Wednesday, August 26, 2015

Moon Musings

Isaiah refers to bodies in our Solar System when he quotes, “…Thus says the Lord, ‘Heaven is My throne and the earth is My footstool…For My hand made all these things, thus all these things came into being’ declares the Lord…” (Isaiah 66:1-2 NAS). In several Bible references the Moon offers praise to the Creator. It is a faithful witness to God’s glory, exuding splendor and supplying the Earth with light.

Of these visible astronomical objects in our sky—the Sun, planets, stars, and the Moon—the Moon inspires a different order of wonder. The 93 million mile distant Sun sustains all earth life with its light and heat on a daily basis but ironically, it is too bright and dangerous to observe with the unaided eye except briefly at sunrise and sunset. Planets many millions of miles distant shine with reflected light in the darkened sky, slowly changing their positions over many months, revolving independently against the field of stars. They are the most numerous of celestial representatives catalogued in our post. Stars glow remotely with their own light in subdued subtlety. Earth’s Moon, however, is our celestial next door neighbor. Shining with reflected light, it is only 238,000 mies away and fascinates us with its close relationship to our planet.

We caution against claiming that Scripture teaches modern scientific truth. This does not make the Bible unreliable in any sense. Scripture’s commentary on astronomical phenomena relies on ancient observations made when Scripture was penned. References to astronomical bodies speak of their origin as the handiwork of the Creator and devotional spiritual object lessons. We find several dozen biblical references to the moon and perhaps three times that many concerning the sun.

Explicit references to the eight named moon phases and stages as we know them today are not found in the Bible. Neither are reports of the revolution of the moon around Earth found in holy writings. The closest we come is frequent Old Testament passages mentioning new moons and several verses describing the full moon. The first sighting of a new moon is the beginning of a new month. Often the new moon was a signal to begin festivals or feast days of the Jewish tradition. The new moon was not an astronomical event of closest alignment of sun, moon, and earth. Rather, it was proclaimed about two days later at the first visual appearance of a thin crescent of illumination.

In our time we note an increase in detailed knowledge of our lunar companion. Examples: The Moon’s diameter is 27% of Earth’s diameter, and the Moon’s mass is 1.23% of Earth’s mass. This is about 1/80 of the mass of Earth. We have noted the stabilizing effect of the Moon in relation to our axial tilt. Our lunar companion is vital for life on Planet Earth. Without a stable axis of rotation Earth life as we know it would be impossible. Earth’s axis tilts at 23.5º from the plane of the Earth’s orbit.

Our planet experiences tides from the Moon. Ocean waters facing the Moon are pulled gravitationally toward it. Opposite the Moon the solid earth is pulled slightly toward the Moon causing an inertial bulge of water on the opposite side of the Earth. The water lags slightly behind the solid Earth. Different configurations of continental land masses cause funneling effects resulting in varying tidal depths from one place to another. The same face of the Moon is always directed toward Earth as the bodies are gravitationally “locked.”

The beautiful phases and stages—new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, and waning crescent—occur in sequence every 29.5 days. This is termed a synodic month, defined by two successive conjunctions of the Moon and the Sun. The moon revolves once every 27.3 days, a sidereal month defined according to the stars. Different phases and stages are caused by different angles of lighting depending on varying configurations of Earth, Moon, and Sun over the synodic month.

We close by briefly discussing the current widely accepted theory of the Moon’s formation. Very early in the history of the young Solar System a giant impactor dubbed Theia, possibly as large as Mars, crashed indirectly into Earth. Much debris from the impact splayed about and some coalesced into what later became the Moon. Apollo Moon explorations have determined Moon rocks to be slightly younger than Earth, consistent with the impactor theory. Many origins theorists have presented substantial evidence and confidence in the impactor theory of Moon formation. We present these ideas as a viable hypothesis, not as fact.

In modern times we are gifted with ability to correlate discoveries in order to acquire a fuller picture of truth concerning the Moon. Astronomy offers plentiful opportunities to give glory to the God of order and purpose. As students we may focus on fascinating details relative to the Moon as we have in this post, or on the store of knowledge we have accumulated on a multitude of other astronomy topics.
    
