9/3/2010AST 207 Fall 2010 151 Pegasi⎯3 Sept• Course goals• to generate and evaluate scientific evidence and explanations• to understand the nature and development of scientific knowledge• to participate productively in scientific practices and discourse• Michael Mayor & Didler Queloz discovered something important by studying the star 51 Pegasi.• The steps to discovery1. Examine the data for the facts. What is the evidence? Collect clues. Done.2. Brainstorming. What are models that explain the evidence? Done3. Developing your idea4. Testing your idea Does any clue refute any part of the model?5. What was discovered?• Homework 1• Due Friday, Sept 10.• You may work with your Ast207 buddies, but you must write your own homework. (No copies.)• Missouri (Show me) Club on Wed, Sept 8.• Homework is accessible on angel. Link is on the syllabus.Motion of 51 Peg Away & Towards Us • In 1994, Michel Mayor and Didler Queloz began to observe the motion of the star 51 Pegasi. They found that it moves towards us and then away from us and the towards us, etc. It repeats every 4 days and 5 hours. The fastest it moves is 60m/s or 120mi/hr, which is unusually slow for an astronomical object. (Earth moves 5000 times faster.) ⎯ MSU Kids’ College, 19989/3/2010AST 207 Fall 2010 2Clues and proposed modelsModelsI. 51 Peg is in a circular orbit.II. Two planets orbit 51 Peg and pull it towards them.III. 51 Peg and a planet orbit each other around a point that is very near 51 Peg.IV. 51 Peg orbits an unseen black hole.Clues1. The star moves away, then toward, then away, etc. The motion repeats every 4days & 5 hours.2. The speed away and speed towards match.3. The fastest speed is 60m/s.4. The speed is very slow compared with the Earth’s speed around the sun (30km/s).Develop the modelsRevised ModelsI. 51 Peg is in a circular orbit.II. Two planets orbit 51 Peg and pull it towards them. [Eliminate for now; analyze the case of one planet.]III. 51 Peg and a planet orbit each other around a point that is very near 51 Peg. IV. 51 Peg orbits an unseen object with a stellar mass (such as a black hole, faint star, or neutron star). ModelsI. 51 Peg is in a circular orbit.II. Two planets orbit 51 Peg and pull it towards them.III. 51 Peg and a planet orbit each other around a point that is very near 51 Peg.IV. 51 Peg orbits an unseen black hole.9/3/2010AST 207 Fall 2010 3Develop the modelsRevised 2ndtimeAssume circular orbits for both models.I. 51 Peg and a planet orbit each other around a point that is very near 51 Peg. II. 51 Peg orbits an unseen object with a stellar mass (such as a black hole, faint star, or neutron star). Revised ModelsI. 51 Peg is in a circular orbit.II. Two planets orbit 51 Peg and pull it towards them. [Eliminate for now; analyze the case of one planet.]III. 51 Peg and a planet orbit each other around a point that is very near 51 Peg. IV. 51 Peg orbits an unseen object with a stellar mass (such as a black hole, faint star, or neutron star).Develop the modelsI. 51 Peg and a planet orbit each other around a point that is very near 51 Peg. II. 51 Peg orbits an unseen object with a stellar mass (such as a black hole, faint star, or neutron star). 1. How would the observations differ if model I, rather than model II were true?A. There is no difference.B. The period would be longer.C. The speed would be greater.D. The shape of the curve would change, such as a faster rise and slower fall.• To answer this, we need an analogy from our previous experience.• Two race cars take the same time to circle the track. The outside car moves faster.• Two guys on a see-saw. The pivot is near the middle. A guy & a cat on a see-saw. The pivot is near the guy.9/3/2010AST 207 Fall 2010 4Orbit of 51 Peg• How big is the orbit?• Speed is 60m/s. Period is 4day 5hr = 101 hr.• Circumference is 60m/s*(3600s/hr)*101hr=22,000km• Circumference of Earth is 40,000km• Sun is 100 times bigger.• Planet causes 51 Peg to move in a circle that is 1/200thof its circumference.Testing your idea Does any clue refute any part of the model?1. Clue 1 refutes model I. Clue 1 refutes model II.A. TTB. TFC. FTD. FF2. Clue 2 refutes model I. Clue 2 refutes model II.A. TTB. TFC. FTD. FFModels:I. 51 Peg orbits an unseen object with a stellar mass (such as a black hole, faint star, or neutron star).II. 51 Peg and a planet orbit each other around a point that is very near 51 Peg.Clues:1. The star moves away, then toward, then away, etc. The motion repeats every 4days & 5 hours.2. The fastest speed is 60m/s.3. The speed is very slow compared with the Earth’s speed around the sun.9/3/2010AST 207 Fall 2010 5Testing your idea Does any clue refute any part of the model?1. Clue 1 refutes model I. Clue 1 refutes model II.A. TTB. TFC. FTD. FF2. Clue 2 refutes model I. Clue 2 refutes model II.A. TTB. TFC. FTD. FFModels:I. 51 Peg orbits an unseen object (such as a black hole, faint star, or neutron star).II. 51 Peg and a planet orbit each other around a point that is very near 51 Peg.Clues:1. The star moves away, then toward, then away, etc. The motion repeats every 4days & 5 hours.2. The fastest speed is 60m/s.3. The speed is very slow compared with the Earth’s speed around the sun.Mayor & Queloz discovered the first planet outside the solar systemExtrasolar planets• Mayor & Queloz discovered an extrasolar planet.• Q: What key clue says they discovered a planet and not a faint star?a. Period is 4days 5hr.b. Speed of star is 60m/s.c. Motion repeats.d. They did not see the companion
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