January 16, 2014

I was driving home from work a day or two ago, and I noticed the newly risen moon in my rear-view mirror.  I was trying to decide how close it was to being full, and also trying to stop paying attention to the (beautiful) moon in my mirror and look at the (boring) traffic on the highway in front of me.

I’m used to enjoying the beauty of the sunset during my drive home (only during some times of year, of course), but I don’t often see the moon rising. For a moment it threw me that I was seeing it, then I reminded myself that I was driving west but seeing the eastern sky in my rearview mirror.

That got me thinking about how to figure out when to look for the moon and where in the sky, and about the phases of the moon in general. I have a fairly long commute (at least forty-five to fifty minutes, depending on traffic), so I had plenty of time trying to construct diagrams in my head.

I understand how the different phases work in terms of the relative positions of earth, moon, and sun, in terms of how much and which part of the moon is illuminated, but I never remember how to factor in time of day. And the one thing I just couldn’t make sense of, in my mental diagrams, was the new moon.

Read the rest of this entry »

No sky show here tonight

January 9, 2014

I was excited this morning to read that I might finally have a chance to see the northern lights tonight. Predictions were that they might be visible even in Iowa, and according to one map we’re right at the border of where “poor” shades into “fair” chances to see them.

Trees and light pollution would probably make viewing conditions in our neighborhood shift us back into the “poor” range, but if the weather was good I’d be willing to drive somewhere for a chance to finally see the aurora borealis. The sky is currently overcast, however, with no likelihood of it getting any better (instead the cloud cover will increase until it starts raining sometime tomorrow).

At least I can look at photos online, and imagine what I might be seeing if I were in someplace like Norway instead of Iowa. And I learned what causes the northern lights. I had always just thought of it as an atmospheric phenomenon, and never realized that the sun was involved.

According to the National Geographic article, the sunspot group that caused this week’s coronal mass ejection is still active, so there just may be another powerful solar blast on the way. So what are the chances it does happen, and conditions are again right for the resulting northern lights to be visible in Iowa, and it comes on a clear night (there are a few forecast next week)? I won’t be planning my schedule around it. But I can hope.

A fisheye view

June 29, 2010

I suppose a true “fisheye” view of things would be from underwater, just as a bird’s eye view is from the air. But the view created by using a fisheye camera lens can give an extraordinary look to ordinary scenes. If I had the time and money, I could have a lot of fun creating photographs like these.

I didn’t start out this evening looking for unusual photographic techniques, however. I was just checking out the Astronomy Photo of the Day. Today’s photo, titled “Trees, Sky, Galactic Eye,” is a fisheye photo that shows more trees than stars – which is perhaps one reason I like it so much. The round shape made me think of my Springbok jigsaw puzzles, and a puzzle made from that photo would be a lot of fun to put together.

The text beneath the photo points out that it can be a scavenger hunt  of sorts, and suggests some items to find. The tent is pretty easy, and I’m pretty sure I see the lights of Saint Philippe. The shoreline and volcano are harder, though I think I may have identified them. Knowing how to change the orientation of Windows on my monitor (see one of my posts, from a few weeks ago, on Upside down windows), made it a bit easier to view the photo from other angles (without having to turn my head at uncomfortable angles).

Optical delusion

January 20, 2010

If I had seen this picture without a caption, I’m not sure what I would have guessed it was. My first thought was of chocolate pudding with whipped cream and chocolate flakes mixed in. Or some very muddy water with pond scum swirling about. Maybe something microscopic? But on closer examination I can see that my initial impression of a wet surface is incorrect, because in places the surface has the look of blown sand.

It is blown sand, but the colors don’t match any landscape I’ve ever seen. Of course, the earth has such varied terrain, there are no doubt many amazing landscapes I’ve never seen, even in a photograph. But this one isn’t any place on earth. This photo was taken in space, near the north pole of Mars.

It doesn’t look at all like photos I’ve seen previously of the surface of Mars. They tend to be monochrome and – to my eye – fairly monotonous. What are those things sticking up in lines, as though they’re growing out of the surface? And what is the white that looks almost like snow or ice?

The white stuff is ice, apparently – but it’s not frozen H2O, it’s frozen CO(carbon dioxide). And those things sticking up? Well, they’re not actually sticking up, they’re lines of dark sand cascading down a slope made mostly of lighter colored sand.

My eyes don’t want to believe this. The lines are clearly sticking up out of the ground. I remind myself that our eyes are easily fooled, as many books of optical illusions can easily illustrate. Moreover, there is no reference point here, no familiar feature that lets us estimate the scale of the picture. Those apparent hills and valleys of sand could be the sort you make with your feet when you walk on loose sand at the beach, and the dark lines sticking up could be blades of something like grass. Or the hills could be mountains, and the apparent trees the size of California redwoods.

Of course, I know there aren’t trees or grass on Mars, and the astronomer who wrote this caption has studied detailed photos of Mars, and those really are drifts of dark sand. But I have trouble getting my eyes to see that.

