Saturday, May 15, 2010

Care for a Milky Way?


I tried to capture the Milky Way coursing through the treetops last night but was thrwarted by clouds. Just a hint of it is at center. The star Vega is at top while Deneb in the Northern Cross is to the left above the pointy spruce. Details: 24mm lens at f/2.8, ISO 1600 and 40-second time exposure. Photo: Bob King

After watching an episode on disk of HBO's "Rome" series yesterday night I had to stretch my legs and like Caesar search beyond the living room for plunder. It was nearly 11:30. Stepping outside, the stars looked fiery bright between swiftly-moving banks of clouds. Vega was well up in the east and below it the Northern Cross and Milky Way.
When the summertime Milky Way nudges its way into the sky on late nights in May one's first impression might be that clouds are pushing in from the east. You'd not be far from the truth except you're seeing clouds of stars not vapor, most of them at distances so vast their light blends into a continuous milky band stretching northeast to southwest. The name Milky Way is a direct translation of the Latin "Via Lactea" or Way of Milk, a reference to milk spilt by Hera, wife of Zeus, as she breast-fed her infant son Heracles.

The Milky Way that will become prominent in the summer months is on the rise in the east before midnight in May. This map shows the sky around 11:30 p.m. local time. Created with Stellarium

With our naked eye we see stars sprinkled along the Milky Way's length but only through binoculars and telescopes do we really begin to understand its nature just as Galileo did back in the early 1600's upon seeing it for the first time through one of his homemade telescopes: "For the Galaxy is nothing else than a congeries of innumerable stars distributed in clusters."


An "edge-on" view of our galaxy reveals it's a disk with a large starry bulge. The sun and the approximate tilt of the planets revolving around it are shown. I've exaggerated the sun's size and planet orbits for clarity. In reality the sun would be lost among the many stars in the disk. Credit: NASA image with my annotations

Well, yes, clusters but also some 400 billion stars, no doubt millions of planets, countless gas clouds called nebulas, black holes and all the rest arranged in a flattened disk some 100,000 light years end to end. It would look much like a thin-crust pizza if it wasn't the bulge of stars concentrated in the galaxy's center called the nucleus. This makes the Milky Way galaxy resemble some pointillistic version of Saturn writ large. The sun is a little more than halfway from the bulge to the edge, and the planets revolve around the sun at a steep angle to the galaxy's disk.


In this artist's depiction, based on the latest information about our galaxy, we see the Milky Way from above. Since the stars are concentrated in the disk, when we look through it -- instead of above or below the disk -- the stars quickly pile up to form the concentrated band of light we call the Milky Way in the night sky. Above and below the disk, the stars thin out.  Credit: NASA

Every star you see belongs to our Milky Way galaxy. Only telescopes equipped with cameras begin to resolve other galaxies into stars. Visually galaxies look like round or oval cocoons of glowing light often brighter at the center where more stars are concentrated. You have to remember as you look at one through a telescope that that bit of haze is the combined glow of billions of stars. Drill down to the next level and picture planets around many of those stars, and then imagine another pair of eyes on one of those planets with a level of curiosity that matches your own.



A wonderful video of the Milky Way rising in Australia with clouds and lightning.
One last reminder -- the Eta Aquarid meteor shower peaks tomorrow morning shortly before dawn. John Chumack captured not one but two Eta Aquarids two mornings ago in this image. Very nice!
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