[ FirstLight Astronomy Club ] The Skies Above

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How the Moon was Born

The Solar System >

Go out this evening and look down. There under your feet is the crust of the earth. It is a solid part of our planet, globally broken into a dozen monstrous plates only miles thick, and riding atop a great layer of gooey molten rock called the mantle.

We have a thin-crust planet, as thin as a peel on an apple, relatively speaking. All the other planets like ours have thicker surfaces, so thick that they don't move about and buckle and crack like ours does in a little process we like to call "plate tectonics."

How did we get short crusted?

Rising in the eastern skies this evening is the answer to this long hidden mystery. In that big ball we call the Moon lies most of our old crust. Here's the latest on how this all may have worked out:

About 4.4 billion years ago our toddler solar system was congested with probably a couple dozen newly formed planets. Infant Earth was moonless then --- for a time anyway.

Back then Earth was a wee smaller and composed of a thick crust layer more typical of the other planets. And our early atmosphere was probably much thicker, too, and absolutely not right for life.

Then it happened.

One day a baby planet about twice the size of Mars collided with the Earth. Striking neither head-on nor at a glance, but somewhere in between, this impact changed the course of Earth history.

In The Impact both of our relatively thick, light crusts were sheared away and thrown scattered into orbit around a devastated Earth. The guts of the other body became one with our planet. This trauma took less than 24 hours!

But what came next was a beautiful thing to behold.

Because the collidor's guts were absorbed into the New Earth, there was now more red-hot radioactive stuff, like uranium and thorium, below the surface. Hot molten material rises, and when it does forces the crustal plates above it all to move and split and cram into each other driving plate tectonics for eons --- if the crust is thin enough.

But the impact thinned out the crust of New Earth; as a result it could be easily moved about. Now, via tectonics, there could be land and oceans, mountains and valleys, rivers and streams. And tectonics' recycling of minerals made fertile lands all over the planet.

Moreover, the atmosphere of New Earth, which was eventually reestablished, was much thinner and now conducive to life, which would be appearing soon.

And, of course, we got a new Moon out of the whole shebang. This heaven-sent heavenly body is not merely a garbage collector of tossed-up crust, oh no! The crusty Moon stabilizes our orbit, keeps us from wobbling over, and its pull on us has slowed our spin down to a comfortable 24-hour day. It also provides the ebb and flow of tides that allow a whole menagerie of life along all coasts.

If the colliding body had arrived just hours earlier or later none of this would have happened. We would still have a thick immovable crust, a heavy, sterile atmosphere, and no stabilizing Moon.

Bottom line? If this Collision hadn't occurred exactly when and where and how it did, we wouldn't be here!

A lesson here for us? Immeasurable good can rise from the flames of events that seem utterly and hopelessly devastating at the time.

Until next time, clear skies!

Posted by Administrator at 2001.09.29 08:10 AM | Comments (0)

Astrology's Foe: Precession

Science >

Modern day astrology claims that the position of the sun, moon, and planets in the sky somehow influences a person's life. Ironically, the true positions of those heavenly bodies cause one to seriously question the validity of astrology --- that, and a little thing called precession.

For millennia humans noticed how the sun and Moon influenced everyday life. The sun told us when to plant and reap. It gave light and warmth to all life. The Moon caused tides and was somehow connected to many biological rhythms. So, understandably, there were some people who gave reverence to the greater and lesser lights of the heavens, even deifying them.

Planets, being in the heavenlies with the sun and Moon, were thought to have some mystifying influence on life here, as well.

Over time the study of the positions of these influential, mysterious bodies evolved into a sophisticated belief system known as astrology.

One aspect of this belief system was that the position of the sun and planets at one's birth influenced that person's personality and future.

The positions of the sun and the planets actually appear to move very slowly through the fixed stars behind them. The Sun crawls along through the starry constellations, just a tiny bit each day, on an imaginary line called the ecliptic, taking a year to go once completely around us through the heavens.

The ecliptic goes right through a zoo of background constellations called the zodiac. The planets "travel" though the zodiac, as well. Hence we have phrases like "the Sun is in Scorpius" or "Mars is in Gemini."

Adherents to astrology note the positions of all these celestial players at the moment of birth. Where the sun is thought to be determines one's "sign." But where is the Sun actually? Therein lies our problem. Thinking cap time!

