Paul Derrick's Stargazer

Stargazer Columns 1998 (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 pjderrick@aol.com.

Dec. 12, 1998: The Star of Bethlehem
Nov. 28, 1998: The Leonids Finally Give Us a Good Meteor Shower
Nov. 14, 1998: Leonid Meteor Shower
Oct. 31, 1998: Iridium Flares
Sep. 19, 1998: Angular Distances
Sep. 5, 1998: Milky Way Triangle
July 25, 1998: The Macho Quadrangle
June 27, 1998: What's to Be Seen in the Night Sky?
June 13, 1998: Heavenly Hair
May 30, 1998: The Color of the Sky
Apr. 18, 1998: Let's Play Cosmic Baseball!
Apr. 4, 1998: Viewing in the Dark
Mar. 21, 1998: High Tide's Coming In
Mar. 7, 1998: Voyager 1 Still Going
Feb. 21, 1998: Periodic Immortality
Jan. 24, 1998: Constellations

Dec. 12, 1998

The Star of Bethlehem

Around Christmas each year, amateur astronomers frequently encounter the question: What do you think the star of Bethlehem was? A comet, a nova, a supernova, a planetary conjunction?

Responding to this question is both touchy and difficult. It's touchy because it involves deeply held religious beliefs shared by many, a few of whom don't even appreciate the question.

To those who believe the story involved a miracle -- an event outside the laws of nature -- it is senseless to seek an astronomical explanation. Astronomy, like the other sciences, is based on the premise that all events can be understood within nature's laws. Few scientists, therefore, would offer a miraculous explanation.

Many folks, like those asking the question, believe the star probably existed as a natural event. Whether its occurrence was mysteriously coincidental with Jesus' birth, or was simply something ascribed special meaning by those present, it would still be possible to try to identify the natural event.

Unfortunately, looking for such an event is difficult, in part, because neither the date nor even the year of the birth of Jesus are known. (Few scholars hold that Jesus was actually born on December 25 or in the year 1.)

Knowing a birth date would help in such a search as computer programs can simulate the night sky for any date hundreds, even thousands, of years ago. With a specific date, we could look for things like unusually close pairings (called conjunctions) of planets with other planets or bright stars, or the approach of known periodic comets. But even if nothing out of the ordinary was discovered, that wouldn't rule out the possibility of things even computer programs cannot know about, like novae, supernovae, unknown comets or other ephemeral events.

Still others, both Christian and non-Christian, believe the star of Bethlehem story is apocryphal -- part of the lore of the Jesus story but not a real historical event. For them, seeking to associate it with an actual astronomical occurrence is akin to looking for Dorothy's Yellow Brick Road somewhere in Kansas.

So, what was the star of Bethlehem? Astronomy simply cannot, at this time, offer an explanation, nor can it confirm or refute the story. Regardless, the Stargazer wishes you and yours a love-filled holiday season shared with family and friends.

Nov. 28, 1998

The Leonids Finally Give Us a Good Meteor Shower

While we didn't have the hoped for storm, the recent Leonid meteor shower did produce a much better-than-average show in most of the U.S. The best displays seem to have occurred Nov. 16/17 from around midnight to 4 a.m.

Even from within light-polluted Waco and surrounded by trees which hid much of the sky, the Stargazer had some luck. I went out in my yard for a few minutes every hour on the hour, starting at 9:00 p.m. Monday evening. During the first four outings--no meteors. At 1:00 a.m., there was only one but it was a dandy, brighter than Jupiter and streaking from Gemini to Auriga. Then things picked up. Between 2:00 and 2:45 a.m., there were several more, one of which was brighter than any stars. Undoubtedly, I would have seen many more from a darker, clearer viewing site.

Accounts from friends, both locally and afar, indicated good but varied experiences. One friend, observing a few miles outside of Waco, saw 14 meteors between 12:30 and 1:00 a.m., and reported that several left "blazing trails that hung around the sky for 10 seconds or so." Another saw 70 meteors between 2:00 and 4:00 a.m. from near Waco's Texas State Technical College.

