The distance of far space objects are defined with "light year".How is it measured?

Answer 1

By using the method of trigonometric parallax, astronomers were able to measure distances to the Moon and planets in the solar system. However, this failed miserably when astronomers tried to find the distances to stars. This is because the Earth is too short a baseline when calculating distances as immense as those to stars. It wasn't long before astronomers came up with the idea to use opposite sides of the Earth's orbit around the Sun. By doing so, a baseline of nearly 300 million km (186 million mile s) becomes available for measuring distances to stars.
In 1838, German astronomer F.W. Bessel used this method to measure the parallax of a star – 61 Cygni. He found its annual parallax to be one-third of an arc second (about one-thousandth of a degree) and thus calculated its distance from Earth to be over 100 million million km (62 million million miles). But such numbers are too big for daily use, so instead astronomers devised a system that measured astronomical distances in light-years or parsecs.
A light-year is based on the distance light travels in a single year. The speed of light is constant – it is always approximately 300,000 km/s (186,300 miles/s) – so light moves about 10 million million km (6 million million miles) in a year. It takes 11 .2 years for light from 61 Cygni to reach us, so 61 Cygni is 11.2 light years away. Parsec (pc) is a unit which is widely used by astronomers, mainly because it is linked to parallax measurement. 1 parsec equals 3.26 light-years. So 61 Cygni's distance fr om Earth In parsecs is 3.43.
Trigonometric parallax may be an excellent method to measure distances of nearby planets and stars, but it becomes useless when measuring distances beyond 1,000 light-years. As such, astronomers have to use indirect means of measurement. These allow them to determine the distances to remote objects millions and even billions of light-years away.
Most indirect methods use what are called "standard candles" – objects whose real brightnesses are known. If an object's absolute magnitude (luminosity) is known, then its distance can be calculated with how bright it seems from Earth

Answer 2

The distance to stars within a couple hundred light years can be measured by their parallax, which is basically triangulation using the Earth's orbit as the base line. When using this method, the distance is calculated in parsecs, where a parsec is the distance that causes a parallax of one arc second.

A light year is just a made up number that is equal to the distance light would travel in a year. There is no real connection between the unit called "light year" and the methods used to measure the distance to stars.

For stars more than a few hundred light years away, the parallax is too small to measure so they use various indirect methods usually related to calculating the actual brightness of the star from physical models and measuring how dim it looks from Earth.

Answer 3

It is based on a system that calculates the apparent brightness of stars and galaxies.
Pulsars are believed to be the same in all areas of the universe.
By assuming the brightness and estimating the distance of nearby pulsars they estimate the brightness of galaxies and from this their distance.
The estimates could have errors of as much or more than 50%.
Until something better comes along this will have to suffice.

Answer 4

A light year is the distance light travels in one year. Since light goes 186,282 miles in a second, a light year is a very large distance. None the less, the distances to even close stars are several light years and the distance across our galaxy is around 100,000 light years. In other words, it would take light around 100,000 years to go across our galaxy. For light to get to the Andromeda spiral galaxy would take over 2 million years!

Answer 5

We had a presenter come into class and explain this just yesterday. A light year is the amount of time it takes light to travel in a year. Light travels at 186,000 miles per second, or 5,865,696,000,000 miles per year. So it's an easier way of saying something is 5,865,696,000,000 miles away.

Answer 6

Hi. The nearer stars can be directly measured by parallax. (Observe with Earth at one side of it's orbit, then again six months later. Triangulate) Every other measurement builds on this.

Answer 7

Light travels at 186,000 miles per second. (297,600 km)
1 light year is the number of miles light will travel in 1 year.

(365.25 x 24 x 60 x 60 x 186,000 miles/year).
(365.25 x 24 x 60 x 60 x 297,600 km/year)

Answer 8

A light year is the distance light travels in a year (about 5 trillion miles or 9.5 trillion kilometers)

Answer 9

A light year is the distance light will travel in a year. It is equal to about 9,460,730,472,580.8 km.