Earth spins on an axis. Its axis is slightly tilted with respect to our orbit around the sun. But we are spinning with the same tilt all year long, our axis "pointing" in the same direction toward the North Star, Polaris. We go through our life month after month, season after season, with Earth pointing at the same star with nary a noticeable change.

But if you could live for hundreds or thousands of years, you'd notice our axis actually drifts!

This drift is more like the wobble of a top. Spin a top for all it's worth and you'll notice that although it's spinning pretty fast, it begins to wobble slowly.

Earth wobbles like a top. This is called precession. But for Earth to wobble just once takes over nine million spins --- about 26,000 years! Now for the astrology connection:

Thousands of years ago when the first horoscopes were being developed, our axis was pointing to a different part of the sky. And if you were there on the first day of "January" the sun would be in Capricornus.

But precession happens. We have wobbled. And we have adjusted our calendar through the centuries to adjust for the wobble.

But this adjustment of the calendar has had profound effects on the horoscope. A baby born today on January 1, although referred to by believers as a "Capricorn" is not a Capricorn. The sun at that baby's birth is in Sagittarius! In fact, the sun on January 1 hasn't been in Capricorn for more than 500 years. Yikes!

It turns out that because our planet wobbles almost everyone has a different "sign" than what is given in the common horoscopes. Hmmm ...

Precession is just one problem astronomy has dealt to its distant cousin astrology. We'll examine others in months to come.

Posted by Administrator at 2001.09.15 08:13 AM | Comments (0)

The Summer Triangle

Observing >

Let's take a look at an extraterrestrial geometric figure --- the Summer Triangle --- and learn a little about stars at the same time.

Go out this evening and look straight up. There is the bright, blue star, Vega. Face southeast now and look "down" just a little to bright Altair.

Go back up to Vega, but look now just a little to its left. That bright star is Deneb.

These three brilliant stars make up the Summer Triangle.

Vega, in the constellation Lyra, gets most of the attention of the three mostly because of its prominent electric brightness. In 1850, it was the first star to be photographed at the Harvard Observatory. It was the star of Carl Sagan's Contact. And most importantly, Chevrolet named a really attractive car after it back in the '70's.

Vega is a big star to be sure, nearly four times bigger than our sun and spewing out over 70 times the amount of energy. But a great contributing factor to Vega's brightness is that it's right next door, a mere 25 light years away. Its light takes 25 years to reach us. In a cosmic case of irony, the light now reaching our eyes from Vega left the great star about the same time the last of the Chevy Vegas were leaving the assembly line.

Altair in Aquila is another star benefiting from its distance from us. It is only a pitiful two-and-a-half times larger and 18 times more "luminous" than our sun. But what makes it extra bright in the sky is the fact that it is even closer than Vega --- a mere 17 light years away. The light we see now left Altair as the Olympic flame burned over Los Angeles in 1984.

But the most overlooked star of the Triangle is lowly Deneb, in Cygnus. This is the star that proves the adage that we shouldn't judge a star by its brightness. It is the dimmest of the three, but it is the brightest by far! Excuse me?

Astronomers look at a star's brightness in two ways: how bright they appear to our eyes and how bright they would be on a level playing field.

How bright a star appears to our eyes is called, to no one's surprise, apparent brightness. The Sun "appears" really bright --- its apparent brightness is enormous --- but only because it's close enough to throw a spaceship at. Put it farther away, out with other stars, and its claim as Brightest Object in the Sky dims considerably.

Is there a fairer way to evaluate a star's brightness? Yes. It's called absolute magnitude. To get this we imagine lining up the stars at a given distance and only then comparing.

When we do this the sun turns out to be an average ho-hum star. Vega and Altair are bright compared to most, to be sure, but not too much brighter than the average. No, it's in this Line-Up that Deneb is the real star of the show.

Deneb, in a class of stars called white supergiants, would shine (sit down!) with nearly 400,000 times more energy than our Sun! It is nearly 300 times bigger!

And going star-to-star with upstart Vega, Deneb would outshine it by a factor of thousands!

Deneb appears so dim because it is so very far away --- over 3000 light years. That's over 18,000 trillion miles. The light we see from Deneb left about the same time Moses and the Children of Israel left Egypt!

Until next time, clear skies!