   
      
     







Tuesday, August 18, 2015

Adapting to Seasons

“Snow birds” describes a population of US northern climate residents who  take refuge from cold winters by migrating to the south, perhaps Florida or Arizona, during the harshest winter months. In the world of wildlife some animals, notably birds and a few insects, also journey to a warmer wintering spot in the southern US, Central America, or even South America. The “snow bird” phenomenon would not occur without the existence of Earth’s axis tilt. The slanted axis results in fascinating meteorological and astronomical variety. The case could be made that Earth would be an arguably less interesting planet without the tilt of its axis.

It is well known that Earth’s axis of rotation is slanted 23.5º from an orientation perpendicular to the plane of Earth’s orbit. This is known as axial tilt or obliquity. The axial tilt has been very constant—close to 23.5º, varying only slightly on a cycle of 41,000 years. The plane of Earth’s orbit, from which axial tilt is measured, has been virtually the same for millions of years. Earth’s motion of revolution locates the plane of  our planet’s orbit. All Solar System planets orbit in a plane similar to Earth. Their collective orbits appear like a flattened disc surrounding  the sun.

In the days when the Old Testament was written, the scientific details mentioned above were not known. Astronomical observations were based on visual glory and predictability and the ability of heavenly bodies to inspire worship of the Creator. One of the most famous passages comes from Genesis 8:22 in a promise made to Noah. “As long as the earth endures, seedtime and harvest, cold and heat, summer and winter, day and night will never cease” (NIV). This verse, while lacking astronomical specifics, accurately describes the effects of rotation and revolution, outcomes of axial tilt, the wondrous phenomena of plant growth and harvest cycles, and the glorious variety of environmental conditions provided for the thriving of man and all created living things.

Earth’s moon is an unusual satellite in a planetary system. It is unusually large among the Soar System planets. Scientists have determined that the moon acts to stabilize the axial tilt of Earth and provides not only the presence of seasons on our planet, but also their enduring consistency over extended geological time frames. Three of four points in the Genesis 8:22 reference are related to seasons directly or indirectly. Without Earth’s axis tilt there would be no seasons at all.

In our imagination we could speculate on the effect of reducing Earth’s axial tilt to 0º. There would be adjustments in agriculture. Some cold weather crops would not thrive. Grain crops which thrive in temperate climates during warm seasons would no longer thrive. Primarily, Earth’s food supply for seven billion souls would be devastated. Natalie Wolchover writing on the LiveScience website echoes the statements of many analysts: “Without Earth’s tilt, humanity would be in a sorry state.” Genesis 8:22 implies the importance of “seedtime and harvest, cold and heat, summer and winter” for the benefit of humanity. We invite readers to research detail on their own concerning the importance of seasons.

Here is a 2011 post from our blog archives:




  








      

Thursday, August 13, 2015

Seasons by the Stars

Several weeks ago after family members observed the close conjunction of the crescent moon and planet Venus, my 10-year old grandson pleased me by asking if the Summer Triangle was visible. Last summer we had pointed out to him this popular asterism. Our family astronomy tutorials had been on hold since last summer. Sure enough, three bright stars were rising toward our zenith from the eastern sky. These jewels are the standouts of three constellations of which they are members: Vega, brightest of the three, fifth brightest in the sky, a member of constellation Lyra; Altair, twelfth brightest in the the night sky, a member of constellation Aquila; and finally, most distant of the three, giant Deneb, is a member of constellation Cygnus, 19th in apparent brightness of all visible stars.

In preparation for this post, I stepped outdoors last night about 11 PM. The three bright stars of the Summer Triangle were directly overhead. They presided over one of the most beautiful summer evenings one could imagine. Cloudy wisps of light stretching across the heavens passed through the triangle and across the sky, reminding us that we are a part of a giant galaxy of billions of stars—the Milky Way. The “cloudy wisps” are composed of billions of distant stars. With naked eye we see perhaps 2000+ above our horizon on the most ideal nights of the year, far more with a good set of binoculars. As we graduate to more powerful telescopes the number of visible stars increases geometrically.

