1. Astronomy 1010 Planetary Astronomy Fall_2015 Day-3

2. Course Announcements Smartworks Practice: Due Fri. (Aug. 28) Smartworks Chapter 1: Due Fri. (Sep. 4) Read Chapter 1 (if you haven’t already) Read Chapter 2.1, 2.2 Physics Dept. picnic – Today – come by the office for details.

3. Definitions & Terms -1 Orbit: Path a planet takes around its star; Path a moon takes around its planet … Year (yr): A measure of TIME; for this class we will assume 365.25 days, the time it takes the Earth to orbit (revolve around) the Sun. Day (d): A measure of TIME; for this class will will assume a Solar Day = 24 hours = 86,400 seconds. A Sidereal Day ≈ 23h 56m Second (s): A measure of TIME; the fundamental time unit of the mks system (of SI). Kilogram (kg): a unit of MASS; the fundamental mass unit of the mks system (of SI).

4. Definitions & Terms -2 Kilometer (km): A unit of DISTANCE = 1000 meters Meter (m): A unit of DISTANCE; the fundamental distance of the mks (SI) system. Astronomical Unit (AU): A unit of DISTANCE; the average distance from the Sun to the Earth; ≈1.496 X 10 8 km Light-Year (ly): A unit of DISTANCE = the distance light will travel in 1 year ≈ 9.5 X 10 12 km Parsec (pc): A unit of DISTANCE ≈ 3.26 ly = the distance at which 1 AU subtends 1 arc-second (an angular measure)

5. Home Work - 1 Between now and class time on FRIDAY. Turn in Friday at class time: Go outside, at night, and look at the sky. Try to avoid street lights. Sketch what you see. Bright stars, the moon (show phase), and some “local” landmarks. 1-3 hours later, repeat. What changed?

6. The Universe is Vast! Scale: The Earth is small, Orbits a medium star, In a small group On the edge of the Virgo Supercluster (a smallish cluster)

7. … which is one of billions of galaxies … NASA/ESA/S. Beckwith (STScI) and the HUDF Team in a universe that is 13.7 billion years old.

8. Light travels at a finite speed: Solar System

9. Longer Distances The Closest Star Our Galaxy The Closest Big Galaxy The Universe

10. Measuring Distances The universe is vast. We need to handle great distances and long times. We can do this through the travel time of light. Light travels 300,000 km every second. We often use times to denote distances. For example, we may say a friend’s house is two hours away. Astronomy is a time machine!

11. Measuring Distances Close to home (Solar System) we will use: Kilometers (for distance to Moon, sizes) Astronomical Units (AU) or light-minutes – distance to most planets light-hours for distances to the farther planets

12. The Inner Solar System

13. Lecture-Tutorial: Sun Size – p. 113 Work with a partner Read the instructions and questions carefully Talk to each other and discuss your answers with each another Come to a consensus answer you both agree on If you get stuck or are not sure of your answer ask another group If you get really stuck or don’t understand what the Lecture Tutorial is asking as one of us for help