Astronomy 1010-HFall_2015

Day-3Planetary Astronomy

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.

Solar System

Longer DistancesThe Closest Star

Our Galaxy

The Closest Big Galaxy

The Universe

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