Sunday, September 25, 2005

'Scuse Me While I Miss The Sky

Check out this episode of "The Simpsons," which I just saw last week. I love this show.










Meteor Crater

Here are two pictures I took during my honeymoon last August. This is Meteor Crater, also known as Barringer Crater -- a very large hole in the ground in eastern Arizona. It's 4,150 feet wide and 570 feet deep. Dess and I stood near the rim with the evening summer winds blowing very hard at us -- but not quite hard enough to throw us in.


The picture below was taken the next morning.



The Crater shows up quite nicely on Google Earth, especially if you tilt the view; then you can actually make out a depression in the earth. The surrounding rim, which rises 150 feet, is noticeable. Look for it about 20 miles west of Winslow, AZ (the coordinates are 35 degrees, 1 minute, 37 seconds North, and 111 degrees, 1 minute, 22 seconds West).

An image taken from the web:



On the web there's an estimate that the meteor was 150 feet across (compared to the one that is proposed to have caused the extinction of the dinosaurs, at perhaps 10 miles across). It weighed roughly 300,000 tons, and was traveling at a speed of 40,000 miles per hour. The force generated by its impact was equal to the explosion of 20 million tons of TNT, or about a thousand Hiroshima bombs. (A few nuclear bombs have been more powerful than Meteor Crater). It happened about 50,000 years ago, which was probably well before humans had ventured into the Americas from eastern Asia, although these days theories are being overturned so fast that you never know.

The most interesting thing I learned from the onsite tour? That the native inhabitants of this land probably stayed away from the crater and regarded it as an evil place.

A great site about the crater is here.

Thursday, September 22, 2005

Green River redux

Here are my two photos from the post below, as nearly as I could reproduce them on Google Earth. I set the altitude in each case for nearly 30,000 feet, to match the plane's height, and then adjusted the tilt in order to view the ground at a slant.



Is it just me, or does Google Earth seem to stretch the earth's surface vertically in their images, especially in this second photo? I can get a Google image that looks closer to the photo I took, but only by flying the plane at 40,000 feet and at other heights that cannot be right. How photo-realistic is Google's imagery?

Sunday, September 18, 2005

Google Moon

Speaking of Google Earth, this is a very similar page at which you can zoom in on the surface of the Moon. The highest zoom reveals a surprise:

http://moon.google.com/

Google Earth


I sometimes call this photo "Earth," and I keep it in my astronomy collection. I snapped it a year ago, on the last day of my honeymoon in the Southwest. Dess and I were on a plane headed back to New York, and flying over many places we had just visited, so it was possible to recognize a few things from that far up. The way I remember it, I recognized the Grand Canyon and got the camera out, a little late; by the time I took the photo above, I did not recognize the terrain I was seeing outside the window and I feared that we'd left the Canyon behind; but I still regarded my photo as showing the easternmost reaches of the Canyon. I just figured that such a winding river must be the Colorado. I was almost right about that. But the photo does not actually show any part of the Grand Canyon. I know because I found photos of the very same terrain on Google Earth this past week. Don't read any further if you're into the challenge and you want to try to find it yourself. Be my guest -- it took me 4 hours to find.

When I took the photo, the plane was actually about two hundred miles from the north rim of the Grand Canyon. If you look just above the center, you'll see something like a heart shape. It's much clearer in the next photo, taken with a zoom of 3x. Look at the top right.


That "island" in the shape of a heart was actually carved out by the Green River, somewhat north of the place where the Colorado and Green rivers meet. The gorge around the little island is called Spring Canyon, and it's in eastern Utah, actually not too far from Arches National Park. Follow the Colorado on Google Earth until it forks off into the Green River, then follow the latter to Spring Canyon: the satisfaction at finding something so visually similar to what you're looking for is quite memorable. Google Earth allows you to view any given terrain from a particular height or angle, so that you can almost pull up a facsimile of the photo above.

