Eagle Nebula (M16) & Skull Nebula (NGC 246)

Observatory / Course Archives / ASTR 110 Fall 2018 / Luebke and Waldrop

We present two celestial objects, one an emision nebula and the other a planetary nebula (M 16 and NGC 246, respectively). Nebulae are regions of stellar dust and gas frequently left over as the remnants of star death though sometimes also serving as birthplaces of other stars. Nebulae generally and primarily comprise large amounts of hydrogen and helium. If and when a nebula grows to be sufficiently massive, a nebula collapses and a star begins to be born. The closest nebula is approximately 700 light years away from the earth.

The Swiss astronomer, Jean-Philippe Loys de Chéseaux, discovered the Eagle Nebula in 1745. In terms of physical size, the Eagle Nebula is 70-55 light years across. It can be found in the Serpens constellation. Its so-called "pillars of creation," which are 4-5 light years across (not shown in the image), are the site of ongoing star formation. The Eagle Nebula is about 7000 light years away from the earth. This nebula is also an emission nebula, a nebula that gives off an emission spectrum--i.e. a cloud of interstellar gas and dust that emits light. As you can see, it has a reddish hue with most of the stars being white and some that look yellower.

The Skull Nebula is a planetary nebula with a white dwarf star in its center. Planetary nebulae are formed from the death of red giant stars after nuclear fusion has stopped. The small dead star in the center of this nebula was once a star very much like the Sun. The nebula appears as a gray and green cloud surrounding the white dwarf in its center. This nebula is about 1600 light years away from the earth. The skull nebula was discovred in 1785 by William Herschel.

Both nebulae can be seen to give off bright colored light. Both, likewise, are composed primarily of stellar gas and dust. In neither case is the light emitted from either body due to the presence of an active, atomically-fusing star.

Whereas the Eagle Nebula is the site of active star formation, the Skull Nebula is not. Similarly, only the latter has a white dwarf in its center. Where the Eagle Nebula appears mostly in shades of red, the Skull Nebula appears green, grey, and pruple, among other colors. The Eagle nebula has an abundance of stars, whereas teh Skull Nebula has much fewer in comparison. In structre, the Eagle Nebula stretches off in many directions haphazardly, whereas the Skull Nebula maintains a smoother shape. The Eagle Nebula represents the birth of a new star, whereas the Skull Nebula represents the death of an old star. The gas being emitted by the Eagle Nebula comes from hot, young stars. For the Skull Nebula, the gas being emitted comes from its white dwarf.

References:

Garner, Rob. "Messier 16 (The Eagle Nebula)." NASA. https://www.nasa.gov/feature/goddard/2017/messier-16-the-eagle-nebula

MacPhee, Martin. "Awesome Beauty of the Eagle Nebula." EarthSky.org. https://earthsky.org/space/the-awesome-beauty-of-m16-the-eagle-nebula

Nemiroff, Robert and Jerry Bonnell. "NGC 246 and the Dying Star." https://apod.nasa.gov/apod/ap060418.html

"Skull Nebula NGC-246". Gemini Observatory. http://www.gemini.edu/gallery/media/skull-nebula-ngc-246

Wikipedia, "Eagle Nebula." https://en.wikipedia.org/wiki/Eagle_Nebula

Wikipedia, "NGC 246." https://en.wikipedia.org/wiki/NGC_246

Wikipedia, "Planetary Nebula".

Object	Eagle Nebula	Skull Nebula
Right Ascension (J2000)	18:18:48	00:47:03.338
Declination (J2000)	-13:49	-11:52:18.94
Filters used	B (Blue), C (Clear), R (Red), V (Green)	B (Blue), C (Clear), R (Red), V (Green)
Exposure time per filter	B (160s), V (88s), and R (105s); C (160s)	B (220s), C (60s), R (60s), V (60s),
Image dimension	1,053x703 pixels	546x368 pixels
Date/time observed	11/7/18, 1:30am	11/6/18, 1:56pm