Light From Above, Lava From Below

Anti-crepuscular rays appear to "focus" toward the eastern horizon near sunset last night. Photo: Bob King

The evening began well. On the way home from work yesterday, a striking series of anti-crepuscular rays shot out below a line of low clouds over Lake Superior. They were bunched as tightly together as a bar code. Crepuscular (kree-PUSS-cue-lurr) rays are those sunbeams we often see bursting from behind clouds. They’re rays of sunlight shining through gaps within and between clouds that illuminate dust and other atmospheric particulates. Rays alternate with cloud shadows to create glorious crowns of light around the sun and moon. Occasionally only a crack or two will open up and the ray will look like  some heavenly spotlight. The beams are parallel to one another, but because of perspective they often appear to radiate in a circle around their source.

Anti-crepuscular rays are really nothing more than the extension of crepuscular rays all the way across the sky to the opposite horizon. Notice that in the photo that they appear to converge toward the horizon. That’s an illusion again. Like railroad tracks in the distance, they’re still parallel to one another. Anti-crepusculars are generally fainter than standard crepusculars but no less beautiful.  Watch for them in the direction opposite the sun shortly before sunset or after sunrise.

After sunset, clouds worried the sky until 11 o’clock when it finally cleared for good. I set up my telescope in a dark place north of the city and looked at galaxies and variable stars until after midnight. Fall was very much in evidence. Temperatures in the 40s, the night insects silent, and before I knew it, the Seven Sisters cluster stood high in the eastern sky. Is summer really coming to a close? In September the Milky Way is directly overhead during evening hours. Time to lie on a blanket and align both body and thoughts in parallel to both its majesty and the new season.

Cones formed by hot lava running over water or ice. The cones are similar in size and shape to ones found in Iceland and formed the same way. Gigantic hi-res image. Credit: NASA/JPL/UofA/

The Mars Reconnaissance Orbiter recently captured a photo of a bizarre volcanic landscape in the planet’s Amazonia region. The cones in the photo were formed when hot lavas ran over water-soaked ground. Lava heated the water to boiling which then rose up as steam through the flow as exploding bubbles of molten rock. Fiery lavas must have been flung everywhere, sending sprays of liquid rock raining down on the landscape.The cones appear in chains because the land was moving over a fixed magma “hot spot” at the time. As it crept along, molten rock punched through the surface time and again creating one cone after another. This process is similar to the way the chain of Hawaiian islands were formed -  a tectonic plate moving over a magma source below the crust. The Hawaiian hot spot is currently under the Big Island of Hawaii. Each island is made up of one or more volcanoes that originated from erupting lavas. Too bad Mars lost its water over the eons or the “Amazonian Islands”, located at a similar latitude as our own Hawaii, would have made a choice vacation spot.

The crescent moon beautifies the eastern sky at dawn tomorrow morning joining the familiar constellations of winter. This map shows the sky around 5 a.m. Created with Stellarium