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The Christmas Eclipse

Observing >

Under usual circumstances, the announcement of both a new millennium and a Christmas solar eclipse would be rather exciting. Unfortunately, though, this year’s announcement is a little anticlimactic.

There was such a big deal made last January over the arrival of the “new millennium” that when the real thing comes next week it’s sure to pass with a whimper.

There was no Year 0, so the first century started with the year A.D. 1. The second century, therefore, started in A.D. 101, and so on. By keeping with this pattern, the 21st Century really starts in the year A.D. 2001.

Last year we celebrated the flipping of the calendar’s odometer from 1999 to 2000. But for most people it was a two-for-one gala as they celebrated the arrival of the new millennium, as well.

In the great scheme of things, of course, it’s not a big deal. Calendars are rather arbitrary, anyway. And after the last election revealed our shortcomings in the counting arena, we may find some Americans celebrating the new millennium in the year 2002.

Now to Christmas news.

Our Christmas Star is being eclipsed by the Moon! That is, on Christmas morning the Moon, in its never-ending orbit around the Earth, will slowly move in front of the Sun, partially blocking it. Unfortunately, the Moon is near apogee, so it won’t be a total eclipse.

Apogee just means the Moon is at its greatest distance from us in its orbit. When it’s farther out it has a greater difficulty covering the whole sun.

Imagine a light bulb several feet away from you. You can block out the entire bulb with your thumb if your thumb is close enough to your eye. But move your thumb toward the light and you’ll soon find it no longer blocks out the whole bulb. This is what’s happening with the Sun and Moon in their present positions.

Moreover, because of the positions of every body involved, the place to be for the most “sun blockage” is in the north and east of North America. Hmmm… we are in the south and west. Sadly, our eclipse will be minor. But we do get some!

And if you’re game, here’s how to “see” it.

First: never, ever, ever, look directly at the Sun - even during partial eclipses - unless the Sun is completely eclipsed by the Moon or you have a special filter. A partial eclipse can destroy your vision.

If you want to use a filter, use only the commercially available kind. (A good telescope store will have them.) You can also use #14 arc-welder’s glass.

Or you can play it safe and do a family project, creating a classic pinhole camera, like the one pictured.

Take a piece of cardboard and poke a good-sized hole through it. Tape a piece of aluminum foil over the hole. Then make a small hole through the foil with a straight pin.

Let the sun’s light pass through the hole to another piece of cardboard a couple feet away. That tiny disk of light is an image of the Sun. On Christmas morning, that little disk will have a bite taken out of it. See below.

The eclipse peaks here around 8.30 AM. Maybe after you open your gifts early Christmas morning, you and your family can go outside for another, more heavenly, gift.

Images and movies of the eclipse await you at firstlightastro.com. Click on iColumn.

Until next time, clear skies, a blessed Christmas, and a safe new Millennium!

Posted by Administrator at 2000.12.25 08:55 AM | Comments (0)

The Shuttle in Orbit

Science >

We’ve all seen images of Shuttle astronauts floating around the spacecraft trying to hold themselves in place or just clowning around in their weightlessness. Do they float around up there because there is no gravity? No! It’s because they are falling!

To understand this, we need to use our imagination. Let’s use a modified mental model that Isaac Newton gave us centuries ago. (Newton used a cannon; I'll use a bow and arrow

Imagine being at the top of a very high mountain. You hold a bow in one hand and pull back a suction-tipped arrow with the other. You now weakly shoot the arrow straight out towards the horizon. As expected, it falls to earth. Taking another arrow from your quiver, you fire it, but with more power this time. To no one’s surprise, it goes farther.

Now, after having downed a full can of spinach, you launch another arrow with Popeye-like strength. This arrow goes far into the distance. But farther than expected!

The Earth, you see, is not flat. It is a sphere, and over great distances, it curves significantly. The arrow got a chance to fly farther before landing because the Earth below it curved away.

The next time you fire off your arrow, after two cans of spinach, the arrow goes so far it actually flies over the horizon and out of sight “downrange” somewhere.

Is it possible to shoot the arrow with such great velocity that, even as gravity pulls the arrow down, the Earth curves out of the way so that the arrow can’t “land” at all? Yes!

After a Costco dose of spinach, you now have the strength to fire the suction-tipped arrow so fast that it travels around the Earth and eventually smacks you on the back of your unsuspecting head. That’s what being “in orbit” is all about.

Notice that gravity was acting on the arrow the whole time as the arrow was trying desperately to fall to the Earth.

How do you feel when you freefall on an amusement park ride? You feel weightless; it’s like floating. That’s what happens on the Shuttle.

The Shuttle is launched, and - observant people will notice - it rolls over and turns toward the eastern horizon, rockets firing furiously the whole time. They are trying to be the arrow that goes so fast that even as gravity tries its best to bring it back, the Earth is curving safely out of its way.

But to achieve the speed that will allow this they must travel over 17000 miles an hour, a quick clip by any standard. Once they reach this speed (and, of course, are above the atmosphere), the engines are shut off. They are in orbit.

And the astronauts aboard - even the Shuttle itself - are falling to Earth, all day long. To those inside the Shuttle it appears as if gravity has just vanished.

Imagine trying to eat or drink or get around in a place where everything is “floating.” It’s a whole new world. I won’t go into the details NASA had to work out so that the astronauts could use the bathroom without major embarrassment. Think seatbelts and vacuums.

There are images and movies waiting for you at firstlightastro.com/icolumn.html.

And you can watch the Shuttle astronauts for the next year as they build the Space Station. And as you watch them, if someone should shout out, “Look! There’s no gravity up there!” don’t fall for it.

