How do they calculate the distance of a star when they have no idea when the light from that star began its. .

Question

journey

Answer 1

Light waves are measured by what color they emit. Light traveling toward you emits a different tone than that traveling away from you. By measuring the color and wavelength of a known star...The Sun, they are able to compare that known variable with that of unknowns. Light speed is a constant, but distances can be determined by the legnth of the wave, and it's color shift.

They figured this out a long time ago, but I cannot accurately describe it...I'm tired, but I hope I gave you a little good info.

Answer 2

Ok, the earth goes around the sun with in a elliptical orbit, with a diameter of roughly 186 million miles, right?

We look at the same star 6 months apart and if it is in a slightly different part of the sky, the tiny angle generates maps to the diameter of Earth's orbit. We use trigonometry to get the distance.

This is the origin of the term parsec - parallax arc-second. That means that the star is observed to move one second in angle. This is 1/3600 of a degree, and a parsec is 3.26 light years.

Now, we have the close up stars, that we can use parallax. We use those to measure the relative brightness of stars that emit various kinds of radiation. Stars that emit mostly in the blue are very bright and burn out fast. Stars that are red are generally very dim. -- this is assuming that the star is a "main sequence" star, and using the Hertzsprung-Russell diagram, which relates the wavelength of light to its mass.

Now, the assumption is that the brightest star in a cluser or galaxy is the same everywhere. So, if the star is 1/4 as bright as a comparable star, it's probably twice as far away.

This was an entire lecture during my astronomy class in college.
I'm leaving out the details about red giants, but there is good science, and distances are at best estimates.

Answer 3

Using a technique based on the polarization of light spectrum wavelengths.

Polarizing filters only pass light that vibrates at certain angles and by measuring the time differences among the various filters, the differential can then be equated at the speed of light in a vacuum, to provide a value of distance.

Answer 4

They also measure the parallax (I think that's what it is). As the Earth moves, a star can be observed at different points. The angle that the star's appearance changes is used to figure out its distance. Somehting like that.

Love Jack

Answer 5

Parallax works for close stars. As for distant objects, we have to rely on Hubble's Law, which says that distance is a linear function of relative velocity. The relative velocity we CAN measure directly using red shift comparisons.

Answer 6

Close stars are measured by parallax, as described above. More info:

http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit1/distances.html

Galaxies are measured by a really neat method. There are stars that vary in brightness up and down in a regular way, call Cepheid variables. Their brightness is known by how fast they go up and down. This was discovered by looking at close Cepheid by parallax.

So people look for these in galaxies. They measure the speed that they go up and down, get the real brightness. They know how bright they appear. That gives them the distance. More info:

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

And here's a site which discusses some really obscure ways they measure distance.

http://www.astro.ucla.edu/~wright/distance.htm

Answer 7

we just use method of triangulation. We measure the angle of direction of the star durinjg opposite positions in the orbit of earth. Then its just about calculating the distance by math.

Answer 8

Just my opinion, but I reckon a lot of these immense calculations are rough estimates at best. I mean, 100 billion billion light years is surely just a way of trying to express the unexpressible to other humans, right?

Answer 9

They use something called The RED SHIFT.