ECLIPSE PRIMER
STUDENT RESEARCH
ECLIPSE PRIMER
(A.K.A. – Everything you ever needed to know about solar and lunar eclipses…)
1. Go to the following website:
(mreclipse.com)
*note: this website is a bit ‘dated’ (2009), but the simplicity and clarity of its explanations make it a very valuable resource to us as both ‘learners’ and ‘teachers’ of astronomy
2. Click on SOLAR ECLIPSES in the pull-down menu. Then click on the first link
titled‘Solar Eclipses for Beginners’ and read through the material.
3. Return to the pull-down menu and click on LUNAR ECLIPSES. Then click on the first link titled
‘Lunar Eclipses for Beginners’ (some content is repeated in both sections) and read through
the material.
4. Develop an ‘ECLIPSE PRIMER’ using the content reviewed within the links listed above as well
as any other resource info that you find useful. Follow the directions below if you plan on filling this out on the computer otherwise fill in answers with a pencil:
a)Copy the following text (beginning below the line) and paste it into a new Microsoft Word document.
b)Save the document as ECLIPSE_PRIMER.doc
c)Make a header on the document that lists ASTR 405, assignment title, and your name.
d)Using the information on the website, insert the correct answers into the blanks/spaces and make the color of your answers RED.
To understand solar and lunar eclipses, we must first know something about the moon. The moon is the earth’s only natural satellite. The diameter of the moon is ______and is approximately ______(what fraction) of the earth’s diameter. The moon orbits (or revolves) around the earth. The orbital period of the moon is ______days. As the moon travels around the earth in nearly one month’s time, it changing position relative to the sun makes the moon appear to go through ______.
It is important to note that on any given day (or night) approximately half of the moon’s surface is illuminated by the sun. The moon’s surface is bumpy and gray and reflects (like a bad mirror) about 12% of the sun light that hits it. We only see a portion of that illuminated surface because of the position of the moon in its path around the earth. Study the diagram below and be familiar with the positions, amount of the illuminated surface that is visible in each position, and the pattern that occurs monthly.
*image from National Maritime Museum Resources
In the diagram above, if the Sun were to be drawn in the proper position, where would it be? (to the right or left, below or above the diagram)
A solar eclipse occurs during the ______moon phase when the moon passes between the Sun and the earth in such a way that the shadow of the moon falls on a portion of the earth. What might a ‘sketch’ of this phenomena look like?
*image from
Differentiate between the umbra and the penumbra:
To view a total solar eclipse, one must be located in a space known as the ______which is only about 100 miles wide although its approximately 10,000 miles in length during a solar eclipse. This is part of what makes it a rarity to experience a solar eclipse. Another factor contributing to the infrequency of viewing a solar eclipse is the path of the moon around the earth.
The moon’s path around the earth is ______rather than circular. Therefore, the distance of the moon from the earth can range by as much as 13%. When the moon is closer to the earth, it can completely block the Sun but when the moon is at the furthest point in its orbit around the earth, then it can only block a majority of the sun leaving a bright ring of light around a black disc. This type of eclipse is called ______eclipse.
Another important factor that contributes to solar (and lunar) eclipses not being ‘common’ occurrences is the orientation of the moon’s orbit around the earth. There is about a 5% tilt between the moon’s orbit around the earth with respect to the earth’s orbit around the Sun. This results in the ‘shadow’ of the moon often missing the earth completely during its monthly trip around our planet.
Whether it’s a total solar eclipse (in the umbra), partial solar eclipse (in the penumbra) or an annular solar eclipse (in the antumbra) or a ‘combo’, our planet averages ______per year. The next total solar eclipse that will be visible in the United States will occur ______.
But what about lunar eclipses…if solar eclipses occur when the ______blocks the sun’s light from reaching the ______, then a lunar eclipse occurs when the ______blocks the sun’s light from the ______.
A solar eclipse can only occur during the new moon phase and a lunar eclipse can only occur during the ______moon phase. The lunar eclipse occurs when the moon (reflecting the sun’s light) moves into the shadow of the earth (that is always being cast into space). A diagram of this might look like:
*image from
When the moon is passing through the penumbra portion of the earth’s shadow, then the moon appears slightly dimmer but is very difficult to detect with the naked eye. But when the moon (either entirely or a portion of) passes through the umbra of the earth’s shadow we see a partial or total lunar eclipse and its cool!!
But how can we ‘see’ a lunar eclipse if the earth blocks the sun’s light from reaching the moon? (include in your explanation why the eclipsed moon often appears reddish in color)
The next total lunar eclipse that will be visible from the U.S. will occur on ______.
JUST A LITTLE BIT MORE INTERESTING ‘STUFF’ ABOUT THE MOON…
The ‘dark side of the moon’ is often referred to in pop culture. But is there a ‘dark’ side of the moon??…Confusion can arise because the side of the moon that faces the earth is constant through an entire lunar cycle. Does this mean the moon revolves but doesn’t rotate? What is ‘really’ happening? Find a place in your dorm room, home, or apartment than you can walk in a circle (yes, get up and do this now)! Take an object and designate it as the earth and place it in the center of the circle. Now designate a ‘distant’ location from which the sun’s rays are traveling toward you and your ‘earth.’ You are the moon. Place yourself directly between the distant sun and the earth.
What lunar phase do you represent at this location? ______
What type of eclipse could be possible at this moment? ______
How much of the moon’s illuminated surface can people on earth see when you (the moon) are at this location? ______
Now move ¼ of the circle such that you are now in the ‘first quarter’ position.
Approximately what % of the moon’s surface is illuminated by that distant sun now? ______
Approximately what % of the moon’s surface can people on earth see? ______
Now move ¼ of the circle such that you are directly lined up with the earth between you and the distant sun. Remember you are representing the moon.
What lunar phase do you represent at this location? ______
What type of eclipse could be possible at this moment? ______
How much of the moon’s illuminated surface can people see when you (the moon) are at this location? ______
Finally move ¼ of the circle such that you are now in the last quarter (or third quarter) position.
Approximately what % of the moon is illuminated at this location? ______
Approximately what % of the moon can people on earth see? ______
As you move to your starting position (you = the moon), replay the orbital period you just completed. If the front of your body was always facing toward the ‘earth’ which would be similar to the same ‘side’ of the moon always facing toward earth, do you rotate during your 29.5 day trip? ______
If yes, at what was your rotational period? ______
If no, ‘walk thru’ the process again. Picture a ‘stick’ that emerges from your head. Does the stick ‘turn’ as you travel through the lunar month? ______
So the moon spins on its on axis in almost the same amount of time it takes to travel around an external point (the earth)…thus, we (on earth) “see” the same side of the moon all the time. And although there is a dark side of the moon at any given location, it is not PERMANENTLY dark since the moon is rotating as it revolves.
What is the rotational period of the moon? ______Think of it as this is the length of ONE day on the moon. Only one sunrise and one sunset every month.