Describe how you measure the parallax between the earth and a star?

Question

I need help quick

Answer 1

The earth's orbit is 186 million miles in diameter. For a star in a direction at right angles to the diameter, the shift in position will be largest, and may amount to as much as one second of arc. The triangle with the "short" side as the earth's orbit diameter, and opposite angle one second of arc, has long sides defined as a parallax-second, or parsec. It is something like 3.8 light years.

Answer 2

cosmo is right except that you don't divide by 2.

You take pictures of the star at several times of the year and the amount it moves as seen against the background of more distant stars over that 1 year long period is its parallax. Distance (in parsecs) is just 1/parallax, where the parallax in in arc seconds. An arc second is 1/3600 of a degree, just like a regular second is 1/3600 of an hour.

Answer 3

You take a picture of the star and surrounding stars once every few months for a year. If the star is fairly close to the Earth, then the position of the star compared to the surrounding stars will make little ellipse over the course of a year. Measure the long axis of that ellipse, in units of seconds of arc. Divide by 2. Take the reciprocal. That's the distance to the star in parsecs.

Answer 4

hold your index finger up in front of your eyes between your head and the monitor.

close your left eye... where is your finger pointing?

open your left eye and close your right eye.

now where is your finger?

parallax measures the apparant movement agains the background by photographing nearby (chuckle) stars against the far away background. a little trig and whamo... a distance