Discovering the Universe for Yourself

Discovering the Universe for Yourself E W N © 2010 Pearson Education, Inc. Annual Motion – Apparent • As the Earth orbits the Sun, the Sun appears to move eastward along the ecliptic. • At midnight, the stars overhead are opposite the Sun in the sky. © 2010 Pearson Education, Inc. The Milky Way and Galactic Plane A band of light making a circle around the celestial sphere. What is it? Our view into the plane of our galaxy. © 2010 Pearson Education, Inc. The Milky Way https://youtu.be/KMZf2JYhvHU © 2010 Pearson Education, Inc. The Milky Way © 2010 Pearson Education, Inc. © 2010 Pearson Education, Inc. https://commons.wikimedia.org/wiki/File:Orientation_of_astronomical_coordinat es_projected_on_the_Celestial_Sphere.jpg https://www.linkedin.com/pulse/%E0%AE%9A%E0%AE%B0%E0%AE%AF%E0%AE%A9%E0%AE%95%E0%AE%95%E0%AE%B0%E0%AE%95%E0%AE%99%E0%AE%95%E0%AE%B3%E0%AE%8F%E0%AE%A9-%E0%AE%B5%E0%AE%B5%E0%AE%B5%E0%AE%B1%E0%AE%95%E0%AE%A3%E0%AE%A4%E0%AE%A4%E0%AE%B2-%E0%AE%B5%E0%AE%B2%E0%AE%AE%E0%AE%B5%E0%AE%B0%E0%AE%95%E0%AE%A9%E0%AE%B1%E0%AE%A9-ganapathi-ponmudi/ © 2010 Pearson Education, Inc. © 2010 Pearson Education, Inc. ICQ • The night sky doesn’t look the same at 9 PM now as it did at 9 PM back in March. What causes this? A. the spin of the Earth around its axis B. the movement of the Moon in its orbit around the Earth C. the movement of the Earth in its orbit around the Sun D. the changing tilt of the Earth’s axis © 2010 Pearson Education, Inc. ICQ • One morning you see the Sun rises exactly due to the East. What day of the year is it? A. You cannot tell since the Sun rises exactly due East every day. B. It could be summer or Winter solstice. C. It could be spring or fall equinox. D. It is a trick question. The Sun never rises exactly due east unless you live on the Earth equator. © 2010 Pearson Education, Inc. The Reason for the Seasons © 2010 Pearson Education, Inc. CLOSER means MORE right? © 2010 Pearson Education, Inc. CLOSER means MORE right? • Heat – The closer you are the hotter it is © 2010 Pearson Education, Inc. CLOSER means MORE right? • Heat – The closer you are the hotter it is • Sound – The closer you get, the louder it is © 2010 Pearson Education, Inc. CLOSER means MORE right? • Heat – The closer you are the hotter it is • Sound – The closer you get, the louder it is • Light – The closer you get, the brighter it is © 2010 Pearson Education, Inc. Complete this statement! When the Sun is ______ it is summer, and when the Sun is _______ it is winter. © 2010 Pearson Education, Inc. Complete this statement! When the Sun is CLOSER it is summer, and when the Sun is FARTHER it is winter. © 2010 Pearson Education, Inc. Why doesn’t distance matter? • Variation of Earth-Sun distance is small — about 3%; this small variation is overwhelmed by the effects of axis tilt. © 2010 Pearson Education, Inc. How do we mark the progression of the seasons? • We define four special points: summer solstice winter solstice spring (vernal) equinox fall (autumnal) equinox © 2010 Pearson Education, Inc. The Seasons Earth’s axis of rotation is inclined vs. the normal to its orbital plane by 23.5°, which causes the seasons. © 2010 Pearson Education, Inc. The Seasons (2) Northern summer © 2010 Pearson Education, Inc. When the Sun is high in the sky, the amount of direct sunlight received is greater. This results in SUMMER The Seasons (2) Sothern Winter © 2010 Pearson Education, Inc. When the Sun is low in the sky, the amount of direct sunlight received is less. This results in WINTER The Seasons (2) Northern summer = southern winter © 2010 Pearson Education, Inc. Northern winter = southern summer When the Sun is high in the sky, the amount of direct sunlight received is greater. This results in SUMMER © 2010 Pearson Education, Inc. When the Sun is low in the sky, the amount of direct sunlight received is less. This results in WINTER What causes the seasons? © 2010 Pearson Education, Inc. Summary: The Real Reason for Seasons • Earth’s axis points in the same direction (to Polaris) all year round, so its orientation relative to the Sun changes as Earth orbits the Sun. • Summer occurs in your hemisphere when sunlight hits it more directly; winter occurs when the sunlight is less direct. • AXIS TILT is the key to the seasons; without it, we would not have seasons on Earth. © 2010 Pearson Education, Inc. Season Simulator • https://astro.unl.edu/naap/motion1/animations/seasons_ecliptic.html • Click on the link and Start the simulation. – Change “orbit view” to “celestial sphere” while the animation is running. • Does the sun’s motion make sense? – Move the little human up and down while animation is running. • Does the sunlight angle in different location make sense? – Change the “Sunlight angle” to “Sunbeam spread” while animation is running. • Does the seasons make sense now? © 2010 Pearson Education, Inc. ICQ • Consider the drawing below, which shows three different regions of Earth (northern hemisphere, equatorial region, and southern hemisphere) at two different times of the year, 6 months apart. Which of the following statements is correct? A. B. C. D. E. It is summer at positions 3 and 4 It is the day of an equinox at positions 2 and 5 It is winter at positions 1 and 6 Both A and B are correct Both A and C are correct © 2010 Pearson Education, Inc. We can recognize solstices and equinoxes by Sun’s path across sky: Summer solstice: Highest path, rise and set at most extreme north of due east. Winter solstice: Lowest path, rise and set at most extreme south of due east. Equinoxes: Sun rises precisely due east and sets precisely due west. © 2010 Pearson Education, Inc. Seasonal changes are more extreme at high latitudes Path of the Sun on the summer solstice at the Arctic Circle © 2010 Pearson Education, Inc.