| 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. 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
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."
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.
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 http://sofia.arc.nasa.gov.
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.
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.
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?
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.
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.
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?