Why has the Summer Triangle asterism been so named? It shines prominently and majestically in the night skies of our Northern Hemisphere summer months, arcing across the dome of the sky each day from sunset to sunrise. This is caused by the rotation of Earth. Rotation causes the diurnal (daily) movement of the Summer Triangle and many other star groups. Owing to Earth’s rotation, every star in the heavens circles 360º around pole star Polaris every 24 hours. Stars such as Vega, Altair, and Deneb, therefore, rise and set each day. Sometimes stars rise or set during daylight hours. The 360º daily swing of each star in the sky relates to rotation of our planet. Rotation causes night and day. Revolution, a 365-day earth movement, causes Earth’s four seasons to cycle annually.

Summer in the Northern Hemisphere occurs only when the constant tilt of Earth’s axis is oriented toward the sun. This orientation results in warm, summer weather. During the night, the Summer Triangle shines overhead. Sky observers look out at the heavens from the night side of the Earth during these warm summer months. And what do they see? The prominent stars of the Summer Triangle shine like rulers of the night sky! 

Summer Triangle stars during the winter are approximately 180º away from their summer position because Earth is 180º removed in its orbit. Changes in position of stars due to revolution of the Earth are slow—about 1º per day because on each of 365 Earth days we revolve about 1º. On winter nights these stars are below the horizon and by day they are not visible in the bright sky.

We cannot resist highlighting another astronomical seasonal herald. Each December a beautiful constellation begins its ascent in the eastern skies as evening transitions to night. It is the constellation of Orion the Hunter, identified by the stars of Orion’s belt, sword and other bright stars. Famous in the mythology of many ancient cultures and mentioned three times in Scripture—Job 9:9, Job 38:31, and Amos 5:8—Orion is beloved among sky watchers. As winter grips the Northern Hemisphere and progresses during cold months, evening observers watch Orion slowly crawl across the winter skies. (This slow crawl is superimposed on the much more rapid daily trek of stars due to Earth’s rotation.) After the winter months springtime evening skywatchers observe it slowly descending into the western horizon over several weeks as warm weather approaches. By July, August, and September an old player appears once more on the sky stage. It is time for the Summer Triangle to manifest itself in all its glory once more.

The Bible does not dwell on lessons of astronomy such as modern discoveries concerning rotation and revolution. Short of being a modern textbook on science, the Holy Book is rich in insightful spiritual applications based on observation of the natural world. Figurative language is sometimes used to strengthen a particular personal interpretation of Bible statements. This problem was prevalent in Galileo’s day. It is still prevalent today. Today’s scientific discoveries, rather than casting doubt on the truth of Scripture, highlight the order and purpose of God’s created world.        



     

      






    





Sunday, August 9, 2015

Copernicus Affirmed

Observers on Earth have been examining the skies for thousands of years. Today’s young people are not often challenged to explain the movement of stars, planets, the moon, and the sun. They may not notice any movement of these bodies in just a few minutes or even an hour. Teachers instruct students that our earth rotates on its axis and revolves around our sun using video animations of solar system mechanics. These animations may not support their assertions with extensive experimental evidence.

The best science teaching is a discovery-based approach when possible. Without prior instruction it is doubtful that contemporary observers of the heavens would conclude that diurnal (daily) motion of the sun and stars is not real but instead, apparent. Historically, thousands of brilliant natural philosophers did not grasp this truth. Natural philosophers, renamed “scientists” in 1833 thanks to William Whewell, mostly accepted the heliocentrism of Nicolaus Copernicus. In the centuries prior to Copernicus, very few natural philosophers adhered to the heliocentric (sun-centered) concept that the earth rotates on its axis and revolves around a central sun. They were geocentrists believing earth was central with sun and stars revolving around us.

The centuries since Copernicus’ proposal of heliocentrism did not produce unanimity. In the 17th century brilliant astronomer Galileo was sentenced to house arrest by a church tribunal in the last years of his life. The commonly accepted interpretation that scripture taught a motionless Earth at the center of the universe was a difficult hurdle to overcome. In 1992 under Pope John Paul II the Catholic Church formally absolved Galileo. A church spokesman stated, “We today know that Galileo was right in adopting the Copernican astronomical theory.”

