# Parallax method

1. May 18, 2010

### yukkuy

how will you find the distance to the star sirius using parallax method using eath based telescpoes?

i know the distances and angle in association with the equation....but i dont get how u accuatly get those data. The very first step in achieving those data.

like for eg ...the distance is 2.63 parsecs and the parallax angle is 0.38 arcseconds.....how did they actually get those data ????
i know if you find one of those data ...it will help the forumlar :)
just dont understand how they got them :)

2. May 18, 2010

### Staff: Mentor

Look at the sky - can you measure an angle between any two stars (or other objects)?

3. May 18, 2010

### yukkuy

to be honest i dont really understood that
but ... measuring the angle between any two stars would be ..........0? cause u cant have a angle unless theres 3 points ?

4. May 18, 2010

### Staff: Mentor

You are third point.

5. May 18, 2010

### yukkuy

sooo.......The point is at say june ....then the second point will be at around december (earth revolve ....180*)
...so that forms the baseline of my triangle, and with sirius makes the 3 . but how do i measure those angles with telescopes?

6. May 18, 2010

### Staff: Mentor

It really isn't that difficult. See for example

http://en.wikipedia.org/wiki/Octant_(instrument [Broken])

Bear in mind this is an outdated instrument, designed hundreds of years ago.

There are many ways, to be honest, I have no idea which one is used routinely in todays astronomy. Probably more than one though.

Last edited by a moderator: May 4, 2017
7. May 20, 2010

### Agent M27

I didn't follow the link above so I apologize if this is a repeat. What they do is using that base line technique as described above, they watch/measure how the star moves laterally with respect to the backround sky from each respective point in space ( measure once in June and once again in December). Using a little trigonometry you can obtain the inside angle by creating a right triangle and doubling the quantity. This can be demonstrated rather easily. If you extend your hand out directly in front of your face while holdinh your hand in a fist with your thumb up, alternate closing one eye at a time and your thumb will appear to shift positions even though your hand hasn't moved. Hope that helps.

Joe