A hardy friend who spent the night in a field near Paris, TX, saw "over 100 meteors, both large and small," between midnight and 6 a.m. An early-riser on his way to work in Washington, D.C., related, "At 5:20 a.m. as I was driving to the train I saw a huge meteor flare due east of Lovettsville (VA). I stopped my pickup and saw several lesser streaks across the sky."

And from Tennessee: "We saw several just before midnight. However, I spoke to several people out at 3 to 4 a.m. who saw as many as 100 in an hour." Family in Salem, MA, and Scarsdale, NY, said they weren't so lucky as they were clouded out.

A most dramatic account comes from Central Texas Astronomical Society member Dick Campbell of Hewitt: "(A family emergency) found us on the road Monday night driving to Milwaukee. I awoke shortly after midnight and relieved my wife of driving duties. We could see meteors falling to the horizon through the windshield every few minutes, and this lasted for over 4 hours. Every once in a while there would be a very bright one with a long visible ion trail and glowing orange head that would flash briefly and wink out."

"Suddenly," he continued, "the whole sky lit up, like a flash bulb had gone off. It was visible through the windshield even with the headlights. I looked out my left window, and saw the most incredible meteor I had ever seen. It was cutting a very bright, blue white swath, like a paint brush almost, not just a thin line, from Ursa Major all the way back to Cassiopeia. The head glowed a bright purplish orange and I actually saw it break into fragments that appeared to burn up in pieces as it faded. I was in south central Missouri (about 1:45 a.m.). The ion trail lingered prominently for several minutes." (Glad you didn't run off the road, Dick.)

Given the history of the Leonids, we might also expect good shows the next two years. Here's hoping.

Nov. 14, 1998

Leonid Meteor Shower

Last month's Draconid meteors were a fizzle in our part of the world. Two weeks later the Orionids were rained out over Texas. So, diehards, let's try once more with this week's Leonid meteor shower. It could be really interesting this year.

What's the basis for this guarded optimism? The Leonids come from Comet Tempel-Tuttle, a periodic comet which visits the inner solar system about every 33 years. Its most recent visit was last February, leading to hopes that it left in its wake a new supply of cometary litter which gives us meteor showers.

In most years November's Leonids are little to get excited about. But increased Leonid activity the past two years offers hope that 1998, 1999 and maybe 2000 will be good years. (These periodic peaks can span 2 or 3 years before or after a comet's closest approach to the Sun.)

Further reason for optimism comes from the Leonids' history. Many, but not all, of Tempel-Tuttle's visits have produced storms of thousands of meteors. The comet's last passby in 1966 produced a breathtaking storm; 1933 was a bust; 1900-01 and 1866-68 were excellent; 1832-33 and 1799 were dramatic.

So how will the Leonids turn out in 1998? Well, you'll just have to go out and see for yourself, remembering that predicting meteor shower intensity is as risky as predicting Texas weather.

The prime nights will be Monday and Tuesday. While you might see meteors anytime after dark, the best prospects will come in the hours from midnight to dawn. Leo, from which the meteors appear to come, rises about 1 a.m. in the east. Still, they might be seen throughout the night and in any part of the sky.

They can even be seen from urban areas, but the further one gets from city lights, the better. If staying up late isn't your thing, consider rising early for some predawn viewing.

The best strategy is simple: just lay out on a blanket or reclining lawn chair and keep looking up. Binoculars are not needed, but warm clothing, hot chocolate and good company are highly recommended.

Oct. 31, 1998

Iridium Flares

Have you recently seen and wondered about some very bright, fleeting lights high in the early evening or early morning sky? These seemingly mysterious and short-lived flashes can be brighter than the most brilliant stars, even outshining dazzling Venus, although only for a few seconds.

One could easily mistake them for especially luminous, slow-moving meteors. Some might think they'd seen a UFO. Actually, these objects are of neither cosmic nor extraterrestrial origin. They are a relatively new phenomenon called Iridium flares.

The source of these flares is a fleet of 70-plus Iridium satellites, part of a new worldwide communications system. The flares come from sunlight reflecting off satellite antennae. Each satellite has flat, silver-coated 3 by 6 feet rectangular panels which act as mirrors orbiting at an altitude of nearly 500 miles, periodically sending brief sunbeam bursts to Earth.

