Mike Brown's Planets: moon

Showing posts with label moon. Show all posts

Millard Canyon Memories

The Station Fire started near JPL on Thursday and went crazy yesterday, expanding to 20,000 then 35,000 and now who-know-how-many acres. Remarkably few structures have been lost.There is a good chance, though, that the little cabin that I lived in when I first arrived at Caltech is now ash (it's NOT! I just got word from an old neighbor that the canyon was saved. so hard to imagine looking at all of the destruction in the region). I might be wrong; in the major fires 15 years ago Millard Canyon was saved when fire skipped over the top of it. But from everything I can see things don't look good. The firefighters started protecting structures in the real city, not crazy cabins up in the woods. The cabin was at least 100 years old and had survived floods and fires that had slowly gotten rid of the cabins throughout the rest of the San Gabriels mountains.

It was a wonderful if somewhat eccentric place to live. I write about it in my forthcoming book (sadly, books take way too long, even after you finish writing them, so forthcoming means perhaps a year), and I wanted to give a little excerpt here, in memory of the little cabin that I fear met its doom yesterday or last night.

----

When I first started looking for planets, I lived in a little cabin in the mountains above Pasadena. Though I cannot prove it, I am willing to bet that I was the only professor at Caltech at the time who lacked indoor plumbing and, instead, used an outhouse on a daily (and nightly) basis. I worked long hours, and it was almost always dark, often past midnight, when I made my way back into the mountains to go home for the night. To get to my cabin, I had to drive up the windy mountain road in to the forest, past the National Forest parking lot, down to the end of a dirt road, and finally walk along the side of a seasonal creek along a poorly maintained trail. For some time after I first moved in I tried to remember to bring a flashlight with me to light my way, but more often than not I forgot. Eventually I had no choice but to give up on flashlights entirely and, instead, navigate the trail by whatever light was available, or, sometimes, by no light whatsoever.

The time it took to get from the top of the trail to the bottom, where my cabin waited, depended almost entirely on the phase of the moon. When the moon was full it was almost like walking in the daylight, and I practically skipped down the trail. The darker quarter moon slowed me a bit, but my mind seemed to be able to continuously reconstruct its surroundings from the few glints and outlines that the weak moonlight showed. I could almost walk the trail with my eyes closed. I had memorized the positions of nearly all of the rocks that stuck up and of all of the trees and branches that hung down. I knew where to avoid the right side of the trail so as to not brush against the poison oak bush. I knew where to hug the left side of the trail so as to not fall off the twenty foot embankment that we knew as “refrigerator hill” (named after a legendary incident when some previous inhabitants of the same cabin bought a refrigerator and had hauled it most of the way down the trail before losing it over the embankment and into the creek at that very spot; I never lost a major appliance, but I took extra care – and used ropes – one time when I had to get a hot water heater down the hill to install at the cabin; it was rough going, but the new found ability to take hot showers was definitely worth it).

I had almost memorized the trail, but, every 28 days, I was reminded that, really, there is quite a big difference between memorization and almost-memorization.

Every 28 days the moon became new and entirely disappeared from the sky and I was almost lost. If by luck there were any clouds at all in the sky I could possibly get enough illumination from the reflected lights from Los Angeles, just a few miles away, to help me on my way, but on days with no moon and no clouds and only the stars and planets to light the way I would shuffle slowly down the trail, knowing that over here – somewhere – was a rock that stuck out – there! – and over here I had to reach out to feel a branch – here! It was a good thing that my skin does not react strongly to the touch of poison oak.

These days I live in a more normal suburban setting and drive my car right up to my house. I even have indoor plumbing. The moon has almost no direct effect on my day to day life, but, still, I consciously track its phases and its location in the sky and try to show my daughter every month when it comes around full. All of this, though, is just because I like the moon and find its motions and shapes fascinating. If I get busy, I can go for weeks without really noticing where it is in the sky. Back at the time I lived in the cabin, though, the moon mattered, and I couldn’t help but feel the monthly absences and the dark skies and my own slow shuffling down the trail.

Contrary to how it might sound, however, back then the moon was not my friend. The 2 ½ year-old daughter of one of my best friends – a girl who would, a few years later, be the flower girl as I got married, would say, when asked about that bright object nearly full in the night sky: “That’s the moon. The moon is Mike’s nemesis.” And, indeed, the moon was my nemesis, because I was looking for planets.

----

The moon is nearing full tonight, but it's no longer my nemesis. That honor will now go to the Station Fire which I fear has taken away that place I loved so well.

