Howard B
September 1st, 2019, 06:33 PM
Interacting galaxies
Andromeda
RA 00 57 41
DEC +43 47 28
Magnitude 13.9
3616
NGC 317 A/B and PGC 3432 was suggested by Jimi as an interesting object at the 2019 Oregon Star Party – which had wonderfully dark and smoke-free skies this year. The main appeal of NGC 317 was that it’s a pair of beautiful interacting galaxies, with a PGC galaxy off to the side. It looked great on the DSS image on Jimi’s laptop, but what could we see with my 28-inch scope?
Quite a lot as it turned out. NGC 317 A (mag 13.86) is the bright elliptical galaxy just above the messed up looking edge-on spiral of NGC 317B (mag 13.95) below it. PGC 3432 is in the upper right corner of the DSS image, and all three were easy to see, even PGC 3432 (mag 16.7).
The spiral arm of 317B opposite of 317A was seen dramatically sweeping out into intergalactic space, and became quite long with averted vision. Beautiful.
The most difficult detail to see was a small knot in 317B’s other spiral arm, the one being directly pulled on by 317A. You can see it just left and slightly up of the NGC 317B label in the DSS image above. At the time Jimi and I thought it could be a star cloud or perhaps even a third galaxy caught up in the interaction. Without a decent internet connection we couldn’t go online and find out then.
So just now I looked up NGC 317 in the DR15 Navigate Tool (http://skyserver.sdss.org/dr15/en/tools/chart/navi.aspx) and quickly saw the knot was really three faint stars bunched together, so they’re simply a chance alignment of faint Milky Way stars.
3617
Out of curiosity I clicked on each of these stars to see what their magnitudes are, but it only gives the magnitude of the reddest star of the three, the one on the lower left in the image below. For some reason all three stars in the clump have been assigned the same magnitude as the reddest star. Astoundingly, it’s shown as magnitude 20.09!
No doubt all three stars together combine into a bright enough glow that experienced observers with a 28-inch scope can reasonably detect under dark skies, so I’m not suggesting that this “star-clump” is really magnitude 20.09. Based on experience, I’ll guess their combined glow is probably around 17-ish magnitude. Pretty cool even so.
3618
My observing notes from July 28, 2019:
“Fabulous field of view – NGC 317 A/B shows their connecting tidal tail and the opposite spiral arm being flung into space. Also saw a small knot in 317B, and PGC 3432 is surprisingly easy to see. 547x, 21.90 SQM.”
3619 3620
NGC 317 A/B and PGC 3432 are easily found just a few degrees northeast of M31, so give them a go and let us know!
Andromeda
RA 00 57 41
DEC +43 47 28
Magnitude 13.9
3616
NGC 317 A/B and PGC 3432 was suggested by Jimi as an interesting object at the 2019 Oregon Star Party – which had wonderfully dark and smoke-free skies this year. The main appeal of NGC 317 was that it’s a pair of beautiful interacting galaxies, with a PGC galaxy off to the side. It looked great on the DSS image on Jimi’s laptop, but what could we see with my 28-inch scope?
Quite a lot as it turned out. NGC 317 A (mag 13.86) is the bright elliptical galaxy just above the messed up looking edge-on spiral of NGC 317B (mag 13.95) below it. PGC 3432 is in the upper right corner of the DSS image, and all three were easy to see, even PGC 3432 (mag 16.7).
The spiral arm of 317B opposite of 317A was seen dramatically sweeping out into intergalactic space, and became quite long with averted vision. Beautiful.
The most difficult detail to see was a small knot in 317B’s other spiral arm, the one being directly pulled on by 317A. You can see it just left and slightly up of the NGC 317B label in the DSS image above. At the time Jimi and I thought it could be a star cloud or perhaps even a third galaxy caught up in the interaction. Without a decent internet connection we couldn’t go online and find out then.
So just now I looked up NGC 317 in the DR15 Navigate Tool (http://skyserver.sdss.org/dr15/en/tools/chart/navi.aspx) and quickly saw the knot was really three faint stars bunched together, so they’re simply a chance alignment of faint Milky Way stars.
3617
Out of curiosity I clicked on each of these stars to see what their magnitudes are, but it only gives the magnitude of the reddest star of the three, the one on the lower left in the image below. For some reason all three stars in the clump have been assigned the same magnitude as the reddest star. Astoundingly, it’s shown as magnitude 20.09!
No doubt all three stars together combine into a bright enough glow that experienced observers with a 28-inch scope can reasonably detect under dark skies, so I’m not suggesting that this “star-clump” is really magnitude 20.09. Based on experience, I’ll guess their combined glow is probably around 17-ish magnitude. Pretty cool even so.
3618
My observing notes from July 28, 2019:
“Fabulous field of view – NGC 317 A/B shows their connecting tidal tail and the opposite spiral arm being flung into space. Also saw a small knot in 317B, and PGC 3432 is surprisingly easy to see. 547x, 21.90 SQM.”
3619 3620
NGC 317 A/B and PGC 3432 are easily found just a few degrees northeast of M31, so give them a go and let us know!