Posted by Administrator at 2000.12.11 08:57 AM | Comments (0)



Looking for something?	« November 2000 \| Main \| January 2001 » The Christmas Eclipse Observing > Under usual circumstances, the announcement of both a new millennium and a Christmas solar eclipse would be rather exciting. Unfortunately, though, this year’s announcement is a little anticlimactic. There was such a big deal made last January over the arrival of the “new millennium” that when the real thing comes next week it’s sure to pass with a whimper. There was no Year 0, so the first century started with the year A.D. 1. The second century, therefore, started in A.D. 101, and so on. By keeping with this pattern, the 21st Century really starts in the year A.D. 2001. Last year we celebrated the flipping of the calendar’s odometer from 1999 to 2000. But for most people it was a two-for-one gala as they celebrated the arrival of the new millennium, as well. In the great scheme of things, of course, it’s not a big deal. Calendars are rather arbitrary, anyway. And after the last election revealed our shortcomings in the counting arena, we may find some Americans celebrating the new millennium in the year 2002. Now to Christmas news. Our Christmas Star is being eclipsed by the Moon! That is, on Christmas morning the Moon, in its never-ending orbit around the Earth, will slowly move in front of the Sun, partially blocking it. Unfortunately, the Moon is near apogee, so it won’t be a total eclipse. Apogee just means the Moon is at its greatest distance from us in its orbit. When it’s farther out it has a greater difficulty covering the whole sun. Imagine a light bulb several feet away from you. You can block out the entire bulb with your thumb if your thumb is close enough to your eye. But move your thumb toward the light and you’ll soon find it no longer blocks out the whole bulb. This is what’s happening with the Sun and Moon in their present positions. Moreover, because of the positions of every body involved, the place to be for the most “sun blockage” is in the north and east of North America. Hmmm… we are in the south and west. Sadly, our eclipse will be minor. But we do get some! And if you’re game, here’s how to “see” it. First: never, ever, ever, look directly at the Sun - even during partial eclipses - unless the Sun is completely eclipsed by the Moon or you have a special filter. A partial eclipse can destroy your vision. If you want to use a filter, use only the commercially available kind. (A good telescope store will have them.) You can also use #14 arc-welder’s glass. Or you can play it safe and do a family project, creating a classic pinhole camera, like the one pictured. Take a piece of cardboard and poke a good-sized hole through it. Tape a piece of aluminum foil over the hole. Then make a small hole through the foil with a straight pin. Let the sun’s light pass through the hole to another piece of cardboard a couple feet away. That tiny disk of light is an image of the Sun. On Christmas morning, that little disk will have a bite taken out of it. See below. The eclipse peaks here around 8.30 AM. Maybe after you open your gifts early Christmas morning, you and your family can go outside for another, more heavenly, gift. Images and movies of the eclipse await you at firstlightastro.com. Click on iColumn. Until next time, clear skies, a blessed Christmas, and a safe new Millennium! Posted by Administrator at 2000.12.25 08:55 AM \| Comments (0) The Shuttle in Orbit Science > We’ve all seen images of Shuttle astronauts floating around the spacecraft trying to hold themselves in place or just clowning around in their weightlessness. Do they float around up there because there is no gravity? No! It’s because they are falling! To understand this, we need to use our imagination. Let’s use a modified mental model that Isaac Newton gave us centuries ago. (Newton used a cannon; I'll use a bow and arrow Imagine being at the top of a very high mountain. You hold a bow in one hand and pull back a suction-tipped arrow with the other. You now weakly shoot the arrow straight out towards the horizon. As expected, it falls to earth. Taking another arrow from your quiver, you fire it, but with more power this time. To no one’s surprise, it goes farther. Now, after having downed a full can of spinach, you launch another arrow with Popeye-like strength. This arrow goes far into the distance. But farther than expected! The Earth, you see, is not flat. It is a sphere, and over great distances, it curves significantly. The arrow got a chance to fly farther before landing because the Earth below it curved away. The next time you fire off your arrow, after two cans of spinach, the arrow goes so far it actually flies over the horizon and out of sight “downrange” somewhere. Is it possible to shoot the arrow with such great velocity that, even as gravity pulls the arrow down, the Earth curves out of the way so that the arrow can’t “land” at all? Yes! After a Costco dose of spinach, you now have the strength to fire the suction-tipped arrow so fast that it travels around the Earth and eventually smacks you on the back of your unsuspecting head. That’s what being “in orbit” is all about. Notice that gravity was acting on the arrow the whole time as the arrow was trying desperately to fall to the Earth. How do you feel when you freefall on an amusement park ride? You feel weightless; it’s like floating. That’s what happens on the Shuttle. The Shuttle is launched, and - observant people will notice - it rolls over and turns toward the eastern horizon, rockets firing furiously the whole time. They are trying to be the arrow that goes so fast that even as gravity tries its best to bring it back, the Earth is curving safely out of its way. But to achieve the speed that will allow this they must travel over 17000 miles an hour, a quick clip by any standard. Once they reach this speed (and, of course, are above the atmosphere), the engines are shut off. They are in orbit. And the astronauts aboard - even the Shuttle itself - are falling to Earth, all day long. To those inside the Shuttle it appears as if gravity has just vanished. Imagine trying to eat or drink or get around in a place where everything is “floating.” It’s a whole new world. I won’t go into the details NASA had to work out so that the astronauts could use the bathroom without major embarrassment. Think seatbelts and vacuums. There are images and movies waiting for you at firstlightastro.com/icolumn.html. And you can watch the Shuttle astronauts for the next year as they build the Space Station. And as you watch them, if someone should shout out, “Look! There’s no gravity up there!” don’t fall for it. Posted by Administrator at 2000.12.11 08:57 AM \| Comments (0)
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