Q.Jupiter is at a distance of 824.7 million km from the Earth. Its angular diameter is measured to be 35.72$''$. Calculate the diameter of Jupiter.

Direct instruments like a scale or caliper cannot reach the height of a tree, let alone the distance to the Moon or a planet -- these need indirect geometric or wave-based methods.

Triangulation method (for the height of an accessible object): stand at point $C$, a known horizontal distance $x$ from the base $B$ of a tower/tree of height $h=AB$, and measure the angle of elevation $\theta=\angle ACB$ to the top $A$ with a range finder. From the right triangle $ABC$: $\tan\theta=h/x$, so

Parallax method (for the distance of a far-away object like a planet or star): parallax is the apparent shift in an object's position against a distant background when it is viewed from two different points; the separation between those points is the basis, $b$. If the small parallax angle subtended at the object is $\theta$, and $x$ is the (large) unknown distance, treating the basis as a small arc of a circle of radius $x$ gives $\theta=b/x$, so

Application -- distance of the Moon: observe the Moon simultaneously from two diametrically opposite points $A,B$ on Earth (basis $b=AB=$ Earth's diameter), each against the same distant background star; the individual parallax angles $\theta_1,\theta_2$ add to give the Moon's total parallax $\theta=\theta_1+\theta_2$. Since the Earth-Moon distance $MC\approx AM$, $\theta\approx AB/MC$, so $MC=AB/\theta$. …