Around Venus by Balloon Suggested Activities for Use in the Classroom July 2007 1. About This Product This film is a pilot educative film part of a mission proposal, the European Venus Explorer (EVE), submitted in response to the Announcement of Opportunity (AO) issued by the European Space Agency´s (ESA) Science Programme in the framework of the Cosmic Vision Programme. In this document we present possible uses of this film in the classroom. Even though the main topic of the film is scientific, science is more and more cross disciplinary and we therefore suggest cross disciplinary activities. Ideally, teachers from different areas join together and coordinate activities around this film. In this document activities are indicated in red (in bracket the classes they could possibly best fit in) and next described in more detail. We follow the structure of the main film (division in section is the same as in the document with the integral text). We welcome feedback, comments and suggestions. Links: EVE: http://www.aero.jussieu.fr/EVE/ ESA: http://www.esa.int/ ESA Science Programme: http://sci.esa.int/ Cosmic Vision: http://sci.esa.int/science-e/www/area/index.cfm?fareaid=100 Venus Express Lesson Plans from the British National Space Centre: http://www.bnsc.gov.uk/lzcontent.aspx?nid=5385 The Text (English): The integral texts of the main film and the extra film (extra on the DVD only) are available as pdf files on the same site as this document. The text of the film can be studied in english class and the film can be viewed afterwards. The film also includes subtitles in english to help better understanding of the text while viewing. This activity would ideally be coordinated with the other teachers who want to use the film and is probably best done as a first activity. 2. Introduction Balloon Release Experiment (Physics and Arts): Ages: 10 - 18 In the first minute of the film, a standard helium balloon release experiment performed at a high school in Portugal is shown. The purpose of the experiment was to study the regional atmospheric winds on the day of the launch. A total of fifty students (between 12 and 18 years old) participated and each student launched three balloons. Each student wrote a message on three postcards and most postcards were decorated too. The postcards were attached to the balloons. The message on the postcard included an explanation about the purpose of the experiment and a request to the finder of the postcard to send it back to the school indicated the time and location where it was found (the postcards had stamps on it and were addressed to the school). In this particular case, no postcards were returned, probably because the wind that day took the balloons over sea. This activity can be performed in a physics / environmental class and combined with an arts class (decoration of the postcards). In terms of illustration, the technique of the drawing hand has been applied in four places in the film, as opposed to sophisticated computer generated animations. Even though these animations have become very common in these kind of products, and they do serve their goal, we wanted to include a more human element in the film. We suggest that this can be used in an arts class, stimulating students to carefully observe their environment, as well as reduce abstract concepts to an illustration. Note that scientific illustration was a very important technique in many sciences until the upcoming of easy-to-use computer drawing programs in the past say 20-30 years. Very famous examples of scientific illustration are of course those made by Leonardo DaVinci. Weather Forecasts (Physics): Ages: 10 - 18 The extra film on the DVD provides with some more explanation on weather stations and balloons and their use. There are over 800 sites on Earth where regular balloon launches take place. The balloons rise vertically up to about 20 km altitude, twice the altitude where airplanes fly and well within the stratosphere. These measurements provide with important observations on a local scale (local both in terms of space and time). This can be used to discuss the importance of in situ (local) measurements combined with remote sensing measurements (global, from weather satellites) to learn about the climate and make more accurate predictions. In planetary research, we most often only have remote sensing data, because in situ mission are very expensive and complex. This limits the amount of details we can learn about a planet. The European Venus Explorer, if selected, will have both a remote sensing platform (orbiter) and two in situ platforms (balloon and lander). 