What experimental evidence is involved in proving that the earth rotates on its axis and revolves around the sun? After having taught extensive units on astronomy many years ago, I reviewed the unit notes I retained. We devoted considerable time to the study of experimental evidence and performing classroom demonstrations to reinforce the heliocentric view of astronomy. I have selected two topics supporting belief in Earth’s rotation (Coriolis effect, and the Focault pendulum), and two topics supporting belief in Earth’s revolution (seasonal changes in angles of insolation, and the shift in constellations throughout the year). Following is a brief description of each.

CORIOLIS EFFECT (Indicator of Earth’s rotation): In the northern hemisphere, moving objects are deflected to the right. Southern hemisphere moving objects are deflected to the left. Wind flowing over the earth’s surface is an example. If a low pressure area exists, air tends to flow from high to low pressure, always deflecting to the right. This explains why moving air in a low pressure system such as a nor’easter or hurricane has counterclockwise wind circulation. Rotating playground carousels illustrate the effect. A moving ball rolled across the platform is deflected to the right if the platform is rotating counterclockwise as does Earth in the northern hemisphere and to the left if the platform is rotating clockwise as in the southern hemisphere. Airline pilots must correct for this effect otherwise they will miss the destination they “aim” for. If Earth did not rotate, there would be no such effect. Gustave de Coriolis described this effect in 1835.

FOCAULT PENDULUM (Indicator of Earth’s rotation): Science museums around the world have exhibits of the Focault pendulum. Physicist Leon Focault devised an experiment in Paris in 1851. He suspended a 28kg mass on a 67m long wire. Wikipedia describes an idealized experiment performed at either the north or south pole of the Earth: “…the plane of oscillation of a pendulum remains fixed relative to the distant masses of the universe while the Earth rotates underneath it, taking one sidereal day to complete a rotation.” At Franklin Institute in Philadelphia PA, my classes observed a working Focault pendulum many times.

CHANGING STAR CONSTELLATIONS throughout the year (Indicator of Earth’s revolution around the sun): We invite you to read our past post on The Bible Zodiac. The detail in this post should help you understand the proof for Earth’s revolution around the Sun:


DIFFERING ANGLES OF INSOLATION from season to season (Indicator of Earth’s revolution around the Sun): Insolation refers to the angle at which the rays of sunlight strike the surface of the Earth at noon each day. This angle changes from season to season. Direct (straight overhead) rays arrive at the Tropic of Cancer on June 22 and the Tropic of Capricorn on December 22, six months later. On March 22 and September 22 direct rays fall on the equator. These dates correspond with beginnings of seasons. The angle of insolation varies 47º to produce seasonal cycles depending on the location of earth in its orbit. This results from Earth’s constant 23.5º axis tilt. Our understanding of Earth’s revolution is strengthened by knowledge of these facts.

God has perfected an intricate, orderly Solar System to produce the wondrous cycles we observe. Humanity was slow to understand cause and effect within our system. Proof was difficult to accept because men imposed personal interpretations of reality upon what they observed. The Creator gifts man with ability to observe, analyze, and explain in search of truth concerning our Solar System.    

            







    



  


Monday, August 3, 2015

Is Seeing Believing?

In Holy Scripture there are many descriptive passages engendering wonder at the glory of the sun, moon, stars, and planets. Bible authors described what they saw in the heavens and assigned spiritual significance to their perceptions. One poetic King James passage describes the rising and setting of the sun as inspiring devotion and worship: “From the rising of the sun unto the going down of the same the Lord’s name is to be praised” (Ps. 113:3 KJV). Along with many descriptive and devotional passages with respect to heavenly objects, we note that the real motions of the earth such as rotation on its axis or revolution in its orbit were not discussed or envisioned by scripture authors. It remained for Copernicus (1473-1543) to set humanity on the path of discovery concerning Earth’s real motions.    

Instruction in astronomical basics is a fascinating, yet challenging task for science teachers. Astronomy was one of my favorite earth science topics as a classroom instructor and the favorite of many students. The subject matter is visually accessible every clear night. To a lesser extent daylight hours also provide lessons in astronomy, sometimes overshadowed by the realities of meteorology.