Lunar dreams

Forty years is a long time, particularly if you are only a smidge over forty yourself, like me. When I was a kid, I wanted nothing more than to be an astronaut and go to the moon like those guys did 40 years ago today. The father of everyone I knew – mine included – was some sort of engineer working to build the Saturn rockets to send men to the moon (for a while as I child I thought that when you grew up you became a rocket engineer if you were a boy and you married a rocket engineer if you were a girl; few other options in the world appeared to exist). When Neil Armstrong stepped on the moon, I was pretty sure that that was exactly what I was going to eventually be doing, too. I drew picture story books of rockets and command capsules and lunar modules and splash down. I made cardboard models of Lunar Rovers and designed outposts where, I was pretty sure, I would eventually live.

The moon landings have faded into history as simply one of those amazing things that happened a long time ago that we don’t do any more, like dog treks to the south pole, first ascents of unscouted peaks, and world wars.

Every once in a while, though, something happens that pulls the moon landings out of the abstract haze of history and makes me remember: these things were real! They really happened. Here are two:

A few years ago I was giving a talk in New York City at the Hayden Planetarium, and I decided to spend the afternoon visiting the Planetarium itself and the Museum of Natural History. I was particularly interested to see how they were dealing with all of the controversy over Pluto, the then-embattled 9^th planet. And I was mesmerized by the best example I had ever seen of a Pallasite meteorite – a chunk from the boundary between the inner iron core and the rocky mantle of a little dwarf planet in the asteroid belt which got smashed to little bits, one of which I was staring at. But the part of the visit that unexpectedly took my breath away was staring at the pictures that were strewn on the walls of the hallways of the Planetarium with little fanfare. These were full sized prints of pictures taken by the Apollo astronauts, prints so large that you could stick your face right up to them and see details that you would never seen in the typical book or TV show or anything else. And most of them I had never seen before, anyway. There are only a few canonical moon shoots that we have all seen over and over and over but most of the hundreds and hundreds of pictures have not gotten much light of day. And oh what pictures. Standing and staring at those pictures took me back 35 years to when I wanted to be an astronaut. They were really there. You could almost taste the moon dust.

My favorite of all of the pictures, and the one that made me suddenly re-remember how spectacularly far-fetched the whole idea of going to the moon was, was a shot where you could see the lunar rover in the near foreground and way way way way way in the distance was the lander. And suddenly I realized: these two men are so far removed from home that the chance they will ever make it back alive seems miniscule. They are hundreds of yards from the rover, which is miles from the lander, which has to take off from the surface of the moon, rendezvous with the command module, return to the earth, drop out of the sky, and splash down into the ocean. And it all has to work. What were they thinking?

I stumbled across one of my other favorite Apollo moments a few years ago through some sort of random web surfing, looking for I-can’t-remember-what. My eye was grabbed by a link to an annotated transcript of the Apollo 11 landing. I clicked and started reading. I looked up 30 minutes later in a sweat, my heart pounding, and, again, thinking: who possibly thought that this would work? These guys were insane. I was too young at the time of the Apollo 11 landing to have known at the time whether or not people paid attention to how close Apollo 11 came to not making it. And how nail-bitingly suspenseful to know if they were going to land or crash or abort or something else entirely. I won’t give away the ending (perhaps you know it already), but instead simply point you in the right direction. I can read the whole thing over and over again (and pause for all of the audio clips and film clips), but if you feel the need to cut to the chase, start at 102_48_08 with “Eagle, Houston. You’re Go for landing. Over.”

I just did it again. To get the link right here I searched for the page again and while I was at it I read the whole thing. And my heart rate is still going strong.

Just in time for the big anniversary there are a slew of new books about the moon, of course. I recently got two of them to whet my lunar appetite. They both have that ability to make me re-remember my astronaut-yearning days, but each in very different ways.

Who could not like the idea of Moon 3-D: The Lunar Surface Comes to Life? As long as you can get over reading the book while looking through built-in 3D glasses (and thus looking pretty silly to anyone around you, including even 4 year olds), the book is a pleasure to look through. I never realized that the astronauts purposefully tried to take 3D image. They didn’t have any of the bulky dual camera stereoscopic equipment that people usually use, they simply took a picture and then moved left or right a few feet and took another. The results range from hard-to-figure-out to spectacular. And the 3D really works most of the time (enough so that after the 4 year old was finished making fun of me for the funny glasses she wanted to look through them herself and she made ooohing and ahhhhin sounds and kept taking off the glasses to make sure nothing funny was happening). A personal favorite of mine is an Apollo 15 picture looking back at the lander with desolate mountains in the background and footprints all around the base. Even with 3D none of the pictures quite has the impact of the large prints on the wall of the Hayden Planetarium, but if you’re not headed into New York anytime soon, this might be the way to relive the moon.

