Stellarium – The Eclipse of the Moon
Astronomy 5 Name: _______________________ Date: _________________________ Total Eclipse of the Moon (Stellarium Exercise #5) An eclipse is one of the most dramatic occurrences in nature. During a ‘lunar eclipse’ the bright, full Moon will gradually darken, turning a deep red color for up to an hour! During a ‘solar eclipse’ the daytime sky can become dark enough for a few minutes that bright stars can be seen! Many ancient cultures attributed these dramatic events to supernatural causes, but today we know that eclipses are produced by the alignment of the Sun, Moon and Earth. Our understanding of the Moon’s orbit around the Earth and the Earth’s orbit around the Sun are quite precise and, as you will see in this exercise, we can predict the timing of the different ‘contacts’ of eclipses down to the nearest few seconds and we can also predict with extreme accuracy where on Earth an eclipse will be visible. Part A: Lunar Eclipses A lunar eclipse occurs when the Earth blocks the Sun’s light from reaching the Moon. In other words, a lunar eclipse occurs when the Moon passes into the shadow of the Earth. Stellarium is an excellent resource to help us understand exactly how this occurs, and if you follow these steps you can view an eclipse! • • • • • • • • Q1: • Launch Stellarium. Make sure you are viewing the sky from Los Angeles. Change the date and time to May 26, 2021, at 1 hour (1 am). Make sure the Atmosphere and Ground are turned off (use the ‘A’ and ‘G’ keys). Put a check mark in the Show Planet Markers box in the SSO sub-menu of the View window. Close the View window. (If you don’t see them, you can 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’. You are now viewing the sky from the perspective of the Sun! (Important Note: You may need to turn the Atmosphere and the Ground off again…they sometimes reset when changing views.) Now search for the Moon and center it. (After selecting the Moon from the Search window, press the ‘space bar’ to center the Moon.) Make the Ecliptic horizontal by Switching to Equatorial Mount (use the telescope icon button in the bottom toolbar, or you can use ‘CTRL-M’ to do this as well). Zoom in until the Moon is fairly large. (The Field of View, FOV, should be around 0.01°). The Earth should be about 4 times larger than the Moon and on the left side of the screen. 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 make time run faster than normal. Continue watching all the way through the eclipse until the Moon is visible again. Q2: Describe what happens. _______________________________________________________________ ____________________________________________________________________________________ Q3: In this simulation, which object is appearing to move…Earth or Moon? _________________________ Q4: During an actual eclipse (and at all moments in time), the Earth and the Moon are both moving through space. However which object’s motion is the most significant in producing the eclipse…Earth or Moon? _____________________________ 1 Q5: When the Moon goes behind the Earth like this, how much sunlight will reach the Moon? (Remember, you are viewing the Moon from the perspective of the Sun!) __________________________________ You just viewed a Lunar Eclipse from the perspective of the Sun. The Earth appears to move between the Sun and the Moon, blocking the Sun’s light from hitting the Moon. Below is a diagram of what’s happening…note how the Moon moves into the Earth’s shadow between points B and C. Let’s see what is happening from our perspective here on Earth during this lunar eclipse. • • • • • Click on the Earth to select it, then press ‘CTRL-G’ to go to the Earth (from the Sun, where you are now). The ‘Atmosphere’ and ‘Ground’ may reappear…turn them off with the ‘A’ and ‘G’ keys as usual. Now Search for the Moon to select and center it. (Remember to press the ‘space bar’ to center the Moon. The Moon will stay centered on the screen as we go through the simulation.) Change the time back to 1 hour (1 am) on May 26, 2021. Lastly, zoom out to a ‘Field of View’ of about 0.8° (or until the Moon fills most of the screen). You should now be looking at the Moon again at 1 am on May 26, 2021, from Los Angeles. • Press ‘L’ three times and watch carefully for a few minutes. You should see a dark, curved shadow begin to move across the Moon from the left side. This is the shadow of the Earth, as the Moon begins to enter the eclipse. Important Note: The shadow may not be easily noticeable at first, but by 2 am the shadow will be a little less than one fourth the way on the Moon. If you don’t see the shadow moving across the Moon by 2 am, go back in time and watch again…carefully! This outer shadow of the Earth is called the Penumbra. The moment when the Penumbra first touches the Moon, is called