Iridium satellites, like other human-made satellites, make no light of their own. They are only seen when reflecting sunlight, so we never see them deep into the night when the Sun is on the other side of Earth. The best times for seeing Iridium flares is within an hour or so after sunset or before sunrise. Binoculars and telescopes are not needed.

The precise positioning, speed and angles of these satellites make the flares highly predictable. A free prediction service is available on the internet, which even the Stargazer, with his old computer and limited internet savvy, was able to access.

For general information go to http://www2.satellite.eu.org/sat/vsohp/iridium.html. Or directly access the prediction service at http://www.gsoc.dlr.de/satvis/ and indicate your viewing location from a database of cities. Waco is in the database, but if your city isn't, enter your latitude and longitude.

The Stargazer thanks Melvin Schuetz of Waco for the web site data and for suggesting this as a column topic.

Sept. 19, 1998

Angular Distances

Suppose some evening you're out looking at the night sky and spot something interesting you wish to point out to a friend. You say, "See that bright star over there? What I'm looking at is to the right of that star by about..."

And you pause, at a loss for how to express the apparent distance to your companion. Does it seem a few inches from the star, a few feet, or many feet? You quickly realize that feet and inches are of no help. What might seem like 6 inches to you could look like 10 feet to someone else.

Fortunately there's a simple solution using what we call angular distances. It's based on the fact that from horizon to horizon across the sky is one-half of a circle, or 180 degrees. So we express apparent distances in degrees. For example, Polaris (the North Star) is about 30 degrees from the nearest star in the bowl of the Big Dipper.

Maybe you're thinking: "That's great, but how can I measure degrees without special equipment?" Again, the solution is easy. You have all the equipment you need at the end of your arm -- your hand and fingers. While they don't give precise measurements, they are close enough for casual stargazing.

Hold your hand out at arm's length in the direction you are viewing and close one eye. At this distance, your index finger is about 1 degree across, twice the diameter of a full Moon. (Most folks think of the Moon as larger and are surprised to find their finger can cover it.) A fist is some 10 degrees across, and a wide open handspan from thumb tip to little finger tip about 20 degrees.

This little gimmick works for adults and children, regardless of hand size. People with larger hands generally have longer arms, making their hand appear about the same size as one belonging to a person with a smaller hand and shorter arm.

You can practice using angular distances with the Milky Way Triangle discussed in our last column. Vega, the brightest star high overhead, is about 25 degrees from bright Deneb in the northeast, or about one handspan and half a fist.

For more practice, measure Polaris' distance above the horizon, which is always the latitude of the observer. In central Texas that is close to 30 degrees, or 3 fists.

Sept. 5, 1998

Milky Way Triangle

High overhead in the early evening of late summer is the Milky Way Triangle, formed by three bright stars: Vega, Altair and Deneb. Also called the Summer Triangle, this large figure embraces a wealth of cosmic beauties, many of which require a telescope to see. But the triangle stars themselves are easily seen, even from light-polluted urban areas.

Vega, the fifth brightest star in the entire night sky, is in the constellation Lyra the Musical Lyre. At a distance of 26 light years, Vega is three times the size of our Sun. Those familiar with the movie "Contact" (based on Carl Sagan's novel) might recall that Vega is the star from which The Message came. Another curious fact about Vega--in 12,000 years, it will be Earth's North Star, the role occupied in this era by Polaris.

Altair, the alpha star of Aquila the Eagle, is the night sky's 12th most luminous star. Located a mere 16 light years away, this neighboring star is 1 1/2 times the size of Sun. Altair has one of the fastest rotations of any star known, turning on its axis about every six hours, or nearly 100 times faster than our Sun. This would make it extremely fat around its equator. If there are any Altairians on an orbiting planet, they would likely see their sun as a fat pancake rather than a round ball.

