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Module 3 Life of a Star Ancient Cosmic Explosions Activity Guide ANCIENT COSMIC EXPLOSIONS - ACTIVITY GUIDE 1 Introduction In this project you will study LCOGT observations of supernova remnants to measure how fast they are expanding and calculate how long ago the supernova explosion occurred. Materials • • FITS file of a supernova remnant A computer with ds9 image editing software installed Background Science Supernovae Supernovae are the violent explosions of stars occurring at the end of their lives. On average, one supernova goes off every 50 years or so in our Galaxy. Supernovae release more energy in a single instant than the Sun will produce in its whole lifetime! If the nearest massive star, Betelgeuse in the constellation Orion, were to go supernova it would (for a short time) be brighter than the full moon. There are two main types - Type Ia and II. Type II are the explosions of very massive stars with mass greater than 8 times the mass of the Sun. Type Ia are the explosions of stars similar in mass to the Sun, which have a binary companion and become unstable. In order these images show an artist’s impression of a Type II supernova, a Type Ia supernova and the Spaghetti Nebula supernova remnant. Credit: ESO Type II -These are caused by massive stars that 'live fast and die young', using up all of their hydrogen and helium fuel in only a few million years — thousands of times faster than the Sun burns its fuel. When the fuel supply is exhausted the star must burn heavier and heavier elements until, finally, when it can do no more to keep itself alive, the inner parts of the star collapse to form a neutron star or black hole, and the outer parts are flung off in an explosion we call a supernova. ANCIENT COSMIC EXPLOSIONS - ACTIVITY GUIDE 2 Type Ia - These happen when a star similar in mass to the Sun reaches the end of its life as a white dwarf star - a hot, dense core. If this hot core has a binary companion star (two stars orbiting around a common centre of mass), the white dwarf will pull matter from the companion star onto its surface, until it becomes unstable and explodes as a supernova. Type Ia supernova can also be caused by two white dwarfs merging to the same end. Supernova Remnants No matter whether it is a Type Ia or Type II supernova, the enormous explosions from these stars ejects material into the surroundings at very high velocities, sweeping up the surrounding interstellar gas into a shell or a giant bubble. This is known as a supernova remnant. The ejected material and the swept-up compressed gas are very hot. The shell (or bubble) shines at different wavelengths, mainly in the X-ray, optical and radio. Supernova remnants are studied at many different wavelengths from optical light to X-rays. Different things are happening in different wavelengths; when we observe in, say the X-ray, we are looking at the bits of the shell that are much hotter than the bits shining in the optical. In this activity we will concentrate on the optical emission that comes from the interaction between the outward moving shell and the interstellar material that surrounds the supernova. The material is compressed and heated to 10 thousand degrees Kelvin. In the optical we can see the shocks caused by the expanding material as it sweeps outwards at high velocities. Using the H-alpha filter we will specifically see hydrogen gas. Cassiopeia A Cassiopiea A is the brightest radio object in the sky so it is very well studied (and very beautiful)! It exploded about 300 years ago. It is around 11,000 light years away and is about 8 arcmin across. It was a Type II Supernova i.e. it was formed by the explosion of a massive star. E0102 72: E0102-72 is a supernova remnant located in a nearby dwarf galaxy called the Small Magellanic Cloud. Summary of Terms symbol description value KE kinetic energy of shell 1044 J density density of surroundings 10-21 kg m-3 D distance to the supernova Find this value on the web ANCIENT COSMIC EXPLOSIONS - ACTIVITY GUIDE 3 Preparation In this project you will choose one of the following supernova remnants to study with the final goal of using observational data to calculate its expansion velocity and its age. 1. Cassiopeia A (Cas A), 1. E0102-72 You can either use observations from the LCOGT data archive or make your own observations. If you are using images from the LCOGT data archive visit: http://lcogt.net/observations Use the search bar to find images of the supernova remnant you have chosen. Find an image taken using the red (R-band) or H-alpha filter. Once you have clicked on an image the filter will be listed on the right-hand menu. Just go to the webpage and type in the name of the supernova remnant you want, click on the relevant thumbnail and select ‘FITS” from the right-hand options bar. Be aware that the red filter may be listed as ‘Bessell-R’. If you are taking you own observations, please note that these