# limitations of trigonometric parallax (1 Viewer)

#### pqd

##### New Member
ok so i have that the parallax is very small and that the atmosphere blurs images.
can i also write that our solar system, the star whose distance we want to measure, and the distant background stars have some relative motion between them, or does that not influence anything.
i guess since we already make the approximation tan p = p, this relative motion may have even less of an effect on the answer than this approximation?

#### someth1ng

##### Retired Nov '14
Well, for starters, the baseline limit is the diameter of Earth's orbit around the Sun.

We find that you can only measure up to 100parsecs or so with any reasonable level of accuracy. In addition to this, the relative number of stars in this area is pretty miniscule. The nearest star system is already 4 ly or so - 100 parsec isn't a lot. Especially when there's a few hundred billion stars in our galaxy which is one galaxy of several hundred billion galaxies.

In addition, you need to wait half a year to take the measurements - total pain.

The parallax angle is often very small so equipment needs to be insanely precise - higher precision is typically higher cost.

#### pqd

##### New Member
yeah that much i know (forgot to write that it take 6 months) but what i want to know is whether our assumption that there is no relative motion between anything a limitation of this technique or does the assumption not matter?

#### someth1ng

##### Retired Nov '14
You're comparing against extremely distant objects. Our relative motion when considering such a distance is negligible.