The final triangle star is Deneb, the tail of Cygnus the Swan. With a diameter 60 times that of our Sun, it is one of the largest known supergiants. At a distant 1,600 light years away, Deneb is vastly further than Vega or Altair, yet it is still our 19th brightest star. Cygnus is also known as the Northern Cross, with Deneb at the top of the cross. Of symbolic significance to Christians, the cross stands nearly upright on the western horizon in the early evening hours of December.

Finding the Milky Way Triangle is not difficult as the three stars are the only 1st magnitude stars directly overhead. Vega is the very brightest. Not as bright, but still brighter than any other stars in this part of the sky, Deneb is to the northeast and Altair to the southeast. If you are viewing away from city lights, notice that the Milky Way runs through the triangle, hence its name, with Vega on the western side, Altair on the eastern side, and Deneb smack dab in the middle.

July 25, 1998

The Macho Quadrangle

The evening summer sky is famous for its breathtaking display of the star-rich center of our galaxy, an area which, under dark skies, looks like ethereal cotton candy. Lesser known, however, is a battle taking place above this part of the Milky Way. Four stars form a ring which features everything needed for a colossal cosmic wrestling match. I call this region the Macho Quadrangle.

The ring's four corner posts are easy-to-see 1st magnitude stars. Reddish Antares, now due south in the early evening, is a third of the way up from the horizon. The opposite corner post, Vega, is the brightest star high in the northeast. The third post high in the west is Arcturus, reddish like Antares but brighter. The fourth, Altair, is half way up in the east. (The ring is rather cattywompus, but the wrestlers knocked it that way, not me.)

And now for the contestants. In the north corner (straight overhead) we have the well-known champion of the cosmos, Hercules, the Strongman. (Loud applause, please.) His opponent in the south corner (above Antares) is the lesser-known challenger Ophiuchus, the Serpent Slayer. (And now, boos.) While both these guys are big, unfortunately neither is very bright, so they're difficult to see from urban areas.

In such contests, fighters usually weigh in, so we find Libra, the Scales, just outside the ring's southwestern ropes. And in an attempt to intimidate Hercules, Ophiuchus is clutching a slain serpent in two parts: Serpens Caput, the Serpent's Head, is in one hand, and Serpens Cauda, the Serpent's Body, is in the other.

And, of course, there are the trophies for which the foes vie -- a crown and a shield. Corona Borealis, the Northern Crown, is next to the champion just inside the western corner of the ring (near Arcturus). Scutum, the Shield, is just outside the ring's southeastern ropes.

So there you have it -- the Macho Quadrangle cosmic wrestling match. You might find it more interesting than the television versions, and if you need help identifying the players, consider the Stargazer's upcoming classes.

June 27, 1998

What's to Be Seen in the Night Sky?

Amateur astronomy is often called stargazing, so it's no surprise that many folks getting their first view through a telescope ask to see a star. But that often turns out to be disappointing as single stars are rather boring. So, what's the big deal? What's fun to see in binoculars and amateur scopes? Well, lots of things.

For starters, telescopic views of the Moon, Saturn and Jupiter draw the most "oohs" and "aahs" from novice viewers of all ages. It's not uncommon for a youngster, upon first seeing Saturn, to comment skeptically: "That's not real. You've got a picture in there." So the larger solar system objects, namely, planets and moons, are fun to view.

Beyond our solar system are countless other objects. Double stars are lovely, especially when they are different colors or brightnesses. Stars typically are born in nebulae, spend their youth in clusters, disperse in maturity, and then eventually die. Each of these stages provides rich viewing.

Star-forming nebulae, like the Orion Nebula, look like cosmic clouds sprinkled with stars. These clouds of gas and dust appear white or gray visually while photos show them to be breath-taking reds, blues and greens. These colors, while quite real, are generally too faint for direct detection by our eyes.

Star clusters come in many sizes. Most contain hundreds to thousands of stars. A few are nearby, such as Coma Berenices and the Pleiades, and appear large and easily visible to the naked eye. Others, like the Beehive Cluster, best display their richness in binoculars. Hundreds of more distant clusters come into view in telescopes.

Some clusters, like Hercules' M13, are a special type called globular clusters, and are much farther and larger, containing many thousands, even millions, of stars. At lower viewing powers, most look like little fuzzy balls. At higher powers, many individual stars come into view, looking like an unbelievably concentrated swarm of stars.

