they were suppossed to.  This was because sometimes the earth and Jupiter were much closer to each other than other times...  and so, THAT led to the conclusion that it took light a time to travel a certain distance.

The term "light-year" came to be, when humans decided that a star that is so far away in miles (or kilometers) that, rather than write down a large number with 30 or 40 zeroes after it, they could just assign the amount of distance light travels in one year...  this unit of distance is called the "light year."  

The distance of a star 10 light years away is 10 light years.  To convert into miles, 186,000miles per second, times 60seconds, times 60minutes, times 24 hours, times 365.25days = the number of miles in one light year.    

Answer 6

You have a variety of answers, so I will just answer the one about measurement.  To measure the distance to a star, we precisely note it's position in the sky tonight.  In 6 months time, when the Earth is halfway round it's orbit of the Sun, we note that star's position again.  Now, because we know 2 angles and the length of our baseline, simple geometry (your math teacher always told you it would be useful one day) will tell us the height of the triangle, and the distance to the star.  As someone has correctly pointed out, this method, called the parallax method, is only useful for the nearer stars.

Answer 7

Parallax method.

If the parallax is 3.0675 arc seconds, it is 1/3.0675 parsecs away, equal to 10 LY. (1 parsec = 3.26 LY)