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

Follow the ancient way

The sun sets almost directly over the end of Arrowhead Road

in Hermantown yesterday evening. Doesn't this image just say spring

is in the air? Photo: Bob King

OK, OK the photo doesn't exactly connote spring. It's on the dark and spooky side, yet it holds a tidbit of information, a way you can astronomically verify the beginning of the new season.

Many roads both in our cities and countryside are laid out on a north-south and east-west grid. Last night I was driving due west on Arrowhead Road under heavy cloud cover, but just before sunset, our star made a brief appearance from under the clouds. I watched it set and took a few photos of traffic on Arrowhead. On the first day of spring, which occurs tomorrow beginning at 12:32 p.m. Central time, the sun rises due east and sets due west. Since yesterday was the 18th or two days before spring's start, the sun set slightly south of due west. If I took that same trip down any east-west road tomorrow the sun would rise directly at the end of that road at sunrise and set at the other end at sunset. If you're out driving at those hours, take a look and you'll see what I mean.

The sun will continue its northward journey in the sky and by Sunday evening will set slightly north of west. Its furthest north setting and rising points occur on the first day of summer. Our ancient ancestors set up stones and created passageways where the sun's light would align and shine on cave walls and tombs on the first day of spring. Some of these may have had magical significance; others no doubt helped to mark an important date on their calendars. No matter where you live on the planet tomorrow, you can follow the ancient ways yourself by walking down any old east-west road with a clear view of sunrise or sunset. Stay tuned for more on the vernal equinox in tomorrow's blog.

In this new photo of Phobos we see a cratered surface, numerous striations or grooves and a long chain of small craters winding across the moon's northern hemisphere. The "N" (below) marks Phobos' north pole. Credit: ESA/DLR/FU Berlin (G. Neukum)

The European Mars Express spacecraft, which has been studying Mars from orbit since late 2003, made a series of close flybys of its largest moon Phobos earlier this month. New, highly detailed photos of the little moon recently became available. Phobos is shaped very much like a potato measuring 17 x 14 x 12 miles across. The most striking thing about the photo above are the hundreds (thousands?) of parallel or nearly parallel grooves. They've been interpreted as faults, fractures or chains of secondary impact craters caused by a large impact on Phobos. Other astronomers think they may have been created by impact material blasted from Mars which shot into space peppering the little moon. A definitive explanation may have to wait until the new images are studied more closely or until the Russian Phobos-Grunt (Phobos-Soil) sample return mission lands on the little moon late next year and returns a soil sample to Earth. That was one of the other purposes of the Phobos flyby -- to determine good landing sites for the mission. The photo below tells me the mission planners are looking for a smooth, safe, boulder-free location.

The Phobos-Grunt landing site area with choices marked. Credit: ESA/DLR/FU Berlin (G. Neukum)

Posted by: rking@duluthnews.com on 3/19/2010 at 10:13 AM | Comments (0) | Permalink | Edit

Tags: daily updates, astro bob, phobos-grunt, life, spring, equinox, mars, phobos