Wednesday, March 21, 2007

Of Great Magnitude

3/25/07 – 3/31/07
by C. Zaitz

“Star light, star bright, first star I see tonight…” so which one will it be? People often ask, “what’s the first star?” or “what’s the biggest star?” or my personal favorite, “what’s the farthest star?” These questions tend to our desire to catalogue things, rank them, sort and classify. Maybe knowing the biggest, best, and brightest may be a way to make sense of the infinite and chaotic universe.

The problem with far away stars is that they are really hard to see! At the very limit of our view lie the most distant objects we can see; the quasars, with their light so stretched from the billions of years of travel that their spectra have migrated far into the red and infrared extremes. Quasars are strange objects; compact, bright and very distant. They seem to be the cores of ancient galaxies, most certainly with giant black holes at their centers. As of now, the farthest quasar we’ve found is nearly 13 billion light years away. That’s close to the time when we think the first stars and galaxies were forming. Before that, there was no light at all. So we’ll have to be content to say quasars are the farthest “objects” we can see.

What about big? All stars are big, compared to earth. Maybe you’ve heard that the sun a small star. In the great scheme of things, perhaps it’s not as big as, say, Betelgeuse or Deneb, but it’s just right for us. However, there are vast numbers of loftier and heftier stars than our own. Most of the bright stars in the sky would dwarf our sun. They are bright mainly because they are huge. We call the brightness of a star its magnitude. Stars have two magnitudes; the one we see, called the apparent magnitude, and the one it really is, called the absolute magnitude. Imagine trying to compare sizes of sailboats in a lake. It would be easy if they were all the same distance from you, but they’re all over the lake. You could classify them by how big they look, but that’s not really fair for the ones far away- they’ll always look tiny. Unfortunately, it’s very tricky to find the absolute magnitude of stars since they are scattered all over the universe. With sailboats, you might be able to recognize the type of boat by its appearance and infer its size from that knowledge, and that’s what we do with stars. But there’s room for error- what if the same brand of boat comes in 24’ and 32’ and they look very similar? Astronomers have several methods of estimating size and distance, but it’s not an exact science. So we’ll just say that Epsilon Aurigae, in the constellation of Auriga, is 2,700 times bigger than our sun, and that’s one of the biggest we’ve ever seen.

So how does one decide what the first star is? Are we looking for the first star that you see in the evening sky? This answer can be evasive, since the first star is usually a planet. Planets can be very bright, especially Venus. Venus has been greeting the sunset lately, and as twilight fades, its brilliance in the western sky is unparalleled. But it’s not a star. However, when you’re looking for the first of anything in the night sky, look for Venus. Its apparent magnitude is very great, and when it comes to just enjoying the night sky, appearances can be everything!

Until next week, my friends, enjoy the view.

Tuesday, March 13, 2007

What Goes Around

3/18/07 – 3/24/07
by C. Zaitz

I’ve been giving a series of planetarium shows for fourth graders. I’ve heard a lot of interesting things come out of ten year olds, but today they stumped me. I was pointing out the planets that are visible in the early evening. Venus hovers above the sunset, driving light daggers into your eyes as you watch the glow of the sun fade. Saturn, however, lags behind and is only just rising to a nice height at sunset. It is in the southeast, whereas Venus is definitely following the sun into the west.

I told the fourth graders that it was 8:30 at night and I showed them the two planets. Then I asked them where Venus would be by 10pm. They were a verbal group with stretch marks in their armpits from raising their hands so much. I assumed they would say that Venus would go down in the west, like the sun, moon and all the stars. It seemed like a safe question.

Not so. Among the answers I got were, “it will go to the north,” “it will go back to the east” and “it will go south.” I could not BRIBE them to say it went down in the west. So I asked them what was really moving when the sun went down.

