Hi All,

 

I understand the mathmatical and geometric principles involved in calculating the distance to the nearest stars using Parallax.

 

However, all the examples I can find use a star that is conveniently 90 degress from the earth-sun-earth line - obviously to provide the basis for right angle triangle calculations.

 

What I don't understand is how this method would be used for example when you look up into the night sky say in the summer and a star is to the right of the perpendicular and then when you look up again at the same star 6 months later (on the other side of the sun) and the star has moved but is still to the right of perpendicular - how could Parallax be used in this case ?- see attached diagram.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Parallax calculation means looking at the apparent motion relative to a much more distant object. Your diagram doesn't show this.

wiki has a good coverage on the basics of stellar parallax including a diagram

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

Hi All,

 

I understand the mathmatical and geometric principles involved in calculating the distance to the nearest stars using Parallax.

 

However, all the examples I can find use a star that is conveniently 90 degress from the earth-sun-earth line - obviously to provide the basis for right angle triangle calculations.

 

What I don't understand is how this method would be used for example when you look up into the night sky say in the summer and a star is to the right of the perpendicular and then when you look up again at the same star 6 months later (on the other side of the sun) and the star has moved but is still to the right of perpendicular - how could Parallax be used in this case ?- see attached diagram.

The Earth travels in a nearly circular orbit around the Sun. So by picking the correct dates for your measurements you can always assure a 90 degree angle between star direction and the Earth-Sun_Earth Line. In your example for instance, you would make your measurements in Spring and Fall rather than Winter and Summer.

Many thanks for your replies, specially Janus who provided a very short but very usefull explanation of my particular issue.

 

Best Regards to all.

 

Dart15