Aug 21

101 – 2017 Solar Eclipse Podcast Primer


Hi everybody, welcome to the 8 21 17 podcast.  Episode 101, entitled ‘your solar eclipse primer’.  I’m Ed Owen, your host.
This is the first REAL episode of the podcast.  I hope you’ll consider subscribing.  We’ll be doing these weekly, well, at least that’s the plan, all the way up to eclipse week, 2017.  
New episodes will be posted at eclipse made easy dot com, and when you visit that site, you’ll find links to subscribe to the podcast on either iTunes or the Google Play store.
During the course of this series, we’ll talk about a lot of things regarding the eclipse, including telling you what the eclipse is, how to view it safely, and even some tips for making plans if you’re traveling to an eclipse view site.  You’ll hear interviews with eclipse experts and we promise not to get TOO technical.  I like to call this “the people’s eclipse podcast”.
In this episode, we’re going to address quite simply, “What is the eclipse?  What has to happen to make an eclipse occur? And why is the solar eclipse of 2017 SUCH a big deal?”  You’ll also learn a few, basic eclipse terms.  You’re going to hear these terms a LOT over the next 12 months.
And keep in mind, IF you want to review, that you can see the actual text of this podcast, along with the recording, at eclipse made easy dot com.
OK, let’s go.  A lunar eclipse is quite simply when the earth gets between the sun and the moon.  During a lunar eclipse, the reflected light of the sun off the moon is blocked by the earth.
During a solar eclipse, the moon passes between the earth and the sun, and directly blocks the sun and the light it emits.  They are really that simple to explain.  And an eclipse can be either partial, or total.

Graphic courtesy: BBC

A solar eclipse ONLY occurs during a full moon or a new moon.  But, a solar eclipse doesn’t occur EVERY time there IS a full or new moon. For example, in 2016 there are 12 full moons and 13 new moons, but only four eclipses.  Two solar and two lunar.
So why isn’t there an eclipse each time?  Here’s why.  The earth’s orbital plane is called the ecliptic.  IF the moon orbited the earth in the same plane as this ecliptic, we’d have 24 eclipses a year.  12 during the new moon phase,  and 12 during the full moon phase.
The problem is, that the earth and moon are NOT on the same orbital plane.   In fact there is about a five degree difference in the orbits of the two.  (see illustration)
Moon5degreetiltTwice a month the orbits of the earth and the moon intersect at a point called a node.  Depending on the direction of the orbit, these can be ascending nodes, or descending nodes.  IF the moon is close enough to one of these intersecting nodes, then an eclipse is inevitable.   And depending on the precision of the intersection point, you can have a partial eclipse, or a full eclipse.
If you really want to get technical about some of the terms, check out umbra, u-m-b-r-a, penumbra, p-e-n-u-m-b-r-a, and antumbra.  That’s a-n-t-u-m-b-r-a.  Those are parts of a shadow and they’re directly tied in with a solar eclipse.
Each year, there are more eclipses than you realize.  Worldwide, there can be anywhere from 4 to 7 and these can be lunar or solar, partial and total.  But there can ONLY be two total solar eclipses a year.  That’s the way nature works.   
So, you can see that an eclipse at any given point in time on planet earth, is kind of rare.  That’s why many people make it a hobby to view as many of them as they can.
Now, consider two things: 
One, the last full solar eclipse in the contiguous US was in 1979.  And it only touched a few states in the northwest.  There wasn’t the hype of the 2017 eclipse, and not as many people viewed it. ( https://en.wikipedia.org/wiki/Solar_eclipse_of_February_26,_1979 )
Two, the last time America had a solar eclipse track across the nation from coast to coast was 99 years ago. (http://eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle1901/SE1918Jun08Tgoogle.html ) Before social media, before television and radio, before the interstate highway system.
So you can see why the 2017 eclipse which will cross the United States is SUCH a big deal.  It is a once in a lifetime event.  You have tens of millions of Americans interested in seeing this event.  You have more media coverage than for any similar event in history.  You have a nation actively promoting the eclipse and the event.  And top it off with the scores of visitors from outside American borders who will be visiting here in the states.
Now, let’s focus on the event itself.
The eclipse will first touch American soil on a beach in Oregon, just north of Newport at about 10:15 on the morning of August 21st.  It will then make it’s way across the country, in something of a southeastern pattern, before exiting on the east coast near McClellansville, South Carolina at 2:49.  nd then it will be gone.  And ‘we saw the eclipse’ parties will take place all over the country!
Here’s a term I want you to remember.  Center line.  Here’s what that term means.  As the eclipse crosses the United States, the path of total darkness is only about 68 miles wide.  At any given point, the halfway between the northernmost point seeing the full eclipse, and the southernmost point is the center line. For each mile or kilometer you go away from the center line, you’ll lose an amount of total darkness length.
The maximum length a full solar eclipse can be is about 7 1/2 minutes.  Eclipses of this length are very rare.  In fact, you won’t find an eclipse longer than seven minutes until 2150.  For the 2017 eclipse, viewers will be able to observe the eclipse for as short as a few seconds, to as long as 2 minutes 40 seconds.
I think you could say safely that this will be the most viewed sky event in history.  Along the way the eclipse will touch parts of 14 states.  If you hear the number 10 states, that’s also correct.  The center line WILL touch 10 states.  But the eclipse itself will affect 14 states, although several of those will only see darkness in unpopulated areas, and for a very short time.  And then it will be gone.  
That’s it for this episode of the podcast.  Next week, some tips in picking your viewing location and we’ll include some links to make it easy for you.  We’ll give you ‘food for thought’ about what you should be looking for as you plan YOUR eclipse excursion.  In the meantime, PLEASE leave us comments at the website and if you like the podcast, rate us at whichever site you subscribe at.  You can also email me at podcast@eclipsemadeeasy.com.
Until next time, I’m Ed Owen for the 8 21 17 podcast.