The program also names every small feature, and the "bottom" of the heart, where it seems the curving edges of the island might be meeting, is called Bowknot Bend; at that spot the Green River almost meets itself, but not quite. I don't know much about the earth's terrain, but this seems to me like something unique. Have a look at this photo of Bowknot Bend that I pulled up at this web page (through Google Images):

And finally, a long shot of the little island, from the same web page:


Google Earth has amazed me so much that I feel at a loss for good words. Neither poetry not precision seems likely to convey the thrill that I've felt over this. After finding the identity of the canyon in the photo, I started looking at cities, and discovered that I could find satellite images of my own neighborhood, here in Greenpoint. I saw corners and bus stops and churches; buildings that I've lived in, including my current home; structures on the roof of my building where I've set my binoculars or rested my back; even some fuzzy blobs on the back of our apartment building, in the spots where I expected to find our kitchen windows. It was enough to make me imagine the face of the tenant, a friend of ours, who lived in our apartment before we moved in. I say that because some spots in our neighborhood where large condos are rising appear in the satellite images as they were a few years ago -- just empty lots or warehouses. Yet the World Trade Center appears as it does today, an essentially empty lot. The satellite images are composites manipulated by computers, obviously. And they do not have quite enough resolution to reveal human figures, though I did see some very light specks on the Riverside tennis courts in upper Manhattan. I saw what might have been cows in the fields of Massachusetts, near my mother-in-law's house.

It's been like a trek into the past, finding my high school, college, seminary, summer camp. Ecuador, I noticed, does not have the resolution of anything in the United States. Here, streets can be resolved on the maps, probably because so many weather satellites are busy looking at us; and even little schools or restaurants can be named, due to the great wealth and collection of information. In the maps of Ecuador I could plainly see the cities, but individual streets were not resolved, much less named, so it will be a while before I find the houses of my extended family. Dess has said that it's somewhat scary to think the government can spy on us this way. I agree; the government for a long time has been able to peer at us from the skies. But I think it's beyond good that such a map of the Earth is being made available to people -- for free. Google Earth is the visual equivalent of a directory or phone book, but it also has census info and other things; and it's much more than all these things. It's the map of a planet and a home.

Sunday, September 11, 2005

9-11-05


I took this photo earlier this evening: You can see Venus here, the white dot to the left of the Tribute in Light.

Saturday, September 10, 2005

The View from Down Under

I was in touch with Phil Plait, aka The Bad Astronomer, about my photos of the Venus-Moon-Jupiter conjunction. His sky in California has been clouded over but he did say that there were some other nice photos of the conjunction at a blog in Australia called Two Cents, by Beche-La-Mer. Her photos include one bright body that did not appear in mine (the star Spica), and they show the Moon almost touching Venus: Australia turned toward the conjunction half a day after New York was facing it, so Beche saw a Moon that had had about 12 to 14 extra hours to move across the sky. Beche left a comment on my first post and noted how interesting it was to see the perspective from the other side of the planet. I agree, it's actually quite engrossing when you think about it.

Beche's photos have Venus, Jupiter and the Moon in a nearly vertical line while my photos have them close to horizontal. I've been using the sky charts provided by SkyView Cafe and AstroViewer to learn a little more. In Australia (a country I have never visited), the planets and moons of our solar system are rising at a slant in the morning, and setting almost in a vertical line, while in New York the situation is reversed. Consequently Beche was able to catch these bodies while they were still very high in the sky, with Jupiter, for instance, about twice as high at sunset than was the case in New York. (Here, Jupiter was 16 degrees above the horizon at sunset). You can see an astronomical object more clearly the higher it lies above the horizon, not just because the object is far from the city lights typically on the horizon, but because you're looking through less air, clouds, smog, etc. If you saw something directly overhead, you'd be looking essentially through the depth of the earth's atmosphere -- about 100 miles, no more. The light from an overhead object cuts through the air as efficiently as possible before it gets to our eyes. The light from an object sitting just above our horizon has to cut diagonally through our atmosphere before it gets to our eyes. The Moon that I saw the night of the conjunction was clear and white at first but grew more turbulent and yellow as it approached the horizon, which can be seen in the photos I published.

