Transit of Mercury Lab: Motion and Shadows in the Sky A Lab for Upper Elementary Students Educator Instructions What follows is a lab experience developed for upper elementary students by Katherine Benson of Agnes Scott College, using solar telescope images of the transit of Mercury across the sun on 11/08/2006. Student use the solar telescope images, and a solar map on transparency film, to plot Mercury s transit path and a large sunspot visible at the time. With clear step-by-step directions, students establish a scale for their solar map, measure the sunspot, and calculate its actual size. Using an included Reference Sizes chart, they then rank the actual sizes of Mercury, the sunspot, and the moon. Students then consider the transit images, along with images of a solar eclipse when the moon s shadow crosses the sun to rank the apparent sizes of Mercury, the sunspot, and the moon. They then consider, for reflection or classroom discussion, how the different orderings can make sense; that is, why astronomical objects apparent size differs from their actual size, so that larger (but more distant) objects can appear smaller than smaller (but nearby) ones. Student concepts addressed include plotting, map scales, and actual and apparent size of astronomical objects. This lab can be found online as follows: www.mathcs.emory.edu/ mic/kbenson/mercury/eleminstructions.pdf these teacher instructions www.mathcs.emory.edu/ mic/kbenson/mercury/mercuryelem.pdf the lab handout, for students www.mathcs.emory.edu/ mic/kbenson/mercury/allimages.pdf 5 Mercury transit solar telescope images; 2 solar eclipse images; solar grid www.mathcs.emory.edu/ mic/kbenson/mercury/teacherpak.pdf All 3 files concatenated together (if you received this as a printed packet, you have a printout of this file.) To use this lab in your class: Print out, or detach, the remaining pages of this teacherpak. Take out the last page the solar grid and xerox it onto transparency film, one copy per student. The remaining pages form two handouts, to be xeroxed one copy per student: first, the two-page lab handout for students to fill out, and second, the supporting images handout, containing 5 Mercury transit images and 2 solar eclipse images. As noted in the lab handout, students then receive the following to complete the lab: the lab handout, the images packet, the solar grid transparency, an overhead transparency marker, a ruler, 1
and a calculator (there are only 2 calculations, so you could require hand calculation if preferred). Alternatively, if your students can access a computer room, you could have students point their web browser to the online images, and plot by overlaying the transparency grid directly on the images onscreen. This saves paper (no images packet to distribute) and lets you use the computers calculators. However, it does require you to resize the solar grid to the onscreen image when xeroxing it onto transparencies (measure the solar diameter of the onscreen image, divide this by the solar diameter of your printed solar grid, then multiply by 100 to obtain the enlarge/reduce magnification for xeroxing; the resulting overhead solar grid should overlay the onscreen images perfectly, for plotting). Credits and Contact Info: Katherine Benson of the Physics and Astronomy Department, Agnes Scott College, developed this lab for the 2006-07 4th grade of Fernbank Elementary School, Atlanta, Georgia (Dekalb County). Fernbank s 4th grade science teacher, Elisabeth Beckwith, guided selection of appropriate teaching goals, to fit her Outer Space unit in a 4th grade science curriculum coordinating International Baccalaureate and Georgia standards. Work of the author K Benson was supported by NSF grant PHY-0457140. She can be reached at bensonphysics@gmail.com Please e-mail if you use the lab, commenting on the grade, school, and curriculum unit or standards you used the lab for; its success with your students; and any issues you experienced. NOTE: K Benson has also designed a more quantitative lab on this same Mercury transit using student plots to calculate Mercury s orbital speed, then relate to Kepler s second law for high school physics or college intro astronomy students. See www.mathcs.emory.edu/ mic/kbenson/mercury/professorpak.pdf for this more advanced lab. Image credits: 5 Mercury transit solar telescope images live screenshots on 11/08/06 from SOHO solar telescope, from zeus.nascom.nasa.gov/ soc/transits/mercury/20061108/latest MDI dklimb 512x512.gif Now available among archived MDI images at http://sohowww.nascom.nasa.gov/soc/transits/mercury/20061108/realtime.html Solar eclipse image 1 (partial) Downloaded January 2007 from http://users.tellurian.net/skyguy/solar-eclipse-xmas-day-2000.jpg Solar eclipse image 2 (complete) Downloaded January 2007 from http://umbra.nascom.nasa.gov/eclipse/images/freds excellent eclipse img.jpg 2