objects are very faint and require long exposure times. The table below provides information on the exposure time needed for each object and which filters to use. A full guide to observing with LCOGT can be found online at: ANCIENT COSMIC EXPLOSIONS - ACTIVITY GUIDE 4 http://lcogt.net/files/OnSkyGuide.compressed.pdf R-band (s) H-alpha (s) Cas A 120 120 E102-72 200 200 Instructions 1. Start ds9 and open the supernova remnant FITS file you have chosen to work with. 2. Your image may appear black to begin with, try out different options in the toolbars. You are looking for an image that shows as much detail as possible of the supernova remnant. This image of Cas A is shown demonstrating the following values: scale > linear > 99%, colour > cool ANCIENT COSMIC EXPLOSIONS - ACTIVITY GUIDE 5 You will now determine the diameter of the remnant by placing a circle over the shell. This will tell you the angular size of the remnant. 2. Go to Region > Shape > Circle 3. Draw a circle over the supernova, marking out the shape of the shell. Aim to be as exact as possible. 4. Go to Region > Get Information 5. A box will appear showing the centre co-ordinates of the circle. 6. Next, click on the box marked physical next to the Radius values. Select WCS and choose the type of units you want - degrees. The example below shows the radius = 0.0301 degrees. ANCIENT COSMIC EXPLOSIONS - ACTIVITY GUIDE 6 7. Note down your radius values below. Radius in degrees = ___________________________________________________ Now that you know the diameter of your supernova remnant, you will calculate the age of the supernova remnant and find out when the source star exploded. Now that you have the radius, you will need to calculate the distance to your supernova in metres. 8. Calculate the distance to your supernova in metres and not your result in the table below. Remember that 1 light year = 9.5 × 1015 m. ANCIENT COSMIC EXPLOSIONS - ACTIVITY GUIDE 7 Name Distance (light years) Distance (metres) Cas A 10,200 E102-72 190,000 9. The next step is to work out the radius of the supernova remnant in metres by calculating the diameter (d) which is twice the radius. Do this using the equation below: d = D tan (θ) D = distance to remnant in metres d = diameter of remnant in metres θ is the angle on the sky in degrees 10. Begin by calculating the angle on the sky for your supernova. This will be your radius from step 7, but you will need to convert your radius from degrees into radians: 360 deg = 2π rad or 1 deg = 0.0174 rad. Note your result on the table below. 11. Next calculate the diameter of your supernova remnant and use this value to calculate the radius: 0.5 x diameter. Note down your results in the table below. Θ degrees Name Diameter (m) Radius (m) Cas A E102-72 12. Now that you have the radius, you can work out the volume of your supernova remnant, a figure that will allow you to work out its mass. Where V is volume and the R is the radius in metres. Use the equation: V = (4/3) π R3 Enter your result into the table below. In this table you will also find a value for density. Remember that density is a measure of how much mass is in a given volume. For example, the density of water is 1000 kg m-3, whereas the same volume of iron or lead will be much heavier. Lead is 10 times denser than water. During the initial collapse and rebound of the star's core when a supernova occurs, the outer layers of the star's material are ejected, yet most of the gas in a supernova remnant is not from the star but is collected afterward. As the remnant expands, it sweeps up the surrounding interstellar medium, material which builds up around the edge of the shockwave. The volume through which ANCIENT COSMIC EXPLOSIONS - ACTIVITY GUIDE 8 the remnant has expanded and the density of the interstellar medium can be used to calculate the mass of the remnant. In the space between the stars, the density of material is very low - there isn’t much out there! In fact, the average density in space is about 1 x10-21 kg m-3! This is the density value we will be using in the calculations for our supernova remnant. 13. With a value for both density and volume you can calculate the mass of your supernova remnant: Mass = density x volume Enter your result into the table below. Name Volume Density (kg m-3) Cas A 1 x10-21 kg m-3 E102-72 1 x10-21 kg m-3 Mass (kg) 14. The next step is to calculate the velocity of the material in your supernova remnant. A typical supernova explosion will eject about 1044 Joules of energy into the surroundings. This is the value you will use for kinetic energy. Use the following equation, where M is mass: v = (2 K.E. /M)1/2 Velocity =___________________________________ 15. The final step is to calculate the age of your supernova. You can do this using the distance to your supernova remnant and its expansion velocity: Time = distance / velocity Distance is actually the size of the remnant (i.e. the distance the shell has travelled since