We talked through the rotation of the earth and I told them that we are spinning at 800 mph in Michigan. I asked them why they thought we couldn’t feel that motion and we talked about the reasons, such as the fact that we’ve always been spinning on the big earth and as long as it doesn’t speed up or stop, we will never notice its motion. Then to top it all off, I basically pirouetted until I got dizzy to illustrate the motion of the earth. That was my big wind-up. Then I threw it back to them. With excited, baited breath I asked, “So where will Venus be in an hour, my young friends?” I was sure that my antics and explanations had done the trick. But it hadn’t. Not even close. Somehow those young minds had heard or read something that had confused them about the motion of sky objects. And I didn’t know how to undo it.

So I laughed it off and we moved on. Later on the time came to actually move the stars toward the west. I took the opportunity to try once more, so I pointed to Venus and had them watch it as it sank down into the western horizon. I think they saw it. They looked surprised, but I think they finally believed that Venus would follow the sun down in the west. Sometimes seeing is believing. I know that the concept of the earth spinning is pretty abstract, and ten year olds aren’t quite abstract thinkers yet, but I thought that they might have noticed things setting in the west. When I realized they may never have actually seen Venus in the sky, I got a little sad. So to all of you with kids, take them out this month and show them Venus. Just point yourself toward the west at sunset and you’ll see it, clouds willing. And if you have a few moments later on, spy on it again and see where it went. I’m pretty sure that it will have followed the sun down in the west. But it’s always good to see it for yourself.

Until next week, my friends, enjoy the view.

Wednesday, March 07, 2007

Moon Dust

by C. Zaitz

I’ve been thinking a lot lately about dust. Not just the dust that accumulates on the piano or the blinds. Not even the dust mixes with my shedding dog’s hair and ends up big as my fist, rolling across the hardwood floor. No, I’ve been thinking of far away dust, the kind of dust that sheaths the moon.

I have the privilege of working with some students who are involved in special projects. One student is trying to measure the electrical charge of dust that has been exposed to ultraviolet light. She chose this project because it seems that dust on the moon is very clingy. Astronauts who went to the moon and walked around got very dirty, very quickly. As soon as they stepped on the dust, it jumped onto their spacesuits and clung for dear life, almost as if the little dust particles had been waiting for billions of years for a ride to earth and finally it saw the opportunity. She wanted to see how charged dust can get, even here on earth. In that process we’ve both been learning a lot about dust. It’s not very sexy, but it’s pretty important.

Moon dust has some interesting properties. It’s not like the soft dust we find around the house. That dust is made of flakes of skin, pet dander, dirt particles and lint, among other things. Moon dust, however, is craggy and jagged. It’s made when asteroids hit the moon and pulverize rock. There’s nothing soft about moon dust. It’s so sharp that it cut through the seals on containers used to carry it back to earth. You wouldn’t want to step on a dust ball made of moon dust.

One of the problems with moon dust, and even dust on Mars, is that it tends to cling to everything. Scientists have different ideas why. One of the most popular ideas is something we experience all the time; static electricity, or better said, a difference in charges. Think of that dust that collects on your TV screen. The screen gets charged when it’s on, and the neutral dust gets attracted to it. Now think of the moon’s surface. Radiation from the sun knocks electrons off the dust and the particles become charged. Once an astronaut walks through the dust, the difference in charge makes the dust veritably leap onto the astronaut’s spacesuit. Since the dust is so caustic, in time it can cut and poke into the skin of the spacesuit, which is the only thing protecting the astronaut from certain death in the lunar environment. The dust is carried into the lunar lander and can get into sensitive equipment, with the potential of causing disaster.

Studies on how to combat the “stickiness” of the dust and the potential harm from it ended with the Apollo missions, but the rovers on Mars are still hampered by Martian dust as it covers their solar panels and gets into the working parts. It turns out that lowly dust can be a very important issue in future space travel. It could also be a key into understanding how the solar system formed, since current theories imply that the sun and planets coalesced out of space dust and gas. Dust has been around a long time. Perhaps with further study, we will know how to deal with moon dust by the time we get there in 2018. I know I wouldn’t want moon dust ruining my trip to the moon!

Until next week, my friends, enjoy the view.