Around the California Nebula (NGC 1499) there is a huge HII region which lies behind the dust in constellations Perseus and Taurus and thus is only visible in the voids and less dense regions of these molecular clouds. That nebula was already partially depicted in the view of the Milky Way from Taurus to Perseus. The 30°×30° wide-field view of this page (probably) shows entire nebula.
It is assumed that the California nebula is ionized by Xi Persei. Distance estimations are 370pc to 460pc (Gaia EDR3) and 320pc to 470pc (Hipparcos). That interval can be refined slightly by considering the distances of the foreground nebulae:
There are two other HII regions that seem to lie in front of H1, labeled "LBN 749A" and "LBN 749B" here. They are at a similar position as LBN 749 (coordinates of LBN catalog are often inaccurate), which is categorized as a HII region, and together they have a similar dimension as LBN 749.
The brighter part, here labeled LBN 749A, is most likely ionized by HD 278942 at a distance of about 383pc (=1250ly, Gaia EDR3, +/-14pc). The dark nebulae that lies in front of LBN 749A belongs to the Perseus molecular at a distance of about 305pc, see . At this distance the diameter of LBN 749A would be about 5pc (1° apparent), which means that it is almost impossible that this nebula lies within the Perseus molecular cloud.
Another molecular cloud lies between LBN 749A and LBN 749B and H1: that molecular cloud obscures the background nebulae but is does not obscure LBN 749A. The existence of two molecular cloud in that region was also detected by , a CO radio survey which observed double lines in that region. That survey also measured the northern parts of the molecular cloud that obscure H1.
The fainter part of LBN 749, LBN 749B, may be ionized by omi Per. Most exact distance estimations are from Gaia EDR3: 290pc to 380pc. That does not lead to additional information. Also, it is not clear whether IC 348, the nebula south of omi Per and whose distance is about 320 pc (long baseline measurements from  and Gaia EDR3 data) lies in front of LBN 749B or not.
Near VdB 24 there are two young stellar objects that may belong to the molecular cloud that lies between H1 and LBN 749A, BD+38 811 and 2MASS J03494092+3859051, both in a distance of about 430 pc (=1400ly). Unfortunately it cannot be safely detected from visual inspection, whether the large HII region lies in front of that star formation region.
Furthermore the Taurus Molecular Cloud obviously lies in front of H1. Distance according to  is 130pc to 200pc, much closer than LBN 749A.
Thus, the only constraint that can derived from the given data is that the minimum distance of the molecular clouds that lies in front of H1 (and behind LBN 749A) is about 380pc.
Image data are:
|Center position:||RA: 3h48', DEC: 35°|
|Orientation:||North is up|
|Scale:||10 arcsec/pixel (in center at maximum resolution)|
|FOV:||30°×30° (through center)|
Sum of exposure times of all frames used to calculate the image.
Image processing steps where:
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