the explosion) and time is actually the age of the remnant. Your result will be in seconds, convert it to years and note down your result below. Note: this assumes that the exploding material has been travelling outwards at a constant speed. Age of your supernova remnant =________________________________ years ANCIENT COSMIC EXPLOSIONS - ACTIVITY GUIDE 9 Congratulations, you just calculated the age of a real supernova remnant! ANCIENT COSMIC EXPLOSIONS - ACTIVITY GUIDE 10 Ancient Cosmic Explosions Answer Sheet ANCIENT COSMIC EXPLOSIONS - ACTIVITY GUIDE 1 Name Radius (degrees) Distance (metres) Cas A E102-72 Name Θ degrees Diameter (m) Radius (m) Volume Mass (kg) Velocity Cas A Kepler E102-72 Name Cas A E102-72 Name Age Cas A E102-72 Conclusion 1. Energy given off by XX watt light bulb in an hour =. Supernova gives off equivalent energy of XX light bulbs in for one hour, or XX hours with one XX watt light bulb. 2. Mass of Sun = ANCIENT COSMIC EXPLOSIONS - ACTIVITY GUIDE 2 ANCIENT COSMIC EXPLOSIONS - ACTIVITY GUIDE 3 symbol description value KE kinetic energy of shell 1044 J density density of surroundings 10-21 kg m-3 D distance to the supernova Find this value on the web ANCIENT COSMIC EXPLOSIONS - ACTIVITY GUIDE 4 Star in a Box Teacher’s Guide STAR IN A BOX: ACTIVITY GUIDE 1 Introduction Have you ever wondered what happens to the different stars in the night sky as they get older? This activity lets you explore the lifecycle of stars. Star in a Box allows stars with different starting masses as they change during their lives. Some stars live fast-paced, dramatic lives; others change very little for billions of years. The webapp visualises the changes in mass, size, brightness and temperature for all these different stages. Objectives • • • Describe the relationship between a star's mass, its age, and its position on the Hertzsprung-Russell diagram Describe the relationship between a star's mass and its life span Name the stages of a star's lifecycle, in order, for several masses of star Materials • • • • 2x 1-metre ruler Coloured paper (white, blue, orange, red, yellow) Projector and Star in a Box PPT Printed Axis Labels Per student: • Computer with Internet access • Scissors • Stellar Fact Sheet • Star in a Box Student Worksheet (Beginner, Intermediate or Advanced) Preparation Before beginning the activity, clear a table or floor space and lay out your rulers at a 90° angle, these will act as the Y-axis and X-axis for your H-R diagram. The Y-axis will represent Luminosity relative to the Sun (L ), this will be shown logarithmically from 0.0001 to 1000000. The X-axis will show Temperature in Kelvin (K), the hottest temperature should be at least 35,000K and the lowest around 2,000K. STAR IN A BOX: ACTIVITY GUIDE 2 Create a model of the Sun for reference. Using yellow paper, draw a circle with a radius of 2.5cm and cut it out. Place this on the H-R diagram at 6,000 K and 1L Instructions 1. Begin by introducing your students to the lifecycle of a star using the Star in a Box powerpoint presentation. The presentation has been designed to suit a variety of abilities. A rough guide to the levels: ○ ○ ○ Beginner: KS3 Intermediate: KS4 Advanced: KS5 2. Hand out the stellar fact sheets, one per student. Assign each student a star. For beginners or younger students (KS3), stick to the Main Sequence stars. If you are doing the activity with older students (A-level and above) or for the second time, include the Other Stars. 3. Assign each of your students a star. Using the model Sun prepared earlier as a reference for mass and colour, the students will each create a model of their star. 4. Ask the students to collect a piece of paper. They must choose the correct colour for their star based on temperature (e.g. Betelgeuse should be red) Spectral Class Temperature Colour O 30,000 - 60,000 K Blue B 10,000 - 30,000 K Blue-white A 7,500 - 10,000 K White F 6,000 - 7,500 K Yellow-white G 5,000 - 6,000 K Yellow K 3,500 - 5,000 K Orange M < 3,500 K Red 5. They will need to draw a circle of the correct size relative to the Sun model and the other stars on the Stellar Fact sheet. Note that even the largest star will be no bigger than the size of an A4 sheet. 6. Assign any remaining stars to the students so that you end up with circles representing all stars on the sheet. 7. Next, ask the students to place their star on the H-R diagram one at a time. 8. Once all of the stars have been plotted, gather the class around the H-R diagram. Does your plot look like the H-R diagrams you looked at earlier (during the Star in a Box presentation)? Do you see the Main Sequence, red giants, white dwarfs etc? Ask your students the following questions: ○ What is the approximate temperature of the Sun? STAR IN A BOX: ACTIVITY GUIDE 3 ○ ○ ○ What colour would a star with the following surface temperature be: 18000K, 2000K, 10000K What factor affects the colour of a star? What factor affects the luminosity of a star? 9. Ask the students to go back to their seats and ensure each student has access to a computer with Internet access. 