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Messier 76 (NGC 650)
Chad McIntosh

M76

The image above features Messier 76 (M76 for short), a planetary nebula that partly composes the constellation of Perseus. A planetary nebula is a shell of gas ejected by and expanding away from an extremely hot low-mass star that is nearing the end of its life (Franknoi, et al.). Thus, the category of “planetary nebula” is somewhat of a misnomer, as their most notable features (the luminescent gasses) are from stars (sdss.org). Messier 76 is named after astronomer Charles Messier (1730–1817). Interestingly, although it bears Messier’s name, M76 was actually discovered by his friend and colleague, Pierre Méchain (1744-1804) on September 5, 1780. Méchain reported this observation to Messier, who observed it himself approximately one month later. Messier added it to his catalogue of newly-discovered objects which have been posthumously dubbed “Messier Objects”. There are a total of 110 Messier Objects, only four of which being planetary nebula.

Although M76 is its official name, it is most commonly referred to as the Little Dumbbell Nebula (as distinguished from the larger Dumbbell Nebula, M27), due to its dumbbell-like shape, resembling an hourglass. Its unique shape has also earned it titles such as the Cork, Butterfly, and Barbell Nebula. This peculiar shape has led some astronomers to speculate that M76 is actually two partially overlapping nebulae, referred to as a double nebula. Using the image of a Butterfly proves useful in describing the object as it is seen above. The brightest part, or the body of the butterfly, is about 65 arc seconds in diameter. At the very center is a faint blue dot, which is the dying star. The bright glow on each end of the body (upper left and lower right) is densely populated ejecta. The red coloring at the very tips indicates hydrogen. Its wings, or the very faint green glow on the lower left and upper right of the body, extend to about 290 arc seconds in diameter (seds.org). This is less dense ejecta from the star, the green coloring being an indication of oxygen.

References:
Franknoi, Morrison, and Wolff, Voyages to the Planets (Brooks/Cole, 3rd ed., 2004).
“Messier 76” seds.org. Accessed April 19, 2011. <http://www.seds.org/messier/m/m076.html>
“Planetary Nebula G164.8+31.1.” SDSS Image of the Week Archive, ssds.org. Accessed April 19, 2011. <http://www.sdss.org/iotw/archive.html>

Right Ascension 01:42.4 (h:m)
Declination +51:34 (deg:m)
Filters used B (Blue), C (Clear), R (Red), V (Green)
Exposure time per filter B, V, and R (3x10^2); C (6x10^2)
Date observed March 24, 2011

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