Paul Derrick's Stargazer



1999 Stargazer Columns (selected)

 Copyright by Paul Derrick.  Permission is granted for free electronic distribution as long as this paragraph 
 is included.  For permission to publish in any other form, please contact the author at

Dec. 25, 1999: A Cross and a Manger
Dec. 11, 1999: Buying a Telescope
Nov. 27, 1999: SOFIA
Nov. 13, 1999: Mercury Transit and Leonid Meteors
Oct. 30, 1999: The Moon and Stargazing
Oct. 16, 1999: The Princess and the Hero
Oct. 02, 1999: Draco and the Draconid Meteor Shower
Sep. 18, 1999: The Ecliptic and the Solar System Highway
Sep. 04, 1999: Benjamin Banneker, Colonial Astronomer
Aug. 21, 1999: Moons of the Solar System
Aug. 07, 1999: Total Eclipse of the Sun Over Central Texas in 2024
July 10, 1999: Stars Twinkle, Planets Don't
June 26, 1999: Texas Star Party
June 12, 1999: David Levy, Discoverer of Comets
May 29, 1999: Star Light, Star Bright
May 15, 1999: Astronomy Day -- 1999
May 01, 1999: What If the Sun Went Out?
Apr. 03, 1999: Janice VanCleave -- Author of Children's Science Books
Mar. 20, 1999: Jewels of the Southern Skies
Jan. 23, 1999: Once in a Blue Moon

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December 25, 1999

A Cross and a Manger

Two religious symbols in the current night sky bid a special "Merry Christmas" to Christians around the world celebrating the birth of Jesus.  A cross is setting in the northwest as a manger is rising in the east northeast.

The cross is formed by the major stars of Cygnus the Swan, informally known as the "Northern Cross."  At 9 p.m., it will be standing upright with its base on the horizon and its brightest star, Deneb, at the top.  Deneb will be 20 degrees above the horizon, about twice the width of your fist held at arm's length.  The crossbar spans some 15 degrees.

The manger is the lovely star cluster variously called M44, the Beehive, and Praesepe.  (Praesepe is Latin for "manger.") It is in the faint constellation Cancer the Crab, located mid way between the Gemini Twins and Leo the Lion.

To the naked eye, Praesepe appears as a soft fuzzy glow.  However, when viewed through binoculars, a swarm of dozens of individual stars becomes visible, giving rise to its more common name, the Beehive. While both the cross and the manger are briefly in the sky simultaneously, actually seeing them at the same time is difficult.  At 9 p.m., just as the cross begins sinking into the horizon, seeing Praesepe is a challenge as it is only 12 degrees above the horizon.  By 10 p.m., Praesepe will be easier to see, having risen to 25 degrees, but by then the lower part of the cross will be below the horizon.

So, to see each at its best, look for the cross around 8 p.m. when its top will be 30 degrees and its bottom 10 degrees above the horizon.  Then look for the manger around 10 p.m. or later.  (Tonight, a gibbous Moon rises soon after Praesepe and will interfere once it lights up the sky; after tonight, however, it rises later and will be less of a problem.)

This coincidental appearance of a cross and manger during the Christmas season was pointed out some years ago by Jack Horkheimer, PBS's "Star Gazer" (formerly known as the "Star Hustler").  Thanks, Jack, and "Keep lookin' up."

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December 11, 1999

Buying a Telescope

Planning to buy a telescope?  If so, you'll have several decisions to consider, like where to make your purchase.

In smaller cities (like Waco), you will likely find a limited selection of scopes in the larger department stores.  Advantages of buying locally are convenience and immediate availability.  Disadvantages are restricted choices and sales personnel with little (if any) knowledge about telescopes.

For a larger selection and informed assistance, you'll need to visit a specialty dealer.  For central Texans, this means traveling to Ft. Worth, Dallas, Houston or San Antonio.  The nearest to Waco is Skywatch Products in Ft. Worth (817-249-3767).

Another option is buying through a catalog (paper or on-line).  Here you are likely to find the broadest selection and the best prices.  On the down side, you only see pictures rather than the real things, your ability to ask questions is limited, and delivery takes a while.  A reputable dealer I've used is Orion Telescopes; call 800-676-1343 for a free and informative catalog.

Prices of amateur telescopes range from less than $100 for those which are little more than toys to several thousand dollars for those of the highest quality.  A nice scope can be had for a few hundred dollars.

If money is the overriding factor, and you must go for an inexpensive scope, then just compare department store prices (they do vary) and pick one.  But be aware that the quality of these scopes can lead to more frustration and disappointment than satisfaction.  This is especially true if one is misled by the pictures and claims of 400-600 power found on some telescope boxes.  Even my 8-inch scope can't show images like those beautiful photos, and 400 power is beyond its practical reach.

An alternate suggestion: consider spending that $100 on a good pair of binoculars rather than on a low-end telescope.

At the other end, if you're ready for a serious investment, a superb 8- to 10-inch telescope with many bells and whistles, including a computer-operated motor drive system, can be bought for under $3,000.  Unfortunately, you likely won't find one locally, and you certainly will want to do some serious research.