Posted by Administrator at 2001.09. 1 08:15 AM | Comments (0)



Looking for something?	« August 2001 \| Main \| October 2001 » How the Moon was Born The Solar System > Go out this evening and look down. There under your feet is the crust of the earth. It is a solid part of our planet, globally broken into a dozen monstrous plates only miles thick, and riding atop a great layer of gooey molten rock called the mantle. We have a thin-crust planet, as thin as a peel on an apple, relatively speaking. All the other planets like ours have thicker surfaces, so thick that they don't move about and buckle and crack like ours does in a little process we like to call "plate tectonics." How did we get short crusted? Rising in the eastern skies this evening is the answer to this long hidden mystery. In that big ball we call the Moon lies most of our old crust. Here's the latest on how this all may have worked out: About 4.4 billion years ago our toddler solar system was congested with probably a couple dozen newly formed planets. Infant Earth was moonless then --- for a time anyway. Back then Earth was a wee smaller and composed of a thick crust layer more typical of the other planets. And our early atmosphere was probably much thicker, too, and absolutely not right for life. Then it happened. One day a baby planet about twice the size of Mars collided with the Earth. Striking neither head-on nor at a glance, but somewhere in between, this impact changed the course of Earth history. In The Impact both of our relatively thick, light crusts were sheared away and thrown scattered into orbit around a devastated Earth. The guts of the other body became one with our planet. This trauma took less than 24 hours! But what came next was a beautiful thing to behold. Because the collidor's guts were absorbed into the New Earth, there was now more red-hot radioactive stuff, like uranium and thorium, below the surface. Hot molten material rises, and when it does forces the crustal plates above it all to move and split and cram into each other driving plate tectonics for eons --- if the crust is thin enough. But the impact thinned out the crust of New Earth; as a result it could be easily moved about. Now, via tectonics, there could be land and oceans, mountains and valleys, rivers and streams. And tectonics' recycling of minerals made fertile lands all over the planet. Moreover, the atmosphere of New Earth, which was eventually reestablished, was much thinner and now conducive to life, which would be appearing soon. And, of course, we got a new Moon out of the whole shebang. This heaven-sent heavenly body is not merely a garbage collector of tossed-up crust, oh no! The crusty Moon stabilizes our orbit, keeps us from wobbling over, and its pull on us has slowed our spin down to a comfortable 24-hour day. It also provides the ebb and flow of tides that allow a whole menagerie of life along all coasts. If the colliding body had arrived just hours earlier or later none of this would have happened. We would still have a thick immovable crust, a heavy, sterile atmosphere, and no stabilizing Moon. Bottom line? If this Collision hadn't occurred exactly when and where and how it did, we wouldn't be here! A lesson here for us? Immeasurable good can rise from the flames of events that seem utterly and hopelessly devastating at the time. Until next time, clear skies! Posted by Administrator at 2001.09.29 08:10 AM \| Comments (0) Astrology's Foe: Precession Science > Modern day astrology claims that the position of the sun, moon, and planets in the sky somehow influences a person's life. Ironically, the true positions of those heavenly bodies cause one to seriously question the validity of astrology --- that, and a little thing called precession. For millennia humans noticed how the sun and Moon influenced everyday life. The sun told us when to plant and reap. It gave light and warmth to all life. The Moon caused tides and was somehow connected to many biological rhythms. So, understandably, there were some people who gave reverence to the greater and lesser lights of the heavens, even deifying them. Planets, being in the heavenlies with the sun and Moon, were thought to have some mystifying influence on life here, as well. Over time the study of the positions of these influential, mysterious bodies evolved into a sophisticated belief system known as astrology. One aspect of this belief system was that the position of the sun and planets at one's birth influenced that person's personality and future. The positions of the sun and the planets actually appear to move very slowly through the fixed stars behind them. The Sun crawls along through the starry constellations, just a tiny bit each day, on an imaginary line called the ecliptic, taking a year to go once completely around us through the heavens. The ecliptic goes right through a zoo of background constellations called the zodiac. The planets "travel" though the zodiac, as well. Hence we have phrases like "the Sun is in Scorpius" or "Mars is in Gemini." Adherents to astrology note the positions of all these celestial players at the moment of birth. Where the sun is thought to be