Name: ___________________________ Class: ___________________________ Date: ___________________________

Assignment #5: Eclipses & The Moon Eclipses are among the most beautiful and awe-inspiring events in the sky. They were once fearsome signs of the wrath of the Gods, but now we know that they are simply beautiful and exciting alignments of the Earth, Moon and Sun in a straight line. In this assignment we’ll use Stellarium to observe and understand both Lunar and Solar eclipses.

PART A In order to understand what causes an eclipse, we will first have to get a sense of how the Moon moves around the Earth in its orbit. To do this, start Stellarium. Make sure you are located in L.A., then change the Date & Time to August 21, 2007 at 9 PM. Use the C and V keys to display the Constellation Lines and the Constellation Names. Open the View window and, in the Sky sub-menu, in the Planets and Satellites section, put checks next to Show Planets, Show Planet Markers, and Scale Moon, and in the Labels and Markers section put check marks next to Stars and Planets. Close the View window. Turn off the Ground and Atmosphere and Fog (use the G, A and F keys). Find the star Antares in the sky to select and center it. You should see the Moon just to the East of Antares. Zoom in until the FOV is about 40°, and you can just see the Moon as a small disk on screen, with Antares still visible next to it. Click on the Switch Between Equatorial and Azimuthal Mount button on the toolbar at the bottom of the screen until the little icon of the telescope is lit up (or simply press CTRL-M) to make the Ecliptic plane horizontal. Mark the position of the Moon on your screen with a small Post-It note or piece of tape. Click on “=” key. One day will pass. The Moon will move to the East. Keep pressing the “=” key, and count the number of times you press it as you watch the Moon move across the sky. Remember, you’re watching a fixed spot in the sky as the Moon orbits the Earth. The Moon will move off to the left and disappear off your screen. Keep clicking until it reappears on the right side. When it returns to its starting point, stop clicking. You may have to go back and forth an hour at a time (use CTRL = or CTRL – to move an hour at a time) to get the Moon exactly back to where it started. •

How much time did it take the Moon to travel once around the sky and return to the same spot? ____________________________________________________

This number is called the sidereal period of the Moon, or the period of the Moon’s orbit with respect to the stars. This is the approximate length of a month in our calendar. It would be convenient if 12 times this number equaled 365 days, since then we could make a year equal to 12 months, each of which would equal one Lunar sidereal period! Unfortunately, 12 times the Lunar sidereal period falls a few days short of a year, so we have to add a few days to some of the months to make the year work out to the correct length! 1

PART B Now let’s see what the face of the Moon looks like from the Earth over the course of a month. Change the date to March 7, 2008, at 6:00 AM. Open the View window and remove the check mark next to Scale Moon. Close the View window. Find the Moon and zoom in until it fills the screen (you can do this by simply pressing the “/” key once you have found and selected an object). You should be looking at the face of a dark moon. To understand why the Moon is dark at this moment, zoom out until the FOV is about 5º. You should now be able to see both the Sun and the Moon on the screen. •

Why is the Moon dark at this moment? _________________________________________

•

Would you be able to see the Moon if it was in this phase? ___________________________

•

What is this phase of the Moon called? ___________________________________________

Now zoom back out until the (dark) Moon fills the screen again. Press L four times to make time run 10,000 times faster than normal and watch as the hours and days pass. •

What happens to the Moon? ________________________________________________

•

Stop time (use the 7 key) when the Moon is half illuminated. What is the date? ________

This phase of the Moon is called First Quarter. •

How many days have passed since New Moon? _________________________________

Press L three or four times again and watch time pass until the Moon is full. Stop time again. •

What date is it? ___________________________________________________________

•

How many days have passed since the First Quarter Moon? _______________________

•

How many days have passed since the New Moon? _____________________________

Press L a few times again and watch time pass until the Moon is new again. Stop time again.. •

What day is it? __________________________________________________________

•

How many days have passed since the First Quarter Moon? ______________________

•

How many days have passed since the Full Moon? ____________________________

•

How many days did the entire cycle take, from New Moon back to New Moon? _______

•

Compare this answer to the sidereal period of the Moon you got in Part A. What do you notice?_________________________________________________________________ 2

Reset the time to the current time by pressing the “8” key. Look at the Moon, zoom in until it fills the screen, and let the days pass by pressing the “=” key repeatedly. Watch for when the Moon is next in its Full phase. •

What is the date of the next Full Moon? ______________________________________

The phases of the Moon are caused not by the shadow of the Earth falling on the Moon, but by the fact that the Sun shines on the Moon from a different angle each day.

PART C Now that we understand how the Moon moves through the sky, and how its appearance changes during that time, let’s see what happens when it happens to line up with the Earth & Sun. When this happens, it is called an Eclipse. Change the date and time to August 27, 2007, at 11:00 PM. Make sure the Ground, Atmosphere and Fog are turned off. Display the Planets by checking the Show Planets and the Show Planet Markers boxes in the Sky sub-menu of the View window. Close the View window. If you don't see them, display the planets' names by pressing the P key. Use the Search window to find and center the Sun and then go to it by pressing CTRL-G. Now search for the Moon and center it. To to make the Ecliptic is horizontal, make sure the Switch Between Equatorial and Azimuthal Mount button in the bottom toolbar is pressed - the little telescope icon should be lit up. You can use CTRL-M to do this as well. Zoom in until the Moon is visible. The Earth should be just barely on the screen, on the left. Remember, you are looking at the Moon (and Earth) from the point of view of the Sun. •

