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Astr110 Photography Projects, Fall 2007

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M97 Owl Nebula (NGC 3587) , Ron Zaagman

Owl Nebula

This is a photograph of the Owl Nebula. A nebula is simply a cloud of interstellar gas and dust. The reason why there is an apparent cloud surrounding the stellar object in the middle is because this object has run out of fuel to burn and as a result is emitting gas. In this case, hydrogen gas has been burned up and the object shrinks as it emits gases. It is one of the Messier objects and is one of the fainter objects in the catalog. It is one of the four planetary nebulae in that catalog, and it is situated in the constellation Ursa Major. It was first discovered by a French astronomer, Pierre Méchain on February 16, 1781. In 1848 a man named Lord Rosse was the first to describe it as an "Owl Nebula." Through his initial drawings of the Nebula it is easy to see how he came to this conclusion. In fact, you can take a look at his drawing! In 1866, William Huggins recognized its nature as a gaseous nebula. He observed two spectral lines emitted from the gaseous nebula. The Owl Nebula is approximately 2600 light years from earth and it is believed to be around 6000 years old.

In the photograph, it is interesting to note the two dark spots corresponding with what has been described as the "Owl's eyes." Its appearance has been interpreted as that of a cylindrical shell, in which matter from the top and bottom of the cylinder don't project as much as the rest of the nebula. This is what causes the apparent holes in the middle of the photograph. The majority of the inner portion of the nebula is green whereas the outer shell of the nebula has a light red or even violet glow to it. It is interesting to note that the photograph is almost uniformly green save for the red outer shell. Using the spectral lines we can determine the type of gas this nebula is emitting. In this photograph, the green color is oxygen spreading out from the stellar core. The outer red shell is excess hydrogen that never got burned up by the core and is also expanding. The angular size of the image is 167 arc seconds and the linear size of the Owl Nebula is 2.13 light years across.

References:
Darling, David "The Internet Encyclopedia For Science."
<http://www.daviddarling.info/encyclopedia/O/Owl_Nebula.html>

Frommert, Hartmut and Kronberg, Christine. "NGC 3587." Students for the Exploration and Development of Space. <http://seds.org/messier/m/m097.html>

Right Ascension (J2000) 11:14:48
Declination (J2000) +55:01:00
Filters used blue(B), green(V), red(R), and clear(C)
Exposure time per filter 300 seconds in BVRC
Date observed

October 23, 2007 (CBVR) 1:43AM