Here's yet another idea: consider a used scope.  If they have received good care, and most probably have, you can get a good deal.  Check the want-ads or check with your local astronomy club.  Contact me for a phone number as I have a directory of many clubs in the U.S.  And for a copy of Sky & Telescope's "Choosing your first telescope" reprint, send me a SASE.

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November 27, 1999


Actor Steve Martin, author Robert ("All I Really Need to Know I Learned in Kindergarten") Fulghum, folk singer Carolyn Hester and others once lived in Waco, then moved on to become famous.  We now have another star-in-the-making in our midst, but she doesn't act, write or sing -- she flies.

Her name is SOFIA, short for Stratospheric Observatory for Infrared Astronomy. (You see why she goes by SOFIA.)  She's a huge Boeing 747SP airplane being converted into a flying observatory by Raytheon here in Waco.  When placed into service in 2002 equipped with an 8-ft diameter telescope, SOFIA will leave Waco and move on to fill a research void which has existed since the Kuiper Airborne Observatory was retired in 1995.

SOFIA is a joint project of a consortium of entities, including NASA, Germany's space agency, Universities Space Research Associ- ation, the SETI Institute, United Airlines, Raytheon and others.  We have telescopes all over Earth and even in space (like the Hubble Space Telescope), so why an airborne observatory?

Ground-based telescopes must observe the heavens through Earth's atmosphere which even on cloudless days contains water vapor as well as air.  Both distort and block part of what astronomers wish to see and study.  Space telescopes avoid atmosphere problems but are more expensive and less accessible for repairs and modernizations.  SOFIA, a good cost-effective compromise, can fly beyond 40,000 feet, avoiding most atmospheric water vapor, yet still be easily accessible when on the ground.

As her name implies, SOFIA will focus much of her attention on infrared-rays (heat waves), the part of the electromagnetic spectrum most blocked out by water vapor.  The cosmos is full of activity across the entire range of this spectrum from radio waves and infrared-rays at one end to ultraviolet, x-rays and gamma-rays at the other.  Visible light which our eyes see is but a tiny slice in the middle of this spectrum.  So our eyes alone miss much of what's going on out there.

Until modern times we were "blind" to these other parts of the spectrum, unaware they even existed as we lacked any means for detecting them.  For example, we're surrounded by radio waves, yet without a device (we call a radio) to detect and convert them into audible sounds, we would have no idea they were even there.

Infrared waves are also invisible to optical telescopes and human eyes, but SOFIA, with its infrared sensors, will enable astronomers to "see" this range as well.  By studying the heat radiated by distant objects, we can learn more about how galaxies form, the birth and death of stars, black holes, distant solar systems, and maybe even the possibilities for other life.

And, of course, all scientific explorations offer the chance for serendipitous discoveries--things we didn't even know enough to wonder about.  Who knows how famous SOFIA may become...and we can say we knew her when.

In future columns, we'll tell you more about SOFIA and keep you updated on her progress.  You can learn more about her at her web site at

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November 13, 1999

Mercury Transits the Sun and A Leonid Meteor Storm?

This fortnight presents an astronomical day-night double header: a daytime planetary transit and a nighttime meteor shower. 

You'll need special equipment and knowledgeable help to view the transit but not the meteor shower.  Monday afternoon the planet Mercury will pass directly between us and the Sun, a rather rare event called a transit.  As the innermost planets, Mercury and Venus orbit the Sun nearer than Earth's orbit.  If the orbits of these planets were on the exact same plane, transits would occur frequently -- about six times a year for Mercury and once a year for Venus.

But the planets aren't on quite the same plane so Mercury and Venus usually pass slightly above or below the Sun when they come between us and the Sun.  Transits of Mercury occur 13 or 14 times per century while transits of Venus are much rarer, happening 13 or 14 times per millennium.

During the transit, which begins at 3:11 p.m. and concludes at 4:10 p.m., Mercury will look like a tiny black spot slowly moving across the edge of the Sun.  Seeing it requires a telescope which absolutely must be equipped with a proper solar filter.  Looking at the Sun without a solar filter, even for a few seconds, can permanently damage your eyes -- so don't do it.  If you'd like to see this event safely, see below.

Wednesday night (and early Thursday morning until dawn) the annual Leonid meteor shower will peak.  Most years this is a modest shower, but this year could be special -- anything from better than average to a genuine meteor storm.

The Leonids' parent comet, Tempel-Tuttle, which passes through the inner solar system every 33 years, made it's last pass in early 1998.  When comets come near the Sun they experience a partial melt-down, leaving particles of cometary debris in their wake.  As Earth moves through that debris, particles enter our atmosphere at tens of thousands of miles per hour and burn up, producing the breath-taking streaks of fire across our night sky.  While last year's Leonids were well above average, we're hoping, with fingers crossed, this year will be even better.  But unfortunately it doesn't come at a viewer-friendly time.  Leo the Lion, the constellation from which the Leonids seem to radiate, rises in the east soon after midnight, just as the Moon is going down in the west.  So the best viewing will likely come between 1 a.m and dawn Thursday morning.

As with all meteor showers, you'll see more away from city lights.  You won't need binoculars or telescopes.  Just lay back and look high in a generally easterly direction.

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October 30, 1999

The Moon and Stargazing

Recently our family has been graced with the presence of our 2-year old granddaughter, Ellie, visiting from Salem, MA.  To the Stargazer's delight, one of the first words in her vocabulary was "Moon," an object she finds fascinating.

