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The Changing Skies of a Waning Summer Has Much to Offer

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Clear SkiesBy Scott Levine

There’s a certain magic to late August. The start of fall is only about three weeks away, and we can already feel the stickiness and mosquitoes loosening their grip, just a little.

Maybe you’ve noticed we’ve gained about an hour of nighttime since the start of the month.

All the while, we’ve seen a couple of old friends, Jupiter and Saturn, sneak back into the evenings after months hiding in the mornings. It’s not always easy to tell stars from planets, but we can get help from a couple of easy tools.

First, in the northern hemisphere, we always see the planets along a line that runs from east to west along the southern horizon. That’s the ecliptic, which represents the path the sun takes each day. The planets orbit the sun roughly at its equator, so the ecliptic also represents our view of the orbital plane of the entire solar system. If it’s a planet you’re looking for, they’ll always be near that line.

Once we know where to look, we can focus on what to look for. Planets are, as these things go, very close to us. So, their light reaches our eyes from many points, not just one like the light from much more distant stars. This means we see them as subtle discs.

Venus, which is still missing from the evening, and Jupiter are the two brightest objects in the sky other than the sun and moon. When we look at them, we see this effect is particularly apparent. We’ll also notice planets don’t twinkle the way stars do because those discs of light are affected less by disturbances in our atmosphere less than starlight is.

This also makes it easier to pick out colors than we can with most stars. Venus is an icy white. Iron on the surface of Mars makes it look bright red to us. Jupiter’s a soft orange. Saturn is a subtle yellow.

As we flip to September, let’s see if we can use these tools together to spot Jupiter and Saturn in the southeast sky. If we need some help, the moon will join the fun as it glides between them from Sept. 7-11. The almost-full Harvest Moon will be nearly exactly between the pair on Sept. 9 with Saturn to its right and Jupiter to its left.

Any of these nights, we can spend a few extra minutes imagining what we’re really looking at. We can use our minds to follow a jagged line running from our eyes to the moon about a quarter million miles away. From there, a quick jog to the east sends us 500 million miles to Jupiter. By the time we get to Saturn, the line from our eyes runs a billion miles into space.

There, in that one patch of the night, we’ll see our neighborhood’s two biggest planets, and 162 of the solar system’s moons: 79 at Jupiter, 82 at Saturn and our own, the only other world where humans have walked.

From there, we can let our gaze drift to distant, unknown corners of our galaxy and wonder what else is there. I hope you’ll look this month. Clear skies, everyone!

Scott Levine (astroscott@yahoo.com) is an astronomy writer and speaker from Croton-on-Hudson. He is also a member of Westchester Amateur Astronomers, a group dedicated to astronomy outreach in our area. For information about the club including membership, newsletters, upcoming meetings and lectures at Pace University and star parties at Ward Pound Ridge Reservation, visit www.westchesterastronomers.org.

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