10. Hand out the Star in a Box Student Worksheets (one per student) and ask them to log on to http://lcogt.net/siab/ and complete their worksheet. This will take approx. 30 minutes. 11. When the students have finished the online activity, gather them around the H-R diagram again. Ask them to answer the following questions: ○ Most of the stars on the H-R Diagram are classified as which type of star? ○ What type of star has a high temperature but a low luminosity? ○ What type of star has a high temperature and a high luminosity? ○ What type of star has a low temperature but a high luminosity? ○ What type of star has a low temperature and a low luminosity? ○ Is the surface temperature of a white dwarf higher or lower than a red supergiant? ○ What property of a star uniquely determines where it will be on the Main Sequence? ○ If you increase the temperature of a star and leave it’s size the same, which way would it move on the H-R diagram? ○ How do we know a star is larger than the Sun from it’s position on the H-R diagram? ○ What do we know about stars directly below the Sun on the H-R Diagram? STAR IN A BOX: ACTIVITY GUIDE 4 Star in a Box Teacher’s Answer Sheet STAR IN A BOX: ACTIVITY GUIDE 1 Answers 8. What is the approximate temperature of the Sun? 6000 K What colour would a star with the following surface temperature be: 18000K (Blue), 2000K (Red), 10000K (Blue-White) What factor affects the colour of a star? (Temperature) What factor affects the luminosity of a star? (Size and Temperature) 11. Most of the stars on the H-R Diagram are classified as which type of star? (Main Sequence) What type of star has a high temperature but a low luminosity? (White Dwarfs) What type of star has a high temperature and a high luminosity? (Blue Giants) What type of star has a low temperature but a high luminosity? (Red Giants) What type of star has a low temperature and a low luminosity? (Red Dwarfs) Is the surface temperature of a white dwarf higher or lower than a red supergiant (higher) What property of a star uniquely determines where it will be on the Main Sequence? (Mass) If you increase the temperature of a star and leave it’s size the same, which way would it move on the H-R diagram? (Left) How do we know a star is larger than the Sun from it’s position on the H-R diagram? (It sits higher) What do we know about stars directly below the Sun on the H-R Diagram? (They are smaller) STAR IN A BOX: ACTIVITY GUIDE 2 Exploring the Sunspot Cycle Teacher’s Guide EXPLORING THE SUNSPOT CYCLE: TEACHER’S GUIDE 1 Introduction For over 300 years, activity on the surface of our star has been monitored continuously. In this project you will plot and anaylse historical sunspot data to find out if any patterns emerge when sunspot numbers are plotted over time. Does the number of sunspots change in a regular cycle? Can we predict how many sunspots there will be at a point in the future? Do sunspot cycles have a faster rise or decay time? Materials: • • Computer with internet access Excel spreadsheet software or equivalent Learning Objectives • • • • Realise that the number and intensity of sunspots on the surface of the Sun waxes and wanes in an approximate 11-year cycle. Practise working with a spreadsheet programme. Use real scientific data and scientific method to investigate a hypothesis and present your findings. Practise communication skill when presenting your results to the group. Background Information i. The Sun The Solar System is made up of the Sun and everything that orbits around it: the Earth, the planets, asteroids and comets. The Sun makes up 99.9% of all the mass in our Solar System. The Earth orbits around 150 million kilometres from the Sun, although due to the elliptical shape of Earth’s orbit this distance varies throughout the year. The Sun is an average star - there are many other stars which are much hotter or much cooler, and intrinsically much brighter or fainter. However, since it is by far the closest star to the Earth, it looks bigger and brighter in our sky than any other star. EXPLORING THE SUNSPOT CYCLE: TEACHER’S GUIDE 2 With a diameter of about 1.4 million kilometers (860,000 miles) it would take 109 Earths strung together to be as long as the diameter of the Sun. The Sun is mostly made up of hydrogen (about 92.1% of the number of atoms, 75% of the mass). Helium can also be found in the Sun (7.8% of the number of atoms and 25% of the mass). The other 0.1% is made up of heavier elements, mainly carbon, nitrogen, oxygen, neon, magnesium, silicon and iron. The Sun is neither a solid nor a gas but is actually plasma (see below). This plasma is tenuous and gaseous near the surface, but gets denser down towards the Sun's fusion core. ii. Plasma Plasma is one of the four fundamental states of matter (the others being solid, liquid, and gas). When air or gas is ionized, plasma forms with similar