3. Venus Science History (History and Science): The first to point a telescope at the sky was the italian scientist Galileo Galilei in 1610. He discovered the phases of Venus, similar to those of the moon. They are due to the fact that Venus (and Mercury) are closer to the Sun than the Earth. The quality of his telescope was of course very poor. In the mid 17th century, when the dutch scientist Christiaan Huygens pointed his instruments at Venus, telescopes must have given better images. What he must have seen, might have been something similar to the sequence shown in the film. This sequence was obtained by german amateur astronomer Silvia Kowollik on May 11th, 2004 with a 7" Starfire Refractor (Astrophysics) and a Philips ToUcam webcam with UV-IR-Cut Filter from B+W. It is quite an achievement to film Venus and it very realistically shows how Venus appears as viewed through a telescope. The drawing that appears overlain in the film is made by Christiaan Huygens in on March 8th, 1659 and shows the same phase of Venus (page 62 of Oeuvres Complètes, see link below). This section can be used to discuss history of science and basic optics (working of a simple refractor, different types of telescopes). Also, observation of Venus can be done with telescopes (if available at the school). Links: Silvia Kowollik: http://www.sternwarte-zollern-alb.de/mitarbeiterseiten/kowollik/ (website in german) Christiaan Huygens´Oeuvres Complètes: http://gallica.bnf.fr/ark:/12148/bpt6k778636 Density (Physics and Mathematics): Ages 12 - 18 Venus and Earth have similar sizes (Venus is slightly smaller than the Earth) and similar masses. This means that they have similar densities and as a consequence indicates that they are build out of the same material! Density is a very important parameter, which planetary scientists want to know, because it gives access to the possible composition and build up of the celestial bodies. A possible activity is to study the densities of the planets (calculate the densities from the size and masses, this is where the maths come in) in the Solar System and to relate that to their known compositions. Links: The nine planets: http://seds.lpl.arizona.edu/nineplanets/nineplanets/ (there are many sites about the solar system, this is just one of them). Atmospheric Mass (Physics and Mathematics): Ages: 14-18 Venus and Earth have similar sizes, Venus being slightly smaller than the Earth. The atmospheric pressure at the surface of Venus is 92 bars, as opposed to 1 bar at the surface of the Earth. Also, the composition of the atmosphere of Venus is almost entirely carbon dioxide. On Earth most of the carbon dioxide resides in the oceans. A suggested activity is to estimate how much more massive Venus´s atmosphere is compared to Earth´s as well as to calculate the mass of Venus´and Earth´s atmosphere. A simple way to estimate the mass is to multiply surface pressure and surface area (area of a sphere) of the planet and divide by the gravitational constant at the surface (which is slightly lower on Venus and can be calculated simply from g = GM/R2, with G the gravitational constant, M the mass of the planet and R the radius of the planet). A further interesting comparison can be done by estimating the mass of the oceans on the Earth: 1 liter of water is about 1 kg of mass, the oceans have a depth of say 2-3 km and cover 70 % of the surface of the planet. Even further discussion can be developed around the subject of the composition of the Earth´s atmosphere: what would be the mass of the Earth´s atmosphere if all the carbon dioxide that currently resides in the oceans would be released in the atmosphere? How much of the current atmospheric mass on Earth is carbon dioxide (carbon dioxide represents about 0.5 % of the mass of the atmosphere): compare this to Venus. Greenhouse Effect and Clouds (Physics, Chemistry, Arts): Ages: 14-18 Thought Bite 1: Which of the following are greenhouse gases: CO2, O3, H2O, N2, CH4, H2SO4. Answer: They are all except ozone (O3) and molecular nitrogen (N2). The greenhouse effect is a very popular term nowadays. It is associated with carbon dioxide and bad effects on the climate on Earth. However, their is a natural greenhouse effect that is not too often mentioned. As soon as there is a planet with some atmosphere, there is a greenhouse effect. Not only carbon dioxide has greenhouse properties. Other very important greenhouse gases are water vapour, methane, nitrates, and on Venus sulphuric acid, of which the clouds are mainly composed. A suggested activity is to retrieve information on the different cycles of these gases on the Earth (water, carbon dioxide, methane) and to make a wall size drawn or painted scheme of the cycles. Another suggested activity (Ages 16-18) is to calculate what the effective temperature on Earth would be if there were no atmosphere: 1. The Sun emits radiation at a temperature of 6000 K. Each square meter on the Sun´s surface emits E = σTSun4, where σis the Stefan-Boltzmann constant and T the temperature (K). The total output of the Sun is calculated by multiplying by the total surface area of the Sun (radius is about 109 times the radius of the Earth). 2. When it reaches the orbit of the Earth, this energy is spread over an area with the radius of that orbit, which is 1 Astronomical Unit, about 150 million km: each square meter at the orbit of the Earth receives Rsun2 / Rorbit Earth2 less energy. 3. The Earth intercepts this energy with an effective area ofπREarth2, and absorbs only part of this (about 70 %, because is reflects some 30 % back to space: the albedo is about 0.3). 4. Assuming the Earth behaves as a black body, it heats up from the solar energy and the whole planet (4πREarth2) radiates back to space at the equilibrium temperature, like a black body (again the Stefan Boltzmann law: E = σTEquilibrium4). 