# Light from the Sun takes 8 minutes to reach Earth. How long does it take to reach Mars?

## What is the Given & Unkown(s): 8 minutes (light to reach the sun) t=? Approprite formula: ? Conversion of the formula in order to determine your unknown: ? Inserting numbers: 8 min/ 1 Au = t/ 1.52 AU t= (8 min x 1.52 AU)/ 1 AU = 12.2 min Units: ? (I don't know what to put for those 3 parts)

May 11, 2018

Based on speed of light (300,000 km/s): ca. 12 min. 40 sec.
Based on 8 min. from Sun to Earth: ca. 12 min

#### Explanation:

To compute the time, we need the following data:
Speed of light in vacuum: $c = 300 000 \frac{k m}{s}$
(More exactly 299 792 458 m/s, but for our purposes the round figure of 300 000 fits nicely)

Distance from Sun to Mars: 228 000 000 km.
(Distance from Sun to Earth: $150 000 000 k m$, but we don't really need that figure.)
The only two items we need, are really the speed of light and the distance it has to travel, as our calculation then becomes:

time in seconds = Distance / speed of light

= $\frac{228000000 k m}{300000 \frac{k m}{s}}$

= $760 \sec = 12 \min 40 \sec$

If we instead base our computation on the data we have been given, i.e. that the light uses 8 min. = 480 sek. to reach the earth, we must use the ration between Earth's distance and Mars' distance to the Sun, i.e.

$480 \sec \cdot \frac{228 000 000 k m}{150 000 000 k m}$

=$\frac{480 \cdot 228}{150} \sec$ = $730 \sec \approx 12 \min$