When stars die, many go out with a bang, leaving donut-shaped clouds called planetary nebula, like the Ring Nebula. The largest stars die in supernovae, leaving even larger nebula remnants, like the Crab Nebula.

At vastly greater distances are galaxies. One of our nearer neighbors is the Andromeda Galaxy, similar to our own Milky Way galaxy and barely visible to the naked eye. Some others can be seen through binoculars though most require telescopes.

Don't bother looking for black holes or planets orbiting other stars. While they're probably out there by the billions, they are not yet visible with today's technology. But maybe some day.

June 13, 1998

Heavenly Hair

This is the time of year when, after a night of stargazing, one might find heavenly hair on one's clothing. High in the evening sky of late spring is the constellation Coma Berenices, Berenice's Hair. Just how her hair got into the sky is one of the more entertaining stories of ancient sky lore.

Many constellations are associated with legends involving fictitious characters. Coma Berenices, however, is based on an actual person although the story itself is surely legendary.

Berenice II, a Macedonian with long beautiful hair, became an Egyptian queen when she married Ptolemy III in 247 B.C. When Ptolemy went off to war, Berenice bargained with the gods, to wit: if they would watch over her husband and return him safely, she would sacrifice her famed hair in the temple of Aphrodite. Ptolemy survived the war, and Berenice kept her word. The hair, however, mysteriously disappeared from the temple, leaving the royal pair as two unhappy campers.

To the rescue came Conon, the royal astronomer, with a most creative story. He convinced them that the gods were so moved by Berenice's sacrifice that they transformed her esteemed yellow tresses into a heavenly constellation. Fortunately for Conon, Ptolemy III was not as astronomically astute as the later 2nd century astronomer Claudius Ptolemy or he would have known that the cluster was until then viewed as tail hair on Leo the Lion.

Coma Berenices is one of the largest and nearest of several easily visible star clusters. While all other clusters, large and small, reside within other constellations, Coma is the only one designed as a constellation in and of itself.

The Big Dipper is helpful in finding the queen's hair. Facing north, locate the end star of the dipper's handle high overhead; then locate Arcturus, the bright, slightly reddish star nearly straight up. To the west (left) and forming an equilateral triangle with these stars is Coma Berenices. (For those familiar with the Cosmic Baseball Diamond, Coma Berenices is shortstop.)

Under a reasonably dark, moonless sky, Coma Berenices is visible to the naked eye, looking like a course, faint blur about the size of a silver dollar held at arm's length. Binoculars easily resolve many individual stars which just about fill a binocular field of view.

If you happen to come home late some evening with blonde hair on your clothes (and you're not blonde!), just say you've been out stargazing and the hair must have come from Queen Berenice.

May 30, 1998

The Color of the Sky

What's the natural color of the sky? Blue? Pink? Black? Gray? All of the above? Well it depends.

On a clear sunny day, our sky is its familiar beautiful pale blue. Although sunlight contains all the colors in the light spectrum, that light is scattered by molecules in our atmosphere. Light from the blue end of the spectrum is scattered more than light from the red end, and this paints our daytime sky blue.

But near sunrise and sunset, the sky changes colors. Sunlight is seen through more atmosphere than when the Sun is overhead and the light has to pass through more air molecules. This filters out most of the blue light, giving the early morning and late evening skies their lovely pink tint.

So would you say the sky naturally blue or pink? When viewed on a moonless night, far from urban light pollution, the sky is a colorless black. Indeed, this was the "color" of the sky seen by the Apollo astronauts as they stood on the Moon, even during the lunar day. The Moon has no atmosphere to scatter sunlight and create the sky colors we see from Earth. Except when looking directly toward the Sun, the Moon's sky, day and night, resembles our night sky--full of stars and other heavenly bodies.

For the past few weeks, our daytime sky has been more gray than blue, not so much because of clouds but due to the tons of smoke coming from forest fires hundreds of miles away. As stargazers know, this smoke also affects our night skies, hiding much of the cosmos from view even after dark.

