I found an answer from www2.jpl.nasa.gov

The **Parallax Angle** -- How Astronomers Use Angular **Measurement** ...

How do scientists **measure** this **angle**, and how does this information tell them the
**distance** to the star? The Earth revolves around the Sun every year, so that every
...

For more information, see The **Parallax Angle** -- How Astronomers Use Angular **Measurement** ...

I found an answer from www.khanacademy.com

Stellar **distance** using **parallax** (video) | Khan Academy

this technique only works because we have assumed that the **earth's orbit** is
circular. ... Now, the **distance** from the **earth** to the **sun** varies from **about** .98 AU to
1.02 AU, ... true that the **star** we are trying to measure **would** have moved **away**
from the **earth** after **six months** making it so that the triangle is not **an** isosceles
triangle ...

For more information, see Stellar **distance** using **parallax** (video) | Khan Academy

I found an answer from en.wikipedia.org

Altair - Wikipedia

Altair designated **α** Aquilae is the brightest **star** in the constellation of Aquila and
the twelfth brightest **star** in the night sky. It is currently in the G-cloud—**a** nearby ...

For more information, see Altair - Wikipedia

Step 1: Draw a figure based on the data provided.

Distance to the solar system from the star AC = 4.29 ly

Converting light years to parsec

The distance traveled by light in one year is one light year.

1 year of light = speed of light * 1 year [math] = 94608 * 10^{11} [math] m

4.29 ly = 4.29 * 94608 * 10^{11} = 405868.32*10^{11} m

4.29 ly = \frac{405868.32 *10^{11}}{3.08*10^{16}} = 1.32 \text{ persec } \because 1 \text{ parsec } = 3.08 * 10^{16} m

Diameter of the earth AB=3*10^{11} m

Step 2: Calculating the parallax angle \theta

\theta = \frac{AB}{AC}

\theta = \frac{3* 10^{11}}{405868.32* 10^{11} }

\theta = 7.39 * 10^{-6}

Hence, parallax angle \theta = 7.39 * 10^{-6} rad = 1.5 seconds