Katherine Benson, Agnes Scott College: Handout #1 Upper Elementary Outreach January 2008 Purpose: Transit of Mercury Lab: Motion and Shadows in the Sky 1. To observe the transit of Mercury across the sun on 11/08/2006, using images from the solar telescope SOHO 2. To plot Mercury s observed positions and trajectory, on a solar map 3. To observe sunspots present in the solar telescope images of 11/08/2006 4. To plot and measure the large observed sunspot, and calculate its true size 5. To discuss size scales in the universe; especially, the difference between actual and apparent size, as viewed from Earth Reference Sizes: Mercury Sun Moon angular diameter (from Earth) 10 1920 = 0.54 o (200 x Mercury, 1 x moon) 1860 (gives apparent size) physical diameter 4900 km 1,400,000 km (300 x Mercury, 400 x moon) 3500 km (gives actual size) distance to Earth 0.68 AU 1.0 AU (1.5 x Mercury, 400 x moon), 0.0026 AU (on 11/08/06) Conversion: 1 AU = 150,000,000 km Procedure: In this lab you are given 1. 5 images from the solar telescope SOHO, taken during the Mercury transit of 11/08/06 2. two images of a solar eclipse (as the moon transits in front of the sun) 3. A solar map on transparency film 4. a transparency marker 5. a ruler 6. a calculator All images are also online at www.mathcs.emory.edu/ mic/kbenson/mercury/allimages.pdf Using these, you will 1. plot the observed positions of Mercury during the transit 2. sketch Mercury s path across the sun 3. trace and measure the large sunspot on the left side of your images of the sun 4. calculate the sunspot s true size (using the sun s actual diameter to set the scale of your solar map) 5. consider the relationship between solar system objects actual size, and their size as perceived against the sun 1
Plot 1. Lay your transparency map over the first solar image from 11/8/06, lining up the circumference of your longitude/latitude grid with the outside edge of the sun. 2. Using transparency marker on your transparency map, trace the sunspot you see on the left side of the sun, just below the equator. The sunspot has a dark inner core, surrounded by a less-dark margin; trace and show both. 3. Using transparency marker on your transparency map, mark a dot on top of the tiny black spot, below and to the right of the sunspot. This is the shadow of Mercury, crossing in front of the sun. Label this dot 1. 4. Now lay your transparency map over the second solar image, taken 54 minutes later. The sunspot will be unchanged, but Mercury has moved! Mark a dot on top of Mercury, and label it 2. 5. Repeat for solar images 3 through 5, marking dots for the position of Mercury in each one, and labeling them 3 through 5. 6. Draw a line through your plotted points, extending to both edges of the solar disk. This is the path, or trajectory, that we saw Mercury follow across the sun, left to right, during 4 hours and 58 minutes on November 8, 2006! You ve now made your plot of your observations. Next, you will analyze and discuss it. Sunspot Size 1. Measure the diameter of the sunspot you traced on your map, in cm. (Include both the dark inner core and the less-dark margin in your measurement; measure diameter along the largest direction.) 2. Measure the sun s diameter, on your map, in cm. 3. Divide the sunspot diameter you measured, by the sun diameter you measured. This tells us the sunspot s size, as a fraction of the sun s size. (your calculator will give you this fraction, expressed as a decimal) 4. Multiply this ratio you just calculated by 1,400,000 km, the actual diameter of the sun. This gives the actual, or physical, diameter of your sunspot. 5. How does the sunspot s actual diameter compare with Mercury s actual diameter? with the moon s? (Use the Reference Sizes chart on the front for actual diameters of Mercury and the moon.) 6. Put in order of increasing actual diameter: Mercury, the sunspot, the moon. Apparent and Actual Size 1. Consider your 2 pictures of a solar eclipse; that is, of the moon s shadow as it crosses in front of the sun. Comparing to your plot, how does the size of the moon s shadow compare with Mercury s shadow, during its transit? With the sunspot you saw? 2. The size that you see, from Earth, is called the apparent size. This is given by the size you see in all of these solar images, since they are viewed from Earth, against the background of the sun. Put in order of increasing apparent size: Mercury, the sunspot, the moon. 3. You ve now ranked Mercury, the sunspot, and the moon, in two ways: by apparent size, in this section, and by actual size, in the last section. Consider, or discuss with your class, the following question: how can both of your answers make sense: that is, how can apparent size differ from actual size, so much that bigger objects look smaller, even much smaller? Can you think of a demonstration you could do to show your reasoning, right inside your classroom? 2