conductive properties to that of metals. Plasma is the most abundant form of matter in the Universe, because most stars are in plasma state. iii.. Layers of the Sun EXPLORING THE SUNSPOT CYCLE: TEACHER’S GUIDE 3 The Sun can be divided into six layers. From the center out, the layers of the Sun are as follows: the solar interior composed of the core (which occupies the innermost quarter or so of the Sun's radius), the radiative zone, and the the convective zone, then there is the visible surface known as the photosphere, the chromosphere, and finally the outermost layer, the corona. The energy produced through fusion in the Sun's core powers the Sun and produces all of the heat and light that we receive here on Earth. The process by which energy escapes from the Sun is very complex. Since we can't see inside the Sun, most of what astronomers know about this subject comes from combining theoretical models of the Sun's interior with observational facts such as the Sun's mass, surface temperature and luminosity which is the total amount of energy output from the surface. a. Core All of the energy from the Sun that we detect as light and heat originates from nuclear reactions deep inside the Sun's high-temperature "core." This core extends about one quarter of the way from the center of Sun where the temperature is around 15.7 million kelvin (K) its surface, which is only 6000 K. b. Radiative Zone Above this core, we can think of the Sun's interior as being like two nested spherical shells that surround the core. In the innermost shell, right above the core, energy is carried outwards by radiation. This "radiative zone" extends about three quarters of the way to the surface. The radiation does not travel directly outwards in this part of the Sun's interior, the plasma density is very high, and the radiation gets bounced around countless numbers of times, following a zig-zag path outward. It takes several hundred thousand years for radiation to make its way from the core to the top of the radiative zone. In the outermost of the two shells, where the temperature drops below 2 million K the plasma in the Sun's interior is too cool and opaque to allow radiation to pass. Instead, huge convection currents form and large bubbles of hot plasma move up towards the surface (similar to a boiling pot of water that is heated at the bottom by a stove). Compared to the amount of time it takes to get through the radiative zone, energy is transported very quickly through the outer convective zone. c. Convective Zone The convective zone is the final 30 percent of the sun's radius, dominated by convection currents that carry the energy outward to the surface. These convection EXPLORING THE SUNSPOT CYCLE: TEACHER’S GUIDE 4 currents are rising movements of hot gas next to falling movements of cool gas – imagine watching herbs in a simmering pot of water. The convection currents carry photons outward to the surface faster than the radiative transfer that occurs in the core and radiative zone. With so many interactions occurring between photons and gas molecules in the radiative and convection zones, it takes a photon approximately 100,000 to 200,000 years to reach the surface. d. Photosphere The Sun's visible surface the photosphere is about 5,800 K. Most of the energy we receive from the Sun is the visible light emitted from the photosphere. The photosphere is one of the coolest regions of the Sun, so only a small fraction (0.1%) of the gas is in the plasma state. The photosphere is the densest part of the solar atmosphere, but is still tenuous compared to Earth's atmosphere, just 0.01% of the mass density of air at sea level). e. Chromosphere Just above the photosphere is a thin layer called the chromosphere. The name chromosphere is derived from the word chromos, the Greek word for color. It can be detected in red hydrogen-alpha light meaning that it appears bright red. f. Corona Above the surface is a region of hot plasma called the corona. The corona is about 2 million K, much hotter than the visible surface, and it is even hotter in a flare. Why the atmosphere gets so hot has been a mystery for decades; SOHO's observations are helping to solve this mystery. iv. Sunspots Sunspots are regions of the solar surface which are cooler than their surrounding, they appear as dark spots on the surface of the Sun. Temperatures in the dark centers of sunspots drop to about 3700 K compared to 5700 K for the surrounding photosphere. They typically last for several days, although very large ones may exist for several weeks. Sunspots are magnetic regions on the Sun with magnetic field strengths thousands of times stronger than the Earth's magnetic field. They usually appear in groups with two sets of spots; one set will have positive or north magnetic field, while the other set will have negative or south magnetic field. The field is strongest in the darker parts of the sunspots - the umbra. The field is weaker and more horizontal