How did Dreyer miss these (ngc catalogue creator)

[mdstuart]

We often talk about galaxies that messier missed like ngc2093.

Well last night I observed a fine pair of galaxies under the plough. Ic750 and ic749.

Ic750 is a fine oval shaped galaxy..ic749 was much fainter. Like a small ngc 185 from andromeda to the eye.

So my Dreyer..how did you miss these?

Mark

[michael.h.f.wilkinson]

Inetersting. I might have a go at them. Their visual magnitude and surface brightness puts them within range of my scope, I think. All this fog will need to clear, however

[acey]

Dreyer didn't miss them - he compiled both IC catalogues as well as the NGC. According to Wolfgang Steinicke's site, ICs 749 to 752 were all discovered visually by Rudolf Spitaler in 1892 using the 27" refractor at Vienna University Observatory (749/750 on April 22 of that year). Spitaler discovered 64 IC objects in all.

http://www.klima-luft.de/steinicke/index_e.htm

If you're using a 350mm scope then all NGC objects should certainly be visible at a dark site (Bigourdan used a 12" refractor to measure all NGCs above his horizon), and I should imagine that all or nearly all of the visually-discovered ICs should be visible too.

In the case of bright non-NGC objects the first question is usually why the Herschels missed them. Generally it's because they're very small (hence would have been mistaken for stars) or else are in areas that the Herschels didn't sweep, particularly around the Pole. But in this case the objects were also missed by other top observers such as Marth and Swift. Just one of those things.

[michael.h.f.wilkinson]

People miss thing because space is big, REALLY big. You might think it's a long way to the .....

I'll get me coat

[mdstuart]

Well you learn something every day.

Why though did Dreyer split things in to two catalogues?

Mark

[acey]

The first big catalogue was William Herschel's discoveries: 2500 objects in 3 lists, arranged by type and order of discovery. Objects had an H-number. John Herschel augmented this with his own discoveries (and the Messier DSOs) and put everything in order of Right Ascension. Now everything had an h-number, and most of the objects also had an H number. Then in 1864 John Herschel compiled a "General Catalogue" containing his previous one plus all the other DSOs that had been discovered by others in the intervening years, again ordered by RA. These objects had GC numbers (and most also had H and/or h numbers too).

In 1878 Dreyer published a supplement to John Herschel's General Catalogue with about 1000 new objects that had been discovered. Because of the practice of arranging objects by Right Ascension (which is a good logical system) you couldn't just tag on new objects at the end. So it seemed that a complete new catalogue was needed.

Dreyer published his New General Catalogue in 1888. This contained all DSOs discovered up to that time (including some objects that are actually non-existent, and some duplicate entries). Now there were NGC numbers in addition to all the previous numbers (which Dreyer included for cross-referencing). Dreyer didn't want the NGC numbers to become official, but they did.

New discoveries continued to be made, so Dreyer produced 2 index catalogues (IC). Publication dates are 1895 and 1908; the IC is ordered by RA and old publications refer to objects as IC1 or IC2, so I'm not sure quite how Dreyer managed to keep the whole thing ordered - maybe IC2 is a bigger version of IC1. In any case Dreyer eventually catalogued everything discovered up to shortly before publication in 1908.

By that time photography was well established (many ICs were discovered photographically) and it was clear that a mega-catalogue of all DSOs was going to become unfeasible. The last effort of that kind was MOL, the Master List Of Nonstellar Optical Astronomical Objects, published in 1980. It's a big hardback book and I picked up an ex-library copy online for next to nothing. I never use it.

Catalogues since Dreyer have tended to be of specific object types, particularly galaxies (e.g. UGC, PGC etc). So objects typically have lots of designations. But if there's an NGC/IC (or Messier) designation then that's the preferred one.

The NGC/IC were ordered by RA, but since then precession has mixed that up a little, so they are no longer strictly in order. There are lots of ways you can get it in print (generally very cheaply) but the whole thing is also online in lots of places. The most authoritative site is Wolfgang Steinicke's:

http://www.klima-luft.de/steinicke/index_e.htm

I can highly recommend Steinicke's book about the history of the NGC - fascinating reading (not cheap, but worth it).

http://www.klima-luft.de/steinicke/index_e.htm

[mdstuart]

Thank you Acey..a really good read..really appreciated.

Those astronomers were amazing and their work is a lasting legacy..

My limit seems to be about mag14.0 but I sometimes fail on mag 12 or 13 if galaxies have a low surface brightness.but I could see ic749 surprisingly???

I also suffer at lower decs due to atmospheric dust and glow..I for example could not see that ngc 253...

Also the wife limits tha aperture of the scope!

But I still have many discoveries to make I am sure..

Mark

[acey]

It sounds like IC 749/50 is one of those interesting cases of objects that just got overlooked somehow. There are a number of non-NGC/IC objects that are bright enough to have made it into the NGC but didn't. Another possible list there. I agree with you about the problem of low declination - though I managed NGC 253 with my 8" from 55 degrees north (where it rises to just under 10 degrees above horizon). It was discovered by Caroline Herschel at about 51.5 degrees north. Most nights I don't bother looking too near the horizon but on rare nights when you can see stars clearly there it's worth going for objects that would otherwise be inaccessible. Assuming you have a clear southerly view, of course. I've also managed M83 from the same latitude - only about 5 degrees above my horizon - with my 12" last year.