Object of the Week, October 6, 2013 - NGC 604

[Howard B]

NGC 604

Triangulum

RA
01 hour, 34 minutes, 32.8 seconds

DEC
+30 degrees, 47 minutes, 06 seconds

Type: Extra galactic HII region, size 1.93 arc minutes x 1.2 arc minutes


NGC 604 is almost as interesting as all the rest of M33. Why would I think that? First of all, 604 is the largest and brightest HII region in M33. Visually, it has the highest surface brightness of anything in M33 and in actual size is approximately 1500 light years across its longest dimension. Seen from 3 million light years away it's still a pretty impressive sight. For a sense of scale, consider that M42 in our own galaxy is about 24 light years across and about 1344 light years away – a distance smaller than the width of 604!

HST NGC604.jpg

Observers with even moderately dark skies and a scope 12 inches or larger will find that 604 is more than a shapeless blob. I first started observing 604 with a 20 inch scope years ago and was immediately struck by what appeared to be two overlapping triangles of nebulosity. It took about 250x for the shapes to be apparent and they become easier to see with increasing magnification, a benefit of 604’s high surface brightness.

If you have a dark sky you might also notice a fainter fan of nebulosity curving away from the brighter triangle, and a slightly fainter halo around both triangles. Although I've tried my best to see the arc as shown in the HST image above, I've so far come up short. However, Jimi has seen it with his 48 inch scope.

NGC604_crop.jpg NGC604_crop_invert.jpg

This is my latest sketch from the 2013 Oregon Star Party on a night with consistent SQM readings of 21.85 and excellent seeing. Using around 700x, small stellar points glimmered into visibility. I've been able to boost magnification to 1250x with my 28 scope to best see them. I’m not sure if I’m seeing individual stars in 604, because they could be compact groups of stars or highly compressed parts of the nebulosity, but each time I see them I’m astonished to be able to detect this level of detail from 3 million light years away.

“Give it a go and let us know!”

Good luck and great viewing!

(PS, sorry for the late post!)