in the lighter part - the penumbra. EXPLORING THE SUNSPOT CYCLE: TEACHER’S GUIDE 5 v. Sunspot Cycle In 1610, shortly after viewing the sun with his new telescope, Galileo Galilei made the first European observations of Sunspots. Continuous daily observations were started at the Zurich Observatory in 1849 and earlier observations have been used to extend the records back to 1610. The ‘sunspot number’ is calculated by first counting the number of sunspot groups and then the number of individual sunspots. The "sunspot number" is then given by the sum of the number of individual sunspots and ten times the number of groups. Since most sunspot groups have, on average, about ten spots, this formula for counting sunspots gives reliable numbers even when the observing conditions are less than ideal and small spots are hard to see. Monthly averages (updated monthly) of the sunspot numbers show that the number of sunspots visible on the sun waxes and wanes with an approximate 11year cycle. There are actually at least two "official" sunspot numbers reported. The International Sunspot Number is compiled by the Solar Influences Data Analysis Center in Belgium, which we will work with in this activity, and the NOAA sunspot number compiled by the US National Oceanic and Atmospheric Administration. Detailed observations of sunspots have been obtained by the Royal Greenwich Observatory (UK) since 1874. These observations include information on the sizes and positions of sunspots as well as their numbers. These data show that sunspots do not appear at random over the surface of the sun but are concentrated in two EXPLORING THE SUNSPOT CYCLE: TEACHER’S GUIDE 6 latitude bands on either side of the equator. A butterfly diagram showing the positions of the spots for each rotation of the sun since May 1874 shows that these bands first form at mid-latitudes, widen, and then move toward the equator as each cycle progresses. vi. Coronal Mass Ejection The outer solar atmosphere, known as the corona, is structured by strong magnetic fields. Where these fields are closed, often above sunspot groups, the confined solar atmosphere can suddenly and violently release bubbles of gas and magnetic fields called coronal mass ejections (CME). A large CME can contain a billion tons of matter that can be accelerated to several million miles per hour in a spectacular explosion. Solar material streams out through the interplanetary medium, impacting any planet or spacecraft in its path. CMEs are sometimes associated with flares but can occur independently. vii. SOHO SOHO stands for Solar and Heliospheric Observatory and is a satellite that studies the Sun 24 hours a day, 365 days a year without interruptions. The spacecraft has 12 scientific instruments collecting information about the Sun ranging from activity in the Sun's corona to vibrations deep in the Sun's interior. The Sun is the only star close enough to have real and dramatic effects on our life here on Earth, we certainly expect and hope that improving our observations and our understanding of this beautiful, awesome object will in the course of time bring about beneficial applications. While it's never possible to tell where the quest for knowledge will lead, at this time the area where we have the greatest expectation of useful fallout is in the "space weather" arena. Preparation Before beginning this activity familiarise yourself with the terms and concepts covered in the Background Science. Fill out the Sun Trek worksheet to ensure your understanding of the structure and activity of the Sun. Instructions 1. Download a table of historical sunspot numbers from http://sidc.oma.be/. Click on the link for "Sunspot" > "Data" and select " Monthly mean total sunspot number”. Ensure that you select the CSV file. 2. Import the sunspot data into your spreadsheet programme. Note: If you are not familiar with using a spreadsheet programme, be sure to take the time to go through a tutorial before beginning this activity. 3. You will now analyse the sunspot data to test the following hypothesis: EXPLORING THE SUNSPOT CYCLE: TEACHER’S GUIDE 7 What patterns emerge when sunspot numbers are plotted over time? 4. Create a graph of your data with time in years along the x-axis and number of sunspots along the y-axis. 5. To plot sunspot numbers per month, delete all columns except for B and C, these are the date and number of sunspots per month consecutively. The date is shown as the Julian Day Number (JDN), this is the continuous count of days since the beginning of the Julian Period and is used often by astronomers. A scattergraph will allow you to visualize both the monthly sunspot numbers (column D) and the monthly smoothed sunspot numbers (column F). 6. You may want to select a smaller sample size of around 55 years, rather than plotting all the data. The final graph should look similar to the example below. 