How do you calculate lightyears distance?

Question

If going to the next closest galaxy will take us millions of years when going in speed of light, how do we know how far they are without actually living the millions of years to find out the answer? What's the method used? thanks!

Answer 1

Well, we look at the light and determine "this light is about a million years old." :-) Not really, but that's the general idea.

For galaxies of very large distance, we can determine how fast the galaxy is receding from us. The easiest way is the Doppler shift - we can see the galaxy (obviously) and therefore astronomers can determine how big it is, what type of stars must be in them, and therefore what color light we should see. However, the light is slightly redder than what models predict (and what nearby galaxies have). We can measure this "red shift", plug it into Doppler's equation, and determine how fast the galaxy is moving. (This is similar to how when a police siren passes you, it drops its pitch - and how much it changes is proportional to how fast the police car is going.)

Then there's a nice relationship called Hubble's Law, which states that the farther a galaxy is from us, the faster it's receding. This is a consequence of the Big Bang, and indeed the constant in this equation must be the reciprocal of the age of the universe. So we can then estimate (within a few thousand years or so) how far the galaxy must be from us.

For closer galaxies, there are some other techniques. There are certain types of variable stars (stars that, every few hours or days, increase and decrease their brightness) that in order to be stable must vary between two known brightnesses. Of course the brightness isn't exact, but the average among the thousands of variables in a galaxy is very close to exact. Now when we measure brightness (actually, apparent magnitude) from Earth, we see stars dimmer if they're farther from us. But because we know the absolute magnitude of these variables, and we can measure their apparent magnitude, we can calculate the distance we must be for them to become this much dimmer.

There are actually a lot of techniques, which work better for certain distance ranges. Look up the "distance ladder" if you're interested.

Answer 2

A light-year is a unit of length used by astronomers to measure interstellar distance (the distance between stars). A light-year is defined as the distance that light will travel in a year. If the speed of light is 186,000 miles per second (300,000 km per second), then calculate the distance that light will travel in one year. Express your answer in miles per year. [Note: Cancel similar units above and below the dividing line. This process is known as "dimensional analysis."]
Solution:

186,000 mi/sec x 60 sec/min x 60 min/hr x 24 hr/day x 365 days/yr

Answer 3

You're forgetting the time dilation effect when an object is going extremely close to the speed of light. I believe Poul Anderson, in his novel Tau Zero, calculated that if you could get up to 0.99999c, your experienced time would be on the order of decades. Of course, the rest of the universe would age millions of years in the meantime.

Equation to use is:

t = t0 * (1 - (v^2)/(c^2))^0.5 where t is experienced time by the object traveling at velocity v, t0 is experienced time by the universe and c is the speed of light.

Answer 4

i do no longer think in doing all your homework for you, yet i'm going to help clarify. . it would help you to conceptualize what you're doing via finding on the good distance of figuring this out. do no longer forget that for the duration of geometry, in case you already know the two the scale of an attitude of an isosceles triangle, and the scale of the alternative area, you are able to calculate the different angles and lengths, as nicely by way of fact the peak of the triangle, which corresponds to the gap of the celebrity. So, you already know that the scale is finished six months aside, and that the Earth is via definition a million AU from the solar, so the scale of the area is two AU, and the attitude is 0.01 arcseconds. understanding there are 3600 arcseconds in a million degree you ought to transform the attitude into ranges, and understanding a million AU is extra or less ninety 3 million miles, you ought to subsequently calculate the gap to the celebrity. you will possibly additionally be doing a great form of tedious conversions of arcseconds into ranges, and AU or miles into easy-years and parsecs. . yet...there is the straightforward way. all of us understand that a celebrity with a parallax of a million arcsecond has a distance of a million Parsec, and we've a formulation: d=a million/p, the place d is the gap to the celebrity and p is the parallax attitude in arcseconds. in simple terms plug on your p fee (parallax attitude) into the formulation, and you have your answer in parsecs. To get the fee in easy-years, multiply that via 3.26. .

Answer 5

Within our galaxy, we can determine the distance to stars by measuring their positions from opposite points of the Earth's orbit, and tringulating. This gives us a distance to local stars. Knowing the distance to stars, we can determine their absolute luminosity. Using temperature / luminosity rules for nearby variable stars, we can observe stars in nearby galaxies, and infer their distances from their temperature. We use inferences from other phenomena such as novas and supernovas (which can be almost as bright as the rest of the galaxy) to infer distances to more distant galaxies. Finally, there is a relationship between the distance to a galaxy and the rate it is receding as measured by redshift. The most distant galaxies distances are determined by their redshifts.

The nearest giant galaxy is Andromeda, 2,560,000 ly away. The Magellanic clouds are much closer, 168,000 and 200,000 ly away.

Answer 6

the speed of light is 3 lakh km per second. so the distance it will cover in one year (365 days) nonstop will be one light year. so we just guess that how many years it will take to for light to cover the distance between galaxies and then term the results (in years) as so and so light years.

Answer 7

Distances to galaxies that far away are estimated by the red shift of light from known objects, and by the luminosity of Cepheid variable stars. Link to cepheid info

Answer 8

One light year is 6 trillion miles. Simple as that.