During her two week stay, the Moon went from a thin crescent to fullness, yet she still recognized it as "Moon."  While it's beyond her ability to express it, I have wondered what she thought about the strange transformation in the shape, size and brightness of this wondrous thing in the night sky.

While Ellie and many others find the Moon enchanting, amateur astronomers have mixed feelings about Earth's lovely satellite.  To be sure, it is a dazzling object for observation, especially with binoculars and telescopes.

Yet when it is up, its light washes away views of most other stellar objects, similar in effect to urban light pollution.   So stargazers usually avoid the Moon, planning their viewing for times when the Moon is not present.

The Moon is as predictable as time itself, so viewing sessions can be planned weeks, months, even years in advance.  For example, each December the Central Texas Astronomical Society sets its monthly viewing schedule for the entire coming year.   You too can plan your viewing to avoid the Moon using the moon phase schedule published in most newspapers and printed on many calendars.   It's easy.

The Moon's phases are produced by its orbit around Earth which takes about four weeks.  For evening stargazing, there is a 2- week period of moonless viewing which begins a few days after full Moon, includes the 3rd quarter and extends to a few days after new Moon.   The period for morning viewing is nearly, but not exactly, opposite.  It starts a few days before new Moon, includes the 1st quarter and extends to a few days before full.

The Moon is at 3rd quarter tomorrow and new on Nov. 7, thus we are in the period of good (i.e., moonless) evening viewing.   But watch as moonlight increasingly interferes with stargazing following the new Moon.

Nov. 9, 2 days after new, a tiny crescent Moon sets about 7:45 p.m., posing no obstacle to viewing.  The next night, a slightly larger 3-day old Moon is still little problem, setting about 8:30 p.m. Nov. 11, 4 days after new, a larger and brighter Moon begins to pose difficulties until it sets about 9:15 p.m.   By Nov. 12, the 5-day old Moon noticeably interferes until it sets about 10 p.m., largely precluding enjoyable evening stargazing.

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October 16, 1999

The Princess and the Hero

A well-known Greek myth ties together six constellations of the fall evening sky:  Cassiopeia, Cepheus, Andromeda, Perseus, Pegasus and Cetus.  Apparently created by chauvinistic males, the story centers around a beautiful but helpless Ethiopian princess and her bold, super-competent rescuer.  Andromeda, the Princess, is the daughter of Cassiopeia, the Queen, and Cepheus, the King.  The queen, known for her extreme vanity, angered the powerful god, Poseidon, and as punishment, Andromeda was to be sacrificed to Cetus, the Sea Monster.

Enter Perseus, the Hero.  Like modern day cowboys, this hero rode a horse.  However his horse, Pegasus, the Flying Horse, had wings.  Perseus was told he could rescue Andromeda using the head of Medusa, a creature who had snakes for hair.  She was so ugly one glance at her would turn one into stone.  Combining bravery and brilliance, our hero, while avoiding looking at Medusa, cut off her head and put it into a sack.  He then mounted Pegasus and set out to make his rescue.

Finding Andromeda chained to a small island with nearby Cetus licking his chops, Perseus removed the ugly head from its sack and held it forth.  The sea monster took one look, turned into stone and sank into the sea.  Having no further use for her, he tossed Medusa's head into the sea, completed his rescue of the lovely princess, and presumably lived happily ever after.

As a postscript, I wonder what if Andromeda rather than Cetus had looked at Medusa and turned to stone?  Would the story be regarded as a Greek tragedy (except, of course, by Cetus and his family)?  And do you suppose Perseus ever wished he'd kept Medusa's head to show the vain and meddling Cassiopeia after she became his mother-in-law?

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October 2, 1999

Draco and the Draconid Meteor Shower

The annual Draconid meteor shower peaks the evening of Oct. 9.  As is often the case with meteor showers, it comes with good news and bad news.

First, the bad news:  this is typically not a meteor shower to get excited about, and this year could be a bust like most years.  But meteor showers are known for surprises, so don't write this one off too quickly.

Now some good news:  this year's shower coincides with the new Moon, therefore there will be no interfering moonlight.

And more good news:  whatever meteor activity the shower produces this year is predicted to peak in the evening hours.  Since most meteor showers are best seen in the wee hours between midnight and dawn, this one comes at a more viewer-friendly time.

The Dracoid meteor shower, also called the Giacobinid shower, is parented by the comet Giacobini-Zinner.  This comet, which circles the Sun every 6 1/2 years, passed through our area last fall.  Thus there is reason to hope it might have left a fresh deposit of cometary debris in its path -- the material which produces meteors as Earth moves through that path.

If you're planning to be out next Saturday evening, especially if you're away from city lights, you might want to glance toward Draco every now and then.  The shower's radiant, the point from which the meteors seem to emanate, it near Draco's head.

Draco the Dragon is one of the six circumpolar constellations which never set as seen from most of the U.S.  It circles the celestial north pole, and thus Polaris (the North Star), and is always above the horizon.  Although it is not one of the brighter constellations, it is an interesting one.

Looking more like a cosmic snake than a dragon, Draco starts between the Big and Little Dippers, slithers around the Little Dipper, and stops just short of the bright star Vega.

