| The distance to the nearest stars can be calculated by observing how
their positions shift, when viewed six months apart, against the background of more
distant stars. |
| This apparent shift in position is called parallax. |
|
| Proxima Centauri, the nearest
star (other than the sun), is 4.25 light years from earth and has an observed shift in position
of 0.76 seconds of arc, much too small to be measured without a telescope. |
| The first determination
of distance by measuring paralax was made by F. W. Bessel in 1837. For the star 61 Cygni, Bessell
measured a parallax of 0.293 seconds of arc. |
| In this way, we can measure the distances to about 100 light years. How can
we determine the dsitance to stars farther away? |