Now the reason that New York and Australia should see objects setting at different angles, or at any angle, is a complex little problem that has taken up more pages in my personal astronomy journals than any other "problem" or subject. More than once I've tried to work out in my head, or with a globe, the best way to think about it or to describe it. What follows is a new description. Comments are welcome.

Imagine you're on the sun and watching the earth spin, with a dark line running along the equator. And where is that line exactly? Well the sun's view of it changes. At the summer solstice in late June, the northern hemisphere was turned directly toward the sun, so from the sun you would have imagined the equator's line to look like a smile; at the December solstice, with the southern hemisphere turned to the sun, you'd see a frown. At most other times you would see something like a sideways smile or frown, one in which only the left or the right corner of the mouth was curling much. I say "most other times" because there are two brief exceptions. At the September and March equinoxes, you'd imagine a straight line representing the equator, running diagonally across the face of the earth. If you think of the round face of the earth as a clock, you would draw your imaginary line from about 8:13 to 2:13 in September, and from about 9:47 to 3:47 in March. The basis for these reference points is simple: the clock represents 360 degrees, with each hour representing 30 degrees, and 47 minutes representing 23.5 degrees, which is only 1/20 of a degree more than the actual tilt of the earth's axis.

On the dates of the equinoxes, the equator runs in a straight line from the sun's perspective. So if you're on the sun on September 22 of this year, and you're watching the earth spinning from left to right, watch for the city of Quito, Ecuador (a country I have visited, since my parents are from there). Quito is almost directly on the equator. You'd watch the city emerge into view at 8:13 on the clock, and it would appear to be making its way directly towards you. You'd watch it move across the earth's face until it arrived at 2:13 and disappeared from view, in a seemingly direct line away from you. Now, from Quito's point of view you'd see the sun and all the planets rise in a vertical line from a point lying exactly East, travel directly overhead, and sink back into the horizon in a vertical line at a point exactly West.

But this would never happen for Australia or New York. Imagine for a moment that the earth's axis is not tilted: the equator appears from the sun to run from 9 o'clock to 3 o'clock. Objects on the equator rotate from 9 toward 3. Someone on the equator sees the sun passing directly over him, any day of the year. But imagine what someone at the north pole sees. The earth is a ball; someone at the top of the ball is almost on the other side of the ball; if he were very tall, lets say many miles tall, someone at the sun might see this person standing on top of the earth. This person is nearly in night-time. Bring this person back to normal size: he sees the sun peeking just over the horizon. As the earth turns him around, he sees the sun going around in a circle that hugs the horizon. It's an extremely narrow angle, in other words, compared to the 90-degree line that the sun forms with the horizon for an observer at the equator.

So it's the curve of the ball we live on that ensures angles for rising and setting objects. There is another way I think about it which is perhaps more direct and simple. At 9 o'clock you see the line of the equator coming to an intersection, an apparently 90-degree angle, with the edge of the clock. A line running parallel to the equator, either above or below, such as the line of latitude that New York sits on, meets the edge of the clock at something other than 90 degrees. A city at 45 degrees of latitude will meet the edge at an apparently 45-degree angle. (New York sits very close to that line). A line running left to right just below the north pole intersects the top edge of the clock at a very small angle; such a line is almost running parallel with the section of the clock's edge that it cuts off.

All this by itself would produce angles for rising and setting objects. But if we go back and imagine the earth with its actual 23-degree tilt, things become more complicated. Now the equator appears as a straight line from the sun's perspective only on the dates of the equinoxes; at all other times it appears to be either a smile or a frown, as either the northern or southern hemisphere tilts toward the sun. Now the line on which New York sits will meet the edge of the clock at an angle further removed from what we could expect if the earth had no tilt. Whatever the exact angle, however, we know that what happens with New York would be the opposite of what happens with Australia, since only the northern or the southern hemisphere can be turned toward the sun at any one time.