7. Complete the Sunspot Cycles Worksheet. Looking at sunspot cycle onset and decay times (advanced) In this part of the activity you will be using statistical analysis to investigate any difference between the onset and decay time of each Solar Cycle. 1. Go back to the original sunspot data. From the spreadsheet data, identify the beginning, end and maximum of each cycle. Make a table of these values. 2. Use the spreadsheet functions to calculate the onset time and decay time for each cycle. Also, calculate the difference between onset time and decay time for each cycle, and the average and standard deviation for all solar cycles. 3. Compare the results. Is there a difference between onset time and decay time? Is the difference statistically significant? You will be using a "paired t-test" for this calculation. The t-test tells you how confident you can be that your results are not simply due to random chance. 4. Begin by formulating (and note down) your “null hypothesis” -- essentially the opposite of what you want to prove*. EXPLORING THE SUNSPOT CYCLE: TEACHER’S GUIDE 8 5. Select the appropriate statistical test for the data. In this case, the onset time and decay time are paired valued, since each one is describing a different feature of the same solar cycle. The test to use in this case is a ‘paired ttest’. 6. The result of the t-test will tell us, under certain assumptions, the probability that the null hypothesis is true. By convention, the probability is referred to as a “p value” and is given as an inequality. For example, if p < 0.01 means we are 99% certain that our desired hypothesis is true. 7. Use the following link to run a paired t-test on your data: www.physics.csbsju.edu/stats/t-test.html 8. Select “Student's t-test via copy and paste”. On the next page enter your pairs of onset and decay times for each solar cycle. When this is finished click “Calculate now” at the top of the page to get your results. 9. Indicate the p-value with your results displayed and discuss your value with other members of the class. * In this case, the null hypothesis may be that there is no different between onset time and decay time. Additionally you may ask students to test the rate of rise and decay (includes both time and magnitude) – is there a correlation between the magnitude of sunspot activity and the difference in onset vs decay rate? Conclusion Ask the students to present their results in a minute and explain what they found. This data from this activity may be used to complete a follow-up activity “Correlation of Coronal Mass Ejections with the Solar Sunspot Cycle”. Evaluation The students’ answers to the Sunspot Cycle Worksheet can be used as a basis for evaluating their understanding of the subject. The following questions can be used to evaluate students knowledge of the topic in future. 1. What is the solar cycle? 2. What is the average time between the high points (periods of maximum sunspot activity)? 3. What is the average time between the low points (periods of minimum sunspot activity)? EXPLORING THE SUNSPOT CYCLE: TEACHER’S GUIDE 9 4. When will the next sunspot minimum occur? 5. When will the next two solar maxima occur? 6. Where will we be in the sunspot cycle when you graduate from high school? 7. What makes sunspot activity unpredictable? Additional information Source: http://www.spaceweathercenter.org/resources/05/solarscapes/Act2s.pdf EXPLORING THE SUNSPOT CYCLE: TEACHER’S GUIDE 10 Exploring the Sunspot Cycle Student Worksheet EXPLORING THE SUNSPOT CYCLE: STUDENT WORKSHEET 1 Name:_________________________ Date:__________________________ Print out your graph. Number each sunspot maximum directly about the line on your graph. You will now work in groups to discuss the patterns found on your graphs. Record your ideas and answer the following questions and explain your reasoning. Be prepared to share your ideas with the class. 1. Compare what you now know about sunspots and their variation to what you knew when you started this activity. 2. What patterns emerge when sunspot numbers are plotted over a period of time? EXPLORING THE SUNSPOT CYCLE: STUDENT WORKSHEET 2 3. What is the average time between points of maximum sunspot activity? 4. Predict the years for the next two sunspot maxima. 5. Predict the years for the next two sunspot minima. EXPLORING THE SUNSPOT CYCLE: STUDENT WORKSHEET 3 6. Predict how many sunspots there will be for your 30th birthday. 7. Plot two new graphs, one showing sunspot activity over 5 years and one over 100 years. What additional patterns do you see when you observe a short time period compared to a longer period? 