Today’s Halloween, a time to celebrate the night if there ever was one. I hope you’ll be out treating, tricking, handing out candy and otherwise reveling in the fun. The sky has its scary side, too. Things like the Owl Nebula, the Cat’s Eye , the Ghost of Jupiter and even a Medusa Nebula adorn its dark underbelly. One of my favorites is the Witch Head Nebula in Eridanus the River. You’ll find it just west of Orion’s brightest star, Rigel, located in the lower right corner of his rectangular outline.
The Witch Head is a 50-light-year long interstellar dust cloud some 900 light years from Earth. The blue color is caused both by the bluish light from Rigel, a very hot white supergiant, and the fact that the tiny grains composing the cloud reflect the shorter wavelengths of blue better than red. The dust grains are very similar in size to the wavelength of blue light (475 billionths of a meter). which is scattered by very tiny particles more than the greens, oranges and reds which pass on through the cloud and continue on their way. Both the sky and a cloud of cigarette haze appears blue for the same reason.
Speaking of ghostly things, I looked up Comet Hartley 2 last night once it cleared the trees around midnight. It was easy if faint in 8×40 binoculars and still looked like a huge powder puff in the telescope with a brighter spot at center. The comet is slowly moving away from both Earth and sun, and will gradually become fainter through the month of November.
The past week and a half has a been good one for watching the evolution of sunspot group 1117. It made its first appearance around October 19 on the sun’s northeastern limb as a single spot. Within a week it developed into several planet-sized sunspots huddled together in a triangular formation. Today it’s near the sun’s northwestern edge; by tomorrow or the next day, the sun’s rotation will have moved it out of view to the backside. Before bidding us adieu, the region kicked out a couple nice flares this morning.
The still images give you a feel for the increasing complexity of the group, but for the real fun, go to the Solar Dynamics Observatory website data page and see the movie. Here’s how to do it:
1. Click on Browse by Date Range and enter 2010-10-21 to 2010-10-31 or choose from the calendar.
2. Select AIA4500 from the drop down menu. This will show the normal, white-light photos. If you want to see the sun in other wavelengths, many choices are available.
3. Click the Movie button and then Submit.
4. Let the images load, then sit back and marvel.