This past week the north was tilted toward the sun, as it always is between March 21 and September 21. Between September and March the south will be turned toward the sun. On December 21 the south will be turned to its maximum sunward direction, and the north pole will be pointed at a maximum 23 degrees away from the sun. At that time the equator will look from the sun's perspective like a deep and perfectly symmetrical "frown" in which both corners of the mouth look the same: the frown will meet the left side of the clock at the same angle that it intersects the right side. This will be true for all imaginary lines of latitude: their frowns will meet the sides of the clock at angles that are produced according to how close they are to the bottom edge of the clock, as noted, but they will all intersect the sides of the clock in symmetrical frowns. Objects rising in Australian skies will do so at exactly the same angle that they do when they set. Right now objects are setting close to vertically and rising close to horizontally, as we see in Beche's photos; starting on December 21 and going all the way till June 21, it will be more accurate to say that they're setting horizontally and rising vertically. The contrast between sunrise and sunset will be smallest when the two angles "switch" places on December 21, and it will be greatest on March 21, when the contrast will begin to reduce, on its way to finally reversing itself again on June 21.

Confused? Good. There are good and bad ways to explain these things in words, and I hope mine were not too bad, but in the end words are not going to get these things across. A globe is handier, as is personal experience watching the skies.

A final note: Beche's photos captured a descent of Venus, Jupiter and the Moon that was nearly vertical, but to the extent that there was a sideways descent of these bodies, she saw them moving from right to left. This sideways motion, as noted, would currently be more noticeable in Australian sunrises, but it's there at sunset: if you look at the Moon in Beche's photo, the illuminated part of it is the lower-left section, suggesting the presence of the sun off to the moon's left. By contrast, I saw a lunar crescent curved in reverse, on the lower right of the moon's face: I saw the three bodies and the sun descend from left to right. This can also be seen here at sunrise, though currently the sideways motion at dawn is less noticeable than the vertical.

These perceptions of sideways motion do not reverse themselves throughout the year, since this phenomenon has nothing to do with the changing direction of the earth's tilt. It comes about only because someone in Australia must look north to see solar system objects, while someone in New York must look south. To say it this way can be a bit confusing since we see sunrise in the east and sunset in the west, but I've imagined it sometimes by picturing a very large human figure on the ball of the earth. Someone in New York is looking more or less "down" at the equator when looking out at the solar system and everything in its plane (objects well above or below the solar system are a different story), while someone in Australia is looking more or less "up" at the equator. In short, they are facing each other, so each person's "left" and "right" is a matter of perspective. They would use these subjective terms, but they would still speak of the sun rising in the east and setting in the west.

Wednesday, September 07, 2005

Three in a row


From left to right are the Moon, Venus, and Jupiter, at 8:06 pm tonight, forming as straight a line as one could hope for. However they were not so close as last night, when all three bodies fit into a circle only 5 degrees apart; tonight about 8 degrees separated the Moon and Venus, and about 6 degrees lay between Venus and Jupiter. Last night all three could be seen at once, though barely, in the 9x63 binoculars; tonight I could not see any two of them in the aperture.


This shot at 8:27 is the only one I got which shows off the Tribute in Light, which began tonight -- look just to the right of Venus. Jupiter is nearly invisible and about to sink, as it did last night, behind the brilliantly lit spiral top of the Woolworth Building. It did so at 8:28, re-emerged at the other side of the spire two minutes later, and sank for good at 8:32. It hit the Woolworth three minutes earlier than last night, and in a slightly lower spot on the spire.

At 8:33 Venus disappeared behind the Chase Manhattan Bank, the wide box of a building in the middle of the above photo -- the one showing off more office lights than any other. Again Venus flashed blue when less than half of it remained uncovered by the building. When it re-emerged briefly to the right of the Chase Manhattan at 8:38, I did not notice a flash, though perhaps it was because my eyes did not know where the planet would re-appear. Within a minute Venus disappeared again, behind the next building over -- and another blue flash!