Eventually these particular fires will burn out, their smoke will dissipate and our skies will return to their "natural" blues, pinks, and varying degrees of black. But one only wonders how much more industrial, automobile and other human-made air pollution it will take until our descendants come to regard the sky's natural color as opaque gray, day and night--with blue skies and views of the stars only memories recorded by historians and poets.

April 18, 1998

Let's Play Cosmic Baseball!

In sports, we associate spring with baseball. So it's fitting that the spring sky features a stellar baseball diamond.

Perhaps as a kid, you played some "sandlot" baseball. Your bases were probably objects of convenience, like "first base is that bare spot where the grass has died." The resulting diamond wasn't perfect but it was close enough. Sound familiar? Our cosmic baseball diamond isn't perfect either, but it's close enough to help us learn this region of the evening sky of spring.

For home plate we'll use Arcturus, the brilliant reddish star in Bootes, the Herdsman. Home plate should be the brightest, and Arcturus, currently in the east in the early evening, is the spring's brightest star at magnitude 0.

First base will be Spica, the 1st magnitude star in Virgo, the Virgin, now in the southeast. For second base, we'll use Denebola, a 2nd magnitude star in the tail of Leo, the Lion. Third base will be 3rd magnitude Cor Caroli in Canes Venatici, the Hunting Dogs, found beneath the handle of the Big Dipper. The large Coma Star Cluster of Coma Berenices, Queen Berenices' Hair, is shortstop, between second and third.

The stars of the bases, also known as the "Diamond of Virgo," form a convenient spring magnitude scale of decreasing brightness from Arcturus at 0 magnitude to Cor Caroli at 3rd magnitude. All are visible from most urban locations.

In the outfield, the rest of the constellation of Leo is center field. He's big and covers a lot of territory. For left field, we have Leo Minor, the Little Lion. He's not very big or bright but he's all we've got out there. According to the song, right field is where the worst players are found. In our cosmic field, we have three small, faint constellations covering right field: Sextans, the Sextant, Crater, the Cup, and Corvus, the Crow. Few of their stars are visible to urbanites.

Ready to play cosmic baseball? If you need some coaching, consider the Stargazer's upcoming class.

ROYAL ROMANCE UPDATE: Those who have been following our planetary soap opera know King Jupiter and Queen Venus spent most of 1997 on the outs with each other. They've now resolved their differences and are meeting in a most royal manner in the morning skies this week. They will be closest Wednesday and Thursday, very low in the east between 5:30 and 6:30 a.m., with Venus the brighter of the pair. A tiny crescent Moon joins the couple Thursday morning. It will be a sight not to miss.

April 4, 1998

Viewing in the Dark

Stargazers face some challenges viewing in the dark. Seeing faint sky objects, of course, requires the darkness of night, yet reading reference materials requires light. By utilizing certain characteristics of the human eye, we have come up with some tricks which enable us to do these seemingly opposing things.

The first trick for viewing objects of the night sky requires nothing more than time. After being in darkness a while--usually 15 to 20 minutes--our eyes gradually become "dark adapted." As our pupils open wider and our retinas become more light-sensitive, increasingly fainter objects become visible.

Unfortunately, exposure to lights can immediately undo this dark adaption, yet seeing star wheels and sky maps requires light. To get around this problem, we use another trick. Since red light has little effect on the retina's light sensitivity and does minimal damage to dark adaptation, we use red flashlights. "White lights" are not used or welcomed at star parties.

Still another trick, employed for seeing very faint objects, utilizes "averted vision." The nature of the human eye is such that the center of the retina is not as sensitive to faint light as the area surrounding the center. Therefore, this trick entails focusing one's eyes just off to one side of the faint object while continuing to concentrate attention on the object itself. The faint object then actually appears slightly brighter than when looked at directly.

One can practice this trick during the day. Focus on any object, then shift your attention, but not your eyes, to another object a little to one side of the first object. While still focused on the first object, notice that you can see and describe the second object without looking directly at it. You are seeing the second object with averted vision. Try it.

Red flashlights, by the way, can be easily and cheaply made. One can cover an ordinary flashlight with red cellophane held in place with a rubber band. Or the clear light cover can be colored red with a red marking pen.