First Contact (or P1). • • Stop time by pressing the ‘7’ key. Run time backwards and forwards (use the ‘J’, ‘K’ and ‘L’ keys) to try and find the moment of first contact. It may be difficult to determine the exact moment when the Earth’s shadow first falls on the Moon, but do your best! Q6: What is your estimated time of first contact? ____________________________________________ • Go to this website to find some details about this eclipse: https://moonblink.info/Eclipse/eclipse/2021_05_26 Q7: Based upon the information on the website, what will be the actual time of first contact in Los Angeles? (Be sure to convert from Universal Time (UT) to Pacific Daylight Time) _____________________ • Press the ‘L’ key a few times to make time move quickly, and watch the penumbra move across the face of the Moon. Press ‘7’ to stop the motion around 2:30 am. 2 Q8: Which direction does the shadow move in as it crosses the Moon? ______________________________ 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 the real world it can be a bit difficult to tell when the Umbra shadow begins to cross the Moon, however, it should be easy enough with Stellarium! The moment the umbral shadow first touches the Moon is called Second Contact (or U1). • • • Q9: Press ‘L’ two or three times to continue to observe the Penumbra shadow move across the Moon. At a certain moment, you should see the deeper Umbral shadow begin to move across the Moon. Use the ‘J’, ‘K’ and ‘L’ keys to run time back and forward to try and find the moment of second contact. Stop time (press the ‘7’ key) at the moment of second contact (when the umbral shadow first starts to move across the Moon.) What time do you estimate second contact to occur at? ______________________________________ Q10: What is the official time of second contact? (See the ‘moonblink’ website link above, and again, be sure to convert from UT to PDT). __________________________________ • Q11: Now press ‘L’ two or three times and watch as the umbral shadow moves across the Moon. Is the shadow straight or curved? ____________________________________________ Q12: Based on your answer to Question 9, what can you deduce about the shape of the object casting the shadow? ____________________________________________________________________________ (Interesting Historical Note: 2,300 years ago, the Greek philosopher Aristotle deduced the shape of the Earth based upon his observation of an eclipsed Moon, and this has remained an important piece of evidence for the shape of the Earth ever since. The idea the Earth was flat, was never a widely held belief by any culture, but the idea the Earth was at the center of the Universe was indeed believed by all ancient cultures.) Q13: Notice the direction the umbral shadow moves in as it crosses the Moon. Does this direction remain the same, or does this direction change as the shadow moves across the Moon? ______________________ When the Moon has fully entered the umbral shadow, this is the beginning of ‘Totality’. No light from the Sun now reaches the Moon. (The Moon is fully in the shadow of the Earth.) The beginning of totality is called Third Contact (or U2). • Stop time (press ‘7’) when the umbral shadow has just fully covered the Moon. Q14: What is your estimate of the time of third contact? (What time do you estimate the Moon to have entered totality?) ____________________________________ Q15: According to the ‘official’ schedule on the ‘moonblink’ website (link shown above), what time does totality begin? (Convert to PDT!) _______________________________________ Notice that Stellarium shows the Moon has having a deep red color during totality. This is not a mistake, and is an accurate representation of what the Moon looks like during a total lunar eclipse. This deep red color is caused by the fact that long wavelengths of sunlight (which are red in color) pass through the thin atmosphere surrounding the Earth better than short wavelengths do, and when these long wavelengths get refracted by the Earth’s atmosphere (which changes their direction slightly) they light up the Moon to some degree. This red color of the Moon during a total eclipse is sometimes called ‘blood red’, and the Moon is sometimes referred to as a ‘Blood Moon’ during a total lunar eclipse. 