Al Stahler: Where are we going?
You’re walking down the street, and you know just which way you’re going.
But Earth is turning – here in the foothills, we whirl, west-to-east, at some 800 miles an hour. So to really know which way you’re going, you’ve got to add that spin to your walk down the street.
And not only does Earth spin … Earth also circles the sun, at some 65,000 miles an hour.
Just as marbles come in bags, stars come in galaxies. The sun is circling the center of our Milky Way galaxy, at half-a-million miles an hour.
Galaxies, in turn, come in clusters. The Milky Way dances through space with a couple-dozen other galaxies that comprise our local galactic cluster.
And our local galactic cluster – you guessed it – is itself flying through space. We’re being pulled … tugged … dragged … toward we-know-not-what. It’s called the Great Attractor.
If you want to be precise, the calculation of where you’re heading, as you make your way down the street, must take a lot of motions into account. Fortunately, we can see which way we’re going (more accurately, which way we’re falling), just by looking (with the proper instruments).
Of course, for this to mean anything, we’ve got to be able to make our way around the universe.
Chances are, you already know the names of some of the landmarks – skymarks – needed to navigate the universe … names like Virgo … Scorpio … Leo …
Looking out in different directions, we find that all our different motions, adding together, are sending us off in the direction of Leo, the Lion.
Leo will be easy to locate, tonight and tomorrow, by finding the moon. Tonight, the moon will be just behind the lion’s head. Friday, the moon will be just under the lion’s butt.
Two patterns of stars make Leo easy to recognize. The lion’s head is a backwards question mark (a “sickle,” as was once used to harvest grain). The creature’s butt is a triangle of three stars, to the left of its head.
The moon will make Leo easy to locate tonight. Unfortunately, the moon may also make the lion hard to see.
Sun, Earth and moon will be in syzygy (SIGH-zih-gee) – arrayed in a straight line – Sunday night. With Earth in the middle, the sun will be at our back when we look at the moon. Lit full-face by the sun, the moon will be full … and bright.
The almost-full moon, of the next few nights, will very possibly be too bright to allow us to see the stars nearby. But, with patience, we can get around that.
From one day to the next, the moon rises later and later. The full moon rises at sunset. So after it’s full, rising later and later, the moon slowly leaves the night sky. Nights grow dark again, allowing the stars to again shine forth. By the middle of next week, the pattern of stars that paint the lion – the sickle and the triangle – will be easy to see.
If you have trouble seeing Leo, tonight and tomorrow, make note of where the moon is at – over a certain rooftop, near the top of some tree. Then, next week, when the sky is again dark, look again above that tree, above that rooftop, and Leo should be there: The backwards question mark of his head, his triangular butt, should be easy.
Like playing with cards, or dice, playing with unstable – radioactive – atoms is a game of chance. There’s no way of knowing when any particular atom will fall apart … but with a large number of such atoms, we can predict very nicely when some number will decay … even if we don’t know which ones. This makes radioactive atoms into clocks, with which we can determine the ages of rocks.
We keep ourselves alive by doing chemistry – un-gluing atoms from one another, re-gluing them together in new combinations. We un-glue the atoms in our food, and get energy when we re-glue them to make – among other things – carbon dioxide. We cannot find fossils in the oldest rocks … but we can find chemicals.
But a volcano can also glue atoms together to make carbon dioxide. So finding CO2 in a rock is not good evidence that life was living, back when the rock formed. But there are chemicals that cannot be made by volcanoes … or lightning … or by smashing rocks together. Some chemicals can be made only by living things.
Finding such chemicals in old rocks, we discover that live evolved on Earth very soon after the young Earth had cooled enough for water to exist on the surface … which seems to imply that the evolution of life – on a non-living planet – is easy.
Pretty much every introductory astronomy textbook today includes a chapter – usually the last chapter – on biology … how life might have evolved on Earth, and, by extension, how life might have evolved on other planets, elsewhere in the universe. The Perseverance rover that landed on Mars last month is now starting to look for the chemicals of life, in Martian rocks … even as radio telescopes on Earth are finding the chemicals from which those biological chemicals are made … floating in space.
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 email@example.com.
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