Juanita Thompson, age 14, of Philadelphia, Penn., for her question:
How far away is Mars?
Earth and Mars are travel in rings around the sun. But they do not travel side by side like a pair of horses on a carousel. Mars has the outside lane, Earth has the inside lane. Earth travels faster than Mars and Mars has to travel around a larger ring.
Sometimes the two planets happen to be on the same side of the sun. When this happens they may be only 35 million miles apart. At other times they may be on opposite sides of the sun. Then they may be 247 million miles apart.
The closest the two planets come to one another is 35 million miles. They were almost this close in the fall of 1956. In the late fall. of 1958, they will be about 43 million mils apart. The two planets come closest for a few weeks every 15 or 17 years. The rest of the time, the distance between them varies from 35 million to 247 million miles.
The path. of a planet around the sun is its orbit. The time it takes to travel once around its orbit is the planets year. The earth’s orbit, is slightly oval, almost a circle. As it travels around it keeps an average distance from the sun of 93,005,000 miles. Its orbit is 600 million miles in circumference and 186 million miles wide. Our little planet races around that orbit at the speed of 181 miles a second.
Mars travels around its orbit at 15 miles a second. This means that every second, the earth travels three and one half miles further than Mars. If the two planets were running a straight race, the earth would be far ahead. But they are traveling in rings. And these orbits are not the same size or the same shape.
The average distance of. Mars from the sun is 141 million miles. This means its orbit must be some 96 million miles wider than the earths orbit. Mars has much further to travel to complete one trip and it travels much slower than Earth. So the earth, on its inside lane, is forever catching up to Mars and passing fit.
The shape of the orbit of Mars also varies in distance between the two planets. It is an oval‑shaped orbit. A diagram of the two orbits looks a bit like a fried egg. Earth's round orbit is the yolk, set slightly to one end of the oval orbit of Mars. At this end, the two orbits run only 35 million miles apart. When the two planets around this curve at the same time, they come closest to one another. Sometimes earth is at this point while Mars is at the opposite side of its orbit. Then the two planets are at their greatest distance apart. They will be this far apart during the years 1963 to 1967. At such times, a trip to Mars from the earth would be some 247 million miles.
A planets year is the time it takes to waltz once around the sun. The earth's year is, of course 365 days. The Martian year is 687 earth days, almost 23 of our months. The earth makes almost two trips around the sun while Mars is making only one. Earth catches and passes Mars once every year. All this elaborate waltzing in the sky causes the distances between the two planets to vary. And the distance which separates them varies between 35 million and 247 million miles.