I did not notice any flashing with either Jupiter or the Moon.


The moon at 8:45, seconds before it disappeared for the night behind 55 Water Street.

The moon's face was 16% illuminated tonight. It's been four days since new moon, and in another four days the lunar face will be 50% illuminated -- a phase called first quarter, although I usually just call it "half-moon."

I saw a few airplanes fly directly across the moon. One cut through the center, and when it emerged I saw an effect which astronomers sometimes look for in eclipses: when two bodies begin touching or separating, their light interacts like two blobs of water; it's called the "eyedrop" effect, akin to when the setting sun begins touching the ocean. To me it looked as if the airplane's engines were sucking some of the moon's white light, for just an instant, as they pulled away.

Tuesday, September 06, 2005

Evening Moon Conjunction


Photos do not capture the sky, or the wonder that it can induce. This is a new blog, and that's the first thing I wanted to say. It may bear repeating later on. I took the photo above a few hours ago, from the roof of the three-story apartment building where I live with my wife Dess. Three bodies are setting over the Manhattan skyline as seen from Greenpoint, Brooklyn: Venus on the left, Jupiter on the right, and the moon in between. Venus is currently 102 million miles from the earth, and it's about the size of our own planet. The sun, which always sits around 93 million miles from earth, is to the lower right, having set below the horizon 48 minutes before I snapped the photo. Jupiter, a planet with a diameter a dozen times greater than that of Venus, is neverthless more faint due to its great distance from earth, currently 580 million miles. At this time it is sitting on the other side of the sun from us. Our moon, the smallest of all these objects but by far the brightest, is just 245, 000 miles distant. A little over three days ago it stood almost exactly between us and the sun (new moon phase), and tonight only 10% of its face had become illuminated.


Above, a shot just two minutes later, at 8:10 pm. That's the Williamsburg bridge in front of Manhattan. The spiral-topped building near the right edge of the photo is the Woolworth Building, at 792 feet once the tallest building in the world (from 1913 to 1928). Not quite discernible in front of it is the spiral tower of the Municipal Building at 1 Centre Street. Set off to the right of both is a smaller building, the U.S. Court House at 40 Centre Street, which later swallowed up Jupiter; click the photo for more detail and you should be able to see its pyramid top.


Above, a shot at 8:15. The very bright spot above the left-most tower of the bridge is an airplane, probably heading north to LaGuardia.


Finally, a shot of the moon at 8:21. It disappeared within a minute.

Jupiter disappeared at 8:31 behind the spiral top of the Woolworth Building, and re-emerged to the right of that spiral top before disappearing for good at 8:35 -- as mentioned, behind the pyramid top of the U.S. Court House.

Venus disappeared at 8:37 behind the short flat-topped building sitting just to the left of the moon; we can see virtually no office lights within, and only a dull silhouette of the outline is visible. Looking at Venus through 9x63 binoculars, the planet took a few seconds to wink out, flashing wildly as it did so. In fact it flashed blue in the last instant, when only its topmost portion was visible. I wonder if this is at all similar to the "green flash," a rarely seen effect that happens when the topmost portion of the setting sun flashes green for just an instant. See Fred Schaaf's article "Catch the Green Flash" in the September/October 2005 issue of Night Sky magazine.

And see the November/December issue of Night Sky for one of my photos, which will appear under the title, "Morning Moon Conjunction."

I can remember only a few times when the sky has startled me quite like it did tonight. The feeling is not captured here. But I tell you what, even poor photos can witness to one essential fact: the sights in them do happen, and are not to be missed. For all those who did not know that New York skies produced such sights, or for anyone who enjoys the sky: go out and look west tomorrow (Wednesday). The moon will have moved across a large portion of the sky, and from left to right you will see the moon, Venus, and Jupiter in a virtually straight line, about equally distant from one another.

Have a look, and take a picture.