APOD: Arp 78: Peculiar Galaxy in Aries (2011 Jul 07)

[APOD Robot]

Arp 78: Peculiar Galaxy in Aries

Explanation: Peculiar spiral galaxy Arp 78 is found within the boundaries of the head strong constellation Aries, some 100 million light-years beyond the stars and nebulae of our Milky Way galaxy. Also known as NGC 772, the island universe is over 100 thousand light-years across and sports a single prominent outer spiral arm in this detailed cosmic portrait. Its brightest companion galaxy, compact NGC 770, is toward the upper right of the larger spiral. NGC 770's fuzzy, elliptical appearance contrasts nicely with a spiky foreground Milky Way star in matching yellowish hues. Tracking along sweeping dust lanes and lined with young blue star clusters, Arp 78's large spiral arm is likely due to gravitational tidal interactions. Faint streams of material seem to connect Arp 78 with its nearby companion galaxies.

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[Indigo_Sunrise]

the island universe.... sports a single prominent outer spiral arm

While that is a fair statement, it seems - to me anyway - as though there is another rather prominent arm: the 'red' one that is sort of around the spiral from the blue one.
Kinda reminds me of yin yang.

Beautiful image!

[orin stepanek]

Kind of looks like the figure "6"!

[nstahl]

It's unusually quiet around here. Anyone care to explicate on why NGC 770, which seems to be a puny little thing, both visually and actually (for a galaxy, of course), has a lower number than NGC 772?

[Chris Peterson]

It's unusually quiet around here. Anyone care to explicate on why NGC 770, which seems to be a puny little thing, both visually and actually (for a galaxy, of course), has a lower number than NGC 772?

An interesting question. Here's my guess: looking at the two objects out to where their brightness drops off, NGC 772 is 44 times larger in area than NGC 770. If we compare their magnitudes, which are integrated over their areas, NGC 772 is 14 times the intensity of NGC 770. That means that in terms of surface brightness, NGC 770 is actually about three times brighter than NGC 772, and surface brightness is what really makes an object show up visually through a telescope. Given that these low NGC values were based on Herschel's visual observations, I think it is likely that, through his telescope, NGC 770 was actually more apparent than NGC 772.

[nstahl]

Thanks Chris. I think that makes sense.

[Wolf kotenberg]

A cosmic geoduck

[saturn2]

ARP 78 has a spiral arm, but it´s very prominent.

[neufer]

It's unusually quiet around here. Anyone care to explicate on why NGC 770, which seems to be a puny little thing, both visually and actually (for a galaxy, of course), has a lower number than NGC 772?

They are numbered according to their Right Ascension (epoch 1860):

2MASS of NGC 1

Code: Select all

1 		Spiral galaxy 	   Pegasus 	00h 07m 15.8s
2 		Spiral galaxy 	   Pegasus 	00h 07m 17.1s
............................................................
770 	 Elliptical galaxy 	Aries 	 01h 59m 13.8s
772 	 Spiral galaxy 	    Aries 	 01h 59m 19.7s
............................................................
7789 	Open cluster  	 Cassiopeia   23h 57m 24s
7793 	Spiral galaxy     Sculptor 	 23h 57m 49.7s

NGC 1 is a spiral galaxy located 190 million light-years away in the constellation Pegasus. At about 90,000 light-years in diameter, it is just a little smaller than our galaxy, the Milky Way. It is the first object listed in the New General Catalogue. In the coordinates used at the time of the catalog's compilation (epoch 1860), this object had the lowest right ascension of all the objects in the catalog, making it the first object to be listed when the objects were arranged by right ascension. Since then, the coordinates have shifted (due to the Precession of the Equinoxes), and this object no longer has the lowest right ascension of all the NGC objects.

[Ann]

I could have told you that, Art.

Click to view full size image

The beautiful Bubble Nebula, NGC 7635, may be the NGC object that has the highest NGC number and the RA position that is "closest to 00 hours but on the 23 hour side" of the famous NGC objects. Its right ascension position is 23 hours, 20 minutes, 48.3 seconds. Find the picture at http://arnholm.org/astro/deepsky/ngc7635/index.htm.

Click to view full size image

NGC 7814, the famous NGC object that has the highest NGC number. Photo by SDSS and David W. Hogg. However, the RA position of NGC 7814 is 0 minutes, 0 seconds and 14.9 seconds, so it doesn't deserve a high NGC number!



NGC 7840, the object with the highest NGC number. RA 00 hours, 07 minutes, 09 seconds.

NGC 7807 is the NGC object that has the very highest RA, 23 minutes, 54 minutes, 30 seconds. Search for it here: http://server1.wikisky.org/

Ann

[Ann]

I have to say that this APOD looks just splendid!!! The color data has been so carefully recorded that it reveals an incredible wealth of information about the different stellar populations in NGC 772. Of course the image is amazingly beautiful too. Fantastic!