The Big Dipper, usually the key to finding Draco, is not much help in the evening hours of fall.  It is difficult to see now as it is near, and even partially below, the northwestern horizon.

But fortunately, it's not necessary to find Draco to know where to watch for Draconid meteors.  Facing northwest about 9 p.m., look for Vega, the brightest star high overhead.  Draco's head, a group of four stars looking like a misshapen rectangle, is just over 10 degrees below Vega, a little more than the width of your fist held at arm's length.

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September 18, 1999

The Ecliptic and the Solar System Highway

Perhaps you've noticed that the Moon frequently passes near the planets, that the planets often pass near one another, and that the Moon and planets repeatedly pass the same few bright stars.  These regular passings are no coincidence.

The Moon, planets and Sun, as viewed from Earth, follow a common path through our sky.  This path, a band about 15 degrees wide, can be thought of as the solar system highway.  The line of the Sun's route, called the ecliptic, is the highway's center stripe.  The Moon and planets always travel on this highway because they, and Earth, orbit the Sun on nearly the same plane.

To visualize this, imagine a circle dance with one person in the center and the other dancers circling around at varying distances from the center.  As they go around, passing and seeing each other, they can also look beyond the other dancers and see a wall in the background.  Since they are all on about the same plane, neither the ceiling nor the floor will appear as the background to the other dancers -- only the walls.

Now further imagine that the walls, ceiling and floor have stars and constellations painted on them.  As the dancers go round, they will see each others' heads aligned with the stars and constellations painted on the walls, but not those on the floor or ceiling.

This line-of-sight path would be the solar system highway.  Those background constellations on the walls through which the other dancers' heads seem to pass are known as the zodiac. If every dancer was exactly the same height and never bobbed up and down, everyone's head would travel around the circle on exactly the same plane and in line with the exact same background objects.  But people vary in height and dancers bob, so the path of their heads will not be on exactly the same plane.

Similarly with the Moon and planets, whose orbits are nearly, but not exactly, on the same plane.  While they are always somewhere on the solar system highway, they wander from side to side.  Thus they pass each other at varying distances, sometimes several degrees apart, other times spectacularly close.

And objects seen in the background will vary somewhat, depending upon which part of the highway the planet or Moon is traveling.  Within the constellations of the zodiac, there are five bright background stars the Moon and planets regularly pass near: Antares in Scorpius, Aldebaran in Taurus, Pollux in Gemini, Regulus in Leo, and Spica in Virgo.

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September 4, 1999

Benjamin Banneker, Colonial Astronomer

Benjamin Banneker was an 18th century American who lived two lives--one rather common, the other quite extraordinary.  What makes his story all the more remarkable is that he was an African American--a free black man living in a country that held most of his black brothers and sisters in slavery.

Born in 1731 in Baltimore County, Maryland, he became a farmer like his parents. When Banneker was 27, his father died, leaving him responsible for his mother, three younger sisters and the family's 100-acre tobacco farm.  As a black man in a white world, he had limited social opportunities outside his own family.  He never married, never moved from the family home and lived a rather solitary life.  That was one life of Benjamin Banneker.

In his other life, he was a mathematician, astronomer, surveyor and almanac publisher.  And if that wasn't enough, he learned to play the flute and violin, and at age 21, made a wooden striking clock which worked for more than 50 years.  One of his biographers, Salvio Bedini, dubbed him "the first black man of science" in America.

Having no formal education beyond elementary school, Banneker still demonstrated a keen intellect and a passion for reading and learning.  But given his circumstances, these qualities would have been wasted had it not been for the Ellicotts.

A large, well-educated and influential family, the Ellicotts moved into Baltimore County in 1772.  White liberals of their day--sympathetic to the plight of black Americans and active in the anti-slavery abolitionist movement--they befriended their new neighbor, Benjamin Banneker.

An especially strong friendship developed between Banneker and young George Ellicott, 29 years his junior, when they discovered a shared love of nature, science and literature.  George loaned many of his science books and instruments to his older friend who used them to good advantage.

While in his 40s, Banneker learned the basics of surveying and advanced his math knowledge.  In 1791, at age 60, he assisted in the initial survey of the new capital, Washington, D.C.

At age 57, he took up astronomy and became consumed with his newfound fascination.  He was soon making observations and calculating tables of the motions of the Sun, Moon and planets. He became so proficient that from 1792 to 1797, he published the widely used "Benjamin Banneker's Almanac and Ephemeris."

If space permitted, there is even more to tell about this amazing man--like his exchange of letters with Thomas Jefferson over the issue of slavery.  But one is left to wonder:  With more formal education and an earlier start, how much more might Benjamin Banneker, with his great motivation and abilities, have been able to contribute to this new country?

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August 21, 1999

Moons of the Solar System

Our solar system is composed of a star (which we call Sun), nine planets, several dozen moons, millions of asteroids and comets, and countless meteoroids which orbit our star.

Surprisingly, firm definitions of many of these objects are lacking. In recent years, this fuzziness has led to controversy about the status of Pluto, as recently discussed by David H. Levy in Parade magazine: Is Pluto a planet, an unusually large asteroid, an escaped moon or something else?