3 • Press ‘L’ several times and continue to observe the Moon until first the umbral shadow and then the penumbral shadow are completely gone and the Moon is fully illuminated again. The eclipse is now over! Q16: What time do you estimate for the end of the eclipse? _______________________________________ Q17: According to the ‘moonblink’ website, what time does the eclipse actually end? (Convert to PDT!) ___________________________________ (Note: Don’t worry if your answers to Q6, Q9, Q14 and Q16 are not exactly the same as Q7, Q10, Q15 and Q17 respectively…it is not that easy using Stellarium to estimate the times for the penumbra and umbra shadows to begin and end their movements across the Moon.) Q18: How long did the entire eclipse last (from First Contact to the end of the Eclipse)? _____________________________________________________________________ (Note: There are 6 ‘contacts’ total for a lunar eclipse. Here’s the Wikipedia website that lists them all! https://en.wikipedia.org/wiki/Template:Total_lunar_eclipse_contacts) Before we finish with this lunar eclipse, let’s see what things would look like if we were on the Moon! • • • • • • Start by change the time back to 1 hour on May 26, 2021. Then search for the Moon (if necessary), select it, then press ‘CTRL-G’ to go to its surface. You may need to turn off the Atmosphere and the Ground again. (Use the ‘A’ and ‘G’ keys as usual.) Now Search for the Sun, and then press ‘space bar’ to center it and lock it in place. Adjust the ‘Field of View’ (FOV) to about 1°. (You should be looking at a good size image of Sun!) Press ‘L’ three or four times and watch the eclipse! Q19: Describe what you see: ________________________________________________________________ ____________________________________________________________________________________ Q20: If you were on the Moon you would not call this event a lunar eclipse. What would you call it? (Which object is being ‘eclipsed’ or blocked from your view?) ______________________________________ Lunar Eclipses are beautiful, and relatively easy to see – anyone on the side of the Earth that faces the Moon during an eclipse can see the eclipse as it happens. May 26, 2021 is the next time an eclipse will be visible from Los Angeles! Part B: Solar Eclipses Now let’s use Stellarium to help us learn about Solar Eclipses. These occur when the Moon comes between the Sun and the Earth, and so the Moon’s shadow falls on Earth. Here’s a diagram of what’s happening during a Solar Eclipse: 4 • • • • • • • • Start by selecting the Earth by clicking on it and pressing ‘CTRL-G’. Change your location to Cleveland, Ohio by opening the Location menu and typing Cleveland into the Location Search box. Close the Location window. Now Search for the Sun to select and center it. Adjust the Field of View (use ‘page up’ or ‘page down’) to about 1°. Change the Date & Time to April 8, 2024, at 13 hours (1 pm) in the afternoon. Finally, turn the Atmosphere and Ground back on (use the ‘A’ and ‘G’ keys). Press ‘L’ two or three times. You should see the Moon approaching the Sun in the sky. Stop time (‘7’) just as the Moon starts to block the Sun’s edge. Q21: What phase must the Moon be in during this eclipse? __________________________________ Q22: 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. Q23: What time does totality start? _______________________ During totality we can see a part of the Sun that we normally don’t see…the Corona! (No viruses here!) Stellarium shows a nice, accurate image of the corona. Q24: Briefly describe the Sun’s corona as it is shown in Stellarium. _________________________________ ____________________________________________________________________________________ • Now carefully let time pass at normal speed (use the ‘K’ key) until the Sun just begins to peek out from behind the Moon. Q25: What time does totality end? ________________________________ Q26: How long did totality last? ________________________________________ Use this website to check your answers for the Q22, Q23 and Q25. The website has a nice animation too! https://www.timeanddate.com/eclipse/in/usa/cleveland?iso=20240408 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 Pittsburg, Pennslyvania which is a little more than 100 miles southeast of Cleveland. Close the Location window. You are now viewing the Sun from Pittsburg. Remember, at this moment, there is a total eclipse in Cleveland. Q27: Is there a total eclipse in Pittsburg at this time? __________________________ • Press ‘L’ a couple of times to run time forward and watch the eclipse from Pittsburg. 5 Each year on average we have about two lunar eclipses and two solar eclipses that are visible from somewhere on Earth. However, we are not equally likely to view lunar and solar eclipses from a given location on Earth. Q28: Which type of eclipse are you more likely to see from a given location on Earth, a total lunar eclipse, or a total solar eclipse, and why? __________________________________________________________ ____________________________________________________________________________________ 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 describing what you learned in this exercise and mention any difficulties you might have had performing the exercise. __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ 6
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