Understanding Eclipses This really is the eclipse of a generation. This is the first Total Solar Eclipse on the continental USA since 1979; and the first one to cross the continent from ocean to ocean since 1918. There was one that was visible from Hawaii and Mexico in 1991. Mexico closed the border with the US to anyone without hotel reservations because they could not handle the volume of people. It is the first total solar eclipse to be visible from ONLY the US since before 1776. And the first in Missouri since before Europeans got to Missouri. Click the mouse to begin

Celestial Eclipses Result of the interaction between three celestial bodies. Host Body – Location of Viewer Eclipsing Body – Body obstructing view Eclipsed Body – Body where view is being obstructed Most familiar eclipses to us are Lunar eclipses Solar eclipses (Click the mouse to move to next slide)

Lunar Eclipse Lunar Eclipse always occurs during the full moon. Shadow of Earth is cast on the moon Light through earth’s atmosphere makes the moon glow red (Blood Moon)

Solar Eclipse Solar eclipses occur during the new moon. View of the sun from earth is obstructed by our moon. Two moon shadows cast on earth during total eclipse Penumbra – Partial Shadow – large area Umbra – Full Shadow – small area

Under the Umbra

Annular Eclipse Annular Eclipse is when moon is too far from the earth during a solar eclipse to completely block all direct light from the sun. Appears as donut sun with a large hole in the middle. Why don’t we have eclipses every month of the Year? To answer this question we need to understand more about the relationship between sun, moon and earth.

Earth Orbit Johannes Kepler discovered in 1609 that planets and moons orbit in elliptical paths. Elliptical points of importance Focal Point – Center of orbit Periapsis – Closest orbital point to focal point Apoapsis – Farthest orbital point from focal point Earth’s mean orbital distance from the sun is 149.6 million km (92.96 million mi) or one Astronomical Unit (1AU). Perihelion – 91.4 million mi (0.983AU) Aphelion – 94.5 million mi (1.02AU) Orbital velocity – 29.78 km/s (66,621 mph) Orbital Period – 365.26 days (1 year) Force of attraction between earth and Sun F= g (Ms x Me)/

Lunar Details Moon’s average orbital distance from earth is 238,900 mi. Perigee = 225,327 mi Apogee = 251,924 mi Orbital velocity around Earth – 1.022 km/s; 2,286 mph Orbital period = 27.3 E days Rotation CCW = 27.3 E days Orbit and rotation is in sync with Earth’s rotation so same side of moon always faces the Earth.

Lunar Phases Phases of the moon are caused by its orbit around Earth. Moon’s orbital plane around earth is tilted at an angle of 5.14° from earth’s orbital plane around the sun.

Inclined Lunar Orbit around Earth This figure explains how we have to think in 3-D to understand when we don’t get eclipses every month

Few Eclipse Conditions Per Year This figure brings together the earth's orbit around the sun with the moon’s orbit around the earth. Starting on the far left we see that the shadow of the moon is below the earth moving forward 3 months to the bottom-most earth we se that now when the moon gets to new moon it is lined up and we get an eclipse. This lining up happens again six months later when we get to the top most earth. There is an eclipse somewhere on earth every six months but they can only be seen from a small area of the earths surface and they aren’t all TOTAL eclipses.

This is obviously a map of Missouri – which cane from http://www This is obviously a map of Missouri – which cane from http://www.greatamericaneclipse.com/ - you cab find all sorts of graphics are free resources on this site – also here http://www.eclipse2017.org/eclipse2017_main.htm. You may be asked about timing – you can determine the timing of the eclipse for specific locations: https://www.eclipse-chasers.com/php/tseCalculator.php For and given location – the position of the sun will vary slightly. For Missouri it is more or less consistent across the state – so  Here’s a link for people who want a more accurate position of the sun http://www.esrl.noaa.gov/gmd/grad/solcalc/azel.html For CoMO at the time of totality the azimuth angle is 184.4 deg (180 deg = south); evolution is 62deg – which is pretty high.

Safely Viewing Solar Eclipses Only Solar Viewing glasses or welder masks (rating 14) allows us to view the sun directly without damaging our eyes. Viewers must secure solar viewing glasses over their eyes before directly viewing the sun. When ever any sliver of the sun’s disk is viewable, eye protections must be worn. Sun glasses will not protect our eyes from the sun’s light radiation. Do not use them to view the sun. Only during solar totality can eye protection be removed. Solar Viewing Glasses

Safely Viewing Solar Eclipses Viewing solar eclipse through small holes First sheet is opaque with small holes made from a pencil Second sheet displays sunlight passing through the holes in the first sheet.

Immediately precedes and follows Total Eclipse Diamond Ring Immediately precedes and follows Solar totality Return to 1st slide