How do scientists measure distance?

Question

how do they measure distance to a place they've never been like other galaxies if they say something is a billion, trillion miles from earth how do they know

if they say something is a billion miles away is it truly a 1 billion miles away

example mars is 422 millions miles away is that 100% correct

Answer 1

Various techniques: parallax, redshift and variable Cepheid.

To measure by parallax, you basically take to pictures of the same object at two different times of the year, (about 6 months apart) so you are having two very distinct points of view of the same object. If you superimpose those images the star 'moves' by measuring that angle of motion you can by simple trigonometry have an estimate of the distance. The parallax, unfortunately only works in smaller distances. the further away an object is the smaller the shift will be and ergo the error in calculation will be bigger.

Redshift is a bit more precise but is a tad harder. When a star 'burns' its atomic fuel it emits light, we all know that. This light when passed through a prism forms a spectrum (rainbow) that has very distinct black lines sprinkled across it. This lines' distances between each other is constant and gives us a very precise chemical profile of the star. Now these lines 'shift' or slide to the red side of the spectrum the further a star is. Or to the blue side if it is getting closer. By measuring this redshift we can determine the distance.

The most precise method to measure intergalactic distances is the Variable Cepheid Stars. These stars are giant yellow stars that contract and expand ant very precise intervals due to the ionization of heliumin in their atmospheres. The luminosity (absolute magnitude) of the star is proportional to their size, thus this relationship is known as a 'standard candle' and it is compared to the 'aparent magnitude' (luminosity in Earth) and we can determine with a small margin of error their distance from us because luminosity degenerates by distance at a very well known rate.

The error is present no matter which technique you use, and all scientific papers that deal with distances mention the error margin and measuring procedure. Like Andromeda is at 2'530,000 ly away with a ± 22 kiloparsec margin of error.

Answer 2

Alex Q has a good answer. All measurements, and I mean ALL are subject to errors, whether you are measuring the length of a plank or the distance to a star.

When these measurements are reported in the scientific press the estimated errors are virtually always given. So something might be reported as 450 kiloparsecs +/- 45 kiloparsecs.

What appears in the popular media, by which I mean radio, TV or the scientific pages of a newspaper or magazine is not necessarily exactly what the original people who made the measurement wrote. It is likely to be shortened to "450 kiloparsecs".

This is not 100% correct but to be 100% correct the entire original article from the scientific press would have to be reproduced. The editors of a newspaper would not allow that as it would take up too much space and it would take up too much time on TV and radio. Apart from that, there are questions of copyright.

So if you read in a newspaper that something is 450 kiloparsecs or light years away, or 60 million years old, or weighs 3270 tonnes remember to add plus or minus 5% or 10%.

One thing you can be reasonably sure of is that if something is reported as being 2 billion miles away, then while it is unlikely to be 2 billion exactly, it is even less likely to be 20 billion or 2 hundred million miles away.

Answer 3

Many different ways. It is actually quite complicated and entire books have been written on the subject.

The farther away things are, the less reliable the distance measurement is. For distant galaxies they use the redshift. The Hubble law says that the higher the redshift of light from a galaxy the farther away it is. But that is not very accurate, maybe +-50%.
For nearby stars they can triangulate on them from opposite sides of Earth's orbit.
For the planets, we have sent space craft there. Before that it was more triangulation compbined with orbital calculations.

Answer 4

Stellar parallax was commonly used in the past. By beginning with knowledge of Earth's orbit and measureable known distances to Venus and the Sun we correlate parallax angles. To determine such long distances, three things are needed: two vantage points, the known distance between those two points, and the measurement of an angle. The largest seperation between two vantage points is used by Earth's orbit. Pictures of the object to be measured (a star for example) are taken 6 months apart and then compared with respect to background stars. Algebraic formulas are used to convert the angles into arcs then parsecs then light-years to determine a fairly accurate distance measurement.

Cepheid stars are a class of stars in the Universe which have a constant and high luminosity. Using the distances already known for some nearby Cepheids, we are able to calibrate out to great distances today. The Cepheid variable method has great precision and is the most accurate in use. The Hubble telescope recently succeeded in measuring the distnce of the Virgo Cluster at 60 million light-years.

The use of satellites will also assist in measuring distant stars and galaxies.

Measurements inside of our solar system are in astronomical units instead of light-years.

The answer to your additional question is yes.

Answer 5

They Bounce light off of them and measure the time taken and speed to calculate the distance

Answer 6

Most scientist used similar triangles to see the distance between the place they have never been to. There are special technologies that allow them to easily use triangles as a form of measing distance.

Answer 7

Stellar parallax is one way to judge distance. Also, the redshift of distant bodies is another. Yet another, I think, is measuring by the brightness of an object (apparent vs. actual brightness.)

Answer 8

Star distances are measured by red shift. In general, the further away something is the more red shift there will be. If you study astronomy you will learn how this was discovered.

Answer 9

http://www.magic.gov.uk/OnlineHelp/Measure_Distance.htm hope theres something there to help