Generally, planets are large objects which orbit a star, and moons are smaller objects which orbit planets. Asteroids, comets and meteoroids orbit a star like planets but are much smaller.

Moons are among the more interesting members of our solar system. The two innermost planets, Mercury and Venus, have none. Earth has one rather large one, and Mars has two small ones.

Jupiter, Saturn, Uranus and Neptune have multiple moons. The counts keep rising as new moons continue to be discovered. Even Pluto, the smallest and outermost planet, has a moon.

All these moons seem more similar to one another than the planets are to one another. Five planets are mostly solid while four are primarily of gas. All the moons, however, are solid although a couple might have oceans of liquid water beneath a frozen crust, and Jupiter's Io has active volcanoes. But in spite of their similarities, the moons of the solar system seem to have several different origins.

Since our Moon's composition is similar to that of Earth, it is believed to have formed eons ago when part of Earth was broken off in a gigantic collision with an unknown body.

Mars' two tiny moons likely didn't start out as moon. With Mars orbiting just inside the asteroid belt, its moons were probably asteroids which drifted too close to the red planet and were captured by its gravity.

The moons of the giant gas planets likely formed along with the planets themselves, just as the planets formed in the same process that gave birth to our star. Some of the smallest ones, however, might be captured asteroids.

Pluto and its moon, Charon, are mysteries. The origin of Charon is just as uncertain as that of Pluto itself. Some argue that Pluto formed with the other planets and that Charon's origin is similar to that of our Moon. Others believe both are asteroids from the Kuiper Belt, a recently discovered asteroid belt beyond Pluto's orbit. Others think they were moons of Neptune that got knocked out of their orbit around Neptune.

Pluto and Charon remain the only planetary system not visited by any of our space probes. The mysteries of their origins may not be solved until these remote bodies are explored up close, perhaps within the next decade.

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August 7, 1999

Total Eclipse of the Sun Over Central Texas in 2024

The big astronomical happening this week is Wednesday's total eclipse of the Sun. Unfortunately for us in North America, it will only be visible from Europe.

A solar eclipse occurs when the Moon passes exactly between Earth and Sun, casting a shadow across part of Earth's surface. For those lucky enough to be in that shadow, the Sun disappears, the sky darkens and it seems almost like night for a few minutes.

In a round-about way, this eclipse reminds me of a childhood experience that furthered my interest in astronomy. In 1954 when I was 14, an 80-year old lady, Margaret Willets, told me with great enthusiasm of seeing Halley's Comet in 1910. When she told me it was coming back in 1986, she started a clock ticking in my head--for over 30 years I awaited Halley's return. When I finally saw it, I rejoiced and remembered Ms. Willets with gratitude.

So now it's my turn to pass on her legacy and start a clock ticking in your head. This one, however, is a solar eclipse clock: there will be a total eclipse of the Sun visible from Central Texas on April 8, 2024--a mere 25 years from now.

The eclipse path in the U.S. will stretch from Texas to Maine. Most North Americans will see at least a partial eclipse. Central Texas will be within that narrow path of totality. Around noon, our skies will darken, the brighter stars and planets will become visible, and the Sun's corona will come into view. It should be awesome, an event of a lifetime.

If you just can't wait until 2024, there will be a total solar eclipse visible across mid-America in 2017, stretching from Oregon to South Carolina. And there will be several partial eclipses over the next several years, the next one occurring on Christmas day of 2000.

The more mature among you may be thinking: I may not live long enough to see the 2024 eclipse. Maybe, but don't give up too quickly. Ms. Willets lived past 100 and missed seeing Halley's Comet a second time by less than a decade.

And the young among you may be thinking: 25 years is a long time to wait. Yes, it is, but some day you'll hear the little clock start ticking more loudly and know the time is drawing near. Perhaps you'll also remember that your eclipse clock began ticking way back in 1999.

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July 10, 1999

Stars Twinkle, Planets Don't

When viewed in the night sky, the five naked-eye planets--Mercury, Venus, Mars, Jupiter and Saturn--are usually mistaken for stars. As for determining which are which, perhaps you've heard the saying, "stars twinkle, planets don't." Well, this is a good time to find out for yourself if it's really true.

For the past few months Mars has been in the same area of the evening sky as Arcturus, the brightest star in Bootes the Herdsman. They look quite similar as both have a reddish tint and are currently about the same brightness.

Tonight around 10 p.m., or any clear night during the next few weeks, find Venus, the brightest star-like object low in the west. High above Venus, the brightest object will be Arcturus. One can also find Arcturus using the Big Dipper as the dipper's handle "arcs to Arcturus."

Mars is below and left of Arcturus, about half way up from the horizon. It is presently near Virgo's brightest star, Spica, a whitish star not quite as bright as Arcturus and Mars.

Once you've identified Arcturus and Mars, note how their similar color and brightness make them look almost identical. It's easy to see how planets can be mistaken for stars.

Twinkling--also called scintillation--is the rapid changes in brightness and coloration of light. It is produced by turbulence in our atmosphere, not by the stars themselves. Viewed from space or the Moon, which has no atmosphere, stars do not twinkle.

The reason stars, but usually not planets, twinkle has to do with their apparent diameter. While vastly larger than planets, stars are so far away they appear only as points of light, even through telescopes. Being much nearer, planets appear as tiny disks, although the disk-shape is seen only with magnification.

