Post on 13-Dec-2015
Course Announcements• Smartworks Practice: Due Fri. (Aug. 28)
• 9 have attempted it, 6 have recorded grades
• Smartworks Chapter 1: Due Wed. (Sep. 2)
• Read Chapter 1 (if you haven’t already)• Read Chapter 2.1, 2.2
• Physics Dept. picnic – TODAY – come by the office for details.
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).
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 108 km
• Light-Year (ly): A unit of DISTANCE = the distance light will travel in 1 year ≈ 9.5 X 1012 km
• Parsec (pc): A unit of DISTANCE ≈ 3.26 ly = the distance at which 1 AU subtends 1 arc-second (an angular measure)
The Universe is Vast!Scale:The Earth is small,Orbits a medium
star,In a small groupOn the edge of the Virgo
Supercluster (a smallish
cluster)
… 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.
Measuring DistancesThe 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!
Measuring DistancesClose to home (Solar System) we will
use:Kilometers (for distance to Moon, sizes)Astronomical Units (AU) or light-
minutes – distance to most planetslight-hours for distances to the farther
planets
Lecture-Tutorial:Sun Size – p. 113
Work with a partnerRead the instructions and questions carefullyTalk to each other and discuss your answers
with each anotherCome to a consensus answer you both agree
onIf you get stuck or are not sure of your
answer ask another groupIf you get really stuck or don’t understand
what the Lecture Tutorial is asking as one of us for help