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The California Nebula
Diffuse Nebula
aka NGC 1499, LBN 756
Integrated Visual Magnitude: 5
Apparent Diameter: 2.7o

Minimum requirements to view: naked eye through H-Beta filter and very dark skies

Despite its bright integrated magnitude the California nebula is one of the more illusive objects in the sky.  Without the aid of a filter it is one of the most difficult objects to observe in any aperture.  Burnham's describes this nebula as "A difficult object visually."  But in his day they didn't have the deep sky filters that are available to us.  With an OIII, UHC, or H-Beta filter it  is visible to the unaided eye! 

That doesn't make it easy, however.  The basic problem with observing this nebula is that it is very large.  Even though its total integrated magnitude is that of a 5th magnitude star, this light is spread over an area larger than 2.5o.  The large aperture instruments that collect the most light also give smaller fields of view.  The result is that the apparent surface brightness of the nebula is more or less constant with aperture.  In fact, it is probably best detected with a small aperture that affords a field of view large enough to fit the entire nebula. 

Without the aid of a filter, observations of NGC 1499 are very difficult.  It has been reported in basic 7 x 50 binoculars, although it is extremely faint.  In my 18-inch at 94x I get a 44' field of view, which is not optimal to see such a large object.  Nevertheless, I did "sense" a brighter background in the region without the filter.  I was only able to be sure that I was seeing it by comparing the view with a filter in place. 

In my 18-inch an OIII filter didn't seem to help.  It was only when I tried the H-Beta that the nebula appeared distinctly.  It is a very, very smooth, diffuse haze with fuzzy edges.  Actually, it appears as several distinct hazy blobs.  Sweeping the scope back and forth makes them apparent, leaving no doubt that there is something there.

Orion was getting high in the southeast by then so I swung the scope over to the Horsehead with the H-Beta still in place.  The Horsehead is one of the more difficult objects in the sky, for much the same reasons as NGC 1499.  I was surprised to see the IC 434 nebula pop out clearly on this night, including the dark patch in the shape of a horse's head.  It only took a little looking with averted vision to make out the full profile.  The interesting thing is that it appeared to me that IC 434 was actually brighter and more obvious than the bright portions of NGC 1499 (with the H-Beta in place).  This is probably the result of the large surface area of the latter and my relatively small field of view.  It does, however, underscore just how difficult NGC 1499 can be to see in a large scope even with a filter.

The field in a 90mm ETX at 31x. North is up and east is to the left.

David Knisely reports that in a 10-inch f/5 Newt with an H-Beta filter he "...could see some vague diffuse almost filament-like structure along the north and south edges as I panned around.  It was not bright by any means, but it was not terribly difficult either."  This telescope gives over a 1o field of view, which I believe to be the key to his success.

In smaller instruments look for an elongated glow, like a slightly brighter chunk of sky.  I recently had a try at looking through the H-Beta filter with no optical aid.  It's a bit difficult because the stars are greatly dimmed.  I eventually found the correct part of Perseus and sure enough, with averted vision, a faint rectangular glow appeared in the right location. 

Millennium Star Atlas Vol I Chart 117
Sky Atlas 2000 Chart 5
Uranometria 2000 Vol I Chart 95