April Fools! It's Clear! Moon Occults Pleiades!

Well the weather played havoc with my plans to have folks over to view the Pleiades star cluster being occulted by the moon last night. Rain had been forecast for days and all day long the forecast looked gloomy - so gloomy that at 4:30 Bren and I went out to eat, planning to get back by 6:30.

When we went into the restaurant it was total overcast. When we came out it was raining! There seemed no reason to rush, so on the way home we stopped in the bookstore. When we came out we could see some clear sky in the west, but it looked like just a passing slither. Mostly cloudy and still sprinking! Couldn't imagine it opening up. One of my guests called at 6:30 just as we walked in the door. She was going to have to make a quick glimpse of it anyway and I told her it probably wouldn't be worth it, but she might look out her window about 7 to see. Yes, at that moment - 6:30 - you could see the moon through a thin veil of clouds - but all around it the sky was totally overcast.

Boy, was I surprised when I went out to the observatory a few minutes before 7 and had enough holes in the clouds to do a two-star alignment of the telescope. The ground was wet, the air was wet, but the moon was showing through holes in the clouds - and when I looked in the telescope I could see some Pleiades. I went in and told Bren. She came out, and from 7 pm to 7:10 we used the telescope and binoculars and the telescope finder scope to watch the event. (Binoculars were really good to see the entire show at once - the telescope gave you enlarged slices of it. ) There was the beautiful crescent moon, it's dark part well lit by Earth shine, right in the midst of the Pleiades and just starting to cover them up. Hard to get oriented, though, and know exactly what was what because of the clouds. Bren had to go in for a few minutes, but she said she'd be back out shortly. She went in. The clouds closed in and I thought that was it. Wrong again!

(The above is a computer simulation of the event, as is the second image below - captures it pretty well, though - From Starry Nights software. )

She came back out shortly before 7:30. I had been sitting in the observatory, sipping tea and studying charts. The moon miraculously started to emerge, but it had moved behind a tree. The observatory was useless. Out in the wet grass, though, we had a nice view with so much western sky starting to open up that I quickly went and set up the little 4.5-inch Orion reflector( a sweet little scope with terrific optics.) I put it on a table top. Beautiful! Merope, one of the "seven sisters," was covered. Alcyone, the "sister" who always catches my attention because it is so bright and has two faint companions, seemed in line to get hit next. Bren had commented on how 3-D it all appeared to be.

Yes. That was the overwhelming sensation. You really had depth represented well, something you seldom get when you look at the sky. As we watched, the clouds - at what - 3,000-feet perhaps - skimmed the face of the moon, sometimes veiling it, sometimes hiding it completely. Sometimes we would see the moon and the Pleiades. Sometimes just the Pleiades, or just the moon. The clouds added a special magic to the scene - a sense of life with their varying intensity. Some were solid lumps, some were thin, brownish sheets being shredded by the wind. So many things were happening at once. The moon was sinking in the west. The Pleiades was sinking in the west, Well, of course, the Earth was still moving - eastward. Nothing was sinking. We were just leaving it all behind at the rate of about 600 miles an hour - but, of course, there is no sensation of speed so it's no wonder people didn't believe Copernicus. And the clouds were moving from west to east. And way out there - a quarter million miles away, the moon was moving eastward - slowly.

As everything sank towards the horizon the moon was slightly out of sync with the rest of the sky because it's orbiting around the Earth. In an hour it moves half a degree - that's it's entire apparent diameter. And we could see it now - at 7:30 - slowly, inexhorably, moving closer to bright Alcyone. I got out the 20X80 binoculars and set them up on a mount. Ok - but the view was better in the scope. Bren saw one of Alcyone's companions vanish behind the darkened limb of the moon - there one moemnt, gone the next .

I went and got the 8-inch Antares reflector and set it up. "Hurry," she warned, "or you'll miss it." I put in an eyepiece. focused, and there was Alcyone, right on the - GONE. Just like that. "Did you see it?" I asked Bren. "No," she said. "I was looking at a crater." That, of course, was the other attraction. A moon with a strong eastern libration, showing us all of the Sea of Crisis and nearby craters in a light that was a little different than usual for a three-day moon. The moon does this - it really is, as Juliet told Romeo, "inconstant." It seldom puts on the same show. The lighting is always a bit diffferent.

Juliet to Romeo: " O swear not by the moon, th' inconstant moon That monthly changes in her circled orb,

Got that right.

