How to calculate distance between star and earth ?

Question

How to calculate distance between star and earth ?

Answer 1

The method used is paralax method.

Answer 2

Cepheid variables and supernova Ia  Also, look up the Doppler effect - the more something is moving, the larger a shift we see in it's spectra, and since we know the rate at which the universe is expanding, we can use that to calculate how far away it is from us.for more details

http://spaceplace.nasa.gov/en/kids/phone...

Answer 3

There are several kinds of stars, and a number of ways to collect evidence.  These things determine what formulas and the like that you need to calculate distances.

Now, let's say for the sake of argument that you're a morbidly obese 12 year old with a crush on Brittany Spears. I'm not saying you are, this is just an example. Clearly the distance between you and Brittany is going to be very large.  But the distance between Brittany and the Earth is going to be fairly small.  I mean, the Earth is where she keeps her stuff.

Now let's say that you have timed the orbits of the moons of Jupiter very carefully, and repeated the measurements over the course of a couple years.  You compute their orbits, but there is an anomaly - the Jupiter crossings take place some 16 minutes later when the Earth is on the far side of the Sun from Jupiter than when the Earth is on the near side.  You assume that this is because the speed of light is finite, and you measure the speed of light in the lab using spinning mirrors and such - a very clever and cool experiment that you should be proud of.  From that, you compute that the Sun, which is a nearby star, but not nearly has close as Brittany, for which her fans are grateful, is exactly 1 AU (what a coincidence!).

Suppose you launch a small telescope into low Earth orbit, and it measures the positions of every star brighter than 12th magnitude very accurately. (You might name the satellite Hipparcos). And it does this repeatedly at 6 month intervals.  Well, the Earth has moved 2 AU in that time, so any movement of stars has to be due to the Earth's movement.  You use some fairly simple trigonometry to determine their distances - unless the booster screws up and puts your telescope into a weird elliptical orbit, and you have to do extra work to make your data reduction come out right.

But when you do this work, you discover that there are stars that are too far away, and your small telescope's precision isn't good enough to measure any angle change.  Do you launch a bigger telescope?  No!  You develop highly sophisticated stellar evolution models, so you can compare stars whose distance and brightness you do know with the brightness of similar stars whose distance is too far.  And you also know from the lab that light's brightness goes down proportional to the square of the distance it must travel.  So you measure the the brightness, and do some fairly simple math.

And so on for Cepheid variable stars, only you're too tired to figure it out for yourself, so you look it up on Wikipedia.  And you also check out Wikipedia for type 1a super novas.  And you when even those aren't bright enough, you check out gamma ray bursts, again in Wikipedia.

And you use all this to try to figure out the Hubble Constant (which varies in time, by the way), and discover Dark Energy.

And all that to get her autograph!

Answer 4

The distance to nearby stars can be measured quite accurately using the parallax method.  To learn more read:

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

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

For stars that are beyond the reach of the parallax method, the distance can be estimated by comparing the absolute and apparent magnitudes.  The absolute magnitude can be estimated from H-R diagram based on the spectral type (which can be measured / observed with a telescope).  The apparent magnitude is measured with a photometer.  Then, applying the distance modulus equation you can estimate the distance.  This method is far less accurate then the parallax method.  Also, you need to take into account the effect of extinction, which is the absorbtion of light by dust in the interstellar medium, which can only be roughly estimated.

Answer 5

For stars that are close enough, we use parallax.

We measure the star's position from one spot in our orbit around the Sun.  We measure its position again six months later.

The difference in position gives us the angle at the tip of a large triangle (with its pointy end at the star).

The base of the triangle is the diameter of our orbit.

We cut the triangle in two: this gives us a right-angle triangle, with the right-angle (90 degrees) at the Sun, and the short side is the radius of our orbit (one astronomical unit = approximately 150 million km).

By using trigonometry, we can find the distance (hypotenuse or long side -- not much difference).

Because the small angle is always very small (always less than 1"), we can use a shortcut.

We take the inverse of the small angle and call that the distance in a unit called a "parsec" (parallax second).

One parsec = 3.261631 light-years.

This is the main method to "calculate" the distance.

There are many methods to "estimate" the distance.  They are usually based on assumptions and many of these methods use some preliminary step involving the parallax.

Answer 6

it is a simple method.

you should have a powerful laser.

you incident your laser light on the star and see how much time it takes to return back to you.

half of the time is being taken to reach the star.

So now you know the velocity of the light and the time taken by it to reach the star.

use the formula distance=speed * time

Answer 7

This strongly depends on how far away the stars are.

We can use parallax (described by other answers) for stars within a few hundred light years - which is only this part of our galaxy.

But because there are still a lot of stars within that distance we can calibrate other methods by checking they work on stars which are close enough to use parallax.

Other methods include:

RR Lyrae and Cepheid variables - which pulsate, and change in brightness. The period of the brightness change correlates closely with their absolute brightness - so we can measure the period and the apparent brighness and calculate the distance

Spectroscopic parallax: this uses the difference in density of the gas in giants , supergiant, main sequence and dwarf stars and the effect that has on the width of absorption lines.

We can estimate the size of the star this way, and use the spectrum to get the temperature and thus we know how bright they should be, so again we measure how bright they appear and calculate distance.

Supernovae: These things get very bright and then fade. How they fade (how rapidly) depends on how bright they got, so buy studying the dimming of the supernova we can work out how bright it was and thus how far away it was.

Then there's Hubble LAw - which was calibrated using these other distance measures and shows that there is a correlation between the redshift of the light and the distance of a galaxy. So simply by taking a spectrum and seeing the redshift we can calculate the distance to galaxies...

There are other methods too...