The other book takes a special type of space geek to enjoy. Missions to the Moon, a big glossy book chock full of geeky things like reproductions of Wernher Von Braun’s design for a space station, somebody’s schematic sketch of how an Apollo mission would work, a schematic of the Apollo console with all of the lights and switches indicated, and, my favorite, the lunar module descent monitoring chart, which the astronauts would have used to look out the window and know they were going in the right direction. Couple that with the transcript of the landing itself and see if you can follow the whole thing.

After Lilah got done playing with the 3D glasses she, of course, wanted to know what all of those other things in the other book were, and I explained all about landing on the moon to her. Today, on our drive in to school, we listened to Buzz Aldrin on the radio, and I told her, again, that he was an astronaut who went to the moon.

“Why is everyone talking about the moon today, Daddy?”

And I explained about how on this day, 40 years ago, astronauts landed on the moon.

Forty years is a long and arbitrary time in some ways, but to me, and to Lilah, this was even more meaningful. I am 40 years and 1 month older than my daughter. I remember when Armstrong and Aldrin stepped on the moon 40 years ago today; the things I saw and the things I read and talked about affected the direction of the entire rest of my life. Lilah is, finally, the same age as I was then. What will she remember? Where will she go? No way to know, but I’d like to ask her in 40 years if she remembers a day we looked at books and listened to the radio and tried to remember what it was like 40 years before that when I was a 4 year old watching people on the moon for the first time.

Encore: Yelping at Saints

[I've been watching the moon, which made me remember a much earlier column that almost no one read. Forgive the rerun, but watch the moon!]

If your skies have been clear for the past week you might have been noticing -- as I have been -- the slow but unstoppable growing of the moon. There's nothing new here. It does essentially the same thing every 28 days, but it is still a show worth watching.

In my backyard I see this: each night as the moon moves further and further in its circle around the earth and we see more and more of the illuminated half, the moon is getting just a little brighter. In a few days, as the moon finally goes from just-barely-not-full to finally-completely-full, the moon will finally brighten its last incremental amount and it will be its brightest of the month, though only a little brighter than it was the night before.

This gentle brightening to a muted peak sounds prosaic and reasonable. But it is not true.

I remember once being out on a backpacking trip in the wild mountains inward of the Pacific coast south of Monterey. Some friends and I had hiked all day to make it over a range and down to the bottom of a creek where a little stream of hot water poured out of the earth making a tiny pool in which to soak sore legs and shoulders. We camped a bit away from the hot pool, ate a warm dinner as the sun was going down, and finally began climbing our way to the top of the little ridge separating us from the hot spring. We didn't even bother with flashlights in the dark because the full moon had made the entire woods faintly glow -- plenty of light to get around at night even in the dark of the wilderness. As we had almost reached the top, though, somebody silently flipped a switch and a blinding spotlight was suddenly tracking us from the ridge.

This was miles away from any roads or machinery down a long windy trail, so perhaps I could have reasoned my way out of the situation given a little time for relaxation, but, in the instant, I did what I think most anyone would do when unexpectedly illuminated by a spotlight deep in the woods far from where anyone or anything should be: I yelped. Loudly.

My yelping didn't affect the spotlight, which refused to flinch. It refused to flinch, I realized an embarrassed moment later, because it was no spotlight, it was the moon. It had been hiding behind the ridge until we had gotten near the top, and as we rose over one bump it suddenly revealed itself like the flip of a switch. My credibility as a young astronomer (I had just started graduate school that year) was seriously diminished amongst the friends who had seen me frightened of the moon.

Which is to say that the full moon is really bright.

The fact that the full moon is bright is perhaps not a startling fact, but what is startling is that if I had been coming over the ridge on my way to the hot pool and I had seen the moon a day earlier or a day later, I would never have mistaken it for a spotlight.

You don't have to take my over-tired-from-hiking-all-day's impressions for it. If your skies are clear this week as the moon is finally puffing towards full, go outside and see for yourself. Go out on Wednesday, two days before the full moon, and look around. Check out the barely visible shadows. See what fuzzy shapes you can make out in the distance. Look up and notice that the moon is definitely not fully illuminated, but it is getting close.