What phase is the Moon in at this moment? (Imagine yourself on Earth, looking at the Moon) __________________

•

Press L three or four times to run time faster than normal and describe what happens. ________________________________________________________________ _______________________________________________________________________

•

When the Moon goes behind the Earth like this, how much sunlight will fall on the Moon? Remember, you are standing on the Sun! ___________________________

You are watching a LUNAR ECLIPSE. The Earth comes between the Sun and the Moon, blocking the Sun’s light from hitting the Moon. Here's a picture of what's happening:

3

Let’s see what is happening on the Moon during such an eclipse. Click on the Earth to select it, then press CTRL-G to go to the Earth (from the Sun, where you are now). Now Search for the Moon to select and center it. Change the time back to 11 PM, and zoom out until the Moon fills the screen. You're now looking at the Moon, again, on the night of August 27, 2007, from L.A.. Press L twice and watch carefully for a few minutes. You should see a dark, curved shadow begin to come across the upper left edge of the Moon. This is the shadow of the Earth, as the Moon begins to pass into an Eclipse. This outer shadow of the Earth is called the Penumbra. This moment, when the Penumbra first touches the Moon, is called first contact. Stop the time by pressing the 7 key. Go back and forth in time to try and find the moment of First Contact. The Penumbra is difficult to see, but do your best! •

What time is First Contact? _______________________________________________________

Press the L key a few times again and watch the penumbra move across the face of the Moon. •

In which direction does the shadow move? _____________________________________

•

Is the shadow straight or curved? ____________________________________________

•

What can you deduce from the previous answer about the shape of the object casting the shadow? (Aristotle made this very deduction 2300 years ago!) ______________________________________________________________________

The Penumbra is followed by a deeper shadow, called the Umbra, which is caused by the Earth completely blocking the direct light from the Sun from hitting the Moon. In Stellarium (and in the real world!) it's hard to tell the Umbra from the Penumbra – they just look like one big shadow! Keep watching the Umbra and Penumbra move across the Moon until the shadow completely covers the Moon. The eclipse is now in totality. •

What time did totality begin? _________________________________________

Notice the orange color of the Moon during totality. We discussed in class the cause of this orange color – it is caused by sunlight refracting through the thin atmosphere surrounding the Earth and then indirectly lighting up the Moon. Continue to let time pass until the penumbral shadow is completely gone and the Moon is fully illuminated again. The eclipse is now over! •

What time did the eclipse end? _____________________________________________

•

How long did the entire eclipse last (from First Contact to the end of the Eclipse)? _____________________________________________________________________

4

To see what this eclipse would look like if you were on the Moon, Click on the Moon to select it, then press CTRL-G to go to its surface, and then Search for the Sun to center it. Change the time back to 11 PM on August 27. Press L a few times to let time pass and watch the eclipse. Lunar Eclipses are beautiful, and relatively easy to see – anyone on the side of the Earth that faces the Moon can see the eclipse as it happens! PART D Now let’s look at a Solar Eclipse, which occurs when the Moon comes between the Sun and the Earth. Here's a picture of what's happening during a Solar Eclipse:

Go to the Earth by clicking on it and pressing CTRL-G. Change your location to Nashville, Tennessee by opening the Location menu, typing Nashville into the Location Search box, and clicking on Nashville, United States. You can also enter Nashville's latitude and longitude directly: the Latitude of Nashville is 36°10' N, and the Longitude is 86° 47' W. Close the Location window. Now Search for the Sun to select and center it. Change the Date & Time to August 21, 2017, at 8:00 in the morning. Finally, turn the Atmosphere and Ground back on by pressing G and A. Press L twice to let time pass quickly. You should see the Moon approaching the Sun in the sky. Stop time just as the Moon starts to block the Sun’s edge. •

What phase must the Moon be in during this eclipse? __________________________________

•

What time is first contact (when the Moon first “contacts” the edge of the Sun)? ____________

Continue to let time pass (you can speed up or slow down time using the L and J keys), until totality begins – when the Moon completely covers the Sun. Stop time (using the 7 key), and go backwards or forwards in time slowly until you see the exact moment when totality begins. •

What time does totality start? _______________________

Now carefully let time pass at normal speed (the K key) until the Sun just begins to peek out from behind the Moon. •

What time does totality end? ________________________________

•

How long did totality last? ________________________________________ 5

The reason Solar Eclipses are so brief is that the umbra – the shadow of the Moon - is very tiny compared to the size of the Earth! That's why total solar eclipses are so rare and difficult to see! Remember, only people in the small umbral shadow will see a total solar eclipse. Those in the much larger penumbral shadow will see a partial solar eclipse. To demonstrate how small the umbra is, go back in time until the Eclipse is in totality, with the Moon completely covering the Sun. Now change your location to Hunstville, Alabama, just 100 miles south of Nashville. Open the Location window, enter Huntsville in the search box, and click on Huntsville(Alabama), United States. Close the Location window. This puts you in Huntsville. Remember, at this moment, there is a total eclipse in Nashville. •

Is there a total eclipse in Huntsville, Alabama at this time? ______________________________

•

Is it easy to see a Solar Eclipse? Why or why not? _____________________________________ ______________________________________________________________________________

Eclipses are fascinating and beautiful events that can tell us a lot about how the Earth, Moon and Sun move around each other. By simply applying the laws of gravity and some geometrical intuition, we can understand eclipses in a deep way. Write a conclusion that explains what you learned in this assignment. _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________

6