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NGC 672 (and partner IC 1727) & NGC 7217
Lisa & Phil Terwilliger

NGC 672 NGC 7217
NGC 672 (left) IC 1727 (right) - Lisa Terwilliger NGC 7217- Phil Terwilliger

NGC 672 and NGC 7217 are both galaxies.  A galaxy is a large group or system of millions to billions of stars that are gravitationally bound to each other.  Our own sun is a part of a system of stars called the Milky Way galaxy, and contains most of the stars that can be seen with the eye.  Using telescopes, the stars belonging to galaxies such as NGC 672 and NGC 7217 can also be seen.

NGC 672 is a barred spiral galaxy located in the constellation of Triangulum, about 20 million light years from Earth, and has a diameter of roughly 100,000 light years.  NGC 672 is not a member of the local group of galaxies, but it does have a companion galaxy, IC 1727, that is about 88,000 light years away from it.  Both galaxies are interconnected with each other, like a double star, and share a common envelope of shared gas and intermingling stars.

NCG 7217 is an unbarred spiral galaxy located in the constellation of Pegasus, about 50 million light years from Earth.  As an unbarred spiral galaxy, its nucleus is well defined and its arms are symmetrical and tightly wound. The spiral arms are very faint compared to the central bulge so that's why in the image above they are hard to see.  The nucleus of NGC 7217 has much higher than normal luminosity.  NGC 7217 features the presence of three optical ring-like zones of stars concentric to its bright nucleus, and two spiral arms in the region of its outer ring.  Bright blue stars dominate the outer ring.  Although this galaxy is very gas poor, the outer ring is where the hydrogen gas is concentrated.  NGC 7217 is surrounded by an extensive, nearly circular luminous halo.  It is isolated in space, with no nearby major companions.

In comparison, both NGC 672 and NGC 7217 are spiral-type galaxies, as opposed to elliptical or irregular galaxies.  Both galaxies are not part of the local group, are outside of the local group of galaxies, which includes the Milky Way and Andromeda Galaxies, along with the Larger and Small Magellan Clouds. Both include bright blue young stars as well as older stars.

In contrast, NGC 672 is a barred spiral galaxy while NGC 7217 is an unbarred tightly wound spiral galaxy.  NGC 7217 has no nearby companions, while NGC 672 has IC 7217, a galaxy of similar size, less than a galaxy’s width away.  NGC 7217 is over twice as far away from Earth as NGC 672. 

References:

Block, Adam. Anne’s Astronomy News. Web. 2013. Accessed 11-29-2015.  URL:http://annesastronomynews.com/annes-image-of-the-day-spiral-galaxy-ngc-7217.

"Galaxy." Wikipedia. Wikimedia Foundation, n.d. Web. 03 Dec. 2015. <https://en.wikipedia.org/wiki/Galaxy>.

Merrifield, Michael R.; Kuijken, Konrad.  "Counterrotating stars in the disk of the SAB galaxy NGC 7217." Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 432, no. 2, p. 575-589.  URL:http://adsabs.harvard.edu/abs/1994ApJ...432..575M.  1994.  Accessed 12-02-2015.

Moore, Patrick.  The Concise Atlas of the Universe.  Chicago: Rand McNally. 1974.

 

Object NGC 672 NGC 7217
Right Ascension (J2000) 01:47:54 22:07:52
Declination (J2000) +27:25:58 +31:21:34
Filters used B (Blue), C (Clear), R (Red), V (Green) B (Blue), C (Clear), R (Red), V (Green)
Exposure time per filter B (300s x 2), C (300s), V and R (150s) B (300s x 2), C (300s), V and R (150s)
Image dimension 1092x736 pixels; 6 x 2.4 arcminutes 901x980 pixels; 4 x 3.4 arcminutes
Date/time observed October 25, 2015, 05:54:04 UT October 1, 2015, 10:02 UT

 

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