Go out Thursday. To really do the job right you should go out an hour later than you did the night before, since the moon will have risen an hour later. Look around. You probably won't be able to tell any difference at all from the night before. Same vague shadows, same fuzzy details. And then look at the moon. Definitely bigger, but one edge is still a little flattened. Tomorrow it will indeed be full.

Finally, go out on Friday, an hour later still if you can. Stare right at the moon, if your eyes can stand it. It does look like a spotlight up there in the sky. It is much brighter than it was just the day before. Look at the now-crisp shadows on the ground and the sharp details on the rocks and the plants that you can now pick out. Now go ahead, if you need to, and let out a little bit of a yelp. I'll be understanding.

What is going on with the moon? How can it get so much brighter in just a day? Who turned on the spotlight?

In medieval paintings, saints and anyone else holy are always depicted with a halo around their heads. Unlike modern halo depictions, which look like a gold ring hovering slightly above the hat line, these medieval halos appear more like a general glow coming from behind the entire head. Whenever I see one of these glowing medieval halos I think about how bright the full moon is.

I have a hypothesis -- totally without the benefit of supporting research, necessary expertise, or, likely, even minor merit -- that the medieval painters painted halos like this because they had seen such halos around their own heads. And I know what the painters saw, because I have a halo around my head, as well.

Here's another experiment to try. Go outside on a bright sunny day and start watching your shadow. Walk along until you find a place where the shadow of your head is falling on grass. Focus on your head shadow while you continue to walk, letting the background grass blur in you vision. You will gradually notice that there is a diffuse glow around the shadow of your head. It won't be around any other part of your body, and you won't see the slightest hint around anyone else's head. Point out your halo to any else and they will see precisely the same thing: a halo around their own heads and nothing around yours. Everyone is holy to themselves.

In reality what you are seeing is not some sort of corporeal representation of your own ego or a mystical aura of self-realization, but simply a literal trick of lights and shadows. When you are looking at the shadow of your own head, you are looking, by necessity, directly in the opposite direction of the sun. Stop focusing on your glowing halo for a minute and now focus on the grass itself. You'll notice that in the region where your halo is you will not see a single dark spot due to a shadow of one blade of grass on another. There can't be any shadows; with the sun directly behind you, any piece of grass that you can see can see the sun, so it can't be in shadow. Start looking away from your head shadow and you notice that you are now starting to see collections of tiny shadows, so the overall scene gets darker and darker even though it, too, is fully illuminated by the sun. Your halo is simply the total lack of shadows that can only occur when you are looking almost exactly opposite the sun. I've seen my halo from many places, on many surfaces: on grass or rough dirt or asphalt while walking, even on the tops of a forest full of trees while looking out of the window of an airplane flying low enough right before landing that I could pick out the shadow of the fuselage and see a beautiful glowing ring around. Anywhere you have sunlight and a surface rough enough to make millions of tiny shadows you get to glow the glow of the saints.

And so it is with the moon. When you look at the full moon you are almost looking at where the shadow of you head would be. The sun, though it has set over the horizon, is directly behind you as you face the full moon. If you could see down to the surface of the moon, you wouldn't see a shadow anywhere, not in the craters, not amongst the craggy mountains, but, more importantly not even at the finest scales of the rocky dust that covers most of the surface. The next day, when the moon is just past full, the shadows will begin to reappear and the spotlight will be extinguished.

It happens every month. It's just a trick of light and shadows. But, every now and then, I still look up at the full moon and think about saints and I feel a little bit of a yelp deep inside.

To the moon

My father was a rocket scientist. Well, OK, not precisely. More specifically he was a rocket engineer. Or, more precisely still, he was an engineer who worked on the computers that went into space and navigated the rockets. He worked on the Saturn V that lifted Apollo astronauts toward the moon, he worked on the Lunar Module, which touched down on the moon, he worked on the Lunar Rover, which drove astronauts around on the moon. All of this before he was 30 years old.

I never remember him talking about it at all, talking about what it was like to send men to the moon, to be involved in such a tremendous adventure, but, ten years ago, in the little farming town on the edge of the Mississippi River where he grew up, I had a conversation with one of his friends from those days, and he told me that they all felt like they had lived in a magical time. After the Apollo missions ended, they all later worked on the Space Station and more mundane things like the ticket-taker on the BART trains that I used to take when I was a graduate student living on the San Francisco Bay. But nothing in their lives was ever quite like a being a bunch of thirty-year-old kids living in northern Alabama having the blind optimism to think that if there was a rocket being built they knew enough to put the computers together to make those rockets bring people to the moon. And back. And then actually doing it.

