Wednesday, August 16, 2017

Eclipse Corner #17 MORE KEPLER FACTS

      Kepler’s first law states that planets move in an elliptical orbit, so that the distance between the Sun and Earth is constantly changing as the Earth goes around its orbit.  The earth’s closest point or perihelion occurs in the winter (January 3) and farthest point or aphelion is in the summer (about July 4). For our August 21, 2017, solar eclipse, the Sun is more near the aphelion. Therefore, the shadow is only producing a 70 mile width band as it moves across the US. The shadow width becomes larger as the Sun gets closer and a more winter time eclipse can maximize the shadow up to 166 mile band. 

This picture is exaggerated so that the points discussed can be seen easily.

     Kepler's second law of planetary motion showed that a line between the sun and the planet sweeps equal areas in equal times. Therefore in this picture A = B for a given time. C and D equal the distance traveled within that time. So the speed of the earth in its orbit is not constant. We go faster in the winter at perihelion and slower in the summer at aphelion. The speed of the planet increases as it nears the sun and decreases as it recedes from the sun.  Knowing the exact speed is part of the formula for calculating the duration of totality. There are a few other minor facts that affect the timing, like the Moon is moving away from the Earth at about 1.5 inches per year.  Information like these speeds is used in the math formulas in order to figure out the exact amount of seconds in the duration of totality. Tough math.
     August has a fairly high angle of the sun so that will help our view as the Sun will be lower in the sky in winter. The 1:14 PM puts it high in the sky as well.

     In June, 2017, the Sun had an average of about 16 sunspots as the solar activity is still lessening towards a minimum in 2019. June had 4 spot free days. This means the magnetic solar activity including sunspots, flares, and prominences should be even less in August, 2017. There have been some active occurrences so there are possibilities for seeing these as we view the solar eclipse. The Sunspot cycle peaks every 11 years, but astronomers have rated the current cycle as very weak. Get your Eclipse glasses out early and check the Sun or try check out the status of the Sun. More solar eclipses updates are coming.                                 –Dan Slais

Dan Slais is a retired 8th grade earth science teacher from Waynesville, MO.  He has taught Astronomy and Geology for Columbia College and has worked as a seasonal National Park Ranger for seven seasons. 

Join us August 18-21, 2017 for Midnight at Noon, a four day music festival and eclipse viewing event in Owensville and Rosebud, MO.  For more information click HERE

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