5. It is now easy to write down the equation and to calculate the equilibrium temperature, which is some 30-40K below the real average surface temperature (about 290K). It is interesting to repeat this calculation for Venus, the albedo is on the order of 0.76. It reflects about 76 % of the incoming sunlight. However, this albedo is due to the clouds and is the reason why Venus looks so intensely bright in the sky! In the current situation, the amount of energy reaching the surface of Venus is LESS then that reaching the surface of the Earth, which is easily verified. Venus Express (Science, Society, History, Arts): Ages 14-18 Venus was the second other planet (Mars was the first) where man sent a spacecraft. The first flyby of Venus happened on February 4, 1961 by russian Sputnik 7. Many flyby´s followed as well as orbiting spacecraft and entry probes. The first successful probe entered Venus´atmosphere on June 12, 1967 (russian Venera 4) and the first successful lander touched the surface on August 17, 1970 (russian Venera 7). The first orbiters arrived in October 1975 (russian V9 and V10 missions). The americans came in 1978, with Pioneer 12 and 13 and the Pioneer Venus orbiter and entry probes. The last orbiter before Venus Express operated in the early 1990´s (american Magellan mission). Two missions used Venus to speed up (gravity assist): Galileo (Feb. 1990, on route to Jupiter) and Cassini/Huygens (April 26, 1998 and June 24, 1999 on route to Saturn). Venus Express is a return to Venus and the first European mission to Venus. Venus Express is a second technical child of Rosetta, an ESA mission launched in 2003 to a comet (arrival in 2014 time frame). The first child of Rosetta is Mars Express, a very successful mission still orbiting Mars. Rosetta´s development cost is on the order of 800 MEuros. Mars Express, because inherited a lot from Rosetta, is much cheaper, on the order of 250 Meuros and Venus Express is of that same order. Here the Science Programme of ESA can be studied, by information from the extensive ESA website (see page one for links). The Science Programme is one of the few mandatory programmes within ESA: each member state (17 now) pays an annual contribution to the Science Programme, which has a yearly budget of about 400 MEuros. Most of this budget (about 90 %) is invested by ESA back into in the European Space Industry. In addition to this contribution, each member state normally has a national financial scheme where scientists can apply for money to participate in the analysis of mission data and development of new instrumentation and techniques. This part of the film can be used to discuss and explore the history of space exploration, which is a recent human activity and the current role of space in our daily lives. A link can be made to the exploration of our own planet, which initiated in the 16th century when the portuguese started (and soon followed by many other nations) to explore the oceans and discover new lands. A timeline could be made (drawn, painted) with important milestones of space exploration (use books and the internet to search for information). Also, a discussion around more ethical questions could be held. These questions could be for example (among many others of course): • Is space exploration needed? Is it inevitable? • Why spend so much money (comparison: 1 km of highway costs about 10 MEuros), or do we not spend enough? • What good does space for us? • Does the normal citizen get enough information about space? • What is the importance of space in our daily lives (think for example about telecommunication satellites)? •Can you mention spin-offs from space development? 4. Balloon on Venus Winds on Venus (Mathematics): Ages 10-14: Thought Bite 2: Estimate the wind speed at the cloud level on Venus and compare to winds measured at the cloud levels on Earth (hint: Venus and Earth have similar sizes). Answer: At the cloud tops on Venus (around 60 km altitude) exist very strong winds in the East-West direction. These winds carry the cloud around the planet in about four days, which implies a wind speed of about 110 m/s (400 km/h). The EVE balloon would perform an oscillating motion between some 50 and 70 km altitude. The effective speed of the balloon would be somewhat less (wind speeds vary as a function of altitude), taking it about a week to go around Venus, which is a speed of some 65 m/s. Note that at the surface, the wind speed is virtually zero! Circumference = 2πR = 2π (6100 km) ~ 38,000 km Speed = Δx / Δt = 38,000,000 m / (4 x 24 x 3600 sec) = 110 m/s Or equivalently: Speed = Δx / Δt = 38,000km / (4 x 24 hours) = 400 km/hour 5. European Venus Explorer Orbital Mechanics (Physics, Mathematics): Ages 16-18 Venus is the closest planet to Earth in terms of spacecraft travel. This is easily verified by calculating the time it takes to transfer a spacecraft from Earth to Venus on an orbit that requires minimum energy, which is a simply elliptical orbit around the Sun with a aphelion (point furthest from the Sun) touching the orbit of the Earth at 1 Astronomical Unit (150 million km) and and perihelion (point closest to the Sun) touching the orbit of Venus (0.72 AU). The semi major axis, a, of this orbit is (1 + 0.72) / 2 = 0.86 AU. By using Kepler´s third law (Torbit2 / a3 = 1), it is easily calculated that it takes 0.8 years to complete one tour around the Sun in this orbit. So, it takes half that time (4.8 months) to travel from Earth to Venus! At what position relative to the Earth does Venus need to stand at the time of launch, and what is the relative position when the spacecraft arrives? How long would it take to do a complete roundtrip from Earth to Venus?
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