Why this difference matters is a bit technical, but here's the easy explanation: Starlight, seeming to come from one point in space, is easily distorted by atmospheric turbulence, whereas with light from planets coming from many points on a small disk, the distorting effects of air turbulence tend to be canceled out, making a planet's light seem more steady.

Now look again at Arcturus and Mars, noting the twinkle factor. Does Arcturus seem to twinkle more than Mars? It should, although the effect might be subtle. When the air is steady, stars don't twinkle as much; when it's very unsteady, planets can even twinkle. (They can also twinkle when seen near the horizon.) But generally, and especially when seen through binoculars, it's true that stars twinkle and planets don't.

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June 26, 1999

Texas Star Party

Where can you find skies so dark that Venus casts a shadow and the Milky Way seems to glow? One great place is at the Texas Star Party, held each spring in the Davis Mountains of west Texas.

This May the Stargazer and several other Central Texans joined 600 other amateur astronomers from 30 states for what has become one of the country's premier stargazing events. Founded in 1979, TSP is held on the 3500-acre Prude Guest Ranch, just outside the small town of Ft. Davis and 12 miles from McDonald Observatory.

The area is ideally situated, being virtually free of urban light pollution. The nearest cities of size, Odessa and Midland, are 180 miles away. Lighting restrictions prohibit the use of lights other than subdued red light after dark--no street lights, flashlights, auto headlights, cabin lights, or campfires.

Amateur telescopes cover three viewing fields, one larger than a football field, creating a carnival-like appearance by day. After dark, however, the area is transformed. Although surrounded by scopes and other stargazers, all one sees are dozens of small red lights and faint silhouettes of those nearby. The only sounds are the blended murmurs of restrained voices and the occasional whirring of a telescope drive motor.

Scopes range from the modest to the monsters, the largest I saw being a 36-inch Newtonian reflector. For those not familiar with telescopes, 36 inches refers to its diameter. Being over 10 feet long, this wasn't a scope for the acrophobic--viewing through it required climbing a tall ladder.

Most activity, of course, occurs throughout the night with each having his or her own viewing agenda. After sleeping late in the morning, many peruse the hall where vendors display the latest gadgets. There are also daytime tours to McDonald Observatory, afternoon workshops and early evening talks. Some can't resist driving 30 miles to the south to look for the mysterious Marfa lights in the early evening.

This year, fairly typical according to TSP veterans, the days got hot and dusty with some wind and clouds. But by night, it was usually calm, cool and clear. Some nights even got downright cold. So why do people drive hundreds of miles to encounter heat, cold and west Texas dust? It's those magnificent dark skies, revealing to the naked eye things which even binoculars don't show from urban areas.

Indeed, brilliant Venus did cast a subtle shadow where it was not competing with terrestrial lights. And the Milky Way, hopelessly invisible from cities and only modestly discernible from most rural areas, was stunning--its soft white glow providing a reminder of why it is called the "milky way."

The Texas Star Party is truly a stargazer's mecca.

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June 12, 1999

David Levy, Discoverer of Comets

Over the past 34 years, astronomer-writer David Levy has spent many thousands of hours searching the night sky for comets. At age 50, he recently logged his 11,000th observing session, an average of more than 6 sessions a week since he was age 16.

Those quiet hours in the dark have paid off. Since his first comet discovery in 1984--nineteen years after his hunt began--21 comets now bear his name as discoverer or co-discoverer.

His most famous find, and arguably the most significant comet in astronomical history, was Shoemaker-Levy 9, co-discovered with Carolyn and Gene Shoemaker in 1993. The comet captured worldwide attention in July 1994 when it crashed into Jupiter, piece by piece, after being ripped apart by the planet's immense gravity.

Single most of his adult life, Levy married his wife Wendee only two years ago. So one might suspect that the man whose name is virtually synonymous with comets is obsessed with finding those cosmic fuzzballs.

But regarding his comet quest, he says, "It's not the discovery--it's the search that's the important thing. The discovery is a bonus." He is still fascinated with everything he sees in the night sky--not just comets, but old friends he's seen many times as well as previously unnoticed jewels.

Levy was the featured speaker at the recent 1999 Texas Star Party in the Davis Mountains of west Texas. The afternoon before speaking to 600 attendees, he graciously granted the interview for this column. Even with his celebrity status, he is friendly and approachable, a gentle man with a warm sense of humor.

With two degrees in English, Levy has never taken an astronomy course. Yet he has published 21 astronomy books and numerous articles, and he lectures internationally.

Born and raised in Canada, he moved to the clear skies of Arizona in 1979 where he does most of his stargazing from his home-based Jarnac Observatory. While the 1993 discovery of Shoemaker-Levy 9 brought him his greatest fame, 1997 presented him with some of the greatest challenges of his life.

The year started with the death of his beloved friend, Clyde Tombaugh, discoverer of Pluto. In March he married Wendee, the mention of whom still makes his eyes sparkle. Two months later, he was diagnosed with prostate cancer. Weeks before his surgery, he learned of the automobile accident which took the life of his friend and colleague Gene Shoemaker. In the fall, he was diagnosed with a second cancer and had a kidney removed. This was also the year he became contributing science editor of Parade magazine following the death of Carl Sagan.

