Skip to Navigation | Skip to Content

Previous image Up to Astr111 Index Next image ASTR 110 Photography Projects, Fall 2016

NGC 7538 & NGC 723 (Iris Nebula)
Anna Malchow & Kayla Van Eck

NGC 7538 NGC 723
NGC 7538- Anna Malchow NGC 723 (Iris Nebula)- Kayla Van Eck

The word nebula is derived from the Latin word for cloud. Nebulae are giant, high-density clouds of hydrogen, helium, dust, and plasma. Nebulae are formed as the force of gravity pulls this matter together. Because nebulae are composed of the matter necessary for star formation, they are often referred to as “stellar nurseries” (Williams). Most nebulae can be categorized as diffuse nebulae because they have do not have distinct boundaries. Depending on the composition of the gas cloud, diffuse nebulae may be emitters or reflectors of light. Oftentimes, emission nebulae are red colored, while reflection nebulae may have more blue and green colors.

The nebula NGC 7538 is a diffuse nebula located in the Cepheus constellation. It is roughly 9100 light-years away from the earth. A diffuse nebula is a cloud of dust and gas, if it is big enough it can be a prime location for star formation. Because there are a lot of new stars being formed within this particular nebula, the nebula glows red because of the energized hydrogen gasses. To study a diffuse nebula, scientists have to use long wavelengths because of dust interference. They typically will rely on infrared, microwave, or radio waves to explore NGC 7538. Inside NGC 7538, scientists discovered the biggest protostar, which is roughly 300 times bigger than our solar system!

The Iris Nebula is classified as a reflection nebula. Reflection nebulae do not emit their own light, but rather, they reflect the light from nearby stars. The Iris Nebula is located in the constellation Cepheus and is illuminated by the star cluster NGC 7023, which lies within the nebula. The Iris Nebula was originally discovered by Herschel in 1794 and was first identified as the star cluster NGC 7023. The Iris Nebula spans 6 light years across. Because of its flower-like appearance, the Iris Nebula was named after the purple Iris flower. The Iris Nebula has a blueish appearance because the young star in this nebula is very hot, which corresponds to emitting more blue light. This light reflects off many of the dust particles as it passes through the nebula, allowing us to view it as blue light.

Both of these nebulae can be classified as diffuse nebulae. This is evident as a viewer because neither one of them occupy a clearly defined space. Also, both have characteristics that emit light from the stars that lie within the nebula cloud.

One distinct difference in these two objects is the colors we observe in both of them. The Iris Nebula has a very blue appearance, which is a result of the light it reflects from the very hot, blue stars that lie within the cloud. On the other hand, NGC 7538 has a very reddish appearance. This is a result of the star formation from within the Nebula. Another difference is in the behavior of both nebulae. The Iris Nebula is a reflection nebula and does not produce its own light, while NGC 7538 reflects light and emits its own light.


Iris Nebula, Wikipedia, 26 Sept. 2016, . Accessed 15 Nov. 2016.

Voisey, Jon. Universe Today, 24 Dec. 2015, . Accessed 15 Nov. 2016.

Walker, Jimmy. "NGC 7023: The Iris Nebula ." Astronomy Picture of the Day, NASA, . Accessed 15 Nov. 2016.

Wikipedia, 19 July 2016, . Accessed 15 Nov. 2016.

Williams, Matt. "Nebulae: What are they and where do they come from?." Universe Today24 Dec. 2015, . Accessed 15 Nov. 2016.


Object NGC7538 NGC7023
Right Ascension (J2000) 23:13:45.7 21:01:35.5
Declination (J2000) +61:28:21 68:10:10.001
Filters used B (Blue), C (Clear), R (Red), V (Green) B (Blue), C (Clear), R (Red), V (Green)
Exposure time per filter B (120s), V (600s), R (600s); and C (160) B (140s), V (700), R (700s); and C (700s)
Image dimension 833x514 pixels;18.1x11.1 arcminutes 1092x736 pixels; 23.7x15.9 arcminutes
Date/time observed October 17, 2016 02:47:02 UT October 7, 2016, 06:56:23 UT



Secondary content.


Side content.