Eclipses

In the section of the course, students will learn about the celestial alignments required to produce an eclipse. Whenever the Moon's light is blocked by the presence of the Earth between Sun and Moon, a Lunar Eclipse will occur. Whenever the Sun's light is blocked by the presence of the Moon between Earth and Sun, a Solar Eclipse will occur. Both events are relatively rare considering that the Moon should come between the Earth and Sun every New Moon phase, and that the Earth should come between the Moon and Sun every Full Moon phase. However, the path of the Moon's orbit is not exactly aligned with the path of the Earth around the Sun. The Moon's orbit is about 5 degrees off-line, causing the Moon to either be above or below the Earth-Sun line most of the time. Only when the Moon's path crosses the Earth's path are Sun, Moon, and Earth all on the same plane, but this can happen during ANY phase of the Moon, depending on the position of the Moon in its orbit when it crosses the Earth-Sun line. That line-crossing point is called a "Node," and there are two such nodes per lunar orbit, or two times each lunar orbit when the Moon's path crosses the Earth-Sun line per lunar cycle. If the Full or New Moons happen to occur when the Moon is at a node, then the geometry will be as described in the image below.

Lunar Eclipses

We will first look at Lunar Eclipses. As you can see from the image at left, the alignment has our planet Earth in between the Sun and the Moon, causing the shadow of the Earth to completely cover the Moon. To learn a detailed account of a Lunar Eclipse, click on the image from the Mr. Eclipse website. You will find some wonderful information and pictures at your disposal.

 

 

 

 

 

"Eclipse map/figure/table/predictions courtesy of Fred Espenak, NASA/Goddard Space Flight Center."

Astronomers recognize three basic types of lunar eclipses:

1. Penumbral Lunar Eclipse, when the Moon passes through the penumbral shadow of the Earth. These eclipses are very difficult to see since the shadowing is almost imperceptible.

2. Partial Lunar Eclipse, when a portion of the Moon passes through the umbral shadow of the Earth. These eclipses are discernible, even to the naked eye, but not always as colorful as a total eclipse.

3. Total Lunar Eclipse, when the entire Moon passes through the umbral shadow of the Earth. These eclipses are very beautiful, as the image below attests.


"So Franke, why is the moon red?" you might ask as you see this picture that I took from another eclipse website dealing with astrophotography. Due to the atmosphere of the Earth and the scattering properties of water vapor, the following happens during a total lunar eclipse. The sunlight passes through the Earth's atmosphere, where water vapor scatters the blue wavelengths and allows the red wavelengths to pass freely through. During the lunar eclipse, the red light that passed through the atmosphere strikes the lunar surface and is reflected back toward Earth. Eclipse watchers then see a reddened moon. The Biblical prophet Amos predicted the endtimes to be marked by a moon that turned to blood. The red color of a total lunar eclipse is not consistent from eclipse to eclipse. Due to various levels of global cloud cover, pollution levels, and ash from fires or volcanic eruptions, the Moon's color can be anywhere from relatively bright orange (when skies are clear) to darker shades of brown (as during the eclipse following Pinutubo's eruption in 1991 or Yellowstone's fires from 1993).

Of interest is a story involving Christopher Columbus, the actual guy credited with discovering America, even though we all know that the Vikings came over here over 400 years before Christopher, and that nomads from the steppes of Russia probably were here many millennia before that. Whatever, Columbus was not well liked by the native Americans who did not appreciate his arrogant manners, ruthless negotiations, and numerous diseases that his men brought over here. Imprisoned by the native people, Columbus threatened to pray to his god and call for the moon to turn into blood if the natives refused to give food to his sailors. Columbus had predicted the upcoming event and was careful to call for an answer to prayer at a time that coincided with the lunar eclipse. When the moon turned red, the natives were frightened and gave Columbus and his men what they had asked for.

On the night of February 20, 2008, Minnesotans got to see a Total Lunar Eclipse. I set up the telescope and camera in the front yard and tried my best to capture this wonderful event. During the very early hours of April 15, 2014, the first in a tetrad of lunar eclipses was visible from the deck of our house.

Solar Eclipses

In this image, seen to your left is the alignment when the New Moon is exactly between the Earth and the Sun. The shadow of the New Moon falls on the Earth, and anyone inside that shadow will witness a Solar Eclipse. The event is absolutely stunning, and I have heard it said on one of my Astronomy videos, that fewer than one person in every thousand will ever see a total eclipse of the Sun. To learn about more details, click on the image at your left to connect to the Mr. Eclipse website. Before we look at the rarity of the total solar eclipse, we must first look at what we might see. Solar Eclipses come in three categories, which are listed below. Unlike lunar eclipses, NONE of the solar eclipse types are safe for naked eye observation. Unless a proper solar filter is used, blindness can result from a very short time of eclipse watching. The three types of solar eclipses are listed:

 

 

 

"Eclipse map/figure/table/predictions courtesy of Fred Espenak, NASA/Goddard Space Flight Center."

