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We can't use parallax to measure a stars distance from the Earth if the star is already too far away. The angles used in parallax measurment are already very small, and if the star is beyond a certain distance from us the angle becomes too small to measure, and no distance can be determined.
To date the largest distance that can be measured using parallax, with the Hipparchos sattelite, is about 1 600 light years. This will be improved with the European Space Agencies Gaia mission in 2012 and 2013.
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∙ 13y ago
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Parallax can't be used on a star if the star is too?
Close.
Why can parallax only be used to measure distance to star that are relatively close to earth?
At farther distances, the parallax becomes too small to measure accurately. At a distance of 1 parsec, a star would have a parallax of 1 second (1/3600 of a degree). (The closest star, Toliman, is a little farther than that.) At a distance of 100 parsecs, the parallax is only 1/100 of a second.
If a star's parallax angle is too small to measure what can you conclude about the star's distance from earth?
It means that the distance is greater than a certain amount - depending on how precisely you can measure the parallax.
If a star's parallax angle is too small to measure what can you conclude about the star's distance from the earth?
It means that the distance is greater than a certain amount - depending on how precisely you can measure the parallax.
Why can't astronomer measure the parallax of a star that is a million lights away?
The farther the object, the smaller its parallax. In this case, the parallax is about 1/300,000 of an arc-second (and an arc-second is 1/3600 of a degree) - way too small to measure. Perhaps you will eventually find a way to measure smaller parallax angles.
If a star's parallax angle is too small to measure what can you conclude about the stars distance from earth?
You can conclude that it is farther than a certain distance. How much this distance is depends, of course, on how accurately the parallax angle can be measured.
Why can't the parallax effect be used to measure distances to other galaxies?
The parallax angle of such distant objects is way too small to be measured. In general, the farther away an object, the smaller is its parallax angle.
If a star's parallax is too small to measure does that mean that it is close or far from Earth?
Nearby stars have a larger parallax angle.
Considering that the more distant an object is the smaller the angle it will make why would parallax measurements be better suited for stars than for galaxies?
At larger distance, the parallax becomes smaller, and therefore harder to measure. Even the closest star (Toliman) has a parallax of less than one arc-second (1/3600 of a degree), which is difficult to measure. Stars that are farther away have a much smaller parallax.
Would it be possible to measure star distances using telescopes in orbit around the Moon and Mars?
In principle yes but an orbit round the Moon is too small to make it worth doing. An orbit round Mars would also be too small. The present system uses the Earth's orbit as the base line, and parallax measurement works by measuring the exact position of a nearby star agains the background of distant stars at intervals of 6 months at opposite sides of the Earth's orbit. The parallaxes are so small that it took until the 1800s for any parallax to be discovered. Before then the lack of parallax was always used as a genuine reason that the Earth could not be moving.
Most stars have such small parallax shifts that accurate measurement is always possible?
On the contrary, if the parallax angle is too small, it can't be measured accurately.
If a star's parallax angle is too small to meaure what can you conclude about the star distance form earth?
It means that its distance is farther than can be detected. For example, if the smallest angle that can be detected is 1/100 of an arc-second, it would mean that the star is farther than about 100 parsec.
