Al Stahler: Space travel has ancient legacy
It’s been more than two years since a spacecraft from Earth has landed on planet Mars. Now, within the next two weeks, not one … not two … but three spacecraft, launched by three different countries, will arrive at the rusty-red planet.
Three spacecraft, arriving at once, is not a coincidence. It relates to something folks saw in the sky, thousands of years ago – way before the invention of the telescope.
Next summer, looking up at the night sky, we’ll see the scorpion. The shape of the body, the curve of the tail, the stars of the sting … without doubt, that is a scorpion. Sky-watchers, thousands of years ago, also recognized that group of stars – without doubt – as a scorpion. Relative to each other, the stars in a constellation don’t seem to move – they are stuck.
The stars of the scorpion – the stars of all the constellations – are stuck. And yet, there exist five stars that are not stuck. Five stars wander – five stars wander from one constellation to another. The Greeks referred to these wandering stars as planets; the word “planet” came from the Greek word for wandering.
Even as they wander, the planets move through the sky at a pretty steady clip. Planets do not move fast through one constellation, slowly through another. Planets move steadily … Sagittarius to Capricorn … Capricorn to Aquarius. Planets don’t shift gears.
Except for Mars.
Thousands of years ago, people noticed that Mars sometimes moves slowly through the sky; and at other times, Mars moves fast. This ancient observation relates directly to this month’s arrival at Mars of three spacecraft … all within two weeks.
Imagine a simple experiment: Get up on your roof, and drop a rock over the edge. As the rock leaves your hand – while it’s still far from the ground – the rock falls slowly. But, as the rock approaches the ground, it falls faster and faster.
Isaac Newton, mid-1600s, realized that Mars and Earth and all the planets … are falling. Not falling toward anything, though. We are all falling around the sun.
That rule we discovered on the roof – that a rock falls slowly when far from the ground, faster as it approaches the ground – that same rule applies to the planets, as we fall around the sun. All the planets, as they follow their orbits, come a bit closer to, then move a bit farther from, the sun. But for Mars, the situation is exaggerated. The orbit Mars follows brings Mars, sometimes, a lot closer to the sun … and, sometimes, a lot farther away.
Like the rock … when Mars is close to the sun, it moves fast … and that makes Mars move fast through our sky. When Mars is farther from the sun, it slows down … which makes it move slowly through our sky. This is the speed-up/slow-down that folks observed thousands of years ago.
Mars orbits farther out from the sun than Earth. So when Mars comes closer to the sun, it also comes closer to Earth. Planetary explorers sending a spacecraft from Earth to Mars can cut tens of millions of miles off the trip by holding off their launch until Mars comes close.
Mars was especially close to Earth – and bright in our sky – last October. Three spacecraft … from the UAE, China, and the USA – all launched a few months before that, in July; all three were roughly half-way to Mars when Mars was closest, in October; and all three arrive this month.
The spacecraft from the UAE is scheduled to arrive as I write, on Tuesday; China’s mission will reach Mars on Wednesday. The American spacecraft will reach Mars, not this week, but next – Feb. 19, a week from today.
The UAE and Chinese plan to go into orbit around the red planet. The American spacecraft will land on the surface.
Al Stahler enjoys sharing science and nature with friends and neighbors in The Union and on KVMR-FM. He teaches classes for both kids and grown-ups, and can be reached at firstname.lastname@example.org.
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