|In the last month,
a ruddy eclipsed moon and bright auroral displays have delghted star gazers
and non-astronomers alike. Christmas has come early to Delmarvaís skies.
These events represent a very different kind of observing phenomena. Auroras and the eclipse unfolded before the observer's eyes, and neither required optical aid. Bright enough that light pollution didnít wipe them out, they were easily recorded with basic tripod astrophotography. Perhaps most remarkable were the colors seen in these celestial shows.
The sky is in fact quite colorful, itís just that most objects there are too dim for our eyes to notice more than tints and hues. Stars shine by their temperature according to thermodynamics. "Black bodies" glow from deep red, through yellow, white and bluish white with increasing temperature. Stars exhibit all these colors, yet pure colors in the middle visible range are rare. Visually, true greens are most evident in planetary and diffuse nebulae. Fluorescence of rarified gasses make them appear bluish-green in the eyepiece.
The eclipsed moon is bathed in all the sunrises and sunsets in the world. If the earth had no atmosphere, its shadow and the moon in it would be pitch black. Eclipsed moons are red and orange for the same reason as a sunset: blue sunlight is scattered away, while the reds penetrate and refract along an oblique path through the atmosphere to the lunar surface. When earthís atmosphere is thick with clouds or volcanic aerosols, the eclipsed moon is deep red and dark. Neither was the case last month: Novemberís eclipse was relatively bright, dominated by yellows and bright oranges
In contrast to the certainty of eclipses, auroras just happen. Charged particles ejected from the sun are caught by the earthís magnetic field. This trapped energy excites oxygen and nitrogen in the ionosphere, fluorescing green and red high in our atmosphere. The display is ever changing, consisting ghostly glows, scarlet ribbons, and whitish rays. With monitoring satellites and solar observatories we can be forewarned or even alerted by email or cell phone. But the auroral display seen by any given observer is inherently unpredictable and dynamic. It is theirs alone to be enjoyed.
For me, this monthís vivid reds and greens represent a sign of the holiday season, certainly more than making up for last summer's dreary skies. So things are looking up (so to speak), and there is much to look forward to in 2004. In January, three rovers will be exploring the surface of Mars. In late spring, two bright comets may grace our skies. On June 8, there will be the first transit of Venus in over a century, the final stages of which will be visible here following sunrise. Can you believe that it will be ten years in July since Comet Shoemaker-Levy 9 crashed into Jupiter? And that it has been a decade since the Cookbook CCD camera began a revolution in amateur astroimaging? With so much to look forward to and reflect upon in the coming year,
Seasons greetings and clear skies!
Click on the aurora photos at right for an animated sequence of images. Moondark is written by Doug Miller, published at the Moondark web site, and printed in the Delmarva Star Gazers' Star Gazer News. This document was last revised on 23 November 2003. Text and images copyright © 2003 by Douglas C. Miller, All Rights Reserved. This material may not be reproduced in any form without prior permission.