Ann

[neufer]

NGC 7814, the famous NGC object that has the highest NGC number. Photo by SDSS and David W. Hogg. However, the RA position of NGC 7814 is 0 minutes, 0 seconds and 14.9 seconds, so it doesn't deserve a high NGC number!

NGC 7840, the object with the highest NGC number. RA 00 hours, 07 minutes, 09 seconds.

NGC 7807 is the NGC object that has the very highest RA, 23 minutes [sic], 54 minutes, 30 seconds.

a 12 arcmin wide region centered on the galaxy NGC 1

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a 12 arcmin wide region centered on NGC 7840

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NGC 1 (= PGC 564), 1860 RA 00 00 04
Discovered (Sep 30, 1861) by Heinrich d'Arrest
A 13th-magnitude spiral galaxy (type SA(s)b) in Pegasus (RA 00 07 15.9, Dec +27 42 32)

Per Dreyer, NGC 1 (= d'Arrest, 1860 RA 00 00 04, NPD 63 04.3) is "faint, small, round, lying between 11th and 14th magnitude stars". The position precesses to RA 00 07 15.8, Dec +27 42 28, within 0.1 arcmin of the center of the galaxy, and there are appropriate stars to the northeast and southwest, so the identification is certain. Based on a recessional velocity of 4550 km/sec, NGC 1 is about 210 million light years away, in good agreement with redshift-independent distance estimates of 175 to 245 million light years. (Another recessional velocity measurement of 2215 km/sec would place the galaxy only 100 million light years away, which seems unlikely, given the redshift-independent results; so it is probably incorrect.) Given that and its apparent size of 2.2 by 1.8 arcmins, it is about 130 thousand light years across. Note: Although close in the sky (see the wide-field image below), NGC 1 and 2 are at very different distances; if stars, they would be called an "optical double". However, NGC 1 is listed as a member of LGG 002 (the NGC 23 Group), which also includes NGC 26, and PGC 619, 654, 830 and 912.
........................................................
NGC 7840 (= PGC 1345780), 1860 RA 23 59 56
Discovered (Nov 29, 1864) by Albert Marth
A 15th-magnitude spiral galaxy (type S) in Pisces (RA 00 07 08.8, Dec +08 23 05)

Per Dreyer, NGC 7840 (= Marth 600, 1860 RA 23 59 56, NPD 82 21) is "extremely faint, small". The position precesses to RA 00 07 06.7, Dec +08 25 46, nearly 3 arcmin north of the galaxy, and a much larger error than for any of the nearby galaxies Marth discovered on the same night (NGC 7834, 7835, 7837 and 7838); but there is no mention of any problem with its identification in any reference, and the observation cannot be a mistaken identification of one of his other discoveries; so although the unusually large positional error is puzzling, the identification seems reasonably certain. The apparent size of NGC 7840 is 0.7 by 0.5 arcmins; nothing else is available.
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NGC 7814 (= PGC 218 = PGC 1501809), 1860 RA 23 56 05
Discovered (Oct 8, 1784) by William Herschel
An edge-on 11th-magnitude spiral galaxy (type SA(s)ab) in Pegasus (RA 00 03 14.8, Dec +16 08 43)

Per Dreyer, NGC 7814 (= John Herschel's GC 5046, 1860 RA 23 56 05, NPD 74 38.9) is "extremely bright, considerably large, extended, very gradually brighter middle". The position precesses to RA 00 03 15.2, Dec +16 07 53, about 0.8 arcmin south of the galaxy's center, but on its southern outline; so the identification is certain. NGC 7814 is sometimes called the Little Sombrero, because of its resemblance to M104. Based on its recessional velocity of 1050 km/sec, it is about 45 million light years away, in good agreement with redshift-independent distance estimates of 40 to 60 million light years. Given that and its apparent size of 5.5 by 2.3 arcmins, it is about 70 thousand light years across. The galaxy is listed as the namesake of USGC 006 (the NGC 7814 Group), which also contains NGC 14, PGC 38, 332 and 889.
................................................................
NGC 7807 (= PGC 33), 1860 RA 23 54 30
Discovered (1886) by Ormond Stone
A 15th-magnitude barred spiral galaxy (type SBab?) in Cetus (RA 00 00 26.6, Dec -18 50 31)

Per Dreyer, NGC 7807 (= Ormond Stone's list I (#271), 1860 RA 23 54 30, NPD 109 33.0) is "extremely faint, pretty small, irregular figure". The second Index Catalog lists a corrected position (per Howe) of RA 23 53 16, NPD 109 37.2. Howe's position precesses to RA 00 00 27.2, Dec -18 50 25, within 0.2 arcmin of the center of the galaxy, so the identification is certain. Based on a recessional velocity of 7655 km/sec, NGC 7807 is about 340 million light years away. Given that and its apparent size of 0.75 by 0.5 arcmins, it is about 75 thousand light years across.