8. Why is it important to plot data over longer time periods before drawing conclusions? EXPLORING THE SUNSPOT CYCLE: STUDENT WORKSHEET 4 Coronal Mass Ejections and the Sunspot Cycle Teacher’s Guide EXPLORING THE SUNSPOT CYCLE: TEACHER’S GUIDE 1 Introduction Using real observational data and scientific investigation, in this activity students will aim to determine whether there is a correlation between coronal mass ejection activity and the solar sunspot cycle, using historical data. Materials: • • Computer with internet access Excel spreadsheet software or equivalent Learning Objectives • • • Become familiar with another solar phenomena: coronal mass ejections. Use real scientific data and scientific method to investigate a hypothesis and present your findings. Practise communication skill when presenting your results to the group. Background Information i. Sunspots Sunspots are regions of the solar surface which are cooler than their surrounding, they appear as dark spots on the surface of the Sun. Temperatures in the dark centers of sunspots drop to about 3700 K compared to 5700 K for the surrounding photosphere. They typically last for several days, although very large ones may exist for several weeks. Sunspots are magnetic regions on the Sun with magnetic field strengths thousands of times stronger than the Earth's magnetic field. They usually appear in groups with two sets of spots; one set will have positive or north magnetic field, while the other set will have negative or south magnetic field. The field is strongest in the EXPLORING THE SUNSPOT CYCLE: TEACHER’S GUIDE 2 darker parts of the sunspots - the umbra. The field is weaker and more horizontal in the lighter part - the penumbra. ii. Sunspot Cycle In 1610, shortly after viewing the sun with his new telescope, Galileo Galilei made the first European observations of Sunspots. Continuous daily observations were started at the Zurich Observatory in 1849 and earlier observations have been used to extend the records back to 1610. The ‘sunspot number’ is calculated by first counting the number of sunspot groups and then the number of individual sunspots. The "sunspot number" is then given by the sum of the number of individual sunspots and ten times the number of groups. Since most sunspot groups have, on average, about ten spots, this formula for counting sunspots gives reliable numbers even when the observing conditions are less than ideal and small spots are hard to see. Monthly averages (updated monthly) of the sunspot numbers show that the number of sunspots visible on the sun waxes and wanes with an approximate 11year cycle. There are actually at least two "official" sunspot numbers reported. The International Sunspot Number is compiled by the Solar Influences Data Analysis Center in Belgium, which we will work with in this activity, and the NOAA sunspot number compiled by the US National Oceanic and Atmospheric Administration. Detailed observations of sunspots have been obtained by the Royal Greenwich Observatory (UK) since 1874. These observations include information on the sizes EXPLORING THE SUNSPOT CYCLE: TEACHER’S GUIDE 3 and positions of sunspots as well as their numbers. These data show that sunspots do not appear at random over the surface of the sun but are concentrated in two latitude bands on either side of the equator. A butterfly diagram showing the positions of the spots for each rotation of the sun since May 1874 shows that these bands first form at mid-latitudes, widen, and then move toward the equator as each cycle progresses. iii. Coronal Mass Ejection The outer solar atmosphere, known as the corona, is structured by strong magnetic fields. Where these fields are closed, often above sunspot groups, the confined solar atmosphere can suddenly and violently release bubbles of gas and magnetic fields called coronal mass ejections (CME). A large CME can contain a billion tons of matter that can be accelerated to several million miles per hour in a spectacular explosion. Solar material streams out through the interplanetary medium, impacting any planet or spacecraft in its path. CMEs are sometimes associated with flares but can occur independently. Preparation Before beginning this activity you must complete the Sunspot Cycle activity. Instructions 1. Use the online catalogue of CME data from the SOHO LASCO instruments to create a table of monthly numbers of CMEs for the time period 1996–present. You can find this data at http://cdaw.gsfc.nasa.gov/CME_list/index.html 2. Each entry in the table contains information about a single CME event. Count up events for each month and create your own data table of monthly CME totals. To make this task quicker, you can divide the number of months between the class, assigning each student a group of months to count. 3. Add the CME numbers to the solar sunspot cycle plot, using a separate y-axis scale. EXPLORING THE SUNSPOT CYCLE: TEACHER’S GUIDE 4 Evaluation Compare the two curves on your graph. Does the number of CMEs rise and fall in a manner similar to the solar sunspot cycle? If so, this demonstrates a correlation between the two phenomena. Remember, though, that correlation does not imply causation. We may have good cause to believe that sunspots and CMEs are somehow related, but the correlation does not prove that one causes the other. EXPLORING THE SUNSPOT CYCLE: TEACHER’S GUIDE 5