Now you know some stargazing tricks for seeing in the dark.

March 21, 1998

High Tide's Coming In

Coastal areas should experience higher than average high tides next Saturday when this month's new Moon coincides with something called perigee. Tides, the regular rising and falling of the levels of oceans, gulfs, bays and other open bodies of water, are mainly a result of the Moon's gravitational pull on Earth. While terrestrial factors also affect tides, these don't occur with the regularity of lunar influences.

If there were no tides, the level of our seas would remain rather constant. But as anyone who has lived near or visited the coast knows, the water level is not constant. It varies, often by several feet.

The Earth's daily rotation on its axis and the Moon's 29.5-day revolution around Earth combine to produce high (and low) tides about every 12 1/2 hours. Tides are high on the sides of Earth facing and opposite the Moon. (There is actually a slight lag time which we'll ignore in this discussion.)

The Sun also affects tides. However, given the Moon's much closer proximity, its influence is two to three times that of the Sun. Ordinarily, the Sun's effect is overpowered by the Moon, but twice during each revolution of the Moon -- at new Moon and full Moon -- the two team up to combine their influence.

During new Moon, when the Moon and Sun align on one side of Earth, their cumulative gravity pulls on Earth from the same direction, creating even greater tidal forces. During full Moon, when the Moon and Sun are on opposite sides of Earth, the effect is similar--more gravitational pull in the directions of the Sun and Moon, and hence higher tides on those sides of Earth facing the Sun and Moon.

Yet another factor affecting tides is the Moon's varying distance from Earth. The Moon's orbit is elliptical rather than circular, so at times it is actually closer to Earth. The point in its orbit where it is closest is called perigee. (The farthest point is called apogee.) Since the force of gravity increases when two bodies are nearer to each other, the Moon's gravitational pull on Earth is strongest at perigee.

When perigee and new Moon occur simultaneously, as will happen next Saturday, their effects are added together to produce even greater tides. But don't run out to your local lake to watch the tide roll in. Closed bodies of water don't have detectable tides.

March 7, 1998

Voyager 1 Still Going

Remember the Star Trek movie where the Starship Enterprise met up with the enormously powerful Vger? The alien entity was on a cosmic mission to acquire knowledge and return its accumulated wealth of information to its "creator." It accomplished the first part as it had become incredibly knowledgeable. However it couldn't seem to find its creator, and it had developed a nasty little habit of destroying all who proved not to be its creator.

Capt. Kirk finally discovered the seemingly alien Vger was actually a human-made satellite launched from Earth centuries before, a satellite named Voyager. The "oya" in the spacecraft's name was obscured so that it looked like "V___ger," hence, its name, Vger. In the end, of course, Kirk's usual quick wits and brilliant oratory saved the Enterprise from Vger.

As fanciful as the Star Trek story is, it is interesting to note that Voyager 1, the planetary explorer launched by the U.S. in 1977, is indeed headed for the cosmos. According to Sky & Telescope's Weekly News Bulletin, Voyager is now more than 6 billion miles away. It has traveled farther from the Sun than any human-made object, and is even beyond the orbit of Pluto.

Incredibly, the durable spacecraft still transmits data and will likely do so for another 20 years. By the time the radio signal reaches Earth (a 9-hour journey), it is "so faint that the amount of power reaching our antennas is 20 billion times smaller than the power of a digital watch battery," according to Project Manager Ed Massey, quoted in the S&T Bulletin.

Traveling at a speed of 39,000 miles per hour, Voyager is heading toward interstellar space. When it escapes the realm of the Sun's influence in 3 to 5 years, it will truly be traveling among the stars. However, don't wait around for Voyager to travel to distant stars, acquire great knowledge and then return to Earth. At its current speed, it would take 73,000 years to reach our nearest stellar neighbor, the Alpha Centauri star system--and it's not even headed in that direction.

ASTRO MILESTONES: Tuesday is the 60th birthday of the Stargazer's longtime friend John Nobis (1938- ) who knows little about the stars but much about life.

