1. Physics 162 Elementary Astronomy Dr. Fortner FW 204MWF mfortner@niu.edu

2. Web Pages My Page: www.niu.edu/~mfortner/ PHYS 162 syllabus and lectures: nicadd.niu.edu/~fortner/course/phys162/ Webassign: www.webassign.net Observatory: www.niu.edu/physics/observatory/

3. Course Topics The course is divided into four broad topics. –Foundations - Tools and rules –Planets - Earth and its neighbors –Stars - How the sun and other stars work –Universe - Galaxies and beyond Each topic includes a written assignment and a test. Each week includes an online homework assignment.

4. Why Astronomy? Astronomy is as old as humans have looked up at the sky. Astronomy is the science of stars and other objects in space. –Physics, chemistry, geology, even some biology –Laboratory for conditions beyond earth-based experiments Astronomy remains newsworthy today. –News stories from NASA and other countries –Movies and popular culture

5. Measurement and Units Scientific measurement requires standard units. –English units – foot, pound, second –Metric units – meter (m), kilogram (kg), second (s) –Derived units – cubic meter (m 3 ), watt (W) –Alternate units – hour (h), light year (ly) The metric system has two major strengths. –Widespread use in science –Prefixes based on powers of ten

6. Scientific Notation In science some measurements can be very large or very small compared to the base unit. Scientific notation uses powers of 10 to represent decimal places. –Positive for large values: 456000 = 4.56 x 10 5 –Negative for small values: 0.00753 = 7.53 x 10 -3 (only one non-zero value to the left of the decimal place)

7. SI Prefixes Prefixes on units are used to represent powers of ten. Prefixes denote powers of ten from  18 to  18 mostly in steps of three. For example a kilometer (km) is 10 3 meters or 1000 meters. Most Common nano (n) 10 -9 micro (  ) 10 -6 milli (m) 10 -3 centi (c) 10 -2 kilo (k) 10 3 mega (M) 10 6 giga(G) 10 9 Common, but the power is not a factor of three.

8. Unit Conversion Conversion between units must be of the same type –Length conversion: 1 in = 2.54 cm –Time conversion: 1 h = 3.6 x 10 3 s No conversion between different types of units. –1 m 3 not equivalent to any number of m

9. Significant Figures Any value is expressed in some number of digits. The number of digits (without left side zeroes) is the number of significant figures. With no decimal point, skip right side zeroes. –382 digits, 2 significant figures –5.063 digits, 3 significant figures –0.00415 digits, 2 significant figures –7,000.4 digits, 4 significant figures –2,0004 digits, 1 significant figure

10. One Ton The rock has a density of 3 x 10 3 kg/m 3. The volume is –10 3 kg/(3 x 10 3 kg/m 3 )=0.3 m 3 Estimate that the rock is a sphere, V = (4/3)  r 3 –d = 2r = 2 (3V/4  ) 1/3 –d = 0.9 m x 100 cm/m = 90 cm Assume the density of a rock is three times that of water. How many centimeters across is a one metric ton (1000 kg) rock?