Partial, when eclipse viewers on Earth are not in the narrow path of totality, but only within the umbral shadow of the Moon. People will see a portion of the Sun blacked out by the disk of the Moon. Partial eclipses always occur during any total eclipse, and the amount of the sun that is gouged out by the lunar disk depends on how close the viewer is to the path of totality.

 

 

 

 

 

 

Total-Annular, when eclipse viewers on Earth are in the narrow path of totality, but the Moon happens to be at or near its apogee during the New Moon phase, so that the lunar disk appears smaller than the solar disk. The entire disk of the Moon will fit inside the disk of the Sun, and will look like a ring of fire. It was this kind of eclipse that captured my attention during the spring of 1994, when I took some Hopkins students to southern Illinois to view it. We looked on the map of the US and found where the exact center of totality would be, and then chose the area of the country within that narrow part that promised the best weather. We drove to Springfield, Illinois, toured the home of Abraham Lincoln, and then set up our telescope at a campground east of town. Within several hours, cars and trucks from 6 different states converged on our little field, and eclipse chasers like us hauled out their equipment for the big event. We spent the night going to telescope to telescope and looking a Messier objects and swapping stories. We were blessed in the morning with a cloudless sky and enjoyed a perfect setting for the last total solar eclipse visible in America for a long, long time. The pictures I took actually turned out, and the Moon is dead center relative to the Sun.

"Eclipse map/figure/table/predictions courtesy of Fred Espenak, NASA/Goddard Space Flight Center."

Total Solar, when eclipse viewers on Earth are in the narrow path of totality, and the Moon is closer to its perigee so that the lunar disk covers the solar disk completely. It is this kind of eclipse that produces the fantastic images of the solar corona, as well as solar prominences along the rim. Depending on the distance of the Moon relative to Earth, the totality can last for up to 7 minutes. A total eclipse took place in the summer of 1991, when the path of totality went directly over the big island of Hawaii, and right over the top of the Mauna Kea observatories. Over 35,000 people showed up on the big island for the event, including several foreign groups that stayed at my Uncle Bill's house. Most were sorely disappointed when clouds obscured the view. Those who were atop Mauna Kea, or out to sea on an eclipse chasing boat enjoyed the view, but islanders were denied the thrill. This serves to remind you that if you want to chase eclipses, be forewarned that there is no guarantee for good weather, so you better have other tourist options to make up for the potential disappointment.

"Eclipse map/figure/table/predictions courtesy of Fred Espenak, NASA/Goddard Space Flight Center."

Few astronomical events are more exciting than an eclipse, and I am thankful to have witnessed several total lunar and two total solar eclipses thus far in my life. I had two students in my course years ago whose father was an eclipse chaser, and he took his family all over the world to see as many as possible (typically one solar eclipse a year). My Uncle Bill went to Turkey in 1955 with the Milwaukee Astronomical Society to study the total solar eclipse of that summer. They recorded their position exactly, and then timed the eclipse event exactly, using radio connections to other teams placed along the path. Their expenses were paid by the US military, who then compiled the data to get a firm fix on the exact locations of several troublesome spots in that part of the world in case missiles needed to be used against those nations. This is not the first time, or will it be the last, when the military used astronomical data for non-peaceful purposes. Since the US did not have space satellites with real-time imaging capability, the data from the 1955 eclipses was quite valuable. Of similar interest is the recent declassification of many US military satellites that were serving our army, but also amassed much space data. Astronomers have been studying that data and using the material to make many interesting astronomical connections to past and present events.

A great deal of thanks must be given to Fred Espenek, also known as Mr. Eclipse for his websites. If you want to know when the next eclipses are to take place in America, please visit:

Next Lunar Eclipses

Next Solar Eclipses

Otherwise, I hope you enjoyed this page.

Now, there is a little assessment waiting for you. It is a test given to the early astronauts to test their thinking and planning skills, and now I am giving you the opportunity to match your skills against theirs. It's entitled, "Stranded on the Moon."

You can now move to material devoted to Lunar Origin Theories, where you will find out what astronomers believe are the events that brought the Moon to our neighborhood. You could also return to the Moon Introduction, or go back to the Syllabus.


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