February 21, 1998

Periodic Immortality

According to legend, Orion and other constellation characters, upon their earthly deaths, were given immortality in the sky. As a younger man, I thought living forever would be great, but as I approach my older years, I'm not so sure.

In her mysterious wisdom, Mother Nature seems to have known what she was doing by making death a part of the cycle of life. As marvelous as life is, eternal earthly life might get to be a drag. Besides, if nothing ever died, birth would have to cease, for where on Earth would we put all the newborns? And if nothing could die, what would we eat?

While I've become reconciled to mortality, there's an aspect of immortality that intrigues me. I would love to follow the unfolding of our future -- not our wars and other stupidities, but our inventions and discoveries, especially in astronomy.

The Brigadoon story sets forth an interesting idea -- what if we could come back to life for a day or so every 100 years. I think I'd like that kind of immortality. Imagine Nicolaus Copernicus (1473-1543) with this periodic immortality.

Upon his first return in 1643, he was thrilled as he peered through the telescope, invented in 1609, with which Galileo (1564-1642) advanced Copernicus' sun-centered model of the solar system. And when he learned of Kepler's (1571-1630) discovery that planetary orbits are elliptical, not circular, he said, "Elliptical orbits, of course! Why didn't I think of that?" With this realization, he could have had a stronger argument for his radical solar system model.

When he returned in 1743 he was pleased to find his ideas about attraction between heavenly bodies developed by Newton (1642-1727) into laws of gravity and motion.

In 1843, he learned of the 1781 discovery of a new planet, Uranus, by William Herschel (1738-1822), and viewed the Milky Way's multitude of stars through vastly improved telescopes.

The discoveries of Neptune (1846) and Pluto (1930) didn't greatly surprise him upon his 1943 visit, but he was astounded to learn of the existence of billions of other "island universes" called galaxies. And he could only shake his head as Einstein (1879-1955) explained relativity theory to him.

When he visits in 2043, he'll certainly be amazed by robots, computers, space travel, and space telescope views of the cosmos. And what will he find in 2143, 2543, 3043? Earthlings living on the Moon, Mars and Europa? Humans bound for the stars using new energy forms and communicating with Mother Earth in ways that defy speed-of-light limits? Contacts with other life forms?

Despite all else, Copernicus knows that on each return, he'll find humans still grappling with the same questions of life, death and meaning. As Rabbi Edwin Friedman said, "Questions are more important than answers, in part, because they are eternal while answers resemble fashions that come and go with age."

January 24, 1998

Constellations

When gazing into the night sky, one of the things people wonder, and often ask, about is constellations.

Since prehistoric times, most of the world's cultures seemed to have identified and named star patterns and other objects of the night sky. To help remember the patterns, they visualized things familiar to them and often made up stories about them. These imaginary figures, largely people and animals, came to be called constellations.

This practice represents yet one more way we humans come to understand and master our environment. Since we're more comfortable with the known than the unknown, making up star patterns and giving them (and other heavenly objects) names -- often the names of gods--probably made our ancestors feel better.

But there were also very practical reasons for learning the night sky, notably related to agriculture and travel. Knowing the constellations helped farmers know when to plant and gave direction to travelers, especially at sea.

Although different cultures saw different things based on their experiences, the 88 constellations now recognized by the International Astronomical Union are of European origin. The 50 "ancient" constellations came from the Greeks while the 38 "modern" ones were added in the 16th through 18th centuries.

Traditionally, constellations were regarded as the figures themselves as outlined by the brighter stars. While this system provided fascination and utility through the ages, it proved to have limitations for modern astronomy.

It's no secret that even with a good imagination, most constellations don't remotely resemble anything recognizable. But more problematic for astronomy: what about stars that aren't part of any pattern--to what constellation do they belong? And exactly where does one constellation end and another begin? To deal with these and other problems, astronomers in 1930 came to regard constellations as regions of the sky, each with clearly defined boundaries.

These 88 regions covering the entire sky generally retain the patterns and names of the traditional constellations. So if an ancient Greek magically appears at your door tonight, take him or her out and point out Queen Cassiopeia or Orion the Hunter. It will make your visitor feel more at home.