I pick one batch of dark lines near the top, and try to imagine what it would look like if there were a sort of a cliff there, with the dark lines coming down the face of the cliff. The top of the cliff doesn’t look as it should – I guess the light sand is blowing over the edge too, so that no actual line  is formed to show the edge. I am beginning to see the dark streaks of sand now, instead of trees.

I pick another spot, near the bottom of the picture, and do the same thing. But when I look away, then look back, my eyes again turn the unfamiliar patterns into an earth-like landscape dotted with trees.

I suppose it’s just as well. I’ll never have to navigate Martian terrain, so my eyes don’t need to adapt to its peculiarities. They do just fine – most of the time – making sense of terrestrial landscapes.

Did you see the blue moon?

January 2, 2010

Did you know we had a blue moon in December? I certainly didn’t, though I admit I haven’t been outside after dark much in the cold weather we’ve been having. Of course, if I had been out and looked at the moon, I wouldn’t have seen any blue tinge. I would have seen a full moon a few days ago, but I doubt I would have realized it was the second one since the start of December.

If I had noticed, and I’d thought about it, I’d have realized how unusual that was. When I was little, there was always a Currier & Ives calendar on the wall of the dining room across from where I sat. It showed when the new moon, first quarter moon, full moon, and last quarter moon were in each month. I didn’t understand why what looked like a half moon was called a quarter moon, and I had trouble remembering which was the full moon and which was the new moon, since they looked the same except that one was a black circle and one was a white circle. And how could anyone remember which was the first quarter and which was the last quarter, since they looked the same except that they faced opposite directions? And why wasn’t there a half moon in between the first and last quarters?

Somewhere along the way I learned enough about the moon and the calendar to know the answer to most of those questions. Though I have to admit that I still can’t tell, looking at a quarter moon, whether it is waxing or waning. And to remember the definition of “waxing” I still have to stop and remember that “waning” means to get smaller, so waxing has to be the opposite.

But apparently I missed the new definition of “blue moon” that spread in the 1980’s. It got into the Genus II version of Trivial Pursuit in 1986, which is the year I was introduced to the game and loved playing it. (I got a second-hand copy a few years ago, but it turns out I have the first Genus edition.) But with as many cards as the set has, it’s not surprising that I could play several times and never hear the question about the definition of a blue moon.

Currently it is defined as the second full moon in a calendar month. (That happens about once every two and a half years, so those old Currier and Ives calendars must have had some examples, I just didn’t happen to remember them.) But that’s a fairly new definition – after all, why would anyone call such an occurrence a “blue moon”?

Read the rest of this entry »

When the sun stands still

December 21, 2009

I like learning word origins, so I was pleased tonight, when reading about the winter solstice, to find out what solstice means. I’ve always had trouble keeping equinox and solstice straight, but if I stop and think about it I know equinox means “equal night,” which is when daytime and nighttime are the same length – which I know is at the beginning of spring and fall. So if those are the equinoxes, the solstices have to go with summer and winter.

So I did know what a solstice was, the day when the day is longest at the beginning of summer, or shortest at the beginning of winter. But I didn’t know why the word solstice meant that, which was why it was hard to remember. This article explains that it comes from the Latin for “sun stands still.” Well, that initially puzzled me even more. I didn’t watch the sun today (I’m not even sure it was visible, as the sky was pretty overcast), but I’m pretty sure it didn’t stand still any more than it does any other day.

The article explains that throughout the summer and fall, the sun’s position in the sky has followed an increasingly lower and shorter arc. Then at the solstice, it seems to rise and set in the same two spots each day for several days, before the arc starts growing higher and longer again. Being a visual person, I’m not sure even that would have made sense to me, if I hadn’t seen a photo of an analemma yesterday.

The analemma shows the sun where it appears at a specified time of day, seen from a fixed spot, over the course of a year. If you had asked me to guess what shape that would take, I have no idea what I would have said, but I’m sure I wouldn’t have guessed a figure-8. If I had realized that it does go higher and lower at different times of year, I would probably have guessed a vertical line.

Read the rest of this entry »

Extra minutes of sunshine

September 23, 2009

Yesterday on worldmagblog, Chas was wondering why the newspaper listing of sunrise and sunset times showed more than twelve hours of daytime, even though it was the autumnal equinox. After all, everyone knows that day and night are exactly the same length on that day, right?

Apparently not. It’s one of many things that “everyone knows” that isn’t quite accurate. I found out from why it’s not the way everyone thinks it is (including me, until now). It has to do with the size of the sun in the sky, and with bending of light caused by earth’s atmosphere.

The first aspect is that we don’t measure sunrise and sunset from when the center of the sun is even with the horizon, but rather when the “top” of the sun (as we see it) appears over the horizon, or dips below it. That way “daytime” is just a little bit longer than if we measured it from the center of the sun’s disk in the sky. And the bending of light by our atmosphere means that the sun is not actually quite where it appears to our eyes, either.

That probably was not one of your burning questions today, or even yesterday when it was more relevant. But it’s one more little bit of knowledge to take the place of what we thought we knew, that wasn’t quite right. And for me, at least, that is always a good thing.