Observing report from Lake Sonoma

3/25/00

by Steve Gottlieb


Based on the streaky cirrus blanketing the local skies in Albany and the iffy weather forecast for the evening, I was on the fence about observing Saturday night. My favorite haunt in the Sierra foothills seemed too long a drive with low prospects for clear skies, but I was considering a closer site such as Digger Pines, along Mines Road near San Antonio Valley.

As it came down to making a decision, David Silva returned my phone call and we decided to drive up together to Lake Sonoma, an easy 75-80 minute drive from Albany up 101 to Geyserville, with excellent horizons, mag 6+ skies and plenty of space to spread out. Forty-five minutes later I swung by his house in El Cerrito, loaded up his AP Traveler in my minivan next to my 17.5-inch homemade dob and headed off for the San Rafael bridge. As we cruised past Santa Rosa, the wispy clouds had all but disappeared and we were heading north into wide open blue skies with smiles on our faces.

I'd encourage those living in SF, Marin, northern Alameda and Contra Costa county to give this site a try. Lake Sonoma is much closer for these folks than Fremont Peak, Coe and Pacheco, the transparency is excellent in the north, west and southwest. The only bothersome light dome is along the south and southeast horizon so for faint objects its best to wait until they transit the meridian. It was not as dark there on Saturday night as the last two times I visited in December and January, but I still I logged a mag 6.2 star in Ursa Minor in the early evening and with no breeze and minimal dewing Dave and I had a great time.

I spent the first hour or so, revisiting some of my favorite planetaries from late winter/early spring and the rest of evening chasing faint galaxies in Leo, Hydra and Sextans. As my descriptions of 14th and 15th magnitude galaxies would cause some eyes to glaze over, here are a few of planetaries I took a look at --


Sanduleak 2-21 = PK 238+7.2 = MCG -03-21-004 = PGC 22854
08 08 44.3 -19 14 02
V = 13.5; Size 40"x40"

Picked up at 100x with an OIII filter as a small, fairly faint disc just 4' WNW of mag 4.4 16 Puppis. Excellent view at 220x and 280x using a UHC filter, particularly with the star outside the field. Appears moderately bright, crisp-edged, roundish, 0.6' diameter with an irregular surface brightness. Sa 2-21 forms the NW vertex of a triangle with two mag 11-12 stars oriented SW-NE with the following star a close, equal double. Also viewed at 380x without filter, although faint at this power and the double star was cleanly resolved.

This planetary was "discovered" in 1975 by Sanduleak in an emission-line survey of the southern milky way, although it had been misidentified early as a galaxy (MCG -03-21-004). Unfortunately, you'll find it plotted with two symbols on amateur sky plotting software -- but there's only one object here.


NGC 2610 = PK 239+13.1
08 33 23.3 -16 08 57
V = 12.7; Size 50"x47"

At 280x using a UHC filter appears moderately bright, ~50"x40", elongated SSW-NNE. A mag 12 star is embedded at the NE edge of the rim. The PN appears to taper near the star although this may be a contrast affect. The rim is sharp-edged and the surface brightness pretty smooth. Located 3.5' SW of a mag 6.5 star.


NGC 2818A = PK 261+8.1
09 16 01.5 -36 37 37
V = 11.8; Size 85"x47"

This moderately bright PN is nestled on the west side of the faint but fairly rich open cluster N2818. At 220x it appears moderately bright, irregularly shaped, ~1.0'x0.8' and elongated roughly N-S. Excellent view at 280x with a UHC filter and unfiltered at 380x. The rim is irregularly brighter giving a weak annular appearance. Appears brightest at the S and SW rim. The center is slightly darker but there is no well-defined halo. The outline is not crisp and seems to change orientation somewhat with averted vision.


Abell 33 = PK 238+34.1
09 39 09.0 -02 48 33
V = 12.6; Size 275"x260"

This is one of my favorite Abell planetaries and 100x provides an excellent view using an OIII filter. The PN is faint but visible with direct vision as a very large, crisp-edged disc over 4' in diameter appearing to hang to the NE of a mag 7.2 star. The subtle variations in surface brightness gives the strong impression of a huge bubble which is slightly darker in the center. Appears brighter along the W and NW rim where some faint stars are embedded.


NGC 3242 = PK 261+32.1 = Eye Nebula = Ghost of Jupiter
10 24 46.1 -18 38 34
V = 7.7; Size 40"x35"

This beautiful PN has a very high surface brightness and a bluish color at 100x. The view at 280x-380x is stunning with a well-defined double shell structure. The bright, narrow inner ring is surrounded by a second fainter oval envelope. Inside the bright lens is a dark, 10", donut-hole with a faint central star marking the center. In moments of steady seeing, the inner ring has a hard-edge and the central star sharpens up.