Astro Bob A look at celestial happenings in the Northland and beyond Bob King View my profile Click here to view previous posts or additional resources

Crust of bread

That's one skinny moon! The crescent's slightly patchy appearance is explained below. If you look closely, you can see the full outline of the moon in earthshine. Details: 400mm lens at f/5.6, ISO 800 and 1/15-second exposure. Photo: Bob King

As I strained to see the one-day-old crescent moon last night around 9 p.m. I thought "Did I screw up and get the date wrong?" Nothing emerged from the inscrutable blue for several minutes and then ... there it was. At 9:05 p.m. the thinnest, faintest crescent I'd seen in years materialized. Just a crust of bread if that.  I hope some of you saw it, too. If so, you may have noticed that the crescent was "bumpy" and unevenly lit. Sunlight grazes the plains and crater rims at such a low angle that shadows are everywhere just as they are around the time of sunrise and sunset here on Earth. The combination of brilliant crater tops alternating with shadowed lowlands breaks the crescent into zones of light and dark. Binoculars show the choppy appearance well. As the moon moves up and away from the sun and the crescent fills out, shadows fill with sunlight and moon's edge regains its smooth appearance. Tonight watch for a slightly thicker crescent to join Venus in the northwest after sunset.

Saturn and its moons last night about 10:30 p.m. through a 10-inch reflecting telescope at 200x. The dark line slicing across the center of the planet is the shadow of the rings. Sketches: Bob King

By nightfall the stars were bright in the clean sky. I pointed the telescope at Saturn and its family of moons. Saturn's rings are at their thinnest now for the next 15 years. Earth, rings and Saturn's equator are almost exactly lined up so we see the rings close to their "edge-on" presentation. While they span 178,000 miles end to end, the rings are only about 30 feet thick. Their current inclination is 1.8 degrees (zero degrees is exactly edge-on) with the north face visible, but as May gives way to June their tip begins to increase. Not until October 2017 will we see them wide open again when their tilt reaches a maximum of 27 degrees.

Jupiter this morning at 4:30 magnified 76x. The north belt was visible despite thick air which blurred the planet and most details.

One good planet deserves another which is why I chose to wake up at 4 this morning to look at Jupiter. By 4:30 it was high enough to see between the lowest tree branches, and although it shone through thick and unsteady air, I could clearly see the northern equatorial belt and three of its four bright moons. As expected, the south belt was not visible.

If you're contemplating a morning foray to view the planet, I recommend starting about 45 minutes before sunup. Center your scope on the planet and then watch it for as long as possible as it exits the atmospheric muck and presents a sharper disk. Thick air close to the horizon tends to distort and blur images through the telescope.

It appears that the International Space Station (ISS) may have to dodge a hunk of space junk making it a little trickier for the space shuttle Atlantis to dock tomorrow morning. If needed the ISS will perform an engine burn tonight to sidestep the man-made orbiting debris. There are few details available about the nature of the space junk, but scientists on the ground are monitoring the situation. It's the not the first time the ISS has had to take evasive manoevers to steer clear of debris. Even before the thousands of new FMOs (flying metal objects) created by the 2007 Chinese anti-satellite test and a 2009 crash of a Russian and an American satellite, NASA and the Space Surveillance Network were already monitoring  more than 19,000 other pieces of debris. For a complete story, please click HERE.

Posted by: rking@duluthnews.com on 5/15/2010 at 9:25 AM | Comments (0) | Permalink | Edit

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