determines one's "sign." But where is the Sun actually? Therein lies our problem. Thinking cap time! Earth spins on an axis. Its axis is slightly tilted with respect to our orbit around the sun. But we are spinning with the same tilt all year long, our axis "pointing" in the same direction toward the North Star, Polaris. We go through our life month after month, season after season, with Earth pointing at the same star with nary a noticeable change. But if you could live for hundreds or thousands of years, you'd notice our axis actually drifts! This drift is more like the wobble of a top. Spin a top for all it's worth and you'll notice that although it's spinning pretty fast, it begins to wobble slowly. Earth wobbles like a top. This is called precession. But for Earth to wobble just once takes over nine million spins --- about 26,000 years! Now for the astrology connection: Thousands of years ago when the first horoscopes were being developed, our axis was pointing to a different part of the sky. And if you were there on the first day of "January" the sun would be in Capricornus. But precession happens. We have wobbled. And we have adjusted our calendar through the centuries to adjust for the wobble. But this adjustment of the calendar has had profound effects on the horoscope. A baby born today on January 1, although referred to by believers as a "Capricorn" is not a Capricorn. The sun at that baby's birth is in Sagittarius! In fact, the sun on January 1 hasn't been in Capricorn for more than 500 years. Yikes! It turns out that because our planet wobbles almost everyone has a different "sign" than what is given in the common horoscopes. Hmmm ... Precession is just one problem astronomy has dealt to its distant cousin astrology. We'll examine others in months to come. Posted by Administrator at 2001.09.15 08:13 AM \| Comments (0) The Summer Triangle Observing > Let's take a look at an extraterrestrial geometric figure --- the Summer Triangle --- and learn a little about stars at the same time. Go out this evening and look straight up. There is the bright, blue star, Vega. Face southeast now and look "down" just a little to bright Altair. Go back up to Vega, but look now just a little to its left. That bright star is Deneb. These three brilliant stars make up the Summer Triangle. Vega, in the constellation Lyra, gets most of the attention of the three mostly because of its prominent electric brightness. In 1850, it was the first star to be photographed at the Harvard Observatory. It was the star of Carl Sagan's Contact. And most importantly, Chevrolet named a really attractive car after it back in the '70's. Vega is a big star to be sure, nearly four times bigger than our sun and spewing out over 70 times the amount of energy. But a great contributing factor to Vega's brightness is that it's right next door, a mere 25 light years away. Its light takes 25 years to reach us. In a cosmic case of irony, the light now reaching our eyes from Vega left the great star about the same time the last of the Chevy Vegas were leaving the assembly line. Altair in Aquila is another star benefiting from its distance from us. It is only a pitiful two-and-a-half times larger and 18 times more "luminous" than our sun. But what makes it extra bright in the sky is the fact that it is even closer than Vega --- a mere 17 light years away. The light we see now left Altair as the Olympic flame burned over Los Angeles in 1984. But the most overlooked star of the Triangle is lowly Deneb, in Cygnus. This is the star that proves the adage that we shouldn't judge a star by its brightness. It is the dimmest of the three, but it is the brightest by far! Excuse me? Astronomers look at a star's brightness in two ways: how bright they appear to our eyes and how bright they would be on a level playing field. How bright a star appears to our eyes is called, to no one's surprise, apparent brightness. The Sun "appears" really bright --- its apparent brightness is enormous --- but only because it's close enough to throw a spaceship at. Put it farther away, out with other stars, and its claim as Brightest Object in the Sky dims considerably. Is there a fairer way to evaluate a star's brightness? Yes. It's called absolute magnitude. To get this we imagine lining up the stars at a given distance and only then comparing. When we do this the sun turns out to be an average ho-hum star. Vega and Altair are bright compared to most, to be sure, but not too much brighter than the average. No, it's in this Line-Up that Deneb is the real star of the show. Deneb, in a class of stars called white supergiants, would shine (sit down!) with nearly 400,000 times more energy than our Sun! It is nearly 300 times bigger! And going star-to-star with upstart Vega, Deneb would outshine it by a factor of thousands! Deneb appears so dim because it is so very far away --- over 3000 light years. That's over 18,000 trillion miles. The light we see from Deneb left about the same time Moses and the Children of Israel left Egypt! Until next time, clear skies! Posted by Administrator at 2001.09. 1 08:15 AM \| Comments (0)
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