# The orbit of the planet mercury around the sun is in elliptical shape with sun at a focus. The semi-major axis is of length $36$ million miles and the eccentricity of the orbit is $0.206$ Find how close the mercury gets to sun?

Toolbox:
• Standard forms of equation of the ellipse with major axes 2a, minor axis 2b $(a >b)$ eccentricity e and $b^2=a^2(1-e^2)$ or $e^2=1-\large\frac{b^2}{a^2}$
• $\large\frac{x^2}{a^2}+\frac{y^2}{b^2}$$=1 • http://clay6.com/mpaimg/19_2_Toolbox.png • Foci(\pm ae,o), center (0,0),vertices (\pm a,0) • End points of Latus Rectum \; (ae,\pm \large\frac{b^2}{a}) and (-ae,\pm \large\frac{b^2}{a}) • Directrices x=\pm \large\frac{a}{e}. • The major axis is y=0 (x- axis) and the minor axes is x=0 (y- axis) • \large\frac{x^2}{b^2}+\frac{y^2}{a^2}$$=1$
• http://clay6.com/mpaimg/19_2_Toolbox1.png
• Foci$(0,\pm ae),$ center $(0,0)$,vertices $(0,\pm a)$
• End points of Latus Rectum $(\pm \large\frac{b^2}{a}$$,ae) and (\pm \large\frac{b^2}{a}$$,-ae)$
• Directrices $y=\pm \large\frac{a}{e}$.
• The major axis is $x=0$ (y- axis) and the minor axes is $y=0$ (x- axis)
• If a point moves so that the sum of its distances from two fixed points is a constant,then the path traced as an ellipse with major axis of length equal to the constant sum and foci at the two fixed points.
Step 1:
In the orbit of mercury,$e=0.206$ and semi-major axis $a=36$(in millions of miles).
Let $F(ae,0),F'(-ae,0)$ be the foci and $A(a,0),A'(-a,0)$ be the vertices of the elliptical path with the sun at $F$.
Step 2:
Mercury is closest to the sun at $A$.
Distance from the sun =$FA=a(1-e)$
$\qquad\qquad\qquad\qquad=36(1-0.206)$
$\qquad\qquad\qquad\qquad=36\times 0.794$
$\qquad\qquad\qquad\qquad=28.584$ million miles.
edited Jun 18, 2013