Some Galaxies

[glenc]

I looked at 37 Dunlop Galaxies this morning with my 12" Dob. The galaxies I saw were NGCs 55, 134, 300, 613, 625, 986, 1269, 1313, 1316, 1317, 1350, 1365, 1380, 1433, 1483, 1487, 1493, 1512, 1515, 1527, 1532, 1533, 1543, 1553, 1559, 1566, 1617, 1672, 1792, 1808, 7552, 7582, 7590, 7689, 7793, IC 5250 and IC 5332.
Here are some images: http://picasaweb.google.com/dunlop1826/DunlopGalaxies

[glenc]

Are any of these galaxies too faint for Dunlop to see, what do you think?
His telescope was a 9" reflector. The speculum mirror was equivalent to a modern 6" or 6.5" aluminium mirror.

[ballaratdragons]

I can't see any pics in your site Glen :shrug: It says 'Loading . . .' so I waited, but after 10 minutes still nothing.

I also clicked on 'Slideshow'. Nothing.

[leon]

Gee's Glen you have been a busy boy, great images by the way. ;)

Leon :thumbsup:

[glenc]

Sorry Ken I just tried Picasa and it works OK for me. I looked at some more Dunlop galaxies last night, NGCs 4696, 5253, 5643, 6861, 6902, 7049, 7083, and 7410. With NGC 1487 (D480) Dunlop may have seen 3 stars in a triangle and with 1533 (D320) he may have seen a line of 3 stars.

[glenc]

The faintest Dunlop galaxies are: NGCs 1487, 7689, 1483 and IC 1633 with magnitudes 11.4, 11.4, 12.3 and 11.6 respectively. Below is a map from SkyMapPro for 4am showing his faintest galaxy NGC 1483 near the center and 1487 near the top.

On 3/12/1837 John Herschel wrote reagarding h2595 = NGC 1483 "I feel convinced this nebula is too faint to have been seen by Mr. Dunlop. Put on the 9" aperture, could not discern the least trace of it. Mirror polished yesterday and in high beauty. Sky Superb."

In 1826 James Dunlop described D428 = N1483 as "An extremely faint ill-defined small nebula. A pretty large nebula (NGC 1433) precedes this." Did Dunlop see N1483. What do you think?

[ngcles]

Hi Glen & All,

I'd hate to really pooh pooh either Dunlop or Herschel's observations but someone has obviously made an error of some sort which is easy to do.

I've not seen NGC 1483 myself so I can't comment directly on its appearance. It's on my to-do list. Based on a view of the DSS image it is small but has pretty good surface brightness. I'd guess it could probably be seen from somewhere dark in a modern 8" near threshold. Dunlop used 9 1/4" but with its speculum optics and pretty basic eyepieces were really only the equivalent of a modern 6" reflector -- at best. Hmmm ...

Assuming Dunlop observed correctly, it is a little odd Herschel couldn't pick it up in 18". This begs the question whether Dunlop might have made a positional error in observing another object. Obviously it wasn't -33. Is there another candidate?

Maybe NGC 1493? It is somewhat brighter at mag 11.8B than -83 at 13.1B and more possibly visible in Dunlop's reflector. There are no other obvious candidates I can see. It is nearly twice as far away (2.8 deg) from NGC 1433 as NGC 1483, displaced a bit north and is a bit larger, but Dunlop's very brief description fits okayish in a general way. NGC 1433 is certainly somewhat larger than NGC 1493 (again kinda fits). For interest I have observed NGC 1493 with 10" from home (average suburban site) and this was the note:

"x86 Reasonably large round faint L.S.B patch of gossamer/haze. 12' NW from a mag 10 *. Only satisfactorily observed with A.V. Brightens modestly to centre. Maybe slightly oval in PA 150. No *s immediately associated."

Maybe they both had a bad night?


Les D
Contributing Editor AS&T

[ballaratdragons]

Regardless of using Speculum, can you imagine how clear and dark the sky was back in 1826.

The whole Milky Way was clearly seen in the suburbs of Sydney when I was a kid back in the late 50's ealy 60's. Streetlights consisted of a light bulb under a what looked like a white porcelain dinner plate upside down. They were dim! and the sky was dark!

1826 would have had ZERO pollution (industrial smoke or light) but probably more dust. The sky would have been extremely dark and the air extremely transparent on a clear night. With very basic gear they would have seen a whole lot more than we can see now with the same equipment.

[glenc]

Les, Herschel saw 1483 with the 18" but not when he reduced its aperture to 9".
Dunlop's position was very good, only 1.6 arc min from N1483 in pa 96 deg.

[ngcles]

Hi Glen & All.

Ahhh ... I see now. So, Hershel could see it with 18 but not with the 9" aperture stop on the his telescope.

Apologies mate, my misunderstanding I mis-read your previous post.

Well given that the position Dunlop recorded is very close to the real position, the offset from NGC 1433 is almost dead-on and the description fits pretty well, I'd have to say the case is pretty conclusive and Dunlop's observation was dinky-di.

As there are no other galaxies of consequence within a radius of 1.5 degrees of NGC 1483, the chances of getting the position and offset-angle so nearly correct and the description at least a goodish fit by pure luck are pretty slim.

I tips me lid to Dunlop -- seeing such a faint object with the effective aperture he was using confirms that he was a great observer of his time.

Les Dalrymple
Contributing Editor AS&T

[glenc]

Well I looked at N1483 again last night and gradually reduced the aperture on my 12" down to 8". I decided it was too faint for Dunlop, but like you say the position and description are both correct. I will be interested to see what others think. Dunlop and Herschel would have seen it on the meridian (altitude 77 deg for Dunlop), I didn't do that.