ELI ON EARTH: NASA Tables Do Not Tell the Truth about East Lansing Partial Solar Eclipse

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Monday, October 13, 2014, 3:00 am
By: 
Aron Sousa
Solar eclipse viewed from Philadelphia, November 3, 2013

Note: ELi is instituting new weekly features! This column brings you Monday’s weekly feature, “ELi on Earth,” providing you news of East Lansing’s natural world, including the heavens, the weather, and our local flora and fauna. Donate to ELi online or by check to support our unique blend of news of East Lansing!

Following the successful East Lansing total lunar eclipse on October 8, a partial solar eclipse may be visible here on Thursday, October 23, from 5:37 pm until sunset at 6:42 pm. Although NASA tables indicate the maximum eclipse will be visible in East Lansing, ELi readers should consider their viewing options carefully.

As ELi covered in a previous article, the time called “sunset” by astronomers is when the last bit of the sun goes below the horizon. NASA tables report the maximum eclipse will be visible in mid-Michigan one minute before sunset, but eagle-eyed ELi readers will recognize that almost none of the sun is above the horizon at one minute before “sunset.” NASA tables suggest East Lansing viewers will be able to see the maximum eclipse at 6:41pm, but that is not possible as the sun will start passing below the horizon at 6:39 pm, three minutes before “sunset.”

The moon will in fact begin blocking the sun at 5:37 pm in East Lansing, and, if they want to see the eclipse, East Lansing residents will need a clear view of the horizon as the eclipse progresses during the setting of the sun.

Solar eclipses occur when the moon lines up directly between the earth and the sun,  forming a syzygy. (ELi has covered recent syzygies here and here.) If the moon orbited the earth exactly in the plane of the earth’s orbit of the sun, there would be a solar eclipse every lunar month. But the moon does not orbit the earth in the same plane the earth orbits the sun, and so the moon does not pass exactly between the earth and the sun with each new moon. Without that exact alignment, the moon’s shadow does not fall on the earth. Only during a solar eclipse does the moon’s shadow fall on the earth.

The moon’s orbit is tilted about five degrees away from the earth’s orbit around the sun.  The plane of the earth’s orbit around the sun is called the ecliptic, and so the moon’s orbit is tilted five degrees off of the ecliptic. That slight tilt from the plane of the earth orbit around the sun is enough to make the moon’s shadow miss the earth for most new moons. Over the course of the East Lansing year, however, the orientation of the moon’s tilt moves from above the plane of the earth orbit (above the ecliptic) to below the earth’s orbit (below the ecliptic) and back.

This relative movement of the moon above and below the ecliptic is just like the relative movement of the earth’s tilt from the sun with the passing of the seasons. Just like the sun moves higher and lower in the sky with the passing of the seasons, the moon moves slightly higher and lower in the sky over the course of a year.  As the moon’s orbit passes from one side of the ecliptic to the other it passes through a midpoint, which is just like the midpoint in the earth’s seasons, the equinoxes. East Lansing just had the autumnal equinox (see ELi’s discussion here), which is when the sun is midway in its movement north to south in the East Lansing sky. As it turns out, the moon is currently midway in its yearly movement from lower to higher in the sky. It is only during these midway points (called nodes) when solar and lunar eclipses can occur. (Lunar nodes are not related to the earth’s seasons and so solar and lunar eclipses do not always occur so close to the equinoxes.)

When a node coincides with a full moon, there is a lunar eclipse (because the earth’s shadow falls on the moon; see ELi’s coverage here and here), and if a lunar node coincides with a new moon, there is a solar eclipse (because the moon’s shadow falls on the earth).

In order to see the upcoming partial solar eclipse, East Lansing residents will need a clear view of the horizon because the sun will be disappearing below the horizon as the eclipse reaches its maximum. If you have a good view of the horizon and the weather cooperates, this coincidence of sunset and the partial eclipse could make for interesting viewing, similar to that in the accompanying photograph.

People should avoid looking at the sun during partial eclipses. As the sun sets its light is bent by the earth’s atmosphere diminishing its intensity, but it is never a great idea to look at the sun directly. That said, the eclipse could lead to a particularly interesting sunset.

Your ELi horoscope: Traditionally the months when the moon crosses the ecliptic are considered malefic, i.e., full of bad luck. But since ELi policy requires fact-based reporting, we are predicting good viewing fun if the weather holds and if you don’t look directly at the sun. If you look directly at the sun, we predict your eyes (a) will hurt and (b) could be damaged.

 

Photo explanation: There was a partial solar eclipse visible on the east coast of the US on the morning of November 3, 2013. The author took this picture of the eclipse in Philadelphia. The brightness of the sun obscured the disk of the moon in this photo. Fortunately, the author’s hotel had double-pane windows. The dirty outer window created an informal “pinhole” camera projecting the inverted image of the eclipse onto the second of the double pane windows as an upside down crescent to the left of the sun.  If the weather is good and viewers are high enough to see the horizon, on October 23 ELi readers may see something similar. Check out “ELi on Earth” next Monday for information on how to create your own pinhole camera.

 

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