Through it all, he still has a zeal for life and stargazing. Indeed, he said he finds "tremendous spirituality in the night sky." He seems to derive strength from the beauty and wonder of the cosmos. And while enjoying the search, he's ready to find that elusive 22nd comet.

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May 29, 1999

Star Light, Star Bright

As even casual stargazers know, some stars are brighter than others. Many are so faint they are barely detectable while some are so bright they can be seen from light-polluted cities. One star in particular--our Sun--is blindingly bright.

To make sense of these variations, astronomers use a measurement scale called visual magnitudes. It's a reverse scale where the brighter the object, the lower the magnitude number.

In 120 BCE, long before the invention of the telescope, the Greek astronomer Hipparchus devised the first scale by which he ranked stars into six levels of brightness. (Our Sun wasn't recognized as a star then.) The brightest stars he considered "first magnitude." Those barely visible were "sixth magnitude." The rest were equally ranked in between. Although imprecise and cumbersome, his scale has been used ever since.

Modern astronomers have made the scale more precise, and have expanded it to measure the full range of brightnesses, from our Sun to objects fainter than the Greeks could imagine. The scale now dips into negative numbers for very bright objects and goes well beyond +6 for objects fainter than the naked eye can see.

The apparent brightness of stars--how bright they appear from Earth--depends upon their intrinsic brightness and distance. Our Sun, a star of average brightness, appears so bright because of its nearness. Its visual magnitude is measured at -27.

By contrast, Orion's supergiant Rigel is 50,000 times brighter than our sun, but at a distance of 900 light years, its visual magnitude is 0, still making it the 7th brightest star in our night sky. At that distance, our Sun wouldn't even be visible to the naked eye.

Polaris, the North Star, at 650 light years away, is magnitude of +2. Venus, which only reflects sunlight but is much nearer than the stars, appears much brighter with a magnitude of -4.

From urban areas, the naked eye can only see objects down to 3rd or 4th magnitude whereas from rural areas, objects of 5th and even 6th magnitude can be seen. Typical 7X50 binoculars easily reveal objects down to 8th magnitude. The Hubble Space Telescope has taken photos of incredibly faint objects at magnitude +30, comparable to seeing a candle flame several thousand miles away.

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May 15, 1999

Astronomy Day -- 1999

Next Saturday the Central Texas Astronomical Society (CTAS) will celebrate Astronomy Day with exhibits at Waco's Richland Mall during the day and evening stargazing at Hewitt City Park.

From 10 a.m. to 6 p.m. near the mall's J.C. Penny store, there will be slide shows, videos, demonstrations of telescope making, astrophotography, and other displays including plans for a future observatory. Telescopic solar viewing will be available outside the Piccadilly entrance if skies are clear.

Members will also have telescopes set up for display. Anyone considering buying a telescope will find this an excellent opportunity to see and learn about different types and sizes of scopes, and to ask questions of owners. (It's even ok to ask the question your mother said was impolite: How much did it cost?)

The Hewitt star party will be held from 8:30 - 10:30 p.m., again weather permitting. All activities are free, open to the public and should be of interest to all ages.

Nationally, Astronomy Day was established in 1974 to promote the enjoyment of stargazing. Locally, this will be the 6th annual celebration sponsored by CTAS, formerly known as the McLennan County Astronomy Club.

Established in 1993 by Michael Green, CTAS currently has a membership of 50, according to secretary-treasurer Johnny Barton. Being the only such organization between Georgetown and Ft. Worth, its members come from several central Texas counties.

The society holds monthly star parties for members at Mother Neff State Park as well as periodic public star parties at various locations including area public schools. Membership (at $10 per year) is open to novice as well as veteran stargazers.

Hope you can make it out to Astronomy Day. If so, stop by and say hello to the Stargazer.

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May 1, 1999

What If the Sun Went Out?

For many reasons, the Stargazer loves doing astronomy programs with kids. They often ask such interesting questions--things adults don't think about or are too embarrassed to ask.

More than one youngster has asked: What if the Sun went out? I respond that it would quickly get very dark and cold, and soon all life on Earth would probably die, including us. I quickly reassure the children that our Sun won't really go out for billions of years, so we needn't worry about it.

But the question still makes for fascinating "what if" speculation. So what would happen?

Let's say the Sun abruptly goes out at 12 noon local time. Since it takes sunlight 8 minutes to reach Earth, traveling at the speed of 186,000 miles per second, we wouldn't know of the Sun's demise until 12:08 p.m. at which time it would instantly become pitch dark, a starry sky would pop out, and the temperature would begin dropping dramatically. Day and night would suddenly become meaningless terms.

Our neighbor, the Moon, whose light is but reflected sunlight, would vanish from sight less than 2 seconds after the Sun.

If the naked-eye planets happen to be aligned with the Sun as it expires, they would immediately come into view with the stars. Since planets, like the Moon, reflect sunlight, they too would go out--but not immediately. Their light takes time to reach us, so they would blink out, one by one, in the order of their distance.

Mercury, the innermost planet, would disappear at 12:15 p.m. followed soon thereafter by Venus at 12:20 p.m. Next Mars would go out at 12:34 p.m. Being much further out, we would see Jupiter until 1:35 p.m. Saturn, the farthest naked-eye planet would blink off at 2:47 p.m.