Bren had seen enough. I hadn't, of course. But after half an hour or so she had gotten a real feel for the 3-D quality - oh, I forgot to mention the third dimension - clouds at 3,000 feet, moon at a quarter of a million miles and the Pleiades out there at 400 light years! Think about it - think of the relative sizes of things. The nearby clouds could obscure the scene and only be a few hundred feet across. The moon - roughly 2,000 miles in diameter, could obscure the Pleiades which are what? Maybe 14 light years across! Fascinating. And what I liked best about this was that you could really experience it. The numbers danced in your head - but the numbers were reinforced by the photons pouring into your eyes. Photons from the clouds reaching you instantly for all pratcical purposes. Photons from the moon reaching you in 1.3 seconds - and photons from the bright, young, blue stars of the Pleiades reaching you having left their place of origin about the time Galileo first pointed his telescope to the sky and Shakespeare was penning those famous words about the inconstant moon as his star-crossed lovers sought one another.

I was sorry, of course, that others had not come out. But all day I had been posting discouraging forecast on my web site. I was wrong. Nature played a great big April Fool's joke on me, opening up the sky at the last minute for a beautiful show. but there was nothing I could do but enjoy it. I thought of calling people and was sure if I called them, the clouds would come in again. So for the next 45 minutes I settled into my comfortable observing chair, the 80-mm Orion ED telescope at my eye, and the moon and the Pleiades doing their incredible dance. The clouds had all but vanished. It was wonderful. That was when I began to absorb the full impact of the 3-D effect. It also, of course, was a wonderful lesson in how small the moon is. The Pleiades are roughly a degree across - the moon half a degree. But show someone the Pleiades and ask them if they thought they were larger than the full moon and just about no one would say yes - in fact, they would guess the moon was five-to-10 times larger. It isn't. It's half the size. It's brightness throws us off - make us feel it is much larger.

And right now nature had one last joke on me, her April Fool. I could see the moon moving towards Atlas and his wife, Pleione, two not-so-bright members of the cluster about to be snuffed out. I could also see that Merope - the first major Pleiad to be covered from my perspective - had now emerged on the bright side of the moon. But I could also see some clouds, low in the West, and the moon and Pleiades were both getting near my western tree line. Ok, I figured, good time to put the telescopes away that I had dragged out so quickly. So I did. I put them all away except the 80 mm. I buttoned up the observatory, and went back to watch Atlas get eaten up by the advancing moon. Wrong! The clouds got there first. Heavy, thick, and extensive. Not a scrap of moonlight and most of the stars were vanishing.

But it was fun while it lasted. There will be other such events this year. Three of them for us in this section of the workd - July 20 (early morning) and Oct. 9 and Dec 3 /4. During these last two the moon will be nearly full and will tend to drown out nearby stars. So none will be so well placed, or timed as this one. Oh, I'll watch again. But it will probably be just me, the moon and the Pleiades. And don't worry. In another 18-years or so the whole thing will repeat. Shakespeare was wrong really. The Moon isn't inconstant. It just does it's changes over such a long cycle that most of us are unaware of it. But it will return to this same little section of sky some night to once more gobble up the Pleiades. What's really inconstant is the weather - this is the third time in a single week that I had expected the observing to be poor or non-existant - and the third time I have been wrong. Changes have occured at the last minute - but hey, this is New England, and once more MarkTwain has been proven right. As he said in part - and he was obviously writing about just such a spring day - :

I reverently believe that the Maker who made us all makes everything in New England but the weather. I don't know who makes that, but I think it must be raw apprentices in the weather-clerk's factory who experiment and learn how, in New England, for board and clothes, and then are promoted to make weather for countries that require a good article, and will take their custom elsewhere if they don't get it.

There is a sumptuous variety about the New England weather that compels the stranger's admiration -- and regret. The weather is always doing something there; always attending strictly to business; always getting up new designs and trying them on the people to see how they will go. But it gets through more business in spring than in any other season.

In the spring I have counted one hundred and thirty-six different kinds of weather inside of four-and-twenty hours. It was I that made the fame and fortune of that man that had that marvelous collection of weather on exhibition at the Centennial, that so astounded the foreigners. He was going to travel all over the world and get specimens from all the climes. I said, "Don't you do it; you come to New England on a favorable spring day." I told him what we could do in the way of style, variety, and quantity. Well, he came and he made his collection in four days. As to variety, why, he confessed that he got hundreds of kinds of weather that he had never heard of before. And as to quantity -- well, after he had picked out and discarded all that was blemished in any way, he not only had weather enough, but weather to spare; weather to hire out; weather to sell; to deposit; weather to invest; weather to give to the poor.

Hmmm. . . wonder if Twain ever watched an occultation? or Shakespeare? One thing I'm sure of - they, and the people of their time, were far more conscious of both the weather and the moon and the stars than we are today. We have shut it all out, living in our artifical, well-lit environments. But the show goes on and the price of admission is cheap - as long as you don't mind being played for a fool once in a while ;-)