Photo Credit & Copyright: NASA/STScI Digitized Sky Survey/Noel Carboni. CLICK photo for full size and see below for links.
Let’s keep Halloween week rolling! Every year in the northern hemisphere as summer begins to cool and the nights begin to grow longer, IC2118 or as it’s known, the “Witch Head Nebula” begins to appear nightly. Located approximately 900 light years distant in the constellation of Eridanus (yep, not Orion), the Wicked Witch of the Winter (as I call her) is actually a 50 light year-long reflection nebula that’s being illuminated by the famous blue supergiant Rigel (not shown) the lest foot of Orion. If you have a photo of the constellation Orion and it’s at an anatomically heads-up position, at the bottom right you will find Rigel and to the right of the star you will see the witches face. It will however be upside down though so you may have some trouble making it out but I suspect pareidolia will kick in and the face will appear. Here, check out this recent post that I did on Orion and see if you can spot her in the image: https://danspace77.com/2014/09/19/objects-in-the-hunter-may-be-closer-than-they-appear/
The reason for the bluish color to this nebula is not just the color of the star but it’s because the particles of material that comprise this molecular cloud are about 1 micron in size thus they pass red light and scatter blue for us to catch in our light collectors. This is the same reason that the sky is blue and also why forest fire smoke, cookout grill smoke etc. often has a blue tint to it.
Before we leave, let’s take a look at the star doing all this work for a moment. Rigel, a blue supergiant associated with IC 2118 is actually in the constellation of Orion though the two are separated at the border between the two pretty much. Rigel lights this nebula from over 40 light years away and is 40,000 times more luminous than the Sun. It emits more light in one minute than our Sun does in an entire month and amazingly….if it replaced Proxima Centauri it would shine as bright as the Full Moon in our night sky.
NAME: IC 2118, NGC 1909, Witch Head Nebula.
WHAT IS IT?: Reflection Nebula.
HOW BIG IS IT?: About 50 light years long.
HOW FAR AWAY IS IT?: Approximately 900 light years.
APPARENT MAGNITUDE?: A very dim 13 or +13.
WHERE IS IT? (General): Constellation Eridanus and reflected by light from the blue supergiant star, Rigel in Orion.
WHERE IS IT? (Exact RA/DEC J2000): RA 05h 02m 00s / DEC -07° 54′ 00″.
NASA APOD for this object: http://apod.nasa.gov/apod/image/0612/ic2118_dss_big.jpg