Astronomy is a multidimensional discipline. For purposes of our discussion we mention only two branches: observational and physical astronomy. We acquire our first astronomical lessons as young children. The purest form of observational astronomy consists of naked eye observation. Observations prior to the advent of reflecting and refracting telescopes beginning in the 17th century were all naked eye observations. If the morning sun arose from the horizon and the evening sun descended below it, what reasonable person would deny that these motions were real? In the sphere of astronomy, “Seeing is believing” requires some qualification.

One effective method of science instruction is to guide students through the historical process of discovery. For example, what did the ancients see in the sky? They visually observed movements of the sun, moon, planets, and stars. What did they conclude about what they saw? In our day, if we did not possess modern knowledge of the Earth’s rotation and revolution, would we conclude from visual observations of the sun, moon, planets, and stars that we are standing on a rotating Earth? Would we conclude most sky objects do not really move around us daily? Perhaps we would not. Aristotle (4th century BC) and Ptolemy (2nd century AD) claimed they couldn’t feel the motion of a rotating Earth. After all, dropped objects fall straight down, and they could not feel the motions of an Earth rotating under them. This was a strong argument in their day!

Little known 3rd century BC Greek astronomer and mathematician Aristarchus had a brilliant insight into Earth’s real motion. He was an original heliocentrist. He claimed the sun was central and that Earth rotates on its axis and revolves about the sun. Aristarchus’ insights did not survive because they were difficult to prove. Copernicus’ conclusions were viewed with suspicion for the same reason. In today’s introductory astronomy classes, “Seeing is believing” may be a difficult principle to reconcile in every case, especially when we interpret perceived motion.

When we teach introductory astronomy to beginners, we teach the difference between real and apparent motion early in the course. Do we believe what we see? Is seeing believing? When we are in a train station, is the movement of a train on an adjacent track real or apparent? Are we moving or are the coaches on the next track moving? In the simplest example, if we turn our head from right to left and we observe stationary objects passing before our fixed gaze from left to right, do we observe real or apparent motion? If our muscle (kinesthetic) sense tells us clearly what really moves, the distinction is easy. If our senses do not give us these clues, we may not correctly judge the difference between real and apparent motion. (If apparent motion results from real motion, the direction of motion is always opposite.)

Apart from discovering truths of astronomy, we must review the lesson of seeking correct interpretations of our observations in the world of nature. I Thessalonians 5:21 exhorts us to test all things: “Prove all things; hold fast that which is good. The passage usually applies to spiritual knowledge, but we may apply its truth to superstition or errant interpretation in any sphere of existence, including the natural world.      




       


Wednesday, July 29, 2015

Movement in the Skies

In our last post we observed that the conjunction of bright Planet Venus with the crescent moon on July 18, 2015 looked like a “Semicolon in the Sky.” As our family members watched the crescent moon and Venus set, thanks to Earth’s rotation, the darkening skies revealed another assemblage of stars—The Big Dipper. This grouping of stars rates as an “asterism,” a conspicuous star pattern or grouping of stars which does not qualify as a constellation.

The Big Dipper is a favorite of young and old. To modern folks, this asterism looks like a container with a handle and a pan (the Dipper). To the ancients, The Big Dipper was only a part of a greater constellation known as Ursa Major—the Great Bear. When my grandson asked if the Big Dipper was visible in the darkening evening skies following our sighting of the Venus/moon conjunction, I first mistakenly replied, “No.” But a quick reappraisal revealed it actually was visible high in the northwest skies if we looked carefully. After a few hours, however, major changes were in store. The star group moved to a new position in the darkening skies.

The seven stars of the Big Dipper are never below the horizon, night or day. The entire Big Dipper asterism visually circles daily around a point on the dome of the sky called the north celestial pole (NCP). The famous star Polaris, the North Star, is fortuitously located almost exactly at that spot. If we journeyed to the Earth’s geographic north pole, the north celestial pole would be straight overhead continuously, night and day. “Why?” we may ask. Even though Earth’s revolution is a long journey around the sun once per year, the Earth’s axis of rotation always tilts to this single spot on the dome of the sky. Stars are incredibly distant so earth’s revolution seems minor in comparison. Earth’s axis is always directed at only one point on the dome of the sky—the NCP.