At this point, the only visible objects in our sky, other than occasional meteors, would be distant stars and other objects beyond our solar system.

As an afterthought, we might wonder: Did all the stars in the cosmos go out, or only the Sun? Stars are so distant it takes years for their light to reach us. Thus we couldn't know about the other stars for years, and chances are we would never know. The light from the nearest star, Alpha Centauri, takes over four years to reach us. By the time it could blink out of view, we humans would likely be extinct--from freezing or starvation.

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April 3, 1999

Janice VanCleave -- Author of Children's Science Books

How many individual stars do you think you've seen in your lifetime? Millions? Probably not. Unless you've done a lot of binocular or telescope viewing, you've likely not seen more than a few thousand stars.

So now think about a million and a half books. That's how many of Janice VanCleave's children's science books have sold in the past 10 years.

And another surprise: this highly successful author resides in Central Texas. A native of Houston, Janice and her husband have lived in the Waco area for the past 14 years.

Before becoming a full-time author in 1992, Janice was a high school science teacher for 26 years and winner of the Phi Delta Outstanding Teacher of the Year award in 1982. She now also travels around the country (and world) conducting workshops with teachers and students and promoting science education.

The majority of her 37 books, most in the Science for Every Kid Series and Spectacular Science Projects Series, are designed for ages 8-12. Her books contain hundreds of fun, safe, low-cost experiments and activities which kids can do at home with easily obtained materials. The Science Projects series describe dozens of projects suitable for science fairs.

Her Play and Find Out Series, written for 4-7 year olds, introduces the very young to the world of science and math with such questions as "Why don't eggs break under a chicken?"

While stargazers have special interest in her astronomy and constellations titles, other book topics range from traditional subjects like biology, chemistry and physics to more specialized areas like dinosaurs, earthquakes, gravity, oceans and weather.

Although some have lamented that her books don't delve deeply into their topics, she says that's not her intent. According to Janice, her aim is "to plant seeds of get kids excited about science." Then hopefully they will want to turn to other sources for further study.

Her books have been translated into 13 languages, enriching children around the world. The English versions are available at local bookstores, and their very reasonable price--most under $15--puts them within reach of nearly every kid.

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March 20, 1999

Jewels of the Southern Skies

Just as the Stargazer views stars by night, his wife is an avid birdwatcher by day. From time to time, she excitedly tells of adding a "lifer" to her list. That's what these avian enthusiasts--who refer to themselves as birders--call a type of bird they've never seen before.

Borrowing this useful term from the birders, the Stargazer must do some crowing about three lifers he just added to his list. (Sorry, I couldn't resist the pun.)

Of the 21 brightest stars of the night sky, called 1st magnitude stars, 15 are visible from most of the U.S. and all of Texas at some time during each year. The other six, however, are too far south ever to be visible from any but extremely southerly U.S. latitudes. Only one of these six, a star named Canopus, is ever visible from central Texas, and just barely at that.

The Stargazer had never seen any of the remaining five--until recently. A camping trip to Falcon State Park in Texas' Rio Grande Valley provided an opportunity for viewing three of these southern jewels. At latitude 26 degrees north, Falcon is 5 degrees further south than Waco, enabling one to see 5 degrees deeper into the southern sky.

The Southern Cross, one of the best-known constellations of the southern sky, contains two 1st magnitude stars. Binoculars helped me spot one of them, Mimosa, as it hovered just above the distant Falcon Dam bridging Texas with Mexico. Unfortunately, Acrux, the cross' brightest star never made it above the horizon.

The other two lifers were Rigel Kentaurus and Hadar, also known as Alpha and Beta Centauri in the constellation Centaurus. Alpha Centauri is our nearest neighboring star system at just over 4 light years. Both of these jewels were also very near the horizon and best seen in binoculars.

While adding these southern jewels to my stargazing lifer list was exciting, it also whetted my appetite for a trip to the southern hemisphere where a whole new world of stargazing awaits. Maybe some day.

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January 23, 1999

Once in a Blue Moon

When something doesn't happen often, we say it happens "once in a blue moon." So how rare is two blue moons back-to-back? That's what we're about to have Jan. 31 and Mar. 31, although it's more of a curiosity than an important astronomical event.

From tradition we give names to each month's full Moon, the best known being fall's Harvest Moon. Full Moons occur every 29 1/2 days so we normally have one per month. But since most months contain 30 or 31 days, occasionally a month will have two full Moons, one early and one late in the month. This happens on average only every 2 to 3 years. When it does, the first gets the traditional name and the second is called a Blue Moon.

The origin of this name is unknown. Blue Moons do not look different and they are not blue. It's not even clear which came first: the saying or the naming of a second full Moon.

What we have this year occurs even less often -- two full Moons in one year separated by a month without a full Moon. This happens on average every 19 years, and it can only happen in January, February and March.

Since February with 28 or 29 days is shorter than the Moon's phase cycle, it is the only month that can possibly miss a full Moon. When that happens, January and March will each have a Blue Moon, as in 1999. This double Blue Moon won't happen again until 2018, although the next Blue Moon comes in Nov. 2001.

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