When bad is good - a productive cloudy night of observing

Clouds! Throughout my observing life I’ve written off cloudy nights as next to useless for the observer. I guess this is due in part to my lack of serious interest in observing planets, because last night was certainly cloudy here, yet we had some excellent views of Venus and Saturn – even a special bonus treat.

It was sort of like this most of the night, although this is a photo from another place and time.

I was drawn out because four members of the “Prime Time: Observing through the Astronomical Year” program were out for their May observing session and Saturn and Venus were high on their list of observing targets this month. But also high were the clouds – not solid cover, but most of the day high, thin stratus and cirrus clouds had caused the sky to be milky white. Had our targets been anything requiring transparency – star clusters, galaxies and nebulae – I would have called off the session. But the Clear Sky Clock indicated it would get better (it did not), so I set up several telescopes and waited.

Shortly after 6 I went out and on a whim, took the 8-inch LX90 out of “park.” (Park allows the telescope to pick up where it left off the night before without any aligning which would have been impossible in daylight. Nice feature if you can leave your scope in one place on a mount over night.) I glanced at where I thought Venus should be – solid, milky white with some dark streaks. The sun was more than an hour away from setting. Oh well – I asked the scope to find Venus. It said it did, but there was nothing in the eyepiece. I glanced in the finder – wow! There it was, a nice bright dot not far from the crosshairs. I put the scope on target and was rewarded with the best view I’ve had of Venus in my life!

The task for the group is to draw Venus to indicate it’s phases. The folks who had been out Friday night – sparkling clear – had found this difficult. Venus was just too bright to get a real clean view and even with a polarizing filter cutting down the glare, the atmosphere was dancing like crazy. That made it very difficult for new observers to detect the phase of Venus. But tonight would be different, I was sure – the clouds were a blessing in disguise. So I called the folks who were due to come out and said come in spite of the clouds.

And they found it worth it.

Not only could they see Venus clearly – by 8 pm it was easily visible to the naked eye, though not so bright in the haze as the past few nights – but in the telescope it also had a companion. This had been predicted, but I had missed the prediction, so this was a pleasant surprise. About 24 arc seconds away (in other words, very, very close) was the 4.8 magnitude star 139 Tauri! Neat. Here’s a simulation of the scene from Starry Nights. But it was much more charming in real life. Starry nights represents the 4.8 mag star the way it normally does, which is a fairly large disc that is way out of proportion to magnitude –4 Venus. Venus, in fact, was shining about 3,000 times as bright as the star!

After drawing and taking the measure of Venus, we switched to Saturn in the LX90, the 5-inch NexStar and the 15-inch Obsession. Beautiful! Again, clouds cut down the light, but the seeing was nice and steady. Not the best possible, but certainly a four out of five. I believe everyone found Cassini’s division, the shadow of the planet on the rings, and Titan and Rhea. The other bright moons weren’t visible, perhaps because of the clouds, but certainly because all three were bunched close to the planet. Even on a more transparent night I suspect they would have been difficult to see.

BTW - the cloudy conditions also allowed me to emphasize the difference between "seeing" and "transparency," concepts new observers frequently have trouble fully grasping.

I should have tried some close double stars to see how they handled the clouds, but forgot to. But the clouds were forgiving enough for everyone to see the Big Dipper and use the Pointer Stars to find Polaris – a hazy spec just able to burn its way into naked eye visibility. (Our limiting magnitude was 2 or 3 for most sections of the sky. ) Again, the haziness and clouds could be counted as a small advantage -when you see only the bright stars, it's easier to pick out asterism such as the DIpper and the Sickle of Leo.

And that was the other main task - find Regulus and the Sickle of Leo, plus the bright triangle that make up the lion’s back quarters. Done. Everyone also got a good look at Regulus as a double star – not that it was spectacular, but Regulus is the bright star of the month for us.

Bottom line – we had a productive two hours of observing on a night I would have normally written off entirely! In fact, I would have been watching reruns if it wasn't for my obligation to the Prime Time group. I sure learn a lot when I attempt to teach others - and that, I would suggest, is the real lesson here ;-)