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Musings from an Amateur Cosmologist

December 21, 2017.  Depending upon where you live, this was the shortest of days or it was the longest of days.  The Northern Hemisphere’s winter solstice and the Southern Hemisphere’s summer solstice occurred on this day, as they do every December.  In June of each year the situation is reversed with the start of summer in the North and winter in the South.   The halfway points between these two solstice events are the March and September “equinoxes” when, for a day or so, both hemispheres receive the same amount of sunlight (hence the word “equinox” or equal  night).

How can this be?  Well, the story begins a long time ago when there were no solstices and every day of the year was an equinox.  About 5 billion years ago, when our solar system first formed from a rotating cloud of gas and dust, the young Earth’s axis of rotation was perpendicular to its orbital plane.  This assured that the sun was always directly above Earth’s equator as the planet rotated on its axis.  Every spot on Earth experienced 12 hours of sunlight and 12 hours of darkness every day of the year.

Then, about 4 to 4.5 billion years ago, there is scientific consensus that an event occurred that changed all that when a Mars-sized proto-planet collided with Earth.  This monumental event not only created our moon (another story), but the impact forced Earth’s axis to tilt away from the vertical by about 23.5 degrees.  Suddenly, the rotating Earth began to experience “seasons” as the amount of sunlight reaching each spot on the planet’s surface now varied from day to day and month to month.  Picture the North Pole now tilting away from the sun during the Northern Hemisphere’s winter solstice and towards the sun 6 months later during the summer solstice.  Of course, the reverse is true for the Southern Hemisphere.

Since Earth’s axis tilt never changes its orientation as the planet orbits the sun, this also means that there are two days each year (the March and September equinoxes) when the poles are equidistant from the sun.  The axis is still tilted 23.5 degrees but neither pole tilts toward or away from the sun (see the diagram below).

chart for Howard's blog

Another result of Earth’s axis tilt is the need to recognize two new global latitude lines – the “tropics”.  The Tropic of Capricorn circles the globe at about 23.5 degrees South of the equator and marks the lowest point (as viewed from the Northern Hemisphere) of the sun’s apparent path across the winter sky.  This is where the sun stops its southward progression and starts to move northward again on the day we call the Northern Hemisphere’s winter solstice.

“Solstice” is a Middle English word derived from the Latin “sol” (sun) and “stit” (stopped).

At approximately 23.5 degrees North latitude, the Tropic of Cancer fulfills this role for the Northern Hemisphere’s summer solstice when the sun stops its northward movement and heads southward again.  Again, the opposite holds true in both cases for the Southern Hemisphere.

Complicated, yes, but what would our home planet be like without seasons?

Incidentally, and counter-intuitively, because of Earth’s elliptical orbit around the sun, we are actually two or three million miles closer to the sun in January than we are in July.  However, being a bit closer to the sun during winter in the Northern Hemisphere is more than offset by the effect of the tilt in Earth’s axis as described above.

Note:  My use of the word “sunlight” throughout these musings implies the entire electromagnetic spectrum of the sun’s radiation that reaches Earth and not just the light we can see.

Howard Horton, OLLI at NC State member

 

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OLLI Readers Theatre Group Touts Benefits of OLLI

We hope you enjoy this OLLI “commercial,” presented by the OLLI Readers Theatre Special Interest Group! The group gets together twice a month to perform scripts such as old radio shows, drama, comedy, and their own creations, such as this video. Enjoy!

Click on the link to watch:

https://drive.google.com/open?id=1PXdCy9YkOJNOsdkpGGRJmbC9nP3p-xER 

Book Review: Angle of Repose by Wallace Stegner (1909-1993)

Angle of Repose

Fifty-eight year old Lyman Ward, the narrator of the story, is a retired historian, wheel chair bound with a painful bone disease. Estranged from his wife and bitter about his life, he makes a decision to return to his family home in Grass Valley, California, and write a biography about his grandmother, Susan Ward, who made her own trip west in the 1800s.

Lyman first introduces his grandfather, Oliver Ward, as an honest man searching for a place to focus on his life’s work. A mining engineer, he believed the West held unexplored opportunities, and he moves his family to different areas there in search of a good life as he tries to succeed in a rough environment.

Susan Ward left a promising future in New York to follow her husband, fully expecting to someday return to the East and resume her art career. In the course of her journey, she and her family confront challenges and endure many hardships, as she becomes more and more disappointed with her life. The couple stays together for sixty years, although not always joyfully. Writing and re-living his grandparents’ lives helps Lyman face his own health and marital problems.

Angle of Repose is an exceptional novel that exposes through a well plotted story the early myth of America’s West as a land of opportunity and glamorous cowboys. This 1972 Pulitzer Prize winner for fiction is based on historical letters of Mary Hallock Foote, a little known 19th century writer. By using the facts found in these letters, Stegner sets his novel in the 19th century while also having his characters spend time in the 1970s. He creates convincing, complex characters who are a meld of America’s past and present.
The title of the book comes from a geological term for the diminished incline that will halt a movement; the steepest angle at which a sloping surface formed of loose material is stabilized. The author’s characters try valiantly to find their own angle of repose. Not all succeed.

William Stegner said of his epic novel, “It’s perfectly clear that if every writer is born to write one story, this is my story.” Through his rich prose, in Angle of Repose he shares his love of the land and impresses on the reader his extraordinary insight into human nature.

