MB, 5/5 - 5/6: 2008 B.C.N. #1!

Marek Cichanski

Well, the subject line says it all, if somewhat cryptically.

I just got back from Montebello, and I managed to experience the first Black Cloud Night of 2008. Sadly, there was some high cirrus that kept it from being a true 'B.C.N.' experience, but it reaffirmed my faith in the marine layer.

I called the MROSD rangers around 2 pm, having decided that an impromptu Montebello night was in order. The sat loops and forecast discussions made it sound like it was going to be a classic case of 'OI Poker', in which it could go either way - it could either be a big 'ol fog-out, or a decent night. A little bell also rang in the back of my head, reminding me that these were the sorts of conditions that sometimes lead to Black Cloud Nights.

For anyone who doesn't know, a Black Cloud Night is when 'marine layer' clouds cover most or all of the Bay Area's lights, or at least those that you'd normally be able to see directly from your chosen observing site. The sky won't necessarily get fully dark in such a situation, because there are usually at least some lights still exposed here and there, and some of the light pollution comes up through even fairly thick clouds, but it can dramatically improve the sky all the same.

When I arrived at Montebello shortly before sunset, it looked rather grim. Fog was pouring over the ridgeline to the north, and fog had pushed through the notch to the south in a big way. Cold wind was blowing from the south, too. Not good. I was ready to pack it in without even setting up, since I didn't have any dew heaters.

After strolling around for a while, though, I noticed something strange... the fog to the south had pulled back! The wind had largely died, too, and it had gotten noticeably warmer and drier. Aha! The night might be salvageable after all!

As it turned out, conditions were somewhat variable. It never got below about 50 F, but it wasn't really a warm shirtsleeve night, either. Breeze from the south was variable, never too bad, but never really gone. Hat, gloves, warm boots, coupla jackets. It was basically a somewhat cold night. But not horribly so.

Around midnight, I was thinking of packing up, and I strolled over to the gate, only to notice... black clouds below! Woo hoo! Unfortunately, there had been some high cirrus all night, which rather spoiled the effect. There was plenty of clearing in the south, and I'd been able to observe quite a bit, but the cirrus reflected back such light pollution as was making it through the clouds, rather nullifying the BCN effect. But, the extra darkness was quite noticeable in some areas. The south got really good. Any hint of Santa Cruz light was gone, daddy, gone. I saw Omega Centauri naked-eye, albeit with averted vision. M3 and M5 were very nice and contrasty in my 10" f/5 scope with a 13mm t6 Nagler.

I had spent a lot of the evening touring around Downtown Virgo using the closeup chart in Pocket Sky Atlas. This made for a very nice tour, and I noticed for the first time that you can extend Markarian's Chain into a big 'circlet' that passes through M91, M90, M89, M87, and back to the M84/86 triangle. I was also pleasantly surprised by what a nice edge-on galaxy NGC 4762 is! This is probably one of those fun objects that we always forget about and discover anew. I'll bet a dollar to holding a donut that it's on the TAC Eye Candy list.

I snagged one of those Orion waist packs today, and spent a few minutes getting it kitted out before I headed up the hill. Now my easy-up scope is fully set, no big toolbox or eyepiece case to schlep around. Just a few collimation tools, a 24 Pan, a 13 Nagler, a 7 Nagler, an eyepatch, and a coupla filters. I managed to remember to make my spectroscope eyepiece part of the package, and I had some fun looking at stellar spectra for the first time in a while. I think that my favorite sight of the night - aside from M3 and M5 - was the spectrum of Arcturus. It has so much detail in it, it's like observing the Moon or a planet. I also got a big kick out of the strong dark hydrogen lines in Vega, and the funky molecular bands in Antares. Always neat to see.

I packed up around 12:30, after deciding that the cirrus was going to keep me from really enjoying the full benefits of the Black Cloud Night. But it was still very nice to have the marine layer treat me kindly, and I'm glad that I got out. I'm keeping my fingers crossed that we can have more Black Cloud Nights this summer, with good transparency and seeing overhead.

Marek