I wish I could ask him about it, but that opportunity is a decade gone.

Being the mid nineteen seventies, he had a marriage and he had three children – me, my older brother Andy, my younger sister Cammy – all before he turned 30, and we all lived in what now seems to me like a huge house in northern Alabama. Being the mid nineteen seventies, the marriage didn’t last. He moved to an apartment across town, then to Maryland, then to North Carolina, then to Houston, and finally, for his last few weeks, back to North Carolina to stay in the house of my sister.

In those last few weeks my brother and I were there at my sister’s house, too. I was in the middle of my third year of being a professor at Caltech and I was still trying to get on my feet. But, that quarter, I simply canceled my class midway through and gave everyone in attendance an “A.” Oddly, I had no complaints. I then flew across the country to meet my father and my sister and soon my brother and we all stayed in North Carolina for a while.

It was too late then to say much. He was mostly groggy from the pain medication. But we talked some about what was happening in all of our lives. Though he never would say such a thing directly, I think he was proud that I done well enough at school to land a job being a professor at Caltech. I remember complaining about some of the more mundane aspects of the job to him and having him softly glare back and whisper: “do you know how lucky you are?”

I told him about a new project I was starting that I was quite excited about. We had just started using an old telescope at Palomar Observatory to make repeated wide-field observations of the night sky in search of particularly large objects in the outer solar system. I told him that I was certain there would be things larger than Pluto out there to see and that I really hoped to be the one to find them. He always liked long-term plans and was happy to see that I finally seemed to have one. “But what if there isn’t anything out there?” he asked, in his always not-quite-so-encouraging way. There will be, I said. I’m sure there will be.

We talked about the long term relationship I was in that, though I didn’t know it at the time, was within a month of finally falling apart. I told him why the relationship was hard and not going so well. I remember perhaps the only words of relationship advice he ever gave me: “There shouldn’t be any fighting. Find someone you don’t fight with.” Though the words resonated with me, my father’s accumulated lifetime credibility in this realm was not high. So I filed the advice away.

He died a few days later. It was ten years ago today.

I’ve missed not having a father for the past decade. I feel we were still, that late in both of our lives, getting to know and understand each other, something we had never had much of an opportunity to do when I was younger.

But, today, I am thinking of the things that I wish I had the opportunity to show him over the past decade. I don’t have much in the way of spiritual beliefs about any afterlife, but, if there is one, and the deceased person can pick his form of communication with the corporeal world, I am pretty sure that my father would pick the web. When he first got cancer nearly 20 years ago he immediately took to the then-new internet as a means of educating himself and everyone else about everything to do with the cancer, the treatments, the options. It’s the sort of thing that everyone does routinely these days, but, back then, it was still quite novel. So if he’s out there anywhere, I like to think of him hooked in through some vast astral server. So this is for him, vial HTML, which he first introduced me to:

Dad –
A lot has happened in the past decade that I think you’d have been proud to have heard about, but there are three that I really wish I could share with you.

Remember that project I told you about ten years ago? The one that started looking over vast swaths of sky for things that moved? The one where I thought I would find another planet? Well, it took a few years before it began paying off, but it has been a pretty spectacular ride. There were indeed things out there to be found. One – so far – was even bigger than Pluto. I wouldn’t have guessed at the time, but all of it caused a big shakeout in the solar system leading to the new decision to recognize only 8 planets. That’s a pretty big change from your lifetime, where Pluto was a planet when you were born and Pluto was a planet when you died. I think you would have enjoyed watching the changes happen. And I sort of suspect that, though you would never actually say it directly to me, you would be somewhat proud of me. I’m sorry you weren’t around to see it.

Some other big news of the past decade: you were right about relationships and fighting, I think. Who would have guessed that? It took me another four years after that conversation, but I did find that person you were trying to guide me towards. I got married to Diane six years ago. I know that you were perhaps always convinced that no one was ever good enough for one of your kids, but, I have to admit, I think you would be charmed. I look at the picture that was taken on our wedding day sometimes, the one that has Diane and me and my brother and his wife and my sister and her husband and their two kids and my mother and my step-father and I wish that you were in the picture too. It would have been a bit awkward, these extended family things always were, but the awkwardness would have been better than the empty spot that I now see every time I see that picture.

