The Scary Side Of Night

The Witch Head Nebula, also known as IC 2118, is a faint cloud of interstellar dust in Eridanus illuminated by nearby Rigel, which is off the frame to the right. Can you see her nose, eye and mouth? Click on the photo for hi-res image. Credit: NASA/STScI Digitized Sky Survey/Noel Carboni

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.

Ghostly blue Comet Hartley 2 plies the star fields of southern Gemini early this morning. The tree in the foreground is blurred because I tracked the comet during the exposure. Details: 200mm lens, f/2.8, ISO 800 and 2-minute exposure. Photo: Bob King

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.

As sunspot group 1117 rotated across the sun's face, it evolved from a single spot to a large and complex group. Sunspots are regions on the sun's surface where intense magnetism welling up from below cool the surface in the form of dark spots. This areas of concentrated magnetic energy sometimes erupt with solar flares. The sun rotates once on its axis about every 27 days. Credit: NASA/SDO

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.

2 Responses

  1. Laura Weir

    Astrobob, please help me. At about 2:30 am last night I went out on my deck (Cotton, MN) to check out the sky. I saw a large twinkling star. I looked at it with binoculars and could see colors – red, blue, yellowish green. I thought it might be an oncoming plane or helicopter, but it didn’t really move. I woke up my poor husband and he said it was it was the Dog star – sirius. Can you explain the colors? Thanks for any info you can give me.

    1. astrobob

      Just check out today’s blog for an answer. I hope it will explain what you saw better. Thanks for writing!

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