 
Reviewed by Mercedes Horton (OLLI Member)

 

Musings from an Amateur Cosmologist

Moon and Sun relationship

Recently, for a minute or two, a few fortunate Americans found themselves to be in the sixty five to seventy mile wide shadow of the moon during the August 21, 2017, total solar eclipse.

However, most of us do not stop to consider that, essentially, we experience a more frequent and much longer solar “eclipse” by being caught in Earth’s shadow as the planet continuously eclipses the sun. This occurs for several hours each day between sunset and sunrise when half of the planet is always in the earth’s shadow (we call this nighttime). The only exception, other than the cosmonauts aboard the Space Station, are the folks who live in the “land of the midnight sun” at that time of the year when, for them, the sun never sets.

By the way, since it is the Earth’s rotation that gives us the illusion of the rising and setting sun, we should really call these events “Earthset” and “Earthrise” respectively, as in “What a beautiful Earthrise this evening”.telescope-e1504807705987.jpg

When it comes to eclipses, one particular historical event stands out. During a total solar eclipse over the South Atlantic Ocean in May, 1919, the British astronomer, Sir Arthur Eddington, was able to confirm one of Albert Einstein’s most famous predictions.

In 1916, Einstein had predicted, as part of his new General Theory of Relativity, that light on its way to us from distant stars would follow a curved path around a massive body, like the sun, because of the “warping” of space-time in the vicinity of that body (sort of like a marble rolling across a trampoline with a bowling ball nestled in it’s center).

By photographing the position of the Hyades star cluster when the sun was nowhere near the cluster’s line of sight to Earth and again, during the eclipse, when the darkened sun was almost directly in the cluster’s line of sight, Eddington found that not only did the stars appear to shift their positions relative to background stars, but by the exact amount predicted by Einstein. This was in conflict with Newton’s theory of gravity which predicted a much smaller, if any, path-bending effect for light. Star light has no mass and, according to Newton, should not be affected by a gravitational field, but Einstein/Edington found that it indeed is.

We now know that gravity is not some mysterious “force acting at a distance” as Newton believed, but is actually the mass-induced curvature of space-time that causes moving objects to “fall” toward each other along curved paths. This means, for example, that our “small” Earth is continuously falling toward the much larger sun, but the planet’s rate of fall is (fortunately, for us) balanced by its orbital speed and momentum in its curved path around the sun.

Interesting, but this is probably not the same thing as saying, “I think I am falling for you”.

Howard Horton – OLLI Member and Book Group Coordinator

 

Telescope photo source – shutterstock wikicommons

Moonphase photo Source – Abraren.wikispace

Fall Semester Kick-Off to Feature Award-Winning Journalist

Cullen Browder Pic

Cullen Browder, one of the nation’s top investigative journalists, will be the speaker at OLLI’s Fall Semester Kick-Off and Open House at 2 p.m. Wednesday, Sept. 6. His timely subject: “The Importance of Investigative Reporting to Our Democracy.”

Cullen knows all about investigative reporting. That’s his beat at WRAL-TV News, where he is the chief investigative reporter. His work has won him major regional and national awards since he joined the station in 1998. It’s likely that his role has never been more challenging than today, with a President accusing the media of “fake news,” and Americans throughout the country debating major issues and how the media cover them.

The Tennessee native has received multiple Emmy awards from the National Academy of Television Arts and Sciences. He’s also been honored by the Associated Press and the Radio Television Digital News Association. The Washington Post has recognized him as one of the best state capitol reporters in America, helping to bring about significant changes in North Carolina state government. He’s also explored issues from citizens battling Alzheimer’s to the challenge of homelessness. Continue reading Fall Semester Kick-Off to Feature Award-Winning Journalist

Celebrating 25 Years: An OLLI Charter Membership

mercedes-horton-vert

In 1990, newspapers in the Raleigh area contained articles about what was then a new idea for over-50-age continuing education that was being talked about at NCSU. Mercedes Horton and her husband Howard had just moved to the area, and as the Encore Program for Lifelong Learning came together in the next year, she found herself intrigued. It didn’t take her long to find the McKimmon Center, and become, in her words, a “proud member.” What an exemplary member she continues to be!

She has seen the membership grow from about 130 people to over ten times that size, as it is now. In fact, one of the classes Mercedes took in the early years had only three members in it. Her memory of that class is that, even for only three students, the presenter was just as committed and thorough as all instructors have been over the 25 years of OLLI.

Volunteer instructors like that, and members like Mercedes, are vital to OLLI. In her 25 year membership, she has volunteered on the Activities and Services Committee, Ad Hoc Committees, and the Advisory Council. She continues to be part of the Writing Group and a staff member at the OLLI newsletter, the Connection. Feeding her love of books, she and her husband Howard have kept the OLLI Book Group together and humming for many years and are still its invaluable leaders. She has been a part of OLLI’s Trailblazers, Epicureans and the Movie Group.

Of course, Mercedes leaves time for classes and study trips, such as to Costa Rica, a wonderful memory of hers. In response to a question about a favorite class over the years, she says that it’s always her current class.

Thank you for reminding us, Mercedes, how to keep on learning!

Phoebe Johnston