There’s one more thing I wish I could show you. Her name is Lilah, and she is a 3 ½ year old bundle of silliness, stubbornness, curiousness, sweetness, and talkativeness. It is part of the mythology from my childhood that you were not particularly pleased about having that third child, but when it turned out to be a baby girl you pretty quickly got over your misgivings. I think you would like Lilah, and I think it would be pretty hard for you to hide. She asks about you sometimes. She asked about you this morning, even. “But Daddy, who was your daddy?” and I tell her about you. “Why did he die?” she asks. I explain about being sick, about having cancer. She understands a little, but, clearly, only a little. “Do you get another daddy when yours dies?” No Lilah. You never do. You never, ever, do.

What Lilah doesn’t yet know is that you don’t want another daddy when yours dies. You just want yours back. And when you realize that that is never going to happen, you at least want a chance to tell him a few things. And you hope that he has some chance of listening in, at least every ten years or so.

Lilah Brown's Planets

Since late summer, my three year old daughter Lilah has been mesmerized by Jupiter. Every night for a few months now it has been high in the evening sky, one of the first things to pop out of the murky twilight and reveal itself night after night after night. Back in the summer we would have to go outside right at her bedtime, when it was just barely dark enough to make out Jupiter, so she could say good night. These days it is plenty dark as we drive home every day, and , for her, the highlight of the drive is the moment after we’ve climbed the little hill to our neighborhood and we take the final left hand turn to point west, and Jupiter suddenly appears in her window, high enough in the sky to even be seen from the moderate depths of her child car seat.

Anyone who, like Lilah, has been following Jupiter has noticed that it is no longer the king of the evening skies. A while back Venus crept up into the twilight to start to steal the show from Jupiter. Or, at least, in Lilah’s view, to share the show. She went from having only one planet to now having two planets to say goodnight to every night.

Lilah sees planets everywhere. You never quite realize – until you have an obsessed 3 year old – how prevalent images of planets are in everyday life. She’s got them on her lunchbox (a gift from friends who thought it would be funny if Lilah carried a lunchbox where Pluto is a planet); she sees pictures in magazines and catalogs; she sees mobiles and puzzles at stores. I would tend to just walk by them without noticing, but she always runs up – “Daddy daddy daddy daddy LOOK!” She always quickly picks out Jupiter (the big one) and, of course, Saturn. She recognizes the globe-like look of Earth. And she gets Venus right more often than I think she should.

A few nights ago, after a long cloudy spell when we couldn’t see the planets at night, Lilah looked up at the sky and was a bit startled. “Daddy daddy daddy daddy daddy daddy daddy LOOK! Jupiter MOVED!’ And she was right. While Venus and Jupiter had been slowly edging closer to each other over the past few weeks, you wouldn’t notice it unless you were watching closely. But now they were suddenly so close that even a three year old could look and see that something had changed.

As much as I am charmed by Lilah picking out pictures of planets in magazines to show me, having her point out to me that Jupiter moved was – for me – the pinnacle of planetary charm. While most kids and adults can name the planets and point out pictures, almost nobody notices the real thing even when it is blazing in the evening sky. Planets are not just things that spacecraft visit and beam back pictures from. They’re not just abstractions to put on lunch boxes. They are really there night after night after night, doing what only planets do: moving.

Last night – Saturday – the show got even better. The sliver moon showed up low in the early evening sky anda began working its way toward Jupiter and Venus. For half of the month, Lilah and I watch the moon get bigger and move east night after night in the evening sky, so we both know what is going to happen next. Based on how far the moon is from Venus and Jupiter, it looks like on Monday night the moon will be packed tightly in the evening sky with Jupiter and Venus. It will, I suspect, be a spectacular sight, with the three brightest objects ever visible in the night sky in an unmistakable grouping in the southwest just after sunset. It’s the sort of site that I think – that I hope – will make even non-night sky watchers suddenly look up and wonder. And when they look the next night, to see if it is still there, they will notice the moon has already moved further east and gotten a little bigger, and they will see that two other bright lights – Jupiter and Venus – are in slightly different spots. Maybe even a person or two will follow the moon’s movement for the next week as it grows to full. Maybe a lucky few will watch as Jupiter gets lower night after night, leaving Venus alone in the sky by next month. It’s a show worth following. I know Lilah and I will.

