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NGC 1491 & Crescent Nebula (NGC 6888)
Hallie Litt & Kelly Looman

NGC6888 NGC1491
Crescent Nebula (NGC 6888)- Kelly Looman NGC 1491- Hallie Litt

The two celestial objects photographed above are examples of emission nebulae. Nebulae are ionized gas clouds and are some of the most colorful and beautiful phenomenons in our universe, coming in a variety of colors, shapes, and sizes. Nebulae can be formed in multiple different ways. Planetary nebulae are formed at the end of a low mass star’s life. A star will “eject its outer layers into space” exposing its very hot core also known as a white dwarf (Bennett). A white dwarf radiates ultraviolet light which ionizes its ejected outer layers, illuminating the area in an array of colors. Other nebulae are byproducts of supernovas; the materials from the explosion ionize the gas and dust around a massive star. Finally, emission nebulae are the result of the interstellar medium (gas and dust) collapsing in on itself, creating new stars. And like the other nebulae, a star’s ultraviolet radiation ionizes the surrouding gas and dust. Nebulae are examples of God’s glory and majesty, and they remind us of not only God’s creativity but his ethereal nature.

The Crescent Nebula (NGC 6888) is an emission nebula located 5000 light years away from Earth in the “Swan” constellation (Cygnus). NGC 6888 was discovered by Friedrich Wilhelm Herschel in 1792. Herschel, both an astronomer and a composer, is perhaps best known for discovering Uranus. However, he also discovered an array of  moons, stars, and nebulae. Located at the center of the Crescent Nebula is a Wolf-Rayet Star (WR 136), a type of star characterized by hot temperatures, large masses, and powerful stellar winds. The star’s ultraviolet radiation ionizes the surrounding gas, forming the Crescent Nebula. The nebula is approximately 25 light years in diameter (NASA). You may be able to see this star during the warm months of summer into early fall.

Located in the constellation Perseus, NGC 1491 is an emission nebula. Emission nebulae have the potential to form new stars; it glows a “deep red because the hydrogen gas in the nebula is energized by [the] hot, massive stars embedded within” (NOAO). In the northern hemisphere, the star can be seen almost every night, while in the southern hemisphere it can only be seen during the winter. NGC 1491 was also discovered by Herschel a few years before the discovery of NGC 6888 (1790). However, the size and distance of the nebula are still undetermined.

As mentioned above, NGC 1491 and NGC 6888 are both emission nebulae. Emission nebulae are clouds of interstellar gas that shine through using their own light emission. Both nebulae are found in different constellations. NGC 1491 is found in the constellation Perseus; named after a Greek hero that is famous for slaying Medusa. HGC 6888 can be found in the Cygnus constellation. Cygnus is also referred to as the Northern Cross because of its shape.

In our images, you can see that both NGC 1491 and NGC 6888 have a red appearance. The red appearance in the nebuale comes from the abundance of hydrogen. The hydrogen gas that causes the red emission light is fueled by the hot, massive stars within the nebula.

References:

Bennett, Jeffrey O. The Cosmic Perspective. 2nd ed. Boston: Addison-Wesley, 2010. Print.

Bright nebula NGC 1491 · Deep Sky Objects Browser. (n.d.). Retrieved November 15, 2016, from http://dso-browser.com/deep-sky/2408/ngc-1491/bright-nebula

Crescent Nebula. (n.d.). Retrieved November 15, 2016, from https://en.wikipedia.org/wiki/Crescent_Nebula

Cygnus. (n.d.). Retrieved November 15, 2016, from http://www.windows2universe.org/the_universe/Constellations/summer/cygnus.html

NASA. (n.d.). Retrieved November 17, 2016, from https://apod.nasa.gov/apod/ap160610.html


National Optical Astronomy Observatory. (n.d.). Retrieved November 15, 2016, from https://www.noao.edu/image_gallery/html/im1266.html

NGC 1491. (n.d.). Retrieved November 15, 2016, from https://it.wikipedia.org/wiki/NGC_1491

National Optical Astronomy Observatory. (n.d.). Retrieved November 15, 2016, from https://www.noao.edu/image_gallery/html/im0834.html

Perseus. (n.d.). Retrieved November 15, 2016, from http://www.windows2universe.org/the_universe/Constellations/perseus.html


Object NGC 1491 NGC 6888
Right Ascension (J2000) 04:03:11 20:12:02
Declination (J2000) 51:18:59 38:21.3:0
Filters used B (Blue), C (Clear), R (Red), V (Green) B (Blue), C (Clear), R (Red), V (Green)
Exposure time per filter B, V, and R (120s) B, V, and R (240s); C (60s x 5)
Image dimension 326x272 pixels; 7.063x5.893 arcminutes 475x348 pixels; 10.292x7.54 arcminutes
Date/time observed November 8, 2016 7:58 UT November 17, 2016 2:20 UT

 

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