How do they calculate star distance?

[Turtle]

___Just an observation on the GPS question; the satellites belong to the US military & they intentetionally introduce errors into the signal that civilian GPS units receive, This is to prevent some terrorist from using a GPS in a missle. The military has access to the full accuracy of the system; as the others have said, GPS has nothing to do with star distances. :surprise:

[goku]

i understand now, when calculating star distances a totally differant system is used.

one that can not be tested, questioned, or disputed. this way the scientists will always have something to say or some numbers to give so they don't look ignorant.

short distance= easy

long distance= difficult

GPS= short distance

stars= long distance

turtle you're probably right. i've always thought with our current technology GPS should be accurate to about a foot, half a foot.

[Erasmus00]

i understand now, when calculating star distances a totally differant system is used.

one that can not be tested, questioned, or disputed. this way the scientists will always have something to say or some numbers to give so they don't look ignorant.

 

Are you trying to be difficult? Many people have explained the method, it is based on simple trig. Try googling cepheid variable star and parallax triangulation for even more explanations. You act as if there is this global scientific conspiracy to hoodwink the unsuspecting.

-Will

[nkt]

___Just an observation on the GPS question; the satellites belong to the US military & they intentetionally introduce errors into the signal that civilian GPS units receive, This is to prevent some terrorist from using a GPS in a missle. The military has access to the full accuracy of the system; as the others have said, GPS has nothing to do with star distances. :surprise:

Actually, Selective Availability (SA) was turned off by Clinton, and the USA has basically given its word to never, ever turn it back on globally, since everyone relies on it now.

 

SA is quite simple. They introduce jitter into the times on the GPS sats. so that the errors go up by about 10x. For a civilian system, which gives ten meters accuracy, this means you are suddenly 100 meters out, but the military system, accurate to just 1 meter, is only ten metres out.

 

Of course, people being clever means that the state-of-the-art for GPS is now down to well under a 10cm error after a few hours. For taking spot point readings, it can't be beaten. Google for "differential GPS".

 

Oh, and GPS is nothing like state of the art. Those GPS sats. are 30 or more years old. The new EU sats. are going to be state of the art! (for ten years ago!)

 

i understand now, when calculating star distances a totally differant system is used.

one that can not be tested, questioned, or disputed. this way the scientists will always have something to say or some numbers to give so they don't look ignorant.

You have such an attitude problem. Open your mind. Get a ruler, and learn the basic maths trick that is triangulation. I remember working it out and learning it for myself at Primary school, in response to a neat little computer game/program we had in the classroom.

 

You can test GPS in your head as a thought experiment, you can triangulate by pointing to objects or drawing on paper. The way to test the brightness distance measurements has been outlined above, though I doubt you understood it well enough to realise that you could check it with nothing more than a maglite and a moonless night.

 

Science is not some huge conspiracy of everyone else vs. YOU. And if you do honestly believe it is, why do you trust a computer designed and built by THEM! to send your messages and not alter what you say in your sleep? :surprise:

[goku]

You have such an attitude problem. Open your mind. Get a ruler, and learn the basic maths trick that is triangulation. I remember working it out and learning it for myself at Primary school, in response to a neat little computer game/program we had in the classroom.

3,4,5 measurements of a 90 degree triangle

The way to test the brightness distance measurements has been outlined above,

the only way to test BDM is to know how bright the star is from a short distance.

 

Science is not some huge conspiracy of everyone else vs. YOU.

i was thinking more like scientists vs. everyone else.

 

could there be the smallest possibillity that scientists don't know how far away the stars are?

[CraigD]

___Just an observation on the GPS question; the satellites belong to the US military & they intentetionally introduce errors into the signal that civilian GPS units receive, This is to prevent some terrorist from using a GPS in a missle. The military has access to the full accuracy of the system

The feature you describe, ”selective availability”, was turned off 5/1/2000. Given equal quality receivers, civilians now enjoy the same GPS precision as the military. In the event of an attack on the US, selective availability would be reactivated.

