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Saturn and Regulus Part 2 - Twinkle and Rings
Observing >
Last time here we took a deeper look into the great Lion of the Sky - Leo. We saw there a new spot on the celestial cat, a spot more familiar to us as Saturn.
Saturn happens to be parked in Leo this year, although we might more accurately call it a rolling stop. The giant ringed planet is traveling very slowly through Leo taking its sweet time to get to Virgo. But because it is so far away - and the laws of planetary motion tell us that the farther away you are from your star the longer it takes to get around it - Saturn will be in Leo until August 2009. Saturn is no Mercury.
But it would be a good thing to see Saturn this year, not next. The next time we come around to its side of the neighborhood, about a year from now, it will not be the Saturn we all know and love. The rings will almost seem to have disappeared.
You see, Saturn has a tilt like we do. By next year the planet will be at that point in its orbit where its position from our point of view will give its rings almost no tilt at all. And the rings are paper thin (actually only tens of meters thick). Bad news for ring junkies. Imagine someone down the street tilting a piece of paper so it is edge-on with your line of sight. Voila! The paper seems to vanish.
And Saturn without its rings is like a lion without its mane. It's not much more than a giant, featureless ball. That ranks low on the Exciting Things To See In The Sky scale.
But it will still have that one bizarre quality that planets possess. It will not twinkle. Yet the stars around it, like bright Regulus right next to it, will. Why?
It has to do with distance, and that annoying outer layer of our planet called the atmosphere.
Regulus is "ginormous," as my young son might say. It is a star over 4 times bigger than our sun. Imagine a sun the size of that sucker in our skies. But it is 78 light years - over 458 trillion miles - away.
Now in your mind"s eye, take Regulus from where our sun is and move it farther and farther and farther away. It shrinks and dims, and shrinks some more. By the time Regulus gets to its actual position in the galaxy, its size in the sky goes almost to a true point. And that, my friends, is the key.
The miniscule shaft of life that hits your eye from that distant star is unimaginably small and subject to even the slightest changes. What changes? Changes it encounters as it hits our atmosphere. It is then that the poor shaft hits our wall of air, air filled with countless pockets of different temperatures.
These different temperatures cause the tiny shaft to change direction every so slightly, but enough so that by the time it hits you the shifting shaft of light makes the star appear to jump around or twinkle.
But Saturn and the rest of the planets don't twinkle. Why? Now you have the tools to figure that out.
The planets, although very much smaller than stars in size, are not nearly as far away. They do not reduce in apparent size down to points of light. They still have a visible disk.
And yes, the atmosphere messes up their light paths, as well. But instead of one little shaft of light slapping you in the eye, here we have light from all parts of the planet's disk firing away at you – from its top, bottom, middle, and sides. They all get bent out of shape as they race through our atmosphere, but all the planet's flood of light more than compensates for any wayward photons that might get bent out of the way of your eye. Overall effect: No twinkling.
Is there anything you would be interested in reading about here? Any burning questions? Let me know.
Until next time, clear skies!
Posted by Mark Ritter at 2008.05. 4 10:31 AM | Comments (0)
