Alan Stahler: Planet spotting
December 5, 2018
With luck — sky and clouds permitting — Friday the 14th will be a good night to spot Mars. The ruddy planet (sporting a freshly-landed probe on its surface) hangs close to the moon in the 14th's night sky.
Earth orbits closer to the sun than Mars, putting us in the fast lane. Mars shone bright in the night sky last summer, when it was close, but we're now leaving it behind, making Mars less bright, night after night.
Planet Venus shone bright in the western sky last summer, the "evening star" after sunset. Orbiting closer to the sun than Earth, Venus travels the passing lane. Having passed us, Venus has disappeared from the western sky, and has now re-appeared in the eastern sky, the "morning star" before sunrise.
The weather forecast says skies might be clear Friday and Saturday. With Venus now at its brightest, catch the planet before dawn, and then you might spot it again, after the sun comes up, if you know where to look.
Recent observations tell us that nearly every star you see at night should have at least one planet going around it.
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When the sky is clear, find Venus, bright in the east, before dawn. Notice where it is, relative to, say, a tree, a rooftop, a satellite dish. Knowing where the planet is before the sun comes up, you're free to do whatever you want (back to bed?) until sunrise.
Once the sun is up, use the trees, the rooftop, the dish, as a guide to look for Venus again; look just a bit higher than it was in the pre-dawn sky.
A little patience should reveal Venus: A white spark in the blue sky.
Even a cloudy sky can be good for planet-watching — watching the workings of our own planet, that is.
Warm air rises. As it rises, air feels less pressure — less air pressing down on it from above. Like a pillow when you lift your head, less-pressed air expands. And as it expands, it cools (compressing air, in the cylinder of a car engine, warms it; expansion, on the other hand, cools the air).
Exhale on a cold winter's day, and your breath forms a cloud, as gaseous water vapor condenses to form tiny droplets. As warm air rises and cools, its water vapor also condenses into cloud droplets. Rapidly-rising air forms dramatic cumulus clouds — the cauliflowers kids like to draw.
Less dramatic — but more intimate — is a cloud that forms when air doesn't rise, but hugs the cold ground, which sucks its heat out. Such a ground-hugging cloud forms fog. Immersed in fog, we see just how tiny are the cloud droplets — way tinier than raindrops. The slightest breeze, created as you move, sets the droplets in motion.
Clouds in layers (rather than rising piles) are stratus clouds. Stratus form low (as fog), medium, and high above the ground. When stratus forms really high up — where the air is really cold — water vapor doesn't condense into droplets. It condenses to form crystals of ice.
As a layer of cirrus falls, the tiny ice crystals remain more-or-less horizontal, but waft back and forth, like dead leaves, fluttering down from a tree. The crystals catch the light of the sun or the moon, bend the light, then send it on. Bent sun or moonlight forms a large ring — a halo. Such a halo is a clear signal that the clouds are composed of crystals of ice, not droplets of water.
Venus, Earth, Mars: Three very different planets. Recent observations tell us that nearly every star you see at night should have at least one planet going around it. What little we've learned so far tells us that some of these planets differ from Earth even more.
Travel is broadening: Learning how others cook, eat, dance, party, school their kids opens us to the possibilities of life … and increases our appreciation of our home country, hometown.
Exploring the solar system — and now, star systems outside our own — increases our understanding and appreciation of our home-planet.
Al Stahler enjoys sharing his love of nature with students of all ages. His science stories can be heard on KVMR-FM (89.5-FM), and he may be reached at email@example.com.
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