The apparent daily 360º journey of the Big Dipper around the NCP is caused by the real rotational motion of the Earth. Our real motion causes the stars such as The Big Dipper to appear to move. In reality, our Earth is moving—360º of rotation per day—but we do not sense any movement. Apparent movement of the Big Dipper and other stars signals we are moving. The confusion about what moves was settled in the days of Nicolas Copernicus (1473-1543). He established that the Sun is at the center of the Solar System while Earth and other planets revolve around it and rotate. These real motions provide us with the joy of witnessing sunrises, sunsets, seasonal changes and many other phenomena, and the interesting circular swings of the Big Dipper and all other visible stars in the sky.

The Creator has provided our system of revolving planets around a central Sun. He has enabled us to decipher the apparent motion of the sun, moon, planets, and stars as well as their real motions. The Big Dipper’s major movements tell us about the rotation of the Earth. Less obvious, more subtle movements  of the stars have enabled astronomers to discover the facts about Earth’s revolution. We now know the Earth revolves around the sun, but how did the brilliant astronomers of several hundred years ago first figure it out? We leave this mystery for an upcoming post.  




        

Wednesday, July 22, 2015

Semicolon in the Sky

My 10-and 11-year old grandchildren journeyed outdoors toward evening last Saturday with their uncle to search for milkweed caterpillars, the larvae of monarch butterflies. Milkweed caterpillar collection has been a summer staple of family nature study in our family for three generations. If captured, each caterpillar greedily devours milkweeds in a jar, soon suspends itself to become a beautiful, emerald green, gold bejeweled chrysalis, and finally, after a few days of quiet development, emerges as a fully developed adult monarch.

Twilight was descending on the neighborhood as the threesome returned from their country caterpillar pilgrimage. A short time before, I noted an unusual conjunction of astronomical bodies in the western sky. The thin waxing crescent moon was positioned just below Planet Venus in the fading twilight. The moon’s diameter is about 0.5 degrees. On that night, bright Venus was only one degree distant from the moon. These numbers make for a stunning close meeting, a “conjunction” of sky objects. The moon is second only to the sun in brightness. Venus ranks number three.

When my grandson first saw the configuration, he volunteered that “it looks like a semicolon.” Indeed, it did. On infrequent instances such unusual positioning of celestial bodies offers rare beauty and an occasion for wonder. I could not resist donning my science teacher’s hat: “Tomorrow night the waxing crescent moon will appear about 12º east, leaving Venus by itself,” I exclaimed. I pointed to the approximate locations of the moon for the next few nights at the same clock time—a visual reminder of the moon’s revolution around the earth, I hastened to explain.

In just over 29 days, our lunar companion would return to the same spot in the sky at the same time by the clock. But during early August Venus dips completely below the horizon so another conjunction would not occur. Our moon, meanwhile, would favor us with its monthly phases and stages: waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, and waning crescent. This sequence of events occurs every 29+ days. Earth residents may count on it!

Careful observers notice movements of the moon and Venus as described above. The moon’s speed of revolution, almost 2300 mph, is noticeable because it is so close to Earth. Venus’ speed of 78000 mph is barely noticeable because it is much more distant. When we compare size, speed, distance, and appearance of astronomical bodies in our Solar System, we have a formula for enjoyment of the world as gifted to us by the Creator.

The semicolon in the twilight sky of July 18, 2015 was a “still picture” of startling beauty. Momentary observations did not reveal changes in position or appearance of the sky objects. But with a little patience, in a few minutes we perceived the twilight fading and the descent of the semicolon below the horizon. These observations resulted from the rotation of our planet—once each 24 hours. Many years ago I challenged my students to witness a sunset patiently for a few minutes in an effort to observe movements not otherwise visible. Our classroom discussions of their experience revealed some students claimed to “feel” the Earth’s rotation. Of course, they did not “feel” the rotation except in a visual sense.

The search for Monarch larvae yielded two tiny caterpillars and one tiny Monarch egg, discovered by my granddaughter. Combined with the aforementioned astronomy lesson in fading twilight, the children experienced two diverse lessons without cost, but full of value. Three generations shared the joy of wholesome natural discovery that evening.