 

Now that selective availability is turned of, Differential GPS (a fixed station at a precisely known position relays a GPS reading to a movable receiver), also known as Wide Area Augmentation System, which before 5/1/2000 had accuracy of +-5-10 m, has accuracy as great as about +-20 cm, though the accuracy decreases with distance from the DGPS ground station (by about 70 cm/100 km to 20 cm/100 km, depending on the specifics of the system). You can get a WASS-enabled receiver in the $200-300 range that’s accurate to +-3 m 95%+ of the time from Garmin and other vendors.

[CraigD]

… could there be the smallest possibillity that scientists don't know how far away the stars are?

Of course there is a possibility that distant, or even nearby star distance measurements are very wrong.

 

Most people who have thoroughly studied the subject believe this possibility is very slight. Perhaps the most compelling reason to believe that current estimates of star distances are reasonably correct is that so many dissimilar methods independently measuring the distance to stars yield close to the same estimates. Also, many different astronomers and observatories in many different countries reach nearly identical results. It’s hard to imagine why all of these people would lie, or feign false certainty.

[Qfwfq]

could there be the smallest possibillity that scientists don't know how far away the stars are?

There is a HUUUUUGE possibility of it.

 

It's actually for sure that we don't know how far away the stars are. We only have a rough idea of their distance, but it's a good idea considering what we are talking about. Have you ever tried studying the stuff that's taught in a first year physics lab course? It only takes basic math and a few everyday materials, they show you that typical measurements in physics have some uncertainty, they teach how to handle the data and various techniques from standard deviation, weighted averages, how to propagate errors through calculations...

 

When you look at publications of experimental researchers, they give all measured values also specifying the uncertainty. I wouldn't say they hoodwink anyone or hide their ignorance.

[Pyrotex]

...i was thinking more like scientists vs. everyone else.

could there be the smallest possibillity that scientists don't know how far away the stars are?

Actually, goku, you are NOT thinking like a scientist at all. You are thinking dogmatically. You are asking the WRONG questions.

 

"Is there a possibility that scientists don't know...?" is a pointless and meaningless question. The PROPER question to ask is "What is the probable error in current measurements of distance to the stars?"

 

The answer is, for the very closest stars (within 100 lightyears) the error is quite small, around 1% or less. Beyond 1,000 lightyears, the error goes up to around 10% or more. At galactic distances, the error goes from 10% to maybe 25% or more. But considering the distances, that's not too bad.

 

And here's the central fact which you should either understand, or go away and leave us alone. The distances to even the closest stars are being re-measured and re-measured and re-measured. Every time they build a new telescope. Every time they have a new class of students. Every time someone thinks they have a better or more accurate way of measuring. Every time a new kind of sensor device is invented. It goes on and on and on, goku. Science does NOT just take one measurement and then decide it's "gospel". Science constantly attempts to whittle its errors down.

[InfiniteNow]

Also, since the stars are always moving, the distance itself is always changing. How far away is that moving airplane? Well, it WAS 500m... then it WAS 530m... then it WAS.... damn, now I can't see it anymore.

[Qfwfq]

And here's the central fact which you should either understand, or go away and leave us alone.

I wouldn't say that Goku was bugging anybody. :hihi: No need for remarks of this kind.

[C1ay]

Actually, goku.....

Actually, you are resurrecting a thread to flame someone that has not visited the site since before Christmas....:hihi:

[nkt]

And here's the central fact which you should either understand, or go away and leave us alone.

 

Actually, you are resurrecting a thread to flame someone that has not visited the site since before Christmas....

Oh, delicious irony!

[Pyrotex]

Oh, delicious irony!

:hihi: Mea culpa.

:pirate: Mea maxima culpa.

:pirate: Mea maxima ironicus culpa.

 

Please, someone shoot me, and stop the pain.

[Boerseun]

It takes a big man to laugh at himself.

It takes a bigger man, however, to laugh at that man.

[Pyrotex]

It takes a big man to laugh at himself.

It takes a bigger man, however, to laugh at that man.

Thank you! I'm still laughing...

... :cup: ouch!

... :) ouch!

... :hyper: ouch!

... :note: ouch!

... :) ouch!

[ingannilo]

WOW! A number of long time questions of mine have been answered in this thread! You guys and Hypography ROCK!