I’m on a flight across the country tonight. I touch down long after Jupiter and Venus and the Moon will all have set in Florida. As I was packing my bags this morning Lilah asked: “Daddy, are you going away to go talk about planets?” Yes, Lilah. I’m going away to talk about planets. I forgot to tell her, though, that I’m going to see some, too. I was sure to pick a window seat on the south side of the airplane so I could watch the show from the air. And when I arrive I’ll call back home and tell Lilah all about it and tell her to go outside right now and LOOK! she can see all of our favorite planets and LOOK! the moon has moved and grown and I’m sorry that planets are taking me far from home tonight but I’m glad we have these here in the sky to share tonight and forever.

It's only a sliver moon

Last week the clouds parted enough in the evening to reveal the just-set sun -- now already setting well north of where it was at the equinox just a few weeks ago-- with a tiny sliver of a new moon hanging like an ornament above it in the not-yet-dark skies. This sliver moon is, to my mind, one of the most impressive sights to periodically grace our skies. To me, the ethereal part is not the sliver itself, looking like a razor sharp sickle glowing in the sky, but the ghostly outline of the rest of the moon that can be faintly seen.

What is that ghostly outline? If you've paid close attention you might even have noticed that it disappears after a few days. By the time the moon is up to first quarter all you see is that bright sunlit half of the orb. It's hard to tell, because as the moon waxes towards full it gets brighter and brighter and you might just think that you're having a harder time seeing that ghostly outline in the presence of that brighter moon. But, no, the outline is indeed getting fainter.

What's going on? With a little thinking about what is illuminating the moon we can figure it out pretty easily and even make sense of the little details of when it is brighter and when fainter.

First, a few well known simple concepts. The moon goes around the earth (counter-clockwise when viewed from above the north pole), and half of it is always illuminated by the sun while the other half is not. The fact that we see sliver moons, quarter moons, and full moons is not so much because the moon is changing, as that our vantage point is changing. On those bright full moon nights we are seeing all of the illuminated side and the back is dark. When the moon is new we're seeing the unilluminated half, but if we could fly in to space to see the back side we would see it look full from there. Just like the earth, the moon always has a day side and a night side.

Now, let's assume that we're looking straight down at the north pole of the earth and that the sun is off in the distance at the 6 o'clock position. The moon is there in its counter-clockwise orbit. How can we see a full moon? First, the moon had better be in the right place. If the moon is at the 12 o'clock position, the part of the moon visible from the earth is fully illuminated by the sun, making it full. But that's not all you need; you will also need to be on a spot on the earth where you can see the moon. The best spot to be would be would be standing at the 12 o'clock position on the earth. That 12 o'clock position is in the middle of the dark side of the earth. It's midnight. If you're outside and you look up and see the moon straight overhead, you know it must be midnight.

You can also tell from this general idea when the full moon must rise and set. The earth, again viewed from above the north pole, also rotates counter-clockwise. Where are you standing when you see the moon on the horizon? At the 3 o'clock and 9 o'clock positions. But notice at these positions you can also see the sun in exactly the opposite direction. If you're standing in the 3 o'clock position and the earth is rotating counter-clockwise, though, the sun is soon going to disappear. Sunset! In the 9 o'clock position the sun is just appearing. Sunrise! The moon, when it is full, is doing just the opposite of the sun. So the full moon rises at sunset and sets at sunrise.

Let's try tonight's (Saturday, April 12th) moon as an example. We are about a day away from the first quarter. In about a week the moon will be full. Where is the moon? In the mental picture we have been painting ourselves it should be easy to see. If we see the moon only half illuminated, it must be in either the 3 or 9 o'clock positions. But we know the moon is moving counter-clockwise in its orbit and that it will be full soon, so it must be in the 3 o'clock position.

Knowing where the moon is immediately tells us when we will see it. Tonight, as the sun sets, look for the moon. The sun setting means that you are standing on the 3 o'clock position on the earth. The moon will be right over head in the sky. (note, though, that I'm ignoring the effects of latitude here. If you're at the north pole, the moon will never actually be overhead in the sky. So when I say overhead, you should take me to mean "as straight over head as it ever gets from where you live." From Pasadena tonight the moon will never get more than 12 degrees -- about the width of 3 hands held at arm's length-- from being straight overhead.)

Tomorrow night the moon really is at the first quarter. When does the moon rise, then? You will first see the first quarter moon when you are standing at the 6 o'clock position, directly underneath the sun. Noon. See if you can go find the moon rising in the east a little after noon tomorrow. To most people the appearance of the moon in the daytime sky is always a bit of a mystery. If you have ever felt this way, make tomorrow the day it is no longer mysterious by setting out to find it by knowing where it should be.

All of this brings us back to sliver moons. How can we see just a sliver of light? We must be seeing mostly the night side, but just a tiny bit around to the day side. If the moon were at the 6 o'clock position, we would see only the night side, and it would be new moon (and we would have the possibility of an eclipse; the reason they don't happen all of the time is that the moon goes around the earth on a circle which is slightly tilted compared to where the sun is, so most of the time the circles actually don't cross. ). A few days after new moon, though, when the sun is at, say, the 5 o'clock position, we should see just the tiniest sliver of the sunlit side against a mostly dark moon.

When does a sliver moon set? If you're standing at the 3 o'clock position, the sun itself has just set, and the sliver moon is low in the sky in the same direction that the sun just set. The sliver moon is always close to the sun in the sky, so it must set soon thereafter.

But wait. What about the glow? If the sliver moon is caused by just seeing a little of the sunlit side of the moon but mostly seeing the dark side, how could there possibly be a ghostly glow coming from the dark side of the moon? The side that is glowing cannot see the sun at all. How can we see it?

The answer comes from thinking about what the earth looks like from the moon. If you were standing on the moon and the moon were full, what would you see? You would be looking at the dark half of the earth. The lights of the major cities would fill the otherwise dark void.

What if there moon were at first quarter and you were looking down? You would see half of the earth illuminated, the other half dark. The people right at the line between light and dark would be the people for whom the sun were just setting. Those people could look straight up in the sky and see you standing on the moon.

Finally, let's look at the sliver moon. When we see only a sliver of light on the moon, people standing on the moon see only a sliver of dark on the earth. The earth itself is almost full.

When the moon is full the nighttime is so bright that you can walk around the wilderness without carrying a flashlight. If you were on the moon and the earth were full, the light in the sky would be nearly 60 times brighter (the earth is both bigger and more reflective). You could read your spacesuit repair manual without carrying any lights at all. The landscape would be illuminated the same as if it were twilight on earth.

And you would see that illuminated landscape from the earth. The part of the moon that should be dark would glow in earth light. When the people on the earth see a sliver moon, the moon sees an almost full earth. The dark side glows with earthshine.

The earthshine also explains, of course, why the glow starts to fade as the moon goes from sliver to quarter. By the quarter moon, like tonight, the earth appears quarter, too. There is only half as much light to illuminate the dark side. And in another week, when the moon becomes full but the earth is new, the earthshine is totally gone.

So while the crescent sliver is light that comes from the sun, reflects off of the moon, and then arrives at the earth, the ghostly glow is light that comes from the sun, reflects off of the earth, arrives at the moon, reflects off the moon, and then arrives back at the earth. The glow is the ghost of us. Tonight, when you look up at the quarter moon (directly overhead at sunset), see if you can see the remainder of the glow on the dark side. And wave at it. The light from your wave will travel up to the moon and be back again 4 seconds later and you'll be part of what I think is the prettiest treat to grace our skies.

Yelping at Saints

This gentle brightening to a muted peak sounds prosaic and reasonable. But it is not true.

Which is to say that the full moon is really bright.

You don't have to take my over-tired-from-hiking-all-day's impressions for it. If your skies are clear this week as the moon is finally puffing towards full, go outside and see for yourself. Go out on Saturday, two days before the full moon, and look around. Check out the barely visible shadows. See what fuzzy shapes you can make out in the distance. Look up and notice that the moon is definitely not fully illuminated, but it is getting close.

Go out Sunday. To really do the job right you should go out an hour later than you did the night before, since the moon will have risen an hour later. Look around. You probably won't be able to tell any difference at all from the night before. Same vague shadows, same fuzzy details. And then look at the moon. Definitely bigger, but one edge is still a little flattened. Tomorrow it will indeed be full.

Finally, go out on Monday, an hour later still if you can. Stare right at the moon, if your eyes can stand it. It does look like a spotlight up there in the sky. It is much brighter than it was just the day before. Look at the now-crisp shadows on the ground and the sharp details on the rocks and the plants that you can now pick out. Now go ahead, if you need to, and let out a little bit of a yelp. I'll be understanding.

What is going on with the moon? How can it get so much brighter in just a day? Who turned on the spotlight?

It happens every month. It's just a trick of light and shadows. But, every now